Melatonin Alleviates Abscisic Acid Deficiency Inhibition on Photosynthesis and Antioxidant Systems in Rice under Salt Stress

Melatonin and abscisic acid,as major plant hormones,play important roles in the physiological and biochemical activities of crops,but the interaction between the two under salt stress is not yet clear.This study investigated the endogenous levels of melatonin and abscisic acid in rice by using exogenous melatonin,abscisic acid,and their synthetic inhibitors,and examined their interactions under salt stress.The research results indicate that melatonin and abscisic acid can improve rice salt tolerance.Melatonin alleviated the salt sensitivity caused by abscisic acid deficiency,increased antioxidant enzyme activity and antioxidant content in rice treated with abscisic acid synth-esis inhibitors,and reduced total reactive oxygen species content and thiobarbituric acid reactive substance accu-mulation.Melatonin also increased the activity of key photosynthetic enzymes and the content of photosynthetic pigments,maintaining the parameters of photosynthetic gas exchange and chlorophyllfluorescence.In summary,melatonin alleviated the effects of abscisic acid deficiency on photosynthesis and antioxidant systems in rice and improved salt tolerance.This study is beneficial for expanding the understanding of melatonin regulation of crop salt tolerance.

Effects of Water Stress on Economic Characters of Water-saving Rice Variety Luhan No.1

[Objective] This study aimed at exploring the utilization rate of water of the new water-saving rice variety ＂Luhan No.1＂ and providing references and basis for the further demonstration and extension.[Method] Water-saving rice variety ＂Luhan No.1＂ and original receptor ＂6527＂ were used for dry processing without aquifer,and rice under regular irrigation conditions was used as the control.[Result] Under conditions which had economized on 67.4% of water compared with the regular irrigation,decreasing rates of 1 000-seed weight,seed setting rate,plant height and effective panicles of ＂Luhan No.1＂ were relatively small and had not achieved a significant level,while the decreasing rates of production of the region,total grains per panicle,theoretical production and filled grains per panicle of the original receptor ＂6527＂ were all over 25% and had attained very significant levels（P0.01）.[Conclusion] ＂Luhan No.1＂ had shown stable production,energy conservation,reducing environmental pollution and other advantages under water-conservating cultivation conditions.

Effects of Water Stress on Some Physiological Characteristics and Yield Compensation of Rice in Booting Stage

[Objective] The physiological characteristics and yield compensation effects of rice in booting stage were studied after water recovery when rice suffered water stress to provide references for improving rice water utilization efficiency and its drought resistance. [Method] The pot experiments with five rice varieties under three different treatments of water stresses were conducted to study physical signs every six days after water water-recovery. [Result] Along with the increase of water recov- ery, leaf water potential, SPAD and Pn values in treatment B （light drought） in- creased fast, and its compensation effect of the soluble sugar content was higher than that of treatment C （severe drought）; all sap flow speeds in treatments with water stresses fell. As for yield components, panicles per plant and spikelets per panicle decreased with water stress degree, and the decline of spikelets per pani- cle, in particular, was greatly influenced by water stress. Seed setting percentages in treatment B most reached peaks of different varieties, except of D you No. 363. The thousand-seed weight and ear weight per plant in treatment B and C both dropped, compared with control group. [Conclusion] When regular management was resumed after rice underwent water stress at booting stage, many characteristics and yield traits of rice got favorable compensation effects in the light water-stress treatments.

Response of ABA content in rice leaves to water stress

The rice seeds of IR661 (indica); Yanjing 2 (japonica) and Shanyou 53 indica hybrid Fwere grown in 15 nursery trays (40×20×15cm~2 each), A water stress treatment was carried out at the leaf age 5 by excluding water for 120h. Leaf water potential (LWP) was determined with chamber pressure. Abscisic acid (ABA) content in rice leaves was measured with radioimmnoassay. The content of ABA in the leaves changed a little when LWP was larger than—0.02 MPa, but increased rapidly when LWP was lower than this value. It could be considered that the critical LWP for obvious accumulation of ABA in rice seedling leaves was about—0.02 MPa.

Beneficial effects of silicon on photosynthesis of tomato seedlings under water stress

Silicon can improve drought tolerance of plants,but the mechanism still remains unclear.Previous studies have mainly concentrated on silicon-accumulating plants,whereas less work has been conducted in silicon-excluding plants,such as tomato（Solanum lycopersicum L.）.In this study,we investigated the effects of exogenous silicon（2.5 mmol L^（-1））on the chlorophyll fluorescence and expression of photosynthesis-related genes in tomato seedlings（Zhongza 9）under water stress induced by 10%（w/v）polyethylene glycol（PEG-6000）.The results showed that under water stress,the growth of shoot and root was inhibited,and the chlorophyll and carotenoid concentrations were decreased,while silicon addition improved the plant growth and increased the concentrations of chlorophyll and carotenoid.Under water sterss,chlorophyll fluorescence parameters such as PSII maximum photochemical efficiency（F_v/F_m）,effective quantum efficiency,actual photochemical quantum efficiency（Ф_（PSII））,photosynthetic electron transport rate（ETR）,and photochemical quenching coefficient（q_P）were decreased;while these changes were reversed in the presence of added silicon.The expressions of some photosynthesis-related genes including PetE,PetF,PsbP,PsbQ,PsbW,and Psb28 were down-regulated under water stress,and exogenous Si could partially up-regulate their expressions.These results suggest that silicon plays a role in the alleviation of water stress by modulating some photosynthesis-related genes and regulating the photochemical process,and thus promoting photosynthesis.

Effects of Water Stress on Reactive Oxygen Species Generation and Protection System in Rice During Grain-Filling Stage

Rice is one of the main staple food crops in the world, but it may suffer serious water stress during growth period. Water stress during grain filling results in decreased grain yeild, but its mechanism generating and scavenging the active oxygen is unclear under continuance of the water stress. The experiment was carried out in growth chamber to investigate the effects of water stress on the production of superoxide free radical （O2）, hydrogen peroxide （H202）, malondialdehyde （MDA）, reduced glutathione （GSH）, ascorbic acid （AsA）, and antioxidative enzyme activities in three rice hybrids with differing drought resistant under both normal and drought conditions during grain-filling stage. The results showed that water stress aggravated the membrane lipid peroxidation in rice leaves, which was more severe in less drought resistant hybrids than that in more tolerant ones. Also O2＇ and H2O2 accumulated more rapidly in less drought resistant hybrids than that in more tolerant ones. During water stress, decreases of GSH, AsA, chlorophyll, and relative water contents in more drought resistant hybrids were obvious less than those in less tolerant ones. Activities of superoxide dismutase （SOD）, catalase （CAT） and peroxidase （POD） in/eaves increased obviously in 0-14 d after heading and subsequently decreased rapidly, and those in more drought resistant hybrids were more than those in less tolerant ones. The results showed that changes of O2, H2O2, MDA, GSH, and AsA contents and antioxidative enzyme activities correlated significantly to drought resistance of rice hybrids, and more drought resistant hybrids possessed high ant oxidation capacity.

Response of Rice Varieties to Water Stress in Sokoto, Sudan Savannah, Nigeria

Pot experiment was conducted at the Botanical Garden of the Department of Biological Science, Usmanu Danfodiyo University, Sokoto Nigeria, during the 2013 dry season. The main objective of this research was to determine the effect of water stress and variety on productivity of rice (Oryza sativa) at Sokoto. The treatment consisted of water stress at three growth stages (Tillering, flowering, Grain filling) and unstress (control) and three rice varieties (FARO 44, NERICA 2 and FARO 15) laid out in a Completely Randomised Design (CRD) replicated three times. The result indicated that water stress significantly (P < 0.05) resulted to decreased in plant height, number of leaves per plant, total biomass, harvest index and grain yield. The results indicated significant (P < 0.05) differences among genotypes. Faro 44 differed significant from in plant height, number of leaves per plant, total biomass, harvest index and grain yield. FARO 44 differed significantly from NERICA 2 and FARO 15 at all the parameters under study. Water is very vital as far as rice production is concern should be applied at every stage of rice production. FARO 44 is recommended for the area for higher yield.

Growth and Physiological Performance of Aerobic and Lowland Rice as Affected by Water Stress at Selected Growth Stages

Aerobic rice technology is still new in Malaysia, and information regarding MARDI Aerob 1(MA1), the first local aerobic rice variety, is still lacking. Therefore, comparative studies were carried out to determine the physiological performance of aerobic rice variety MA1 and lowland rice variety MR253 under water stress given at the panicle initiation, flowering and ripening stages. This experiment was arranged in a randomized complete block design. Stomatal conductance(g_s), chlorophyll a fluorescence(F_v/F_m), leaf relative water content(leaf RWC), and soil moisture content(SMC) as well as yield component parameters such as panicle number, grain yield and 100-grain weight were measured. Results revealed that gs and leaf RWC for both varieties decreased with depletion of SMC. The correlation study between the physiological parameters and SMC indicated that F_v/F_m was not affected by water stress, regardless of varieties. The yield components(panicle number, grain yield and 100-grain weight) for both varieties greatly decreased when water stress was imposed at the panicle initiation stage. This study showed that the panicle initiation period was the most sensitive stage to water stress that contributed to a substantial reduction in yield for both varieties. Under the aerobic condition(control), MR253 produced higher panicle number, 100-grain weight and yield than MA1. Although MR253 is bred for lowland, it is well adapted to aerobic condition.

Transcriptional Profi le by Cold Water Stress at the Booting Stage of japonica Rice

This study was carried out to identify molecular responses of the two varieties with different cold tolerance under cold water stress (13℃) at the booting stage. Transcriptional responses of the genes were analyzed in

Response of Photosynthesis, Growth, Carbon Isotope Discrimination and Osmotic Tolerance of Rice to Elevated CO_2

Four rice ( Oryza sativa L.) cultivars 'IR72', 'Tesanai 2', 'Guichao 2' and 'IIyou 4480' were grown in two plastic house (15 m×3 m) with 35 μmol/mol and 60 μmol/mol CO 2 concentration which was controlled by computer. As compared with rice at ambient 35 μmol/mol CO 2, the changes in photosynthetic rate at elevated CO 2 showed up_regulation ('IR72' and 'Tesanai 2'), stable (unchanged) in 'Guichao 2' and down_regulation type ('IIyou 4480'). Growth rate, panicle weight, integrated water use efficiency (WUE) calculated from Δ 13 C and the capacity of scavenging DPPH · (1,1_diphenyl_2_picrylhydrazyl) free radical were increased at elevated CO 2. An increment in total biomass was observed in three cultivars by elevated CO 2, with the exception of 'IIyou 4480'. Ratios of panicle weight/total biomass were altered to different extents in tested cultivars by elevated CO 2. When leaf segments were subjected to PEG osmotic stress, the electrolyte leakage rate from leaves grown at elevated CO 2 was less than that at 35 μmol/mol CO 2. Those intraspecific variations of rice imply a possibility for selecting cultivars with maximal productivity and high tolerance to stresses adapted to elevated CO 2 in the future.

Alterations of Panicle Antioxidant Metabolism and Carbohydrate Content and Pistil Water Potential Involved in Spikelet Sterility in Rice under Water-Deficit Stress

Two rice genotypes with different drought tolerance, namely Jin 23B （drought tolerant） and Zhenshan 97B （drought sensitive）, were used to study the antioxidant enzyme activities, soluble sugar and starch contents in spikelets, pistil water potential and pollen number on a stigma under water-deficit stress at the flowering stage, which were involved in the spikelet sterility. Compared with respective controls, drought stress induced more serious decreases of superoxide dismutase （SOD）, peroxidase （POD） and catalase （CAT） activities and more significant increase of malonaldehyde （MDA） content in spikekets of Zhenshan 97B than in Jin 23B on 9 and 12 days after water stress （DAWS）. The soluble sugar and starch contents increased significantly in spikelets of Jin 23B, but decreased significantly in spikelets of Zhenshan 97B during 9-12 DAWS. The pistil maintained higher water potential in Jin 23B than in Zhenshan 97B during 3-6 DAWS and 9-12 DAWS. In addition, water stress induced more significant decrease in the pollen number on a stigma as well as the percentage of unfilled grains in Zhenshan 97B than in Jin 23B. Thus, it is suggested that water stress induced spikelet sterility by damaging antioxidant enzyme activities, reducing carbohydrate content in spikelets and decreasing pistil water potential at the flowering stage in rice.

Arbuscular mycorrhizal fungi improve biomass, photosynthesis, and water use efficiency of Opuntia ficus-indica (L.) Miller under different water levels

Opuntia ficus-indica(L.)Miller is a CAM(crassulacean acid metabolism)plant with an extraordinary capacity to adapt to drought stress by its ability to fix atmospheric CO_(2) at nighttime,store a significant amount of water in cladodes,and reduce root growth.Plants that grow in moisture-stress conditions with thick and less fine root hairs have a strong symbiosis with arbuscular mycorrhizal fungi(AMF)to adapt to drought stress.Water stress can limit plant growth and biomass production,which can be rehabilitated by AMF association through improved physiological performance.The objective of this study was to investigate the effects of AMF inoculations and variable soil water levels on the biomass,photosynthesis,and water use efficiency of the spiny and spineless O.ficus-indica.The experiment was conducted in a greenhouse with a full factorial experiment using O.ficus-indica type(spiny or spineless),AMF(presence or absence),and four soil water available(SWA)treatments through seven replications.Water treatments applied were 0%–25%SWA(T1),25%–50%SWA(T2),50%–75%SWA(T3),and 75%–100%SWA(T4).Drought stress reduced biomass and cladode growth,while AMF colonization significantly increased the biomass production with significant changes in the physiological performance of O.ficus-indica.AMF presence significantly increased biomass of both O.ficus-indica plant types through improved growth,photosynthetic water use efficiency,and photosynthesis.The presence of spines on the surface of cladodes significantly reduced the rate of photosynthesis and photosynthetic water use efficiency.Net photosynthesis,photosynthetic water use efficiency,transpiration,and stomatal conductance rate significantly decreased with increased drought stress.Under drought stress,some planted mother cladodes with the absence of AMF have not established daughter cladodes,whereas AMF-inoculated mother cladodes fully established daughter cladodes.AMF root colonization significantly increased with the decrease of SWA.AMF caused an increase in biomass production,increased tolerance to drought stress,and improved photosynthesis and water use efficiency performance of O.ficus-indica.The potential of O.ficus-indica to adapt to drought stress is controlled by the morpho-physiological performance related to AMF association.

Responses of the seedlings of five dominant tree species in Changbai Mountain to soil water stress

Soil water stress was studied on the potted seedlings of five dominant tree species (Pinus koraienes Sieb.et Zucc., Fraxinus mandshurica Rupr., Juglans mandshurica Maxim, Tilia amurensis Rupr. and Quercus mongolica Fisch.ex Turcz) from the broadleaved/Korean pine forest in Changbai Mountain. Leaf growth, water transpiration and photosynthesis were compared for each species under three soil moisture conditions: 85%-100% (high water, CK), 65%-85% (Medium water, MW) and 45%-65% (low water, LW) of 37.4% water-holding capacity in field. The results showed that the characteristic of typical drought-resistance of the leaves is significantly developed. The net photosynthetic rate and water use efficiency of Fraxinus mandshurica were higher in MW than those in CK. But for the other four species, the net photosynthetic rate and water use efficiency in CK were lower than those in MW and LW. The transpiration rate responding to soil moistures varied from species to species.

Changes in DNA Methylation Pattern at Two Seedling Stages in Water Saving and Drought-Resistant Rice Variety after Drought Stress Domestication

Recent studies revealed that DNA methylation plays an important role in plant growth and development. In this study, a water-saving and drought-resistant rice variety Huhan 3 was subjected to drought stress from tillering to grain-filling stages in six successive growth cycles. The variations in DNA methylation pattern between the original generation （Go） and the sixth generation （G6） were analyzed by using methylation sensitive amplification polymorphism method. The results revealed that the methylated loci accounted for 34.3% to 34.8% of the total loci. Among these methylated loci, 83.1% to 84.8% were full- and hyper-methylated and 15.2% to 16.9% were hemi-methylated. The DNA methylation level decreased from the three-leaf to four-leaf stages in Huhan 3. Differentially methylated loci （DML） between generations or/and between different developmental stages accounted for 4.0% of the total loci, most of which were only related to plant development （57.9%）. Compared to Go, the DNA methylation pattern of G8 changed after drought domestication, at the three-leaf stage, de-methylation accounting for 59.1%, while at the four-leaf stage, re-methylation for 47.9%. Genome-wide alternations of DNA methylation were observed between the two seedling stages, and DML mainly occurred on the gene＇s promoter and exon region. The genes related to DML involved in a wide range of functional biology and participated in many important biological processes.

Analysis of Gene Expression Profile Induced by Water Stress in Upland Rice(Oryza sativa L.var.IRAT109)Seedlings using Subtractive Expressed Sequence Tags Library

To identify the water stress induced genes of upland rice cultivar IRAT109, which is resistant to drought, a subtractive cDNA library was developed from polyethylene glycol- （PEG） treated and non-treated seedlings by suppression subtractive hybridization, from which 2112 recombinant colonies were obtained, Eight hundred clones were selected randomly for sequencing analysis, and 384 unique expressed sequence tags （ESTs） were obtained, They were found to be involved in diverse biological processes, such as metabolism, transcription, signal transduction, protein synthesis and others, Notably a number of known functional genes in drought tolerance, including genes related to biosynthesis of osmoprotectants, defense against active oxygen, removal of toxic compounds, recovery of proteins and reinforcement of cell wall were also found in the study, Several genes related to deleterious responses were upregulated by PEG stress, The differential expression patterns of 11 SSH-derived ESTs were confirmed by real-time polymerase chain reaction.

Effect of Different Water Management and Nitrogen Forms on Characteristics of Iron Nutrition of Rice Cultivated Under Aerobic Condition

Although available iron is usually abundant for the growth of rice cultivated in waterlogged condition, the rice crop may suffer from its deficiency when cultivated in aerobic soil since the soil properties are totally different from waterlogged. Solubility of iron is very low in soils with high Eh and/or high pH. A field experiment with five different depth (10, 20, 30, 40 and 50 cm) of groundwater, and a pot experiment with five treatments of ammonium nitrate ratio (100/0, 75/25, 50/50, 25/75 and 0/100) were conducted to study the characteristics of iron nutrition of rice in non full irrigation condition. Moreover, the contents of iron extracted by 1 mol L 1 HCl of rice plant samples of 8 cultivars from both aerobic and waterlogged cultivation were analyzed to study the effect of water regimes on iron content of rice plants. The results were as follows: (1) The average content of available Fe (2.70 mg kg 1 ) of 5 layers of the soil treated with 10 cm depth of groundwater was significantly higher than that (0.83 mg kg 1 ) with 50 cm depth of groundwater, and the iron concentration of rice plant of the former was much higher than that of the later. (2) Iron deficiency of rice became much severe when high ratio of nitrate (more than 75 percent) in nitrogen fertilizer applied at different intervals in aerobic cultivation. (3) The iron concentrations of 3 cultivars, Wuyujing3 (99 mg kg 1 ), Yangdao4 (87 mg kg 1 ) and 9520 (95 mg kg 1 ), of rice plants cultivated in aerobic condition were significantly less than those(195, 197 and 175 mg kg 1 ) respectively in waterlogged condition at tillering stage. And even much significant differences existed in the iron concentrations of different cultivars growing in the aerobic and waterlogged condition at maturity.

Evaluation and Bulked Segregant Analysis of Major Yield QTL qtl12.1 Introgressed into Indigenous Elite Line for Low Water Availability under Water Stress

Near isogenic lines carrying large-effect QTL （qtl2.1）, which has a consistent influence on grain yield under upland drought stress conditions in a wide range of environments, were evaluated under water stress in the fields. The line which gave higher yield under drought was crossed with a local elite line, PMK3, and forwarded to F2：3 generation. Significant variation was found among the F2：3 lines for agronomic traits under water stress in the fields. Low to high broad sense heritability （H） for investigated traits was also found. Water stress indicators such as leaf rolling and leaf drying were negatively correlated with plant height, biomass and grain yield under stress. Bulked segregant analysis （BSA） was performed with the markers in the vicinity of qUl2.1, and RM27933 was found to be segregated perfectly well in individual components of drought resistant and drought susceptible bulks which were bulked based on yield under water stress among F2：3 lines. Hence, this simple and breeder friendly marker, RM27933, may be useful as a potentially valuable candidate marker for the transfer of the QTL qtl12.1 in the regional breeding program. Bioinformatic analysis of the DNA sequence of the qtl12.1 region was also done to identify and analyze positional candidate genes associated with this QTL and to ascertain the putative molecular basis of qUl2.1.

Effect of Water Deficit Imposed during the Early Developmental Phase on Photosynthesis of Cocoa (Theobroma cacao L.)

A greenhouse study was carried out at Cocoa Research Institute of Nigeria, Ibadan to study the effect of water stress on the four popular cocoa genotypes at the institute. F3 Amazon, T1, T7 and Amelonado were raised under different water regimes (daily, 3-day interval, 5-day interval and 7-day interval) at 100%, 50% and 25% field capacities. Data were collected on the height, leaf area, root length, stomata conductance, photosynthetic rate and water use efficiency of the plants. Results showed that plant performances showed genotypic variation in their response to water stress. Generally, there were linear and positive relationships between water level and values in both physiological and morphological responses of cocoa genotypes.

Quantifying the impacts of soil water stress on the winter wheat growth in an arid region,Xinjiang

Wheat growth in response to soil water deficit play an important role in yield stability. A field experiment was conducted for winter wheat (Triticum aestivum L.) during the period of 2002-2005 to evaluate the effects of limited irrigation on winter wheat growth. 80%, 70%, 60%, 50% and 40% of field capacity was applied at different stages of crop growth. Photosynthetic characteristics of winter wheat, such as photosynthesis rate, transpiration rate, stomatal conductance, photosynthetically active radiation, and soil water content, root and shoot dry mass accumulation were measured, and the root water uptake and water balance in different layer were calculated. Based on the theory of unsaturated dynamic, a one-dimensional numerical model was developed to simulate the effect of soil water movement on winter wheat growth using Hydrus-1 D. The soil water content of stratified soil in the experimental plot was calculated under deficit irrigation. The results showed that, in different growing periods, evapotranspiration, grain yield, biomass, root water uptake, water use efficiency, and photosynthetic characteristics depended on the controlled ranges of soil water content. Grain yield response to irrigation varied considerably due to differences in soil moisture contents and irrigation scheduling between seasons. Evapotranspiration was largest in the high soil moisture treatment, and so was the biomass, but this treatment did not produce the highest grain yield and root water uptake was relatively low. Maximum depth of root water uptake is from the upper 80 cm in soil profile in jointing stage and dropped rapidly upper 40 cm after heading stage, and the velocity of root water uptake in latter stage was less than that in middle stage. The effect of limited irrigation treatment on photosynthesis was complex owing to microclimate. But root water uptake increased linearly with harvest yield and improvement in the latter gave better root water uptake under limited irrigation conditions. Appropriately controlled soil water contents can improve the root water uptake and grain yield. Consistently high values of root water uptake and grain yield were produced under conditions of mild water deficit at the seedling and start of regrowth to stem-elongation stages, in addition to a further soil water depletion at the physiological maturity to harvest stage. We suggest that periods of mild soil water depletion in the early vegetative growth period together with severe soil water depletion in the maturity stage of winter wheat is an optimum for limited irrigation regime in this oasis. Considerable potential for further improvement in agricultural water use efficiency in the arid zone depends on effective conservation of moisture and efficient use of the limited water.

Effects of Different NH_4^+/NO_3^- Ratio and Water Condition on Physiological Characteristics of Rice Seedlings

[Objective] This study aimed to further explore the dynamics of related physiological indexes of rