Pattern Of Starch Accumulation Research Articles

Transcriptomic analysis of starch accumulation patterns in different glutinous sorghum seeds

Sorghum is a high-quality raw material for brewing white wine, and the starch content in seeds has a large impact on brewing quality. Transcriptomic data obtained from a glutinous variety (Liaonian3) and a non-glutinous variety (Liaoza10) at 3, 18, and 30 days after pollination were analyzed to identify genes associated with starch accumulation. The amylopectin content was significantly higher in Liaonian3 compared to Liaoza10, but the amylose content and total starch content were lower. There were 6634 differentially expressed genes found in Liaoza10 between 3 and 18 d after pollination, and 779 differentially expressed genes between 18 and 30 d after pollination. In Liaonian3, there were 6768 differentially expressed genes between 3 and 18 d after pollination, and 7630 differentially expressed genes between 18 and 30 d after pollination. Genes were grouped by expression profiles over the three time points and the profiles were analyzed for enrichment of gene ontology terms and biochemical pathways. Profile 1 (decreasing expression from 3 to 30 d) for Liaoza10 was enriched in ribosomes, metabolic pathways, and carbon metabolic pathways. Profile 0 (decreasing expression from 3 to 18 d and consistent expression from 18 to 30 d) was enriched in pathways related to sugar or starch metabolism. Although the starch accumulation rate in Liaonian3 and Liaoza10 showed a profile of increasing and then decreasing, the expression of genes related to starch synthesis gradually decreased with time since pollination, demonstrating the complexity of starch synthesis. According to orthologous gene alignment and expression analysis, 19 genes such as entrzID_8068390 and entrzID_8066807 were found to be the key genes for starch synthesis and glutinous and non-glutinous differentiation in sorghum grains.

Variability in starch granular morphology of Tinospora cordifolia: an important species of Indian Systems of Medicine (ISM).

Tinospora cordifolia is an important medicinal plant species known for therapeutic action of starch along with other medicinal ingredients. The starch prepared from the aqueous extract of fresh stems is used in the Indian Systems of Medicines. The plant extract prepared from T. cordifolia is a promising source for the treatment of COVID-19. This investigation explores for the first time, the morphological details of the starch granules and its accumulation pattern along with its variability among the germplasm of T. cordifolia collected from different parts of India. Starch content was 39.80% on dry weight basis and moisture content was about 28.21%. Starch granule recovery based on stem dry weight and starch content ranged from 14.70 to 20.28% and 52.02 to 71.76%, respectively in different starch settling methods. Starch accumulation pattern in the stem was also studied in the species. Even though wide variability in starch granule shapes was observed among the germplasm, majority of the genotypes had starch granules of round or oval shape. Similarly, starch granule size also varied greatly (38.32–88.03 µm) within and among the genotypes. Significantly small sized starch granules (p = 0.05) were present in the genotype, IC 283650 and biggest (p = 0.05) starch granules were present in the genotype, IC 310610. The information generated in the present study will have application in starch industry for the inclusion of T. cordifolia as an alternative source of starch in addition to its use in Traditional Systems of Medicine.Supplementary InformationThe online version contains supplementary material available at 10.1007/s42535-021-00286-y.

The sugar-responsive circadian clock regulator bZIP63 modulates plant growth.

Summary Adjustment to energy starvation is crucial to ensure growth and survival. In Arabidopsis thaliana (Arabidopsis), this process relies in part on the phosphorylation of the circadian clock regulator bZIP63 by SUCROSE non‐fermenting RELATED KINASE1 (SnRK1), a key mediator of responses to low energy.We investigated the effects of mutations in bZIP63 on plant carbon (C) metabolism and growth. Results from phenotypic, transcriptomic and metabolomic analysis of bZIP63 mutants prompted us to investigate the starch accumulation pattern and the expression of genes involved in starch degradation and in the circadian oscillator. bZIP63 mutation impairs growth under light‐dark cycles, but not under constant light. The reduced growth likely results from the accentuated C depletion towards the end of the night, which is caused by the accelerated starch degradation of bZIP63 mutants. The diel expression pattern of bZIP63 is dictated by both the circadian clock and energy levels, which could determine the changes in the circadian expression of clock and starch metabolic genes observed in bZIP63 mutants.We conclude that bZIP63 composes a regulatory interface between the metabolic and circadian control of starch breakdown to optimize C usage and plant growth.

High day- and night-time temperatures affect grain growth dynamics in contrasting rice genotypes.

Rice grain yield and quality are predicted to be highly vulnerable to global warming. Five genotypes including heat-tolerant and susceptible checks, a heat-tolerant near-isogenic line and two hybrids were exposed to control (31 °C/23 °C, day/night), high night-time temperature (HNT; 31 °C/30 °C), high day-time temperature (HDT; 38 °C/23 °C) and high day- and night-time temperature (HNDT; 38 °C/30 °C) treatments for 20 consecutive days during the grain-filling stage. Grain-filling dynamics, starch metabolism enzymes, temporal starch accumulation patterns and the process of chalk formation were quantified. Compensation between the rate and duration of grain filling minimized the impact of HNT, but irreversible impacts on seed-set, grain filling and ultimately grain weight were recorded with HDT and HNDT. Scanning electron microscopy demonstrated irregular and smaller starch granule formation affecting amyloplast build-up with HDT and HNDT, while a quicker but normal amylopast build-up was recorded with HNT. Our findings revealed temporal variation in the starch metabolism enzymes in all three stress treatments. Changes in the enzymatic activity did not derail starch accumulation under HNT when assimilates were sufficiently available, while both sucrose supply and the conversion of sucrose into starch were affected by HDT and HNDT. The findings indicate differential mechanisms leading to high day and high night temperature stress-induced loss in yield and quality. Additional genetic improvement is needed to sustain rice productivity and quality under future climates.

Leaf Starch Turnover Occurs in Long Days and in Falling Light at the End of the Day.

We investigated whether starch degradation occurs at the same time as starch synthesis in Arabidopsis (Arabidopsis thaliana) leaves in the light. Starch accumulated in a linear fashion for about 12 h after dawn, then accumulation slowed and content plateaued. Following decreases in light intensity, the rate of accumulation of starch declined in proportion to the decline in photosynthesis if the decrease occurred <10 h after dawn, but accumulation ceased or loss of starch occurred if the same decrease in light intensity was imposed more than 10 h after dawn. These changes in starch accumulation patterns after prolonged periods in the light occurred at both high and low starch contents and were not related to time-dependent changes in either the rate of photosynthesis or the partitioning of assimilate between starch and Suc, as assessed from metabolite measurements and 14CO2 pulse experiments. Instead, measurements of incorporation of 13C from 13CO2 into starch and of levels of the starch degradation product maltose showed that substantial starch degradation occurred simultaneously with synthesis at time points >14 h after dawn and in response to decreases in light intensity that occurred >10 h after dawn. Starch measurements in circadian clock mutants suggested that the clock influences the timing of onset of degradation. We conclude that the propensity for leaf starch to be degraded increases with time after dawn. The importance of this phenomenon for efficient use of carbon for growth in long days and for prevention of starvation during twilight is discussed.

Starch Concentrations in Grapevine Leaves, Berries and Roots and the Effect of Canopy Management

Diurnal and seasonal starch changes in leaves, berries and roots of Vitis vinifera L. cv. Cabernet Sauvignon/99 Richter and the effect of canopy management (a combination of suckering, shoot positioning, and 33% defoliation) on these processes were investigated under field conditions. An increase in starch concentration of basal leaves occurred from the morning to the afternoon during the most active vegetative growth period (up to veraison), indicating a proportional change in storage or export of assimilates between day and night. During later developmental stages diurnal starch levels slightly declined or remained the same. Seasonally, leaf starch remained relatively stable until veraison, whereafter it increased, reaching highest concentrations at the post-harvest stage. Canopy management generally increased leaf starch concentrations. Berries contained no significant amounts of starch. Root starch concentrations were usually higher than those of leaves. Diurnally as well as seasonally, root starch accumulation patterns coincided with those of leaves, indicating a close relationship between source and sink tissue. Canopy management resulted in stable diurnal root starch concentrations without affecting the daily mean starch level; afternoon values of treated vines were, however, generally lower. The results imply that carbohydrate supply and starch-synthesising enzyme systems were not limited by manipulating the canopy and decreasing foliage. It seems, however, that particularly late in the season starch accumulation in roots may be delayed by canopy manipulation as applied. This indicates a shift in sucrose partitioning and its utilisation in roots and other sink areas, e.g. the berries, when the canopy is manipulated.

Effects of abscisic acid and an osmoticum on the maturation, starch accumulation and germination of Picea spp. somatic embryos

The aim of this study was to investigate whether ABA, sucrose or Phytagel applied to the maturation medium at different concentrations affected the growth, development and starch content of somatic embryos of Picea abies and Picea omorika. Embryogenic tissues of both spruce species were placed on maturation medium supplemented with various doses of ABA (10, 20, 40 and 80 µM), sucrose (17, 34 and 68 g/L) or Phytagel (4, 6 and 8 g/L). Our results showed that ABA and the osmoticum had a significant effect on the production and maturation of somatic embryos of both spruce species. Supplementing the medium with low concentrations of ABA (10 µM) or sucrose (17 g/L) resulted in the precocious germination of embryos. Adding sucrose to the maturation medium at the highest tested concentration (68 g/L) improved the growth of the radicles of the embryos of both spruce species during the germination stage. Moreover, the intensity of the growth of the hypocotyls and radicles of P. omorika germinating embryos depended on the Phytagel concentration applied to the maturation medium. The starch content and the starch accumulation pattern of Picea abies and P. omorika somatic embryos were dependent on the concentration of ABA, sucrose or Phytagel in the maturation medium. In general, during development, the P. abies somatic embryos accumulated a much greater amount of starch than P. omorika embryos did. The effects of ABA and osmoticum on the starch accumulation pattern of Picea abies and P. omorika somatic embryos are first reported in this paper.

찰옥수수 2기작 재배시 등숙 중 이삭 및 종실 특성 변화

본 연구에서는 간식용 풋옥수수로 이용되는 찰옥수수 주요 품종인 찰옥 4호와 일미찰을 2기작 재배하여 품질 좋은 찰옥수수 생산을 위한 재배법을 확립하고자 이삭과 종실 특성 변화를 조사하였다. 2기작 재배시 출사일수는 후기작이 전기작 보다 약 20일 정도 빨라졌고, 출사에서 수확적기까지는 약 10일 정도 느려졌다. 파종에서 출사까지의 적산온도는 약 <TEX>$1,380{\sim}1,420^{\circ}C$</TEX>, 출사에서 수확까지는 약 <TEX>$590{\sim}630^{\circ}C$</TEX> 정도 범위였다. 이삭무게와 이삭직경은 출사 후 일수가 경과함에 따라 유의하게 증가하였으나 파종시기에 따른 차이는 없었고, 이삭길이와 착립길이는 후기작에서 유의하게 짧았다(p<0.05). 알곡 줄수는 파종시기에 따른 차이를 보이지 않았고, 줄당 립수는 찰옥 4호가 전기작보다 후기작에 재배한 것이 적었으며 변이폭이 컸다(p<0.05). 등숙 중 종실의 길이, 너비, 두께와 100립 생체중, 전분함량은 출사후 일수에 따라 유의하게 증가하였다(p<0.05). 후기작 재배시 저온 등숙으로 전기작 보다 100립 생체중과 전분함량의 증가속도가 느려졌다. 찰옥수수의 전분립은 과피와 가까운 배유의 상단부터 집적되기 시작하여 출사 후 일수가 경과함에 따라 배유 내부까지 집적되었으며, 후기작 재배한 찰옥수수는 전분립 축적속도가 느리고 조밀하지 않은 것이 관찰되었다. 100립 생체중은 springiness(<TEX>$0.80^{***}$</TEX>), cohesiveness(<TEX>$0.44^{***}$</TEX>), adhesiveness(<TEX>$-0.80^{***}$</TEX>), chewiness(<TEX>$0.55^{***}$</TEX>), 전분함량은 springiness(<TEX>$0.79^{***}$</TEX>), adhesiveness(<TEX>$-0.81^{***}$</TEX>), chewiness(<TEX>$0.49^{**}$</TEX>)와 고도로 유의한 정의 상관을 나타내었다. This study was conducted to investigate the ear and kernel characteristics of waxy corn during ripening by double cropping, and to understand the pattern of starch accumulation in endosperm of waxy corn kernels. Chalok4 and Ilmichal were sown at April 20 (first cropping) and July 20 (second cropping) in 2011~2012. The accumulated temperature from silking to harvesting was about <TEX>$590{\sim}630^{\circ}C$</TEX>. It takes 23~24 days when Chalok4 and Ilmichal were sown in April 20, but July 20 sowing takes 32~35 days. Ear length and kernel set length were significantly shorter in second cropping (p<0.05). Kernel length, kernel width, 100-kernel weight, and starch content of waxy corn were increased as ears matured (p<0.05). Growth temperature was getting decreased during the ripening stage of second cropping, the rate of ear and kernel development had slowed. Starch granules started to accumulate in the cells around the pericarp, then developed in the cells around the embryo. In the second cropping, starch granules in the kernel of waxy corn were less compact than the first cropping, harvesting time of waxy corns can be extended. These results will be helpful to farmers for double cropping of waxy corn cultivation and management.

