Chalky Kernel Research Articles

The Response of Grain Yield and Quality of Water-Saving and Drought-Resistant Rice to Irrigation Regimes

Of all the crops, rice is the one that consumes the most water. Rice yields and quality are significantly influenced by irrigation. However, it is still unknown how different irrigation practices would affect the grain yield and quality of water-saving and drought-resistant rice. Hyou 518 (high-yielding rice variety) and Hanyou 73 (water-saving and drought-resistant rice variety) were employed as materials. Three irrigation regimes were set up in the field: conventional flooding irrigation (CF), alternate wetting and moderate soil drying irrigation (AWD), and dry cultivation (D). It was investigated how various irrigation regimes affected the two varieties’ yield and quality. The results revealed the following: 1. D considerably increased water-use efficiency while drastically reducing the yield, compared to CF and AWD. In comparison to other irrigation regimes, the grain yield and water use efficiency of Hanyou 73 enhanced synergistically under AWD treatment. 2. In contrast to CF treatment, AWD and D (especially) treatments decreased perfect rice kernel, total starch content, amylose content, amylopectin content, amylose/amylopectin, gel consistency, and breakdown, but increased green rice kernel, chalky kernel, protein content, and setback. 3. After heading, AWD and D lowered, and D treatment decreased more, the activities of ADP-glucose pyrophosphorylase (AGP), soluble starch synthase (SSS), and starch branching enzyme (SBE). AGP, SSS, and SBE were strongly inversely linked with perfect rice kernel, amylopectin content, gel consistency, and breakdown, but significantly negatively correlated with green rice kernel, chalky kernel, protein content, and setback. The results indicate that with AWD treatment, Hanyou 73 might provide a synergistic boost grain production, water-use efficiency, and quality. D treatment could significantly improve water-use efficiency. Compared with Hyou518, Hanyou 73 could maintain higher AGP, SSS, and SBE activities, head milled rice, perfect rice kernel, amylopectin content, and gel consistency under AWD and D treatment.

Characteristics of Population Quality and Rice Quality of Semi-Waxy japonica Rice Varieties with Different Grain Yields

A primary focus of rice breeding and production is the optimization of yield and quality. Currently, semi-waxy japonica rice is widely planted in the middle and lower reaches of the Yangtze River due to its good eating quality and strong reputation among consumers. However, little information is yet available on grain yield formation and rice quality characteristics of these semi-waxy japonica rice varieties with different grain yields. In this study, three high-yielding (HGY) semi-waxy japonica rice varieties and three low-yielding (LGY) semi waxy japonica rice varieties were compared for population quality and rice quality in 2018 and 2019. The average values of spikelet per panicle, 1000-grain weight, and total spikelet number of the HGY varieties were significantly higher than those of the LGY varieties, while the panicle number and filled grain rate showed the opposite. Compared with the LGY varieties, the HGY varieties had a larger leaf area index at each growth stage, with a larger high efficient leaf area composed of a larger leaf length and width and smaller leaf angles of the top three leaves, as well as a greater single stem-sheath weight, more total dry matter accumulation, and longer growth duration from elongating to maturity. There were significant differences in rice quality between the HGY and LGY varieties. Compared with the LGY varieties, the head milled rice rate of the HGY varieties decreased significantly, and the chalky kernel rate and chalkiness degree increased significantly. Due to the low protein content, high peak viscosity, trough viscosity, and final viscosity and breakdown, as well as low setback, consistence, and pasting temperature of the HGY varieties, their taste values were significantly better than those of the LGY varieties. These results suggest that the HGY varieties could achieve a synergistic improvement of grain yield and eating quality, but the milling quality and appearance quality require further improvement.

Response of grain-filling rate and grain quality of mid-season indica rice to nitrogen application

Nitrogen is one of the important factors for high yield of rice. Apart from high yield, high quality has become the current urgent demand for rice production. Grain-filling stage is crucial for rice yield and quality formation. However, the effect of nitrogen on grain-filling characteristics and the relationship of grain-filling characteristics and rice quality of mid-season indica rice were still unclear. A field experiment was carried out to ascertain the critical grain-filling characteristics that contribute to rice milling quality, appearance quality and cooking and eating quality under nitrogen applications. The results showed that nitrogen applications prolonged the duration of superior and inferior grain filling. The mean grain-filling rate (Gmean) and the maximum grain-filling rate (Gmax) of the inferior grains were positively correlated with chalky kernel rate, chalkiness, and amylose content. The time reaching the maximum grain-filling rate (Tmax G) of the inferior grains was positively correlated with brown rice rate, milled rice rate, and head milled rice rate. Chalky kernel rate and chalkiness were negatively correlated with peak paste viscosity and breakdown viscosity. Less amylose content and more crude protein content were detected in nitrogen application of Liangyoupei 9 and Y Liangyou 2 both in 2016 and 2017. According to the correlation analysis, better cooking and eating quality of Y Liangyou 2 which had less amylose content might result from its higher Gmax and Gmean of inferior grain than that of Liangyoupei 9 in the treatments of nitrogen application. These results indicated that the prolonging grain-filling duration and increasing grain weight at the maximum grain-filling rate of inferior grains contributed to the improvement of milling quality, appearance quality, and cooking and eating quality of mid-season indica rice under appropriate nitrogen applications.

Influence of Nitrogen Management Regimes on Milling Recovery and Grain Quality of Aromatic Rice in Different Rice Production Systems

To examine the effect of nitrogen (N) management regimes on rice quality in different rice production systems, a field experiment was conducted in 2017 and 2018. The experimental treatments comprised of two production systems (transplanted rice: TPR and dry direct-seeded rice: DDSR) and six N management treatments (0, 50, 100, and 150 kg N ha−1 as basal, and 100 and 150 kg N ha−1 in three splits which were regarded as N1, N2, N3, N4, N5, and N6, respectively). The results revealed that the rice quality attributes, i.e., broken rice recovery, abortive kernel, bursting, and curling were increased by 8%, 14%, 8%, and 14%, respectively, under DDSR than TPR. In the case of N management, split application of N reduced the chalky kernel (44%), abortive kernel (23%), opaque kernel (31%), bursting (24%), and curling (31%), while kernel protein contents, water absorption ratio, cooked grain length, and elongation ratio were increased by 41%, 88%, 25%, and 26%, respectively, as compared to the basal application of N. In short, DDSR cultivation reduced the appearance and cooking quality traits but white head rice recovery and nutritional quality were comparable to TPR. However, N application in splits either in DDSR or in TPR potentially improved the grain quality of rice compared with the basal application.

Suppression of starch synthase I (SSI) by RNA interference alters starch biosynthesis and amylopectin chain distribution in rice plants subjected to high temperature

Based on known cDNAs of rice starch synthase isoforms, we constructed dsRNA interference vectors for starch synthase I (SSI) to produce transgenic plants containing starch with a moderately high amylose content. We investigated the effect of SSI suppression on grain quality traits, starch biosynthesis, and amylopectin chain distribution in rice plants exposed to two different temperature regimes. The activities and transcripts of BEs, DBEs, and other SS isoforms were further investigated to clarify the effect of SSI suppression on these key enzymes and their specific isoforms under different temperature treatments. Suppression of SSI by RNAi altered grain starch component and amylopectin chain distribution, but it exerted only a slight effect on total starch content (%) and accumulation amount (mg kernel−1) and on starch granule morphology and particle size distribution. Under normal temperature (NT), insignificant differences in kernel weight, chalky kernel proportion, chalky degree, and starch granule morphology between SSI-RNAi line and its wild type (WT) were observed. However, amylose content (AC) level and granule-bound starch synthase (GBSS) activity in rice endosperms were markedly increased by SSI-RNAi suppression. The chalky kernel proportion and chalky degree of SSI-RNAi lines were significantly higher than those of WT under high temperature (HT) exposure at filling stage. Inhibition of SSI by RNAi affected amylopectin chain distribution and raised starch gelatinization temperature (GT) in two ways: directly from the SSI deficiency itself and indirectly by reducing BEIIb amounts in an SSI-deficient background. The deficiency of SSI expression led to an alteration in the susceptibility of grain chalkiness occurrence and starch gelatinization temperature to HT exposure, owing to a pleiotropic effect of SSI deficiency on the expression of other genes associated with starch biosynthesis.

