Quantitative proteomics analysis of proteins involved in leaf senescence of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.)

Delaying leaf senescence and prolonging the available time for photosynthesis is one of the important approaches to increase grain yield of rice (Oryza sativa L.). Here, iTRAQ-based quantitative proteomics approach was used to comparative analyze the expression profiles of proteins in rice leaves in response to senescence. Totally 5067 proteins were identified. Compared with the proteins in the flag leaves at early stage of grain-filling in rice Liang-You-Pei 9 (LYP9), 240 and 188 proteins were up-regulated and down-regulated in the flag leaves at middle stage of grain-filling, and 387 and 202 proteins were up-regulated and down-regulated in the flag leaves at late stage of grain-filling, respectively. In addition, 39 and 18 identified proteins were constantly up-regulated and down-regulated in the leaves from early to middle and late stages of grain-filling, respectively. Among them, chloroplast chaperonin 10, geranylgeranyl diphosphate reductase, Mg chelatase subunit ChLD, porphobilinogen deaminase, protochlorophyllide reductase B and thioredoxin-like protein CITRX might have involved in the senescence of leaves. This study provided important information for understanding the age-sensitive mechanism of LYP9, and offered a foundation for future studying and improving it.     

Effects of Shading Soybean Plants on N2O Emission from Soil

The effect of photosynthesis on N₂O emission from soil was investigated by shading soybean (Gycline max. L) plant at flowering, pod-setting and grain-filling stages. The results showed that by stopping photosynthesis through shading the plants stimulated N₂O emission significantly at flowering stage and pod-setting stage, and suppressed N₂O emission dramatically at grain-filling stage. At flowering stage, soybean species seem to rely mainly on fertilizer N and shaded plants decreased the N uptake. Interaction between the relative increase in available N for N₂O production by shading and the presence of root exudates promoted N transformation (nitrification/denitrification) and N₂O emission. At pod-setting stage, the available soil nitrogen seems to be a critical limiting factor and without substantial release of symbiotically fixed N through plant roots, resulted in a weak effect of shading on N₂O emission. At grain-filling stage, available N for N₂O production was derived from symbiotically fixed N and was greatly affected by photosynthesis. These results indicated that the effect of soybean growth on N₂O emission from soil varies with plant growth stages as available N for N₂O production is mainly from fertilizer N and organic mineralization during the early growth of soybean plants, while N₂O emission is controlled by the quantity and perhaps also the quality of root exudates, which is closely related with plant photosynthesis in the late season of soybean growth.     

Localization of Chromosome Regions Controlling High Photosynthetic Potential in Russian Rice Cultivars

Breeding practice defined the main ways to increase crop yield: morphotype change, exploitation of heterosis, and increase in photosynthesis effectiveness. We identified donors and sources of high photosynthetic potential genetic system and polymorphic loci controlling photosynthetic efficiency in Russian rice cultivars. Thirty-two Russian rice cultivars were used as material. The content of chlorophyll a and b and carotenoids was measured at the beginning of tillering, heading, and flowering stages by a Genesys 8 spectrophotometer. Twenty plants of each cultivar in two replications were used for measurement. SSR markers were used. DNA was extracted by the STAB method. Polymerase chain reaction (PCR) and visualization of amplification products were performed under the International Rice Research Institute (IRRI) protocol. Donors of high contents of each pigment were found. A high level of polymorphism for the loci connected with photosynthesis effectiveness in Russian rice cultivars will allow us to create new cultivars with improved characters by hybridization. Six markers significantly divided cultivar groups with different photosynthetic rate, three of them (RM154, RM600, RM5508) were related to the content of carotenoids, two markers (RM347, RM240) were related to specific leaf weight (SLW) control, and two others (RM154, RM509) were related to the chlorophyll a content.     

Physiological and proteomic analysis of rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) in flag leaf during flowering stage and milk stage under drought stress

Hybrid rice has the inferiority of early senescence during reproductive stage. Early senescence of leaves induced by drought causes a constraint on crop productivity. Hence, to better understand traits of drought responsive mechanism in hybrid rice flag leaves during sensitive reproductive stage, we performed physiological measurements and conducted 2-D electrophoresis to investigate proteomic profile of rice flag leaves at flowering and milk stage. 43 proteins showed significant changes in silver stained gels were identified by MS/MS at flowering stage and 54 proteins at milk stage. For flowering stage, inactive CO₂ assimilation and ATP synthesis as well abnormal floral development could be postulated from decreased proteins. Additionally, higher levels of defense-related proteins and antioxidases in drought-stressed leaves suggested active ROS scavenging system. For milk stage, both photosynthesis and CO₂ assimilation were impaired. Disrupted oxidative defense and proteolysis system indicated redox imbalance. Upregulation of NADP-MDH facilitated for CO₂ assimilation and antioxidant system. In conclusion, drought stress during reproductive stage impacted a lot on biological processes in rice leaves at protein level, especially energy metabolism and redox balance.     

Water-use efficiency and carbon isotope discrimination in two cultivars of upland rice during different developmental stages under three water regimes

A pot experiment was conducted in a glasshouse to clarify and quantify the effect of plant part, water regime, growth period, and cultivar on carbon isotope discrimination (CID), and to analyze the relationship between CID, stomatal behavior and water-use efficiency (WUE). The experiment was comprised of two upland rice (Oryza sativa L.) cultivars and three water regimes (100, 70, and 40% of saturation moisture) in a completely randomized design. Plants were harvested at tillering, flowering, and maturity. No significant cultivar differences in above-ground dry matter-based WUE (WUE_A) and total dry matter-based WUE (WUE_T) were observed. WUE_A (and WUE_T) increased with water stress up to tillering, but decreased with water stress after tillering. Significant cultivar differences in CID in all the analyzed plant parts were observed at all harvest times. Reduction in CID with water stress was greatest at tillering, and the effect was less pronounced at flowering and at maturity. At each harvest, the effect was most pronounced in newly developed plant parts. Root and grain tended to have the lowest CID values, and stem the highest, at all harvest times. A negative relationship was observed between CID measured at tillering and WUE_A (and WUE_T) measured over the period from seedling to tillering, whereas a reverse relationship was obtained between CID measured at flowering and WUE_A (and WUE_T) measured over the period from tillering to flowering, and an unclear relationship between CID measured at maturity and WUE_A (and WUE_T) measured over the period from flowering to maturity. The ratio of the intercellular and atmospheric concentration of CO₂ (C_i/C_a) were closely associated with CID throughout the water regimes when one cultivar was considered, however, cultivar differences in CID were not related to variations in C_i/C_a. The results indicate that significant cultivar difference existed in CID in all the analyzed plant parts at all harvest times, while corresponding difference in WUE_A (and WUE_T) between the cultivars was not necessarily consistent. Abbreviations: WUE – water-use efficiency; WUEi – instantaneous WUE (or leaf transpiration efficiency); ADM – above-ground dry matter; TDM – total dry matter; WUE_A– ADM-based WUE; WUE_T– TDM-based WUE} CID – carbon isotope discrimination; NL – the newest leaves; FEL – recently fully expanded leaves; FL – flag leaves; P – photosynthesis rate; g – leaf stomatal conductance to water vapor; C_i– intercellular CO₂ concentration; C_a– atmospheric CO₂ concentration; T – transpiration rate; gs – total conductance of CO₂     

Photosynthesis and growth of winter wheat in response to waterlogging at different growth stages

A study on photosynthetic and yield effects of waterlogging of winter wheat at four stages of growth was conducted in specially designed experimental tanks during the 2007–2008 and 2008–2009 seasons. Compared with the control, waterlogging treatments at tillering and jointing-booting stages reduced photosynthetic rate (P _N) and transpiration (E) significantly, it also decreased average leaf water-use efficiency (WUE, defined as the ratio of P _N to E) by 3.3% and 3.4% in both years. All parameters returned quickly to the control level after soil was drained. Damage to the photosynthetic apparatus during waterlogging resulted in a lower F_v/F_m ratio, especially at the first two stages. A strong reduction in root length, root mass, root/shoot ratio, total dry mass, and leaf area index were observed. The responses from vegetative plants at tillering and jointing-booting stages were greater than in generative plants at onset of flowering and at milky stages. The number of panicles per hectare at tillering stage and the spikelet per panicle at the stages of jointing-booting and at onset of flowering were also significantly reduced by waterlogging, giving 8.2–11.3% decrease of the grain yield relative to the control in both years. No significant difference in yield components and a grain yield was observed between the control and treatments applied at milky stages. These responses, modulated by the environmental conditions prevailing during and after waterlogging, included negative effects on the growth, photosynthetic apparatus, and the grain yield in winter wheat, but the effect was strongly stage-dependent.     

Pathogenicity of Hirschmanniella oryzae,H. spinicaudata,and H. imamuri on Rice

In greenhouse experiments Hirschmanniella oryzae, H. imamuri, and H. spinicaudata depressed and delayed the tillering and flowering of rice, and suppressed root and shoot growth and grain yield.     

Root Secretion of Defense-related Proteins Is Development-dependent and Correlated with Flowering Time

Proteins found in the root exudates are thought to play a role in the interactions between plants and soil organisms. To gain a better understanding of protein secretion by roots, we conducted a systematic proteomic analysis of the root exudates of Arabidopsis thaliana at different plant developmental stages. In total, we identified 111 proteins secreted by roots, the majority of which were exuded constitutively during all stages of development. However, defense-related proteins such as chitinases, glucanases, myrosinases, and others showed enhanced secretion during flowering. Defense-impaired mutants npr1-1 and NahG showed lower levels of secretion of defense proteins at flowering compared with the wild type. The flowering-defective mutants fca-1, stm-4, and co-1 showed almost undetectable levels of defense proteins in their root exudates at similar time points. In contrast, root secretions of defense-enhanced cpr5-2 mutants showed higher levels of defense proteins. The proteomics data were positively correlated with enzymatic activity assays for defense proteins and with in silico gene expression analysis of genes specifically expressed in roots of Arabidopsis. In conclusion, our results show a clear correlation between defense-related proteins secreted by roots and flowering time.     

Tiller number is altered in the ascorbic acid-deficient rice suppressed for l-galactono-1,4-lactone dehydrogenase

The tiller of rice (Oryza sativa L.), which determines the panicle number per plant, is an important agronomic trait for grain production. Ascorbic acid (Asc) is a major plant antioxidant that serves many functions in plants. l-Galactono-1,4-lactone dehydrogenase (GLDH, EC 1.3.2.3) is an enzyme that catalyzes the last step of Asc biosynthesis in plants. Here we show that the GLDH-suppressed transgenic rices, GI-1 and GI-2, which have constitutively low (between 30% and 50%) leaf Asc content compared with the wild-type plants, exhibit a significantly reduced tiller number. Moreover, lower growth rate and plant height were observed in the Asc-deficient plants relative to the trait values of the wild-type plants at different tillering stages. Further examination showed that the deficiency of Asc resulted in a higher lipid peroxidation, a loss of chlorophyll, a loss of carotenoids, and a lower rate of CO₂ assimilation. In addition, the level of abscisic acid was higher in GI-1 plants, while the level of jasmonic acid was higher in GI-1 and GI-2 plants at different tillering stages. The results we presented here indicated that Asc deficiency was likely responsible for the promotion of premature senescence, which was accompanied by a marked decrease in photosynthesis. These observations support the conclusion that the deficiency of Asc alters the tiller number in the GLDH-suppressed transgenics through promoting premature senescence and changing phytohormones related to senescence.     

Influence of rice cultivar on methane emission from paddy fields

Influence of rice cultivars on CH₄ emissions from a paddy field was studied using four Japonica types, two Indica types, and two Japonica/Indica F₁ hybrids. In addition, the suppression of CH₄ emission by interrupting irrigation at the flowering stage was investigated. Patterns of seasonal variation in CH₄ emission rates were similar among the eight cultivars. Two of the Japonica types showed the maximum and minimum CH₄ emissions among the cultivars investigated. Neither the number of tillers, shoot length, shoot weight, and root weight correlated with the CH₄ emission rates at the tillering and reproductive growth stages. Following temporary interruption of irrigation at the flowering stage, CH₄ emission rates decreased drastically and remained at very low levels until the harvesting stage, indicating its great effectiveness for the suppression of CH₄ emission from rice paddies.     

超高产杂交稻不同生育期的光合色素含量、净光合速率和水分利用效率

 较为系统地研究了两个超高产杂交稻‘两优培九’、‘华安3号’和多年来大面积推广的常规杂交稻‘汕优63’不同生育期的光合色素含量、净光合速率和水分利用效率。结果表明,在苗期,3个杂交稻的单位叶面积的叶绿素（Chl）含量差别不大,类胡萝卜素（Car）的含量以‘汕优63’为最高。然而,随着发育阶段的推进,到分蘖期,尤其是抽穗期剑叶的单位叶面积Chl和Car含量,两个超高产杂交稻高于‘汕优63’。从苗期到抽穗期,超高产杂交稻‘两优培九’和‘华安3号’的净光合速率（Pn）都比‘汕优63’高,而在苗期的午间强光条件下和分蘖期的早晨以及抽穗期的早晚相对弱光条件下其Pn的差别尤为显著。在苗期,‘汕优63’的水分利用效率（WUE）略高于‘两优培九’和‘华安3号’;到分蘖期和抽穗期,在上午10时之前和下午14时以后的时间段,则是两个超高产杂交稻明显高于‘汕优63’。这些结果说明,超高产杂交稻‘两优培九’和‘华安3号’不仅有较高的Pn和较强的抗光抑制能力,而且还能充分利用早晨和傍晚较弱的光强进行光合作用,这些是它们之所以高产的重要生理基础。此外,超高产杂交稻在生长发育的中后期（分蘖期和抽穗期）具有较高的WUE,有利于节约农业用水。     

Molecular weight averages and 13C NMR intensities provide evidence for branching in proanthocyanidin polymers

Molecular weight distributions for several proanthocyanidin polymers (condensed tannins) have previously been shown to be characterized by DP_w/DP_n > 2, where DP denotes the degree of polymerization. Molecular weight ratios of the size observed experimentally are expected if a few percent of the units form trifunctional branch points. An independent assessment of the extent of branching can be obtained from analysis of intensities of resonances in the ¹³C NMR spectra. Similar branch contents are deduced from DP_w/DP_n and from the spectral analysis. In the case of the Chinese quince (Chaenomeles chinensis) polymer, about 3% of the epicatechin units form trifunctional branch points.     

水稻籽粒灌浆过程中蛋白质表达特性及其对氮肥运筹的响应

采用大田栽培的方式,研究了大穗型水稻金辉809籽粒灌浆过程中蛋白质的差异表达变化模式以及同一施氮量下不同的氮肥施用比例(总施氮量225 kg/hm2,基蘖肥:穗粒肥分别为7∶3和6∶4)对强弱势粒灌浆影响的分子机制。获得了水稻不同灌浆时段籽粒总蛋白的表达图谱,共发现32个在灌浆过程中发生显著差异表达的蛋白点,涉及籽粒的淀粉合成,能量代谢,激素信号转导,基因表达调节和抗逆响应等。在此基础上,进一步构建了不同灌浆发育时段水稻强弱势籽粒响应不同氮肥比例调控的蛋白表达图谱,结果发现强势籽粒响应氮肥调控出现差异表达的蛋白点有8个,而弱势籽粒有26个,可见强势籽粒灌浆具有更强的环境稳定性,相对地,弱势籽粒灌浆则易被环境所调节。在总施氮量不变的情况下,适当增加生育后期氮肥的施用量,有利于增强弱势籽粒中信号转导,促进相关基因的表达,提高物质调运与能量代谢速率,增强抗逆性,增强弱势籽粒的代谢水平,延长其灌浆时期,提升弱势籽粒活性和灌浆强度,增加结实率和千粒重,最终实现高产高效。研究结果对于进一步明确氮素调控水稻强弱势粒灌浆的分子生态特性具有重要的理论与实际意义。     

Heterosis breeding in rice (Oryza sativa L.)

Summary Studies conducted at the International Rice Research Institute (IRRI) during 1980 and 1981 have shown up to 73% heterosis, 59% heterobeltiosis and 34% standard heterosis for yield in rice. The latter was estimated in comparison to commercial varieties: IR36 and IR42 (yield 4–5 t/ha in wet season trials and 7–8 t/ha in dry season trials). Generally speaking, absolute yield was lower and extent of standard heterosis was higher in wet season than in dry season with some exception. Yields up to 5.9 t/ha (22% standard heterosis) in the wet season and 10.4 t/ha (34% standard heterosis) in the dry season were obtained. Most of the hybrids performed better in some season while some performed better in both seasons. Hybrids showed better lodging resistance although they were 5–10 cm taller. F₁ hybrids had significant positive correlations with the parental traits viz., yield (r = 0.446), tillering (r = 0.746), height (r = 0.810) and flowering (r = 0.843). Selection of parents among elite breeding lines on the basis of their per se yield performance, diverse origin and resistance to insects and diseases should give heterotic combination. Yield advantage of hybrids was due primarily to increase in number of spikelets per unit area even though tiller number was reduced. Grain weight was either the same or slightly higher. High yielding hybrids also showed significant heterosis and heterobeltiosis for total dry matter and harvest index. For commercial utilization of heterosis in rice, effective male sterility and fertility restoration systems are available and up to 45% natural outcrossing on male sterile lines has been observed. Consequently, F₁ rice hybrid have been successfully developed and used in China. Prospects of developing hybrid rice varieties elsewhere appear bright especially in countries that have organized seed production, certification and distribution programs and where hybrid seed can be produced at a reasonable cost.     

Effects of free-air CO2 enrichment (FACE) on CH4 emission from a rice paddy field

Methane (CH₄) is a particularly potent greenhouse gas with a radiative forcing 23 times that of CO₂ on a per mass basis. Flooded rice paddies are a major source of CH₄ emissions to the Earth's atmosphere. A free‐air CO₂ enrichment (FACE) experiment was conducted to evaluate changes in crop productivity and the crop ecosystem under enriched CO₂ conditions during three rice growth seasons from 1998 to 2000 in a rice paddy at Shizukuishi, Iwate, Japan. To understand the influence of elevated atmospheric CO₂ concentrations on CH₄ emission, we measured methane flux from FACE rice fields and rice fields with ambient levels of CO₂ during the 1999 and 2000 growing seasons. Methane production and oxidation potentials of soil samples collected when the rice was at the tillering and flowering stages in 2000 were measured in the laboratory by the anaerobic incubation and alternative propylene substrates methods, respectively. The average tiller number and root dry biomass were clearly larger in the plots with elevated CO₂ during all rice growth stages. No difference in methane oxidation potential between FACE and ambient treatments was found, but the methane production potential of soils during the flowering stage was significantly greater under FACE than under ambient conditions. When free‐air CO₂ was enriched to 550 ppmv, the CH₄ emissions from the rice paddy field increased significantly, by 38% in 1999 and 51% in 2000. The increased CH₄ emissions were attributed to accelerated CH₄ production potential as a result of more root exudates and root autolysis products and to increased plant‐mediated CH₄ emissions because of the larger rice tiller numbers under FACE conditions.     

Effects of exogenous hormones on leaf photosynthesis of Panax ginseng

Ginseng (Panax ginseng) is a typical perennial shade plant. Aim of this study was to investigate the effects of exogenous hormones on photosynthesis of P. ginseng. At different growth stages, the aerial parts of P. ginseng plants were cut at the stem base and they were inserted into the nutrient solutions containing different exogenous hormones. Then the leaf photosynthesis and water absorbing capacity (absorbing water mass) of the excised plants were measured. The results showed that exogenous abscisic acid (ABA) decreased significantly net photosynthetic rate (P _N), stomatal conductance, transpiration rate, and absorbed water mass of excised P. ginseng at all growth stages, while both cytokinin (CTK) and indole-3-acetic acid (IAA) enhanced those parameters. Comparing different growth stages, ABA caused more severe inhibition of leaf photosynthesis at the early growth stage, while CTK and IAA showed significant enhancement of leaf photosynthesis at later growth stage. ABA reduced highly intercellular CO₂ concentration of P. ginseng at the flowering and green fruit stages, but it had only a small effect at red fruit early and red fruit stages. During the early growth stage, the inhibitory effect of ABA on leaf P _N might be caused mainly due to the stomatal limitation. However, the reason for this reduction was complex at the later growth stage and it included stomatal and other factors.