Alfalfa nodules elicited by a flavodoxin-overexpressing Ensifer meliloti strain display nitrogen-fixing activity with enhanced tolerance to salinity stress

Nitrogen fixation by legumes is very sensitive to salinity stress, which can severely reduce the productivity of legume crops and their soil-enriching capacity. Salinity is known to cause oxidative stress in the nodule by generating reactive oxygen species (ROS). Flavodoxins are involved in the response to oxidative stress in bacteria and cyanobacteria. Prevention of ROS production by flavodoxin overexpression in bacteroids might lead to a protective effect on nodule functioning under salinity stress. Tolerance to salinity stress was evaluated in alfalfa nodules elicited by an Ensifer meliloti strain that overexpressed a cyanobacterial flavodoxin compared with nodules produced by the wild-type bacteria. Nitrogen fixation, antioxidant and carbon metabolism enzyme activities were determined. The decline in nitrogenase activity associated to salinity stress was significantly less in flavodoxin-expressing than in wild-type nodules. We detected small but significant changes in nodule antioxidant metabolism involving the ascorbate-glutathione cycle enzymes and metabolites, as well as differences in activity of the carbon metabolism enzyme sucrose synthase, and an atypical starch accumulation pattern in flavodoxin-containing nodules. Salt-induced structural and ultrastructural alterations were examined in detail in alfalfa wild-type nodules by light and electron microscopy and compared to flavodoxin-containing nodules. Flavodoxin reduced salt-induced structural damage, which primarily affected young infected tissues and not fully differentiated bacteroids. The results indicate that overexpression of flavodoxin in bacteroids has a protective effect on the function and structure of alfalfa nodules subjected to salinity stress conditions. Putative protection mechanisms are discussed.

Post-Translational Redox Modification of ADP-Glucose Pyrophosphorylase in Response to Light is Not a Major Determinant of Fine Regulation of Transitory Starch Accumulation in Arabidopsis Leaves

ADP-glucose pyrophosphorylase (AGP) is a heterotetrameric enzyme comprising two small and two large subunits that catalyze the production of ADP-glucose linked to starch biosynthesis. The current paradigm on leaf starch metabolism assumes that post-translational redox modification of AGP in response to light is a major determinant of fine regulation of transitory starch accumulation. According to this view, under oxidizing conditions occurring during the night the two AGP small subunits (APS1) are covalently linked via an intermolecular disulfide bridge that inactivates the protein, whereas under reducing conditions occurring during the day NADP-thioredoxin reductase C (NTRC)-dependent reductive monomerization of APS1 activates the enzyme. In this work we have analyzed changes in the redox status of APS1 during dark-light transition in leaves of plants cultured under different light intensities. Furthermore, we have carried out time-course analyses of starch content in ntrc mutants, and in aps1 mutants expressing the Escherichia coli redox-insensitive AGP (GlgC) in the chloroplast. We also characterized aps1 plants expressing a redox-insensitive, mutated APS1 (APS1mut) form in which the highly conserved Cys81 residue involved in the formation of the intermolecular disulfide bridge has been replaced by serine. We found that a very moderate, NTRC-dependent APS1 monomerization process in response to light occurred only when plants were cultured under photo-oxidative conditions. We also found that starch accumulation rates during the light in leaves of both ntrc mutants and GlgC-expressing aps1 mutants were similar to those of wild-type leaves. Furthermore, the pattern of starch accumulation during illumination in leaves of APS1mut-expressing aps1 mutants was similar to that of APS1-expressing aps1 mutants at any light intensity. The overall data demonstrate that post-translational redox modification of AGP in response to light is not a major determinant of fine regulation of transitory starch accumulation in Arabidopsis.

