Diphosphoglucose Pyrophosphorylase Research Articles

SlNAP1 promotes tomato fruit ripening by regulating carbohydrate metabolism

Many studies showed NAC transcription factors play an important role in fruit ripening. Moreover, sucrose and starch metabolism is also closely related to fruit ripening. However, there are a few studies focus on whether NAC regulates sucrose and starch metabolism to influence fruit ripening. In this study, virus-induced gene silencing (VIGS) of SlNAP1 suppressed fruit ripening and delayed color transformation. The chlorophyll (including Chla, Chlb, and Chla + b) degradation and carotenoid synthesis in SlNAP1-silenced fruits were dramatically suppressed. Silencing SlNAP1 decreased soluble sugar and reducing sugar accumulation in fruits, and increased starch content. The activity of starch degrading enzymes, including α amylase (AMY) and β amylase (BAM) was significantly lower in SlNAP1-silenced fruits than in the control fruits, whereas denosine diphosphoglucose pyrophosphorylase (AGP) activity was significantly higher. In addition, the expression of starch degradation-related genes (SlAMY1, SlAMY2, SlBAM1, SlBAM7, SlGWD, SlPWD) in SlNAP1-silenced fruits was significantly suppressed, while starch synthesis-related genes (SlAGPase1, SlAGPase2) was significantly increased. Compared with the control fruits, SlNAP1-silenced fruits showed significantly lower sucrose and glucose content. The expression level of sucrose and glucose metabolism-related genes such as Slsus1, Slsus3, SlSPS, SlHxk1, SlHxk2, SlPK1, and SlPK2 was significantly lower in SlNAP1-silenced fruits than in the control fruits. Overall, this study revealed that SlNAP1 gene might positively regulate fruit ripening by influencing carbohydrate metabolism.

Metabolic factors restricting sink strength in superior and inferior spikelets in high-yielding rice cultivars

Many high-yielding rice cultivars with large sink size (total number of spikelet per unit area × mean grain weight) have been developed, but some japonica cultivars developed in Japan often fail to attain the expected high yield due to low sink strength of spikelets. Although there is natural variation in sink strength of spikelets among high-yielding cultivars, metabolic factors involved in the natural variation and relationships of sink strength in spikelets with final percentage of filled spikelets are not fully understood. In the present study, we examined cultivar differences in sink strength for superior and inferior spikelets (i.e. earlier fertilizing spikelets with faster growth and later fertilizing ones with slower growth, respectively) in a panicle, using each spikelet at 10 d after the onset of development (10 DAD) when starch accumulation in endosperm was actively proceeding. Nine high-yielding cultivars were used: five japonica-dominant and four indica-dominant cultivars. Cultivar differences were observed in starch contents at 10 DAD in each spikelet type, and indica cultivars had higher starch contents than japonica cultivars in both superior and inferior spikelets. In addition, starch contents at 10 DAD were closely related to percentage of filled grains at maturity in both spikelet types. The activities of sucrose synthase (SUS) and uridine diphosphoglucose pyrophosphorylase (UGP), and the protein levels of phosphorylase 1 (Pho1), were higher in indica than japonica cultivars, and were positively correlated with starch contents at 10 DAD for both superior and inferior spikelets; although metabolic states, revealed from relations between intermediate metabolites and starch contents, differed among spikelet types. Consequently, it was considered that SUS and UGP at the step from sucrose cleavage to adenosine diphosphoglucose synthesis, and Pho1 at the starch biosynthesis step, were key metabolic factors involved in cultivar differences of sink strength (ability to synthesize starch).

Enzymatic and transcriptomic analysis reveals the essential role of carbohydrate metabolism in freesia (Freesia hybrida) corm formation