The different influences of drought stress at the flowering stage on rice physiological traits, grain yield, and quality

Seasonal drought is a major threat to rice production. However, the sensitivity of rice to drought stress (DS) at different growth periods remains unclear. The objective of this study was to reveal the different impacts of DS at the flowering stage on rice physiological traits, grain yield, and quality. Field experiments were conducted with two rice cultivars, Yangliangyou 6 (YLY6) and Hanyou 113 (HY113) under two water treatments (traditional flooding (CK) and DS at flowering stage) in 2013 and 2014. Compared with CK, grain yield (GY) under DS was significantly reduced by 23.2% for YLY6 and 24.0% for HY113 while instantaneous water use efficiency (IWUE) was significantly increased by 39% for YLY6 and 37% for HY113, respectively. All physiological traits were significantly decreased under DS and physiological activities did not revert to normal levels at grain filling stage. There was no significant effect on the appearance and nutritional quality except for the significant increase in chalky kernel and chalkiness under DS. Our data suggest that drought stress at flowering stage has a strong influence on rice physiological traits and yield. Stronger recovery capability contributes to maintaining relatively high grain production, which could be a great target for the breeder in developing drought-tolerant rice cultivars.

Effects of slow or controlled release fertilizer types and fertilization modes on yield and quality of rice

There is limited information about the influence of slow or controlled release fertilizer (S/CRF) on rice yield and quality. In this study, japonica rice cultivar Nanjing 9108 was used to study the effects of three different S/CRFs (polymer-coated urea (PCU), sulfur-coated urea (SCU), and urea formaldehyde (UF)) and two fertilization modes (both S/CRF and common urea (CU) as basal fertilizer, S/CRF as basal and CU as tillering fertilizer) on rice yield and quality. CU only was applied separately as control (CK). Results showed that, rice grain yield, chalky kernel rate, chalky area, overall chalkiness, and the content of gliadin, glutenin, and protein, all showed the trends of UF>PCU>SCU within the same fertilization mode, and showed the trends of S/CRF as basal and CU as tillering fertilizer>both S/CRF and CU as basal fertilizer within the same type of S/CRF. In contrast, the contents of amylose, amylopectin, and starch, as well as taste value, and peak and hot viscosity showed trends of SCU>PCU>UF, and the trends of both S/CRF and CU as basal fertilizer>S/CRF as basal and CU as tillering fertilizer. Among S/CRF treatments and fertilization modes, taste values of cooked rice were positively correlated with amylose, amylopectin, and starch contents, as well as gel consistency, peak viscosity, hot viscosity, and cool viscosity, while negatively correlated with globulin, gliadin, glutenin, and protein contents. The types of S/CRF and fertilization modes are important for improving rice yield and quality. Compared to CK, higher yield and similar quality of rice was achieved with UF as basal and CU as tillering fertilizer, and similar yield with improved appearance and eating and cooking quality of rice was achieved with either both UF and CU as basal fertilizer, or PCU as basal and CU as tillering fertilizer.