Storage product synthesis and accumulation in developing grains of wheat

The time course of synthesis and accumulation of the major storage components in developing grain of wheat cv Hereward has been determined. Gluten proteins were first detected at 10 dpa and accumulated most rapidly between 12 and 35 dpa, with little change after 42 dpa. Differences in the accumulation patterns of two different types of ω-gliadins were observed while the synthesis of the HMW subunits was initiated about 2 days later than that of the other gluten proteins. Although protein accumulation had essentially ceased by 42 dpa, grain desiccation was associated with a dramatic increase in the proportion of large glutenin polymers. The accumulation of starch essentially paralleled that of gluten proteins, reaching 55% of the grain dry weight at maturity. This was associated with an increase in the amylose content, from about 20 to 26% of the total starch. The expression patterns of transcripts encoding enzymes of the synthesis (ADP glucose pyrophosphorylase, starch synthases), branching and modification of starch were consistent with the pattern of starch accumulation and with the expression patterns reported for orthologous genes in developing rice grain, showing high conservation between species.

Properties of the Protein and Carbohydrate Fractions in Immature Wheat Kernels

The time course of compositional changes in the polysaccharide and protein fractions, and of changes in protein structural properties, was investigated in grains of two Italian durum wheat cultivars, Ofanto and Duilio, and the pattern of changes was found to be specific to each cultivar. The fructo-oligosaccharide content in ripening kernels was different between cultivars, as was the pattern of starch accumulation. Evaluation of gluten proteins by Western-blotting using broad-specificity anti-gliadin antibodies showed the sudden appearance of immunoreactive proteins during ripening. Protein surface hydrophobicity and thiol content and accessibility were evaluated in conditions apt at assessing changes in protein interaction and/or in aggregative patterns. Proteins in the two cultivars showed differences in their surface hydrophobicity and in their content of accessible thiols. The simultaneous evaluation of changes in the individual components indicates that use of immature grains for the production of functional foods will require accurate monitoring of the rapidly evolving biopolymer patterns, and careful choice of the cultivar.

Early symbiotic responses induced by Sinorhizobium meliloti iIvC mutants in alfalfa.

A mutation in the ilvC gene of Sinorhizobium meliloti 1021 determines a symbiotically defective phenotype. ilvC mutants obtained from different S. meliloti wild-type strains are able to induce root hair deformation on alfalfa roots and show variable activation of the common nodulation genes nodABC. All of these mutants are noninfective. The presence of extra copies of nodD3-syrM in an IlvC- background does not promote nod expression but allows the detection of low levels of Nod factor production. The sulphation of the Nod factor metabolites, however, is not affected. Furthermore, IlvC- strains induce a specific pattern of starch accumulation on alfalfa roots as well as of early nodulin expression. Hence, the pleiotropic action of the ilvC gene in S. meliloti may reveal novel complexities involved in the symbiotic interaction.

Anatomy, chloroplast structure and compartmentation of enzymes relative to photosynthetic mechanisms in leaves and cotyledons of species in the tribe Salsoleae (Chenopodiaceae)

Certain members of the family Chenopodiaceae are the dominant species of the deserts of Central Asia; many of them are succulent halophytes which exhibit C 4 -type CO 2 fixation of the NAD- or NADP-ME (malic enzyme) subgroup. In four C 4 species of the tribe Salsoleae, the Salsoloid-type Kranz anatomy in leaves or stems was studied in relation to the diversity in anatomy which was found in cotyledons. Halocharis gossypina, has C 4 NAD-ME Salsoloid-type photosynthesis in leaves and C 3 photosynthesis in dorsoventral non-Kranz cotyledons; Salsola laricina has C 4 NAD-ME Salsoloid-type leaves and C 4 NAD-ME Atriplicoid-type cotyledons; Haloxylon persicum, has C 4 NADP-ME Salsoloid-type green stems and C 3 isopalisade non-Kranz cotyledons; and S. richteri has C 4 NADP-ME Salsoloid-type leaves and cotyledons. Immunolocalization studies on Rubisco showed strong labelling in bundle sheath cells of leaves and cotyledons of organs having Kranz anatomy. The C 4 pathway enzyme phosphoenolpyruvate carboxylase was localized in mesophyll cells, while the malic enzymes were localized in bundle sheath cells of Kranz-type tissue. Immunolocalization by electron microscopy showed NAD-ME is in mitochondria while NADP-ME is in chloroplasts of bundle sheath cells in the respective C 4 types. In some C 4 organs, it was apparent that subepidermal cells and water storage cells also contain some chloroplasts which have Rubisco, store starch, and thus perform C 3 photosynthesis. In non-Kranz cotyledons of Halocharis gossypina and Haloxylon persicum, Rubisco was found in chloroplasts of both palisade and spongy mesophyll cells with the heaviest labelling in the layers of palisade cells, whereas C 4 pathway proteins were low or undetectable. The pattern of starch accumulation correlated with the localization of Rubisco, being highest in the bundle sheath cells and lowest in the mesophyll cells of organs having Kranz anatomy. In NAD-ME-type Kranz organs (leaves and cotyledons of S. laricina and leaves of H. gossypina) the granal index (length of appressed membranes as a percentage of total length of all membranes) of bundle sheath chloroplasts is 1.5 to 2.5 times higher than that of mesophyll chloroplasts. In contrast, in the NADP-ME-type Kranz organs (S. richteri leaves and cotyledons and H. persicum stems) the granal index of mesophyll chloroplasts is 1.5 to 2.2 times that of the bundle sheath chloroplasts. The mechanism of photosynthesis in these species is discussed in relation to structural differences.

Embryogenesis of Vicia faba L.: Histodifferentiation in Relation to Starch and Storage Protein Synthesis

Summary Seed development of Vicia faba is described and divided into seven stages based on morphological and histochemical characteristics: the globular stage, the early and late heart stage and four stages covering early to late cotyledon development. Specific criteria of these stages allow their easy identification independent of growth conditions and thus provide necessary reference points for any developmental studies. The distribution of mitotic activity followed by cell elongation and endopolyploidisation during seed development suggests a developmental gradient expressed in a specific spatial and temporal pattern at two levels between individual seed organs and within single organs. The accumulation pattern of storage proteins legumin and vicilin and their mRNAs, analysed by immunohistostaining and in situ hybridisation and the pattern of starch accumulation are directly correlated with these gradients, i.e., storage function is related inversely to mitotic activity and directly to cell elongation and endopolyploidisation. All seed organs synthesize storage proteins. Thus the expression of vicilin and legumin genes is not embryo specific but seed specific. Mobilisation of transiently stored storage proteins in suspensor, seed coat and endosperm occurs together with the degradation of the respective cell layers during development in a temporally regulated manner.

Starch synthesis and localization in post-germination Pinusedulis seedlings

Following pine seed germination, lipids in the megagametophyte are converted to sucrose, which is transported to the emerging seedling to support its growth. In several conifer species, an increase in the seedling starch content following germination has been reported. To further characterize this phenomenon, starch accumulation and localization, starch synthase (EC 2.4.1.21) activity (both soluble and granule-bound), and partitioning of exogenous 14C-sucrose were determined following germination of pinyon (Pinusedulis Engelm.) seeds. Starch was a minor component in dry embryos, accounting for only 3% of the dry weight. Starch levels increased 22-fold and 15-fold in the cotyledons and hypocotyl, respectively, by 8 days after germination. Starch accumulated to 65% of the dry weight in the cotyledons and 46% in the hypocotyl. The root and epicotyl accumulated relatively low levels of starch, only about 7%. Starch was localized primarily in the cortex and pith of the hypocotyl, the cortex of the cotyledons, and the root cap. Only granule-bound starch synthase showed a significant increase in activity during germination, and its changes more closely followed the pattern of starch accumulation. Exogenous 14C-sucrose was partitioned primarily into starch. After a 24-h labeling period, starch in both the cotyledons and hypocotyl accounted for 38% of total label (61% of the incorporated label) in these organs. In the roots, starch accounted for only 2.5 and 14%, respectively, of the total and incorporated label. The spatial and temporal pattern of starch accumulation closely paralleled previously reported patterns for the activity of sucrose synthase, which is apparently associated with the sucrose–starch conversion. Starch accumulation in the seedling accounts for approximately 50% of the sucrose transported from the megagametophyte following pinyon seed germination. Thus, starch appears to serve as an important transitory carbon pool for the growing seedling and may serve additional functions during seedling development.

Expression of ADP-glucose pyrophosphorylase in maize (Zea mays L.) grain and source leaf during grain filling.

The time course of ADP-glucose pyrophosphorylase activity and of starch accumulation rate measured in grain, from pollination to maturity, in Zea mays L. plants grown outdoors, was coincident for 2 years. No such correlation was observed in the adjacent leaf, which, furthermore, presented large year-to-year differences in starch accumulation pattern. Analysis of the expression of ADP-glucose synthase at the protein levels, using antibodies directed against the Bt2 or Sh2 subunits, established that the variation of activity in the grain was explained by parallel changes in the content of both subunits. The cDNA for Bt2 and Sh2 subunits were used as probes to quantify the corresponding messenger. In grain, the time course of Bt2 and Sh2 mRNA accumulation anticipated, with a similar pattern, the specific peptide variations, which suggests a transcriptional control of expression. By contrast, the control of leaf activity by protein content was less obvious than in the grain, and changes in leaf enzyme specific activity were suggested during the first 20 d after pollination. A clone homologous to the grain Bt2 subunit cDNA was isolated from a maize leaf cDNA library, and a sequence comparison showed that the leaf clone (L2) was a partial cDNA representing one-third of the mature peptide. A 97% homology was observed between Bt2 and L2 in their coding region, but homology was poor in the 3' noncoding border. This result demonstrates that Bt2 and L2 arise from different genes presenting a tissue-specific expression pattern and provides an explanation for the earlier reported differences between leaf and grain in the size of peptide and mRNA for the Bt2-homologous subunit.

Red Clover Mottle Virus Infection Affects Sink-Source Relationships and Starch Accumulation in Pea Plants

It has frequently been observed that starch accumulates in plant tissues after virus infection. In pea plants infected with red clover mottle comovirus, strain «O», virus replicates in the inoculated leaves and at the shoot apex where it induces lethal top necrosis. Concomitant with the onset of top necrosis, starch accumulates in the intervening leaves which remain substantially virus-free. This pattern of starch accumulation can be mimicked by removal of the apex in uninfected plants. We conclude that in this plant-virus interaction starch accumulation is an indirect consequence of virus infection associated with the removal of the physiological sink for photosynthate

Characterisation of Non-Uniform Photosynthesis Induced by Abscisic Acid in Leaves Having Different Mesophyll Anatomies

The effects of abscisic acid (ABA) on photosynthesis in leaves of Helianthus annuus L. were compared with those in leaves of Vicia faba L. After the ABA treatment, the response of photosynthetic CO2 assimilation rate, A, to calculated intercellular partial pressure of CO2, Pi, (A(pi) relationship) was markedly depressed in H. annuus. A less marked depression was also observed in V.faba. However, when the abaxial epidermes were removed from these leaves, neither the maximum rate nor the CO2 response of photosynthetic oxygen evolution was affected by the application of ABA. Starch-iodine tests revealed that photosynthesis was not uniform over the leaves of H. annuus treated with ABA. The starch content was diffferent in each bundle sheath extension compartment (the smallest subdivision of mesophyll by veins with bundle sheath extensions, having an area of ca. 0.25 mm2 and ca. 50 stomata). In some compartments, no starch was detected. The distribution of open stomata, examined using the silicone rubber impression techniques, was similar to the pattern of starch accumulation. In V.faba leaves, which lack bundle sheath extensions, distribution of starch was more homogeneous. These results indicate that the apparent non-stomatal inhibition of photosynthesis by ABA deduced from the depression of A(pi) relationship is an artifact which can be attributed to the non-uniform distribution of transpiration and photosynthesis over the leaf. Intercellular gaseous environment in the ABA-treated leaves is discussed in relation to mesophyll anatomy.

THE ANNUAL RHYTHM OF CAMBIAL ACTIVITY IN FOUR SUBSHRUBS COMMON IN PHRYGANIC FORMATIONS OF GREECE

The annual rhythm of cambial activity and the pattern of starch accumulation in pith and ray cells of four seasonal dimorphic subshrubs typical of Greek “phrygana,” Sarcopoterium spinosum, Thymus capitatus, Phlomis fruticosa and Cistus incanus were investigated. Cambial activity in all species examined was found to occur during the winter when temperatures are low. During the rest of the year, cambium remains dormant. At the time of high cambial activity, starch content of pith and ray cells diminishes. High accumulation of starch grains was found to occur after cambial activity ceases in S. spinosum and a moderate starch accumulation occurs in C. incanus whereas there is no starch content in the pith of T. capitatus and P. fruticosa throughout the year. These results indicate that concerning their cambial activity, phryganic species behave like typical desert plants.