Starch and sucrose metabolism plays a crucial role in the formation and development of bulbs in bulbous plants. However, these mechanisms remain unclear and unexplored in the corms of Freesia hybrida. Herein, we investigated the dynamics of the major form of carbohydrates and related enzyme activities and profiled the transcriptome of freesia corms at four developmental stages with the aim to reveal the relation between the expression of genes involved in the metabolism of carbohydrates and the accumulation of carbohydrates in corm developmental stages for further exploring the mechanism on the starch and sucrose metabolism regulating the formation and development of corms in F. hybrida. The content of starch, sucrose and soluble sugars followed an overall upward trend across the corm developmental stages. Activities of the adenosine diphosphoglucose pyrophosphorylase, starch branching enzyme and β-amylase generally followed the pattern of the starch and sucrose levels. Activities of sucrose phosphate synthase increased from corm formation till the initial swelling stage and subsequently reached a plateau. Activities of invertase and sucrose synthase peaked at the later rapid swelling stage. These suggested that the starch and sucrose dynamics paralleled corm swelling under the action of metabolic enzymes. A total of 100,999 unigenes were assembled in the transcriptomic analysis, and 44,405 unigenes of them were annotated. Analysis based on Clusters of Orthologous Groups suggested that carbohydrate transport and metabolism (9.34% of the sequences) was prominent across the corm developmental process. In total 3,427 differentially expressed genes (DEGs) were identified and the enrichment analysis detected starch and sucrose metabolism as a critical pathway in corm development, especially at the rapid swelling stage. Further, DEGs encoding key carbohydrate-metabolizing enzymes were identified and correlated to enzyme activities and carbohydrate accumulation. The results construct a valuable resource pool for further molecular-level studies, which are helpful for metabolic regulation of carbohydrates and improvement in F. hybrida.

Genetic Variation Controlling Wrinkled Seed Phenotypes in Pisum: How Lucky Was Mendel?

One of the traits studied by Mendel in pea (Pisum sativum L.) was the wrinkled-seeded phenotype, and the molecular basis for a mutation underlying this phenotype was discovered in the 1990s. Although the starch-branching enzyme gene mutation identified at the genetic locus r is most likely to be that in seeds available to Mendel in the mid-1800s, it has remained an open question as to whether or not additional natural mutations in this gene exist within Pisum germplasm collections. Here, we explore this question and show that all but two wrinkled-seeded variants in one such collection correspond to either the mutant allele described previously for the r locus or a mutation at a second genetic locus, rb, affecting the gene encoding the large subunit of Adenosine diphosphoglucose (ADP-glucose) pyrophosphorylase; the molecular basis for the rb mutation is described here. The genetic basis for the phenotype of one (JI 2110) of the two lines which are neither r nor rb has been studied in crosses with a round-seeded variant (JI 281); for which extensive genetic marker data were expected. In marked contrast to the trait studied by Mendel and the rb phenotype; the data suggest that the wrinkled-seeded phenotype in JI 2110 is maternally determined, controlled by two genetic loci, and the extent to which it is manifested is very sensitive to the environment. Metabolite analysis of the cotyledons of JI 2110 revealed a profile for sucrose and sucrose-derived compounds that was more similar to that of wild-type round-seeded, than that of wrinkled-seeded r, pea lines. However, the metabolite profile of the seed coat (testa) of JI 2110 was distinct from that of other round-seeded genotypes tested which, together with analysis of recombinant inbred progeny lines, suggests an explanation for the seed phenotype.

Analysis of culm elongation in photoheterotrophic status of Dendrocalamus sinicus by comparative proteomics

The differential expression of 36 proteins plays a central role in culm elongation during photoheterotrophic status, which was involved in complicated biochemical and molecular processes, including replication, transcription, translation, energy metabolism, central intermediary metabolism, and woody tissue photosynthesis. Dendrocalamus sinicus is known as the largest bamboo species in the world, characterized by huge woody culms with rapid growth rate. During culm elongation, leaves are not yet shaped and culms are covered by nontransparent overlapping sheaths, forming a photoheterotrophic status in which culms rapidly complete their own growth. To elucidate this phenomenon, proteome analysis as well as enzyme activity were performed. In terms of the enzyme activity, we found significant differences among internodes for adenosine diphosphoglucose pyrophosphorylase, starch synthase, and starch branching enzyme, implying existence of a robust response of starch synthesis throughout culm elongation. At the protein level, 2-DE combined with MALDI–TOF/TOF MS analysis showed 36 differentially accumulated proteins among internodes. Of which, the largest group is the cluster for energy metabolism (27.78%), followed by central intermediary metabolism (22.22%), which suggests that carbohydrate metabolism dominates the process of culm elongation. Especially, four proteins related to the glycolysis pathway were differentially expressed. In addition, a protochlorophyllide reductase associated with chlorophyllide synthesis was down-regulated from basal to top internodes. This implies that culms belong to photosynthetic tissue and woody tissue photosynthesis is involved in the culm elongation. In addition, malate dehydrogenase related to TCA cycle was up-regulated from tender to mature tissues, which indicates that it plays a vital role in energy generation. An inconsistency between the transcript and protein level was found, suggesting that post-transcriptional events are involved in the culm elongation. These results are helpful to disclose the multiple mechanism of culm elongation of D. sinicus.