Change in Yield and Quality Characteristics of Rice by Flooding during the Ripening Stage

벼 등숙시기 및 침관수 조건별 피해에 따른 생육 및 수량, 품질특성에 미치는 영향을 분석한 결과는 다음과 같다. 1. 등숙기 침관수 피해에 따른 수량감소의 요인중 가장 영향이 컸던 요인은 등숙률 이었고, 등숙률은 호숙기(출수 후 14일)대비 유숙기(출수 후 7일)의 감소정도가 컸으며, 침수 조건별로는 탁수이면서 수중에 완전히 잠긴 관수 조건에서 침수기간이 길어질수록 피해가 심하였다. 2. 완전미율은 유숙기(출수 후 7일) 대비 호숙기(출수 후 14일)처리에서 감소정도가 컸으며, 이는 등숙 시기별 전분 합성 단계의 차이에 의한 것으로 생각된다. 3. 침관수 처리 전, 후의 광합성효율을 나타내는 최대양자수율(Fv/Fm)값은 침관수 처리에 따른 큰 변화가 없었으며, 이를 통해 등숙기에 4일 정도의 침관수 처리는 벼의 본체의 동화산물 생산능력 자체에는 큰 영향을 주지 못하였을 것으로 사료된다. 4. 자포니카 벼의 침관수 회피기작에 따라 침수 처리 시 처리별로 간장신장 반응을 보였으며, 이로 인한 이삭으로의 동화산물 공급저하는 출수 후 7일에는 등숙률의 감소, 출수 후 14일에는 완전미율 감소에 더 큰 영향을 주었을 것으로 생각된다. 5. 침관수 피해가 심한 처리구 일수록 수확기 엽색이 무처리 대비 푸른 상태를 유지하였는데, 이는 침관수 피해에 따른 이삭 낟알의 발육정지로 동화산물의 수요부(sink)가 제한되었기 때문으로 보인다. The increase in the frequency of occurrence of abnormal weather could include severe rainfall, which could cause rice submergence during the ripening stage. This experiment was conducted to clarify the effects of submergence during the ripening period on yield and quality of rice. The flooding treatment was conducted at 7 and 14 days after heading. Flooding conditions were created with two conditions, flag leaf exposed and overhead flooding, and each condition was divided into two conditions according to water quality-clear and muddy. Although the yield decrease was more severe at 7 days after heading because of the decrease in the ripening ratio, the head rice ratio was more affected at 14 days after heading because of the increase in the chalky kernel ratio. The maximum quantum yield (Fv/Fm), which indicates the photosynthetic efficiency, did not differ before and after the flooding treatment until flooding continued for 4 days. In addition, stem elongation occurred because of flooding as an avoidance mechanism in japonica rice. This phenomenon was expected to decrease the supply of assimilation products to the spikelet (sink). Overall, it was suggested that additional experiments should be conducted examining the change in the starch synthesis mechanism and transfer of assimilate products resulting from submergence, for development of cultivation techniques corresponding to submergence and breeding of varieties with submergence tolerance characteristics.

Effects of nitrogen fertilizer application rate on nitrogen use efficiency and grain yield and quality of different rice varieties

To provide scientific basis for reasonable application of nitrogen and create varieties with high N use-efficiency, an experiment was carried out to study the effects of nitrogen fertilizer application rate on grain yield, N use rate and quality of different rice varieties. Four different genotypic rice varieties, Nipponbare, N70, N178 and OM052 were used as tested material and three levels of nitrogen application rate (0, 120, 270 kg·hm-2) were conducted. Urea as nitrogen source was applied as basal (70%) and panicle (30%) fertilizer. The results showed that nitrogen fertilizer could raise yield mainly because of the increased effective panicles and filled grains per panicle. When the N application rate was 120 and 270 kg·hm-2, OM052 had the largest grain yield among four varieties, being 41.1% and 76.8% higher, respectively compared with control. Difference in grain yield among four varieties was due to the difference of nitrogen use efficiency. Under 120 and 270 kg·hm-2 nitrogen levels, Nipponbare had the lowest grain yield and N agronomic efficiency (NAE, 40.90 g·g-1 and 18.56 g·g-1), which was a variety with low N use-efficiency. On the contrary, OM052 had the highest grain yield and NAE (145.9 g·g-1 and 81.24 g·g-1), was a variety with high N use-efficiency. N fertilizer application increased the amylose content and protein content, lengthened gel consistency, reduced chalky kernel, chalkiness, and alkali digestion value. With the increase of N fertilizer application, hot paste viscosity, peak viscosity, consistence viscosity and breakdown viscosity were decreased gradually, and setback viscosity was increased. Correlation analysis showed that the yield and yield components had more significant correlations with appearance quality, cooking and eating quality under low N level. This study confirmed that OM052 was a double high variety with extremely high N agronomic efficiency and yield. Reasonable application of nitrogen fertilizer could significantly increase effective panicles and filled grains per panicle, improve rice quality, and ensure high yield and superior quality simultaneously.