Dynamic Changes in Starch Metabolism and Endogenous Hormones during Stolon Formation in Tulipa edulis

The stolon is the main asexual reproductive organ of the medicinal plant Tulipa edulis and has special morphology. In the greenhouse experiment presented herein, the dynamic changes in carbohydrates and related enzymes, proteins, and endogenous hormones of stolons during T. edulis stolon formation were investigated. The results showed that the content of total soluble sugar, sucrose, reducing sugar, fructose, and starch were all significantly enhanced in the middle period when stolon emerged and maintained at relatively high levels until the later period of stolon formation, while protein content decreased during stolon formation. The activities of amylase (AMY), sucrose phosphate synthase (SPS), and sucrose synthase (SS) peaked in the initial period and were negatively correlated with soluble sugars. However, adenosine diphosphoglucose pyrophosphorylase (AGPase) activity increased as stolon formation progressed, and the changes in soluble starch synthase (SSS), granule-bound starch synthase (GBSS) activities presented a single peak, reaching their maximums in the middle period. AGPase, SSS, and GBSS activities were all positively related to starch content. Moreover, quantitative real-time polymerase chain reaction (qRT-PCR) verified the changes in SS and SSS activities via the expression levels of the SS, SSSI, and SSSII genes. The gibberellin (GA) and zeatin riboside (ZR) content attained their maximum in the initial period of stolon formation. Indole-3-acetic acid (IAA) and abscisic acid (ABA) remained at high levels during the initial and middle period and decreased significantly during the later period of stolon formation, inversely to the ratio of ABA:IAA. Analysis of the physiological changes in T. edulis stolon indicated that the accumulation of soluble sugars and starch via various enzymes, a high level of IAA and a low ABA to IAA ratio mainly contributed to stolon development of T. edulis. This paper explored carbohydrate levels and endogenous hormones profiles during stolon formation, which provided the theory basis for further regulating stolon growth of T. edulis.

Dynamic changes in carbohydrate metabolism and endogenous hormones during Tulipa edulis stolon development into a new bulb

The stolon is the main asexual reproductive organ of Tulipa edulis (Miq.) Baker. It has a special morphology and can develop into a new bulb for propagation. In the current greenhouse experiment, the dynamic changes in carbohydrates and related enzymes, protein and endogenous hormones during T. edulis stolon development were investigated. The results showed that soluble sugar levels were basically declining, whereas starch and protein content rose continuously during stolon development. The adenosine diphosphoglucose pyrophosphorylase (AGPase) activity peaked in the initial swelling stage and stayed a relative high level in the middle swelling stage; sucrose synthase (SS), soluble starch synthase (SSS) and granule-bound starch synthase (GBSS) activities followed the same law that showed rising trends during stolon development. SS activity was significantly inversely related to sucrose content but had significantly positive relations with starch content, SSS and GBSS activities. Gibberellin (GA), indole-3-acetic acid (IAA) and zeatin riboside (ZR) peaked in the initial swelling stage and maintained high levels in the middle swelling stage; they then decreased significantly in the later swelling stage. A substantial increase was observed in abscisic acid (ABA) content until the middle swelling stage, followed by a significant reduction in the later swelling stage. The ratios of ABA to IAA, GA and ZR reached their lowest levels in the initial swelling stage. In conclusion, T. edulis stolon development is a process of new bulb morphogenesis along with the starch accumulation catalyzed by AGPase, SSS and GBSS, using the product of sucrose cleavage caused by SS. Initial low ABA content and low ratios of ABA to IAA, GA and ZR, together with the GA, IAA and ZR of high-content, soluble sugars worked more efficiently to induce new bulb formation.

Changes in Carbohydrate Accumulation and Activities of Enzymes Involved in Starch Synthesis in Maize Kernels at Different Positions on an Ear during Grain Filling

Kernels at the upper position of a maize ear usually show slower filling rate and lower weight than those at the basal and middle positions. The mechanism is little understood. The objective of this study was to understand if changes in carbohydrate accumulation and activities of the enzymes involved in starch synthesis in the kernels at different positions on a maize ear were associated with grain filling. A maize cultivar Denghai 11 was planted in spring and summer. Contents of the soluble sugar,sucrose and starch and the activities of the adenosine diphosphoglucose pyrophosphorylase(AGPase),starch synthase(St S),and starch branching enzyme(SBE) in kernels at different positions on an ear and their relationships with grain filling rate were determined. The results showed that kernel number per ear,100-kernel weight,and grain yield were more or higher for the spring maize than for the summer maize. Although the grain yield was different between the spring maize and the summer maize,the maximum kernel filling rate,mean kernel filling rate,100-kernel weight,the contents of both soluble sugar and sucrose in kernels,the maximum starch accumulation rate and mean starch accumulation rate in kernels all exhibited an order of basal position middle position upper position. The activities of AGPase,St S,and SBE in kernels at different positions on an ear showed the changes of single peak curves,and the peak and mean enzymatic activities in kernels at the upper position were significantly lower than those at both middle and basal positions. The starch accumulation rate and kernel filling rate were very significantly and positively correlated with activities of AGPase,St S,and SBE in kernels. The results suggested that a smaller starch accumulation rate and lower weight for the kernels at the upper position on a maize ear are mainly attributed to lower activities of the enzymes involved in starch synthesis in these kernels. A higher kernel weight for the spring maize is closely associated with its stronger ability of starch synthesis in the kernels.

Mid-season nitrogen application strategies for rice varieties differing in panicle size

Application of nitrogen (N) during the mid-season is an important practice in rice production. However, little is known if its timing should vary with the varieties differing in panicle size. We investigated the effectiveness of various mid-season N applications on the grain yield and nitrogen use efficiency (NUE) for rice varieties differing in panicle size. Three high-yielding japonica rice varieties, Yangfujing-8, Lianjing-7 and Huaidao-9 with a small, medium and large panicle size respectively, were grown in the field. Four N treatments during the mid-season, applied at the stages of panicle initiation (PI), spikelet differentiation (SD), heading time (HT) or all the three stages, were adopted with no N application as control. Results show that their effectiveness on grain yield and NUE varied substantially with the variety panicle size. For Yangfujing-8, N applied at PI was the most effective in increasing yield and NUE, while for Huaidao-9, N applied at SD or HT was the most effective. The effectiveness was similar for Lianjing-7 when N applied at PI, SD or N split application at PI, SD, and HT. Nitrogen applied at SD markedly increased crop growth rate during the 15-day period proceeding heading and pre-anthesis non-structural carbohydrate accumulation in the stem at heading. While N applied at HT significantly increased the photosynthesis of leaves. Both treatments of N applied at SD and HT could increase activities of sucrose synthase and adenosine diphosphoglucose pyrophosphorylase in the inferior spikelets of HD-9 at the mid and late grain filling stages. According the results, a mid-season N application strategy is suggested: applying N at PI to increase sink capacity for a variety with a small panicle size, at SD or HT to increase filling efficiency for a variety with a large panicle size, and at either PI or SD for a variety with a medium panicle size.

Changes in Enzyme Activities Involved in Starch Synthesis and Hormone Concentrations in Superior and Inferior Spikelets and Their Association with Grain Filling of Super Rice

The changes in activities of key enzymes involved in sucrose-to-starch conversion and concentrations of hormones in superior and inferior spikelets of super rice were investigated and their association with grain filling was analyzed. Four super rice cultivars, Liangyoupeijiu, IIyou 084, Huaidao 9 and Wujing 15, and two high-yielding and elite check cultivars, Shanyou 63 and Yangfujing 8, were used. The activities of sucrose synthase (SuSase), adenosine diphosphoglucose pyrophosphorylase (AGPase), starch synthase (StSase) and starch branching enzyme (SBE), and the concentrations of zeatin + zeatin riboside (Z + ZR), indole-3-acetic acid (IAA) and abscisic acid (ABA) in superior and inferior spikelets were determined during the grain filling period and their relationships with grain filling rate were analyzed. Maximum grain filling rate, the time reaching the maximum grain-filling rate, mean grain filling rate and brown rice weight for superior spikelets showed a slight difference between the super and check rice cultivars, but were significantly lower in the super rice than in the check rice for inferior spikelets. Changes of enzyme activities and hormone concentrations in grains exhibited single peak curves during the grain filling period. The peak values and the mean activities of SuSase, AGPase, StSase and SBE were lower in inferior spikelets than in superior ones, as well as the peak values and the mean concentrations of Z + ZR and IAA. However, the peak value and the mean concentration of ABA were significantly higher in inferior spikelets than in superior ones and greater in the super rice than in the check rice. The grain filling rate was positively and significantly correlated with the activities of SuSase, AGPase and StSase and the concentrations of Z + ZR and IAA. The results suggested that the low activities of SuSase, AGPase and StSase and the low concentrations of Z + ZR and IAA might be important physiological reasons for the slow grain filling rate and light grain weight of inferior spikelets in super rice.

Agronomic and physiological performance of high-yielding wheat and rice in the lower reaches of Yangtze River of China

Understanding agronomic and physiological performance of crop high yield is essential to make strategies for breeding and crop management. This study aimed to identify major agronomic and physiological traits associated with high grain yields of rice and wheat in the wheat–rice rotation system in the lower reaches of Yangtze River of China. Two high-yielding cultivars, each for winter wheat and rice, were field-grown from 2008 to 2010 for 3 years. Two crop management treatments, the local farmer's practice (LFP) and improved high-yielding cultivation (IHC), were used. The IHC adopted two new techniques, i.e., site-specific nitrogen management in both rice and wheat and alternate wetting and moderate drying irrigation in rice and controlled soil drying irrigation in wheat. Across the 3 years, the IHC yielded an average 9.67tha−1 of wheat and 12.55tha−1 of rice with an annual total of 22.2tha−1, an increase of 26.8% when compared with that (17.5tha−1) under the LFP. The increased grain yield under the IHC was mainly attributed to expanded sink size as a result of more kernels per spike or more spikelets per panicle, increased kernel weight of wheat and increased percentage of filled grains of rice. When compared with LFP, IHC showed a greater percentage of productive tillers, more pre-anthesis nonstructural carbohydrate (NSC) storage in the stem, greater leaf photosynthetic rate and concentration of cytokinins in root exudates, higher activities of sucrose synthase and adenosine diphosphoglucose pyrophosphorylase in grains, more dry mater production during the grain filling period, and higher harvest index. We conclude that (1) expanding sink capacity through an increase in kernels per spike or spikelets per panicle, (2) enhancing grain filling efficiency by an increase in pre-anthesis NSC in the stem, and (3) increasing post-anthesis dry mater production by an enhancement in root activity during grain filling should be considered as three major strategies for further increases in grain yields of wheat and rice in the lower reaches of Yangtze River of China.

Leaf photosynthesis and carbohydrates of CO 2-enriched maize and grain sorghum exposed to a short period of soil water deficit during vegetative development

Among C 4 species, sorghum is known to be more drought tolerant than maize. The objective was to evaluate differences in leaf gas exchanges, carbohydrates, and two enzyme activities of these nicotinamide adenine dinucleotide phosphate-malic enzyme (NADP-ME) C 4 subtype monocots in response to water deficit and CO 2 concentration ([CO 2]). Maize and sorghum were grown in pots in sunlit environmental-controlled chambers. Treatments included well watered (WW) and water stressed (WS) (water withheld at 26 days) and daytime [CO 2] of 360 (ambient) and 720 (elevated) μmol mol −1. Midday gas exchange rates, concentrations of nonstructural carbohydrates, and activities of sucrose-phosphate synthase (SPS) and adenosine 5′-diphosphoglucose pyrophosphorylase (ADGP) were determined for fully expanded leaf sections. There was no difference in leaf CO 2 exchange rates (CER) between ambient and elevated [CO 2] control plants for both maize and sorghum. After withholding water, leaf CER declined to zero after 8 days in maize and 10 days for sorghum. Sorghum had lower stomatal conductance and transpiration rates than maize, which resulted in a longer period of CER under drought. Nonstructural carbohydrates of both control maize and sorghum were hardly affected by elevated [CO 2]. Under drought, however, increases in soluble sugars and decreases in starch were generally observed for maize and sorghum at both [CO 2] levels. For stressed maize and sorghum, decreases in starch occurred earlier and were greater at ambient [CO 2] than at elevated [CO 2]. For maize, drought did not meaningfully affect SPS activity. However, a decline in SPS activity was observed for drought-stressed sorghum under both [CO 2] treatments. There was an increase in ADGP activity in maize under drought for both [CO 2] treatments. Such a response in ADGP to drought, however, did not occur for sorghum. The generally more rapid response of maize than sorghum to drought might be related to the more rapid growth of leaf area of maize.

Pre-anthesis non-structural carbohydrate reserve in the stem enhances the sink strength of inferior spikelets during grain filling of rice

Sink strength plays an important role in grain filling of cereals but how it is related to the pre-anthesis non-structural carbohydrate (NSC) reserves is not clear. This study investigated if and how an increase in NSC reserves could enhance sink strength, and consequently improve grain filling of later-flowering inferior spikelets (in contrast to the earlier flowering superior spikelets) for rice varieties with large panicles. Two “super” rice varieties (the recently bred high-yielding rice) and two New Plant Type (NPT, named in IRRI for the extra-large panicle) rice lines were compared with two elite inbred varieties under field-grown conditions. Three nitrogen (N) treatments, applied at the stages of panicle initiation, spikelet differentiation or both, were adopted with no N application during the mid-season as control. Both super rice and NPT rice showed a greater yield capacity as a result of a larger panicle than the elite inbred rice. However, a lower percentage of filled grains limited the realization of higher yield potential in super rice and especially in NPT rice, due to their lower grain filling rate and the smaller grain weight of their inferior spikelets. The low grain filling rate and small grain weight of inferior spikelets are mainly attributed to a poor sink strength as a result of small sink size (small number of endosperm cells) and low sink activity, e.g. low activities of sucrose synthase (SuSase) and adenosine diphosphoglucose pyrophosphorylase (AGPase). The amounts of NSC in the stem and NSC per spikelet at the heading time are significantly and positively correlated with sink strength (number of endosperm cells and activities of SuSase and AGPase), grain filling rate, and grain weight of inferior spikelets. Nitrogen application at the spikelet differentiation stage significantly increased, whereas N application at the panicle initiation or at both panicle initiation and spikelet differentiation stages, significantly reduced, NSC per spikelet at the heading time, sink strength, grain filling rate, and grain weight of inferior spikelets in super rice. The results suggest that pre-anthesis NSC reserves in the stem are closely associated with the sink strength during grain filling of rice, and N application at the spikelet differentiation stage would be a good practice to increase pre-anthesis NSC reserves, and consequently to enhance sink strength for rice varieties with large panicles, such as super rice varieties.

Effects of soil water deficit on physiological causes of rice grain-filling

Aims Our objective was to elucidate the physiological causes of the influence of soil water deficit on grain-filling and rice (Oryza sativa) yield by evaluating enzyme activities involved in sucrose-starch synthesis during the grain-filling period. Methods Two rice cultivars (‘Shanyou 63’ and ‘Pc311/Zaoxiandang’) were grown in cement containers. Controlled soil water deficit was imposed at 9th day after flowering because the division of endosperm cells is sensitive to water deficit. The activities of key enzymes involved in the metabolism of sucrose to starch during grain-filling were evaluated. Important findings The 1000-grain weight and rice yield under soil water deficit were significantly decreased. The key enzyme activities, including sucrose synthase, adenine diphosphoglucose pyrophosphorylase, soluble starch synthase and starch branching enzyme, involved in the metabolism of sucrose to starch were significantly increased under soil water deficit during 10–20 days after anthesis. However, the activities of these enzymes under soil water-deficit were decreased rapidly 20–30 days after flowering compared to well-watered treatments. Active grain-filling periods of the water-deficit treatments were shortened as a result of the decrease of starch accumulation. Therefore, the rapid decline of the key enzyme activities involved in sucrose to starch metabolism and the shortage of assimilation supply at 20–30 days after anthesis are reasons for decreases in grain weight and yield under soil water deficit conditions.

Analysis of Physiological and Biochemical Characteristics of Six Mutants with Stable High Percentage of Chalkiness in Rice Grains

For explaining the mechanism of chalkiness formation in rice ( Oryza sativa L.), the physiological and biochemical factors for chalkiness formation were analyzed using 6 mutants with chalky percentage higher than 80%, which were obtained from a T-DNA insertion mutant pool of cultivar Nipponbare. The appearance of high chalky percentages of the 6 mutants was proven to result from genetic factors because high temperature stress did not occur during grain-filling period. Based on the activities of key enzymes associated with starch synthesis, sucrose content, starch content, and ratio of amylose to starch in mature grains, the 6 mutants were classified into 3 groups. Compared with the wild type, mutants mu1 and mu2 had lower activities of sucrose synthase (SS) during the whole grain-filling period, higher activity of adenosine diphosphoglucose pyrophosphorylase (AGPase) at early grain-filling stage, and higher activities of SS I and total soluble starch synthase (SSS) at late grain-filling stage. Mutants mu3 and mu6 had lower activities of SS I, total SSS, pullulanase, and isoamylase at early filling stage and higher isoamylase activity at late filling stage than the wide type. Compared with the wild type, mutants mu4 and mu5 exhibited higher SS activity at early and middle stages of grain filling and lower activity of total SSS during the whole grain-filling period; the isoamylase activity increased from a lower level than the wild type at early filling stage to a higher level at late filling stage. All the 6 mutants had white belly grains with no visible differences to the wild type after iodine staining. The contents of fructose, sucrose, and total soluble sugar were higher in the 6 mutants than in the wild type, especially in mu2 and mu5. These results primarily revealed the physiological basis of chalkiness formation during rice grain development.

Post-Anthesis Changes in Concentrations of Polyamines in Superior and Inferior Spikelets and Their Relation with Grain Filling of Super Rice

Success in super rice breeding has been considered a great progress in rice production in China. However, many un-filled inferior spikelets limit the realization of great yield. As polyamines have been frequently described as endogenous plant growth regulators or intracellular messengers mediating physiological processes, this study investigated whether and how poly-amines are involved in the regulating post-anthesis development of rice spikelets. Four super rice cultivars, Liangyoupeijiu and II you 084 (indica hybrids), Huaidao 9 and Wujing 15 (japonica), and two high-yielding check cultivars, Shanyou 63 (indica hybrid) and Yangfujing 8 (japonica), were field grown. Concentrations of putrescine (Put), spermidine (Spd) and spermine (Spm) in both inferior and superior spikelets during the grain filling period and grain filling rate were determined. The relationship between polyamine concentrations and grain filling rate were analyzed, and chemical regulators were applied to verify the roles of poly-amines in grain filling. The results showed that the maximum grain filling rate, mean grain filling rate, and brown rice weight for superior spikelets showed small difference between the super rice and check rice, but those of inferior spikelets were significantly lower for super rice than for check rice cultivars. Changes in concentrations of polyamines in grains exhibited single peak during the grain filling period. The peak and mean concentrations of Put were greater in inferior than in superior spikelets. The peak and mean concentrations of Spd and Spm were greater in the superior than in the inferior, and greater in the check rice than in the su-per rice. The mean grain filling rate and brown rice weight were negatively and very significantly correlated with the Put concen-trations, and positively and very significantly correlated with Spd and Spm concentrations, Spd/Put, and Spm/Put. Application of Spd or Spm to panicle at the early grain filling stage significantly enhanced activities of sucrose synthetase, adenine di-phosphoglucose pyrophosphorylase, and soluble starch synthetase in inferior spikelets, and significantly increased grain filling rate, seed setting rate and grain weight of inferior spikelets. Application of Put or methylglyoxal-bis (guanylhydrazone) (MGBG, an inhibitor of S-adenosyl-L-methionine decarboxylase) exhibited an opposite effect. The results suggest that polyamines play a role in regulating grain filling. Low concentrations of Spd and Spm and low Spd/Put and Spm/Put may be an important physiological reason for the small grain filling rate and low grain weight of inferior spikelets in super rice.

Post-Anthesis Changes in Concentration of Polyamine in Superior and Inferior Spikelets and Their Relationship with Grain Filling of Super Rice

To reveal the physiological role of polyamines and the mechanism involved in grain-filling of rice ( Oryza sativa L.) superior and inferior spikelets, the relationship between grain-filling rate and polyamine concentrations was analyzed and verified using 4 super rice cultivars and 2 high-yielding cultivars (controls). Compared with the controls, super rice had similar maximum grain-filling rate, mean grain-filling rate, and brown rice weight in superior spikelets and significantly lower values in inferior spikelets. The concentrations of putrescine (Put), spermidine (Spd), and spermine (Spm) varied in single-peak curves in both inferior and superior spikelets during grain-filling period. The peak and mean concentrations of Put were greater in inferior spikelets than in superior spikelets. However, the peak and mean concentrations of Spd and Spm were greater in superior spikelets than in inferior spikelets. The control cultivars had higher concentrations of polyamines than super rice. The mean grain-filling rate and brown rice weight were negatively correlated with Put concentration, and positively correlated with Spd and Spm concentrations and the ratios of Spd/Put and Spm/Put. Spraying of Spd or Spm to panicle at early grain-filling stage significantly enhanced activities of sucrose synthetase, adenine diphosphoglucose pyrophosphorylase, and soluble starch synthetase in inferior spikelets, resulting in improvement of grain-filling rate, seed-setting rate, and grain weight. Application of Put or methylglyoxal-bis (guanylhydrazone) (MGBG, an inhibitor of S-adenosyl- L-methioninedecarboxylase) exhibited an opposite effect. These results indicated a regulative function of polyamines during grain filling. The low grain-filling rate and grain weight in inferior spikelets of super rice are probably in relation to the low concentrations of Spd and Spm and the small ratios of Spd/Put and Spm/Put in inferior spikelets.

Metabolic Enzymes, Antioxidants, and Cytoskeletal Proteins Are Significantly Altered in Vastus Lateralis Muscle of K-Depleted Cadaveric Subjects

Molecular mechanisms underlying myopathy caused by prolonged potassium (K) depletion remain poorly understood. In the present study, we examined proteome profile of vastus lateralis muscle obtained from cadaveric subjects who had K depletion (KD) (muscle K<80 micromol/g wet weight) compared to those who had no KD (NKD) (muscle K>or=80 micromol/g wet weight) (n=6 per group). Muscle proteins were extracted, resolved by 2-DE, and visualized with CBB-R250 stain. Spot matching and intensity analysis revealed significant changes in levels of 11 (6 increased and 5 decreased) protein spots in the KD group. Q-TOF MS and MS/MS analyses identified these altered proteins as metabolic enzymes (aldehyde dehydrogenase 1A1, uridine diphosphoglucose pyrophosphorylase, enolase 1, cytosolic malate dehydrogenase, and carbonic anhydrase III), antioxidants (peroxiredoxin-3 isoform b), cytoskeletal proteins (slow-twitch skeletal troponin I and myosin light chain 2), and others. These altered proteins are involved in many cellular functions, including bioenergetics, acid-base regulation, oxidative stress response, and muscle contractility. Validation was done by Western blot analysis, which confirmed the increased level of peroxiredoxin-3 and decreased level of troponin-I in the KD muscle. Linear regression analysis also revealed a significant negative correlation between peroxiredoxin-3 level and muscle K content (r=-0.887; p<0.001), as well as a significant positive correlation between troponin-I level and muscle K content (r=0.618; p<0.05). Our results implicate the important roles these altered proteins play in the development of KD-associated myopathy.

Relationship between activities of key enzymes involved in starch synthesis and accumulation in maize inbred lines during grain filling

Time course of starch production and the key enzyme activities in the grains of four maize inbred lines (two high-starch and two low-starch lines) were studied. Accumulation of grain starch and its components in four maize inbred lines rose continuously after pollination and increased as a sigmoid curve during grain filling. The accumulation rates showed single-peak curves. The accumulation rates of starch and its components reached their peaks on 25–32 days after pollination (DAP), respectively. Activities of adenosine diphosphoglucose pyrophosphorylase (AGPPase) and starch synthase in the grains of four lines followed single-peak curves with the peaks on 24–31 DAP. The highest activity of the starch-branching enzyme (Q-enzyme) in the grains of both high-starch lines appeared on 23 DAP, but that of both low-starch inbred lines showed double-peak curves, the peaks being at 15–20 DAP and 30–35 DAP. There was significant positive correlation between AGPPase, soluble starch synthase (SSS), and starch granule-bound synthase (GBSS) activities. The results indicated the Q-enzyme had different expression patterns in the high-and the low-starch maize inbred lines, and that AGPPase, SSS, and GBSS activities were significantly and positively correlated with amylose, amylopectin, and starch accumulation rates in all lines.

Effects of Soil Moisture and Irrigation Patterns during Grain Filling on Grain Yield and Quality of Rice and Their Physiological Mechanism

The objective of this study was to investigate whether a moderate soil-drying or an alternate wetting and moderate-drying irrigation during the grain filling period could improve the grain quality and increase yield in rice. Two rice cultivars, Wuyujing 3 (japonica) and Yangdao 6 (indica), were grown in pots and cement tanks. Three soil moisture treatments and three irrigation patterns, well-watered (WW, well-watered) and conventional irrigation (CI, continuous flooding), moderate soil-drying (MD, soil water potential at-10～-30 kPa) and alternate wetting and moderate-drying irrigation (W-MD, re-watered when soil water potential reached at-25 kPa), and severe soil-drying (SD, soil water potential at-40～-60 kPa) and alternate wetting and severe-drying irrigation (W-SD, re-watered when soil water potential reached at-50 kPa), were imposed during grain-filing. Compared with WW or CI, MD or W-MD significantly increased grain weight, peak viscosity, and breakdown values, and re-duced chalkiness and setback values. The results were reversed for SD or W-SD treatments. Activities of sucrose synthase (SuS), adenine diphosphoglucose pyrophosphorylase (AGP), starch synthase (StS), and starch branching enzyme (SBE) in grains in mid-dle and late grain-filling stages were significantly enhanced, whereas ethylene revolution rate of grains decreased, under MD or W-MD. The SD or W-SD had the opposite effects. The results indicate that both MD and W-MD can improve rice quality, result-ing from the physiological mechanism of enhancing activities of SuS, AGP, StS, and SBE and decreasing ethylene production in grains.