Effects of common Echinochloa varieties on grain yield and grain quality of rice

Barnyard grass, such as Echinochloa crus-galli var. mitis, Echinochloa crus-galli var. zelayensis and Echinochloa colonum, are the main troublesome weeds in rice (Oryza sativa) paddies. This study aimed to investigate the rice yield (quality and quantity) when grown with these common barnyard grass varieties. A 2-year field experiment was conducted using two high-yielding rice cultivars, Liangyoupeijiu (an O. sativa indica hybrid cultivar) and Nanjing 9108 (an O. sativa japonica cultivar) at different developmental stages from transplant to maturity. Treatments included a weed-free (control), rice grown with Echinochloa. crus-galli var. mitis (Ecm), rice grown with E. crus-galli. crusgali var. zelayensis (Ecz), and rice grown with E. colonum (Ec). The results showed that when barnyard grasses were grown with the same rice cultivar, the order of plant height of the three barnyard grass varieties was Ecz>Ecm>Ec, the growth duration was Ecm>Ecz>Ec and the dry matter accumulation of both Ecm and Ecz was greater than Ec. Compared with the weed-free control, there was no significance difference in rice tiller numbers among the treatments within the same rice cultivar. The Ecm and Ecz treatments for both rice cultivars and the Ec treatment of Nanjing 9108 had significantly lower leaf photosynthetic rate, root biomass, root oxidation activity, and dry matter accumulation at both the heading and maturity stages. Lower rice yield loss was detected for all rice grown with barnyard grass, but the loss in yield differed by treatments. Losses in grain yield of rice were 12.7–42.6% in the Ecm treatment, 22.3–55.2% in the Ecz treatment, and 1.5–12.1% in the Ec treatment. For both rice cultivars, Ecm and Ecz treatments had significantly lower grain yield compared with the control. The Ec treatment for Nanjing 9108 had significantly lower grain yield compared to the control, but there was not a significant difference between Ec and the control for Liangyoupeijiu. In general, the japonica cultivar had a greater loss in grain yield compared with the indicia hybrid cultivar under the same treatment. The degree of yield loss by barnyard grass cultivar was Ecz>Ecm>Ec. Grain quality in head rice, chalky kernel, chalky size, and gel consistency was significantly lower for both rice cultivars in the Ecm and Ecz treatments and also for Nanjing 9108 but not for Liangyoupeijiu in the Ec treatment. We conclude that the reduction in leaf photosynthetic rate, root biomass, root oxidation activity at the grain filling stage, and dry matter accumulation at maturity was caused by interference in canopy light transmission caused by barnyard grass and that these factors resulted in losses in grain yield and quality.

Effects of Cultivars, Transplanting Patterns, Environment, and Their Interactions on Grain Quality of Japonica Rice

With the increasing scarcity of rural labor, the rice transplanting pattern is encountering a shift from artificial transplanting (AT) to mechanical transplanting (MT) in numerous rice‐growing districts of China. The shift of transplanting patterns combined with altered growing environment during the grain‐filling stage in different years presumably affects rice quality. Nevertheless, related information is currently limited. This study investigated the effects of cultivars, transplanting patterns, environment, and their interactions on appearance, milling, eating, and nutritional qualities of four japonica rice varieties. The significant interactive effects of cultivars, environment, and transplanting patterns on almost all rice quality parameters (except Thr, Met, and Ile) were observed. Cultivars and environment were the main factors influencing rice appearance and milling and eating qualities. Cultivar was the primary factor affecting rice nutritional quality. Among all treatments, environment showed the strongest effect on percentage of chalky kernel, milled rice yield, peak viscosity, breakdown, setback, consistence, amylose, Glu, Tyr, and Met contents. However, Leu and Phe contents were unaffected by environment but only by cultivars and transplanting patterns. In addition to amylose and protein, Glu and Met contents were also involved in determining rice eating quality. Amino acid contents (except Cys, Tyr, and Met) were significantly negatively correlated with head rice yield, showing the function of amino acids in controlling rice milling quality. Percentage of chalky kernel as well as protein and almost all amino acid contents were significantly negatively correlated with the difference of maximum and minimum temperature (DMMT) and positively correlated with relative humidity (RH), whereas head rice yield did it reversely. Amylose content and setback were significantly negatively related to daily maximum temperature (DMAT), daily minimum temperature (DMIT), daily average temperature (DAT), and effective temperature accumulation (ETA). However, peak viscosity, breakdown, and consistence had contrary performances. According to these results, we can infer that DMMT and RH are important environmental factors affecting rice appearance, milling qualities, and nutritional qualities and that DMAT, DMIT, DAT, and ETA are key environmental factors influencing rice eating quality.

Effects of High Air Temperature on Rice Grain Quality and Yield under Field Condition

High air temperature (HAT) limits grain yield and quality in rice (Oryza sativa L.). This study was conducted to determine the effects of HAT from R3 (panicle exertion from boot) to R8 stage (physiological maturity) on rice grain yield and quality (milling, appearance, cooking and eating, and nutrition qualities). A split‐spot experiment based on randomized complete design was performed, involving two cultivars (japonica Koshihikari and indica IR72), two temperature treatments, and three replicates. Rice cultivars as main plot treatments were grown in a paddy field. The HAT and natural air temperature (NAT) treatments were regarded as subplot. Percentage of chalky kernel increased, whereas head rice yield, amylose and starch contents, and grain yield decreased in both cultivars under HAT, when compared with those under NAT. The HAT enhanced values of peak viscosity and breakdown, but decreased value of setback for Koshihikari. Conversely, starch viscosity characteristics for IR72 were unaffected by HAT. Relative content of amino acids in grains were enhanced; however, absolute content of some amino acids did not increase due to the reduction of grain weight under HAT. The HAT also increased absolute content of grain protein in IR72, but not in Koshihikari. The present study indicates that HAT decreased rice milling, appearance qualities and grain yield, while it positively influenced not only cooking and eating qualities in Koshihikari but also some nutritional components of grains in both cultivars.

Effects of Differences in Nutriophysiology and Climatic Element during Ripening Period on Chalky Kernel in Nagano Prefecture

Effects of Differences in Nutriophysiology and Climatic Element during Ripening Period on Chalky Kernel in Nagano Prefecture

Double repression of soluble starch synthase genes SSIIa and SSIIIa in rice (Oryza sativa L.) uncovers interactive effects on the physicochemical properties of starch

Soluble starch synthases (SSs) are major enzymes involved in starch biosynthesis in developing rice (Oryza sativa L.) endosperm. Despite extensive studies of SSs in various plant species including rice, the functional modes of action among multiple SS genes are still not clear. Here, we generated transgenic RNA interference (RNAi) repressed lines for seven of the eight members of the rice SS gene family and studied their effects on starch synthesis and grain formation. Consistent with their expression domains, RNAi repression of genes that encode isozymes SSI, SSIIa, and SSIIIa had strong effects on grain development, whereas no obvious phenotypic changes were observed in transgenic plants with the other SS genes being RNAi repressed, indicating functional redundancies among the genes. To study the potential functional interactions of SS genes, we generated SSIIa/SSIIIa double repression lines whose kernels displayed a chalky kernel appearance and had increased amylose levels, increased pasting temperatures, and decreased viscosities. The double mutation also reduced short (degree of polymerization (DP) 5-6) and long (DP 12-23) amylopectin chain contents in the grain and increased the medium long types (DP 7-11). The nonadditive nature of the double mutation line suggests that SSIIa and SSIIIa interact with each other during starch synthesis. Such interaction may be physical via starch phophorylase as indicated by our pair-wise yeast two-hybrid assays on major starch synthesis enzymes. Collectively, the data showed that SSIIa and SSIIIa play distinctive, but partially overlapping, roles during rice grain starch synthesis. The possibility of extensive redundancy or complementarity among SS isozymes is discussed.

Examining Economic Efficiency of U.S. Government Grading System: The Case of Louisiana Rough Rice

This study estimates a hedonic price model for Louisiana rough rice to evaluate the USDA grading system. The parameter estimates suggest that chalky kernel and red rice are significant quality factors that affect prices in the bid/acceptance regional rough rice market. Results also show that head and broken rice are as important characteristic as the USDA grade quality factors. Generalized least-squares estimation indicates that the USDA grades do not fully explain the observed price variations in Louisiana rough rice. The study constructs a modified grading system for rice. Comparisons show that the modified grading system outperforms the current government grading.

Examining Economic Efficiency of U.S. Government Grading System: The Case of Louisiana Rough Rice

This study estimates a hedonic price model for Louisiana rough rice to evaluate the USDA grading system. The parameter estimates suggest that chalky kernel and red rice are significant quality factors that affect prices in the bid/acceptance regional rough rice market. Results also show that head and broken rice are as important characteristic as the USDA grade quality factors. Generalized least-squares estimation indicates that the USDA grades do not fully explain the observed price variations in Louisiana rough rice. The study constructs a modified grading system for rice. Comparisons show that the modified grading system outperforms the current government grading.

Effects of Potassium and Calcium on Root Exudates and Grain Quality During Grain Filling

The purposes of this study were to understand the root activity and root exudates of rice ( Oryza sativa L.) in response to different levels of potassium (K) and calcium (Ca) nutrients and the effect of K and Ca on rice grain quality. Cultivars Yangdao 6 ( indica) and Yangjing 9538 ( japonica) were cultured in hydroponical solutions and treated with different Espino nutrition solutions from heading to maturity, which were supplemented with complete K and Ca (standard Espino nutrition solution, control), half K (1/2K), zero K (0K), half Ca (1/2Ca), and zero Ca (0Ca) nutrition. Compared to the control, the 0K treatment significantly decreased root activity, ATPase activity, and concentrations of citric acid, Ca 2+, K +, and NH 4 + in the root exudates, but accelerated root senescence; and the 0Ca treatment significantly decreased concentrations of oxalic acid, Ca 2+, K +, and NH 4 + in the root exudates. The oxalic acid concentration in root exudates was positively correlated ( P < 0.01) with chalky grain percentage, chalkiness, and gel consistency of rice grain; whereas the citric acid concentration in exudates was negatively correlated ( P < 0.01) with chalky grain percentage, chalkiness, and breakdown value, but positively correlated ( P < 0.05) with setback value. At early (10 d after heading) and mid grain-filling (20 d after heading) stages, the concentrations of K + and Ca 2+ in root exudates were negatively correlated ( P < 0.05) with chalky kernel percentage, chalkiness, and amylose contents, and the NH 4 + concentration was also negatively correlated ( P < 0.05) with amylose content of grain. This result indicates that root exudates are closely associated with grain quality. K and Ca nutrition regulate root exudates and consequently affect grain quality of rice.

Varietal Difference in the Occurrence of Milky White Kernels in Response to Assimilate Supply in Rice Plants (Oryza sativa L.)

We examined the association of assimilate supply in the occurrence of milky white kernels in three cultivars with different percentages of milky white kernels in the field condition: ‘Hatsuboshi’, ‘Koshiibuki’ and ‘Koshihikari’. Five days after heading, the plants were placed in four controlled-environment chambers with either a high or low night temperature and elevated or normal [CO2] supply. Plants in each chamber were either defoliated with only flag leaf remaining, flag leaf and second leaf remaining or left intact (control). The percentage of each type of chalky kernel was examined. The percentage of milky white kernels was increased by defoliation and decreased by elevated [CO2], associated with assimilate supply. No association was observed between assimilate supply and white back or basal white kernels. The percentage of milky white kernels was negatively correlated with assimilate supply at a high night temperature in all cultivars. At a low night temperature, there was a clear threshold of assimilate supply, over which the percentage of milky white kernels was nearly zero. Cultivar differences were observed in the relation between the percentage of milky white kernels and assimilate supply. In conclusion, we found a varietal difference in the occurrence of milky white kernels in response to assimilate supply. In the cultivars used in this study, ‘Hatsuboshi’ was more sensitive to the low assimilate supply than ‘Koshihikari’.

Relationships of Ethylene Evolution Rate and 1-Aminocylopropane -1-Carboxylic Acid Concentration in Grains during Filling Period with Appearance Quality of Rice

To elucidate the relationship between ethylene evolution from the grains and the appearance quality of rice, ten different rice genotypes were used to determine the ethylene evolution rate, 1-aminocylopropane-1-carboxylic acid (ACC) concentration in grains during grain filling and the appearance quality of rice, and the effects of chemical regulators on concentrations of ethylene and ACC in the grains during grain filling were also investigated to verify the roles of ethylene in the rice quality formation. The ethylene evolution rates and ACC concentrations in grains during the mid and late grain filling stages were very significantly and positively correlated with chalky kernel percentage and chalkiness. The cultivars with a low ACC concentration in grains exhibited a close amyloplast arrangement and small space between starch granules, whereas those with a high ACC concentration in grains showed a loose arrangement and wide space between the granules. Application of 1 μmol/L ACC to panicles at mid and late grain filling stages significantly loosened amyloplast arrangement and increased chalky kernel percentage, chalky area and chalkiness, and the results were reversed when 1 μmol/L amino-ethoxyvinylglycine, an inhibitor of ACC synthesis enzyme, was applied to panicles. A practice of moderate dry-wet alternate irrigation reduced ethylene evolution and ACC concentration in grains and thereby reduced chalkiness. The results suggested that ethylene and ACC in grains play an important role in the endosperm structure and appearance quality of rice, and the appearance quality would be improved by reducing ethylene evolution and ACC in grains through either variety breeding and selection, or chemical regulations or cultivation techniques.

Dissecting the Opaque-2 regulatory network using transcriptome and proteome approaches along with enzyme activity measurements

The Opaque-2 (O2) gene encodes a transcriptional activator specifically expressed for grain development of maize. o2 mutants have an opaque and chalky kernel, with a decrease in zein storage protein content, and an increase in the proportions of lysine and tryptophan. In this review, we present recent results investigating genetic properties of the O2 network, using transcriptome and proteome approaches, associated with measurements of activities of enzymes of the aspartate pathway and lysine degradation. The structural polymorphism at the O2 locus was investigated by RFLP in a collection of 51 maize inbred lines. Most polymorphic sites were found outside the coding regions. We then searched for relationships between RFLP polymorphism and (i) mRNA abundance of O2 and of known or suspected target genes, (ii) activity of SDH and (iii) amount of zein isoforms. Polymorphic restriction sites in the 5' upstream regions of the O2 gene were found associated with O2 mRNA abundance (three sites) and the amount of two 19 kDa alpha-zein isoforms (two sites). One restriction site on the 3' side of the O2 gene was found associated with Lor/Sdh mRNA abundance. Our results indicate relationships between polymorphism at the O2 locus and the expression of some of its target genes. Evidence of these associations has to be confirmed on larger samples, and the analysis of the O2 gene sequence should allow more precise testing of the actual involvement of O2 polymorphism in its own transcriptional expression, and in the expression of its target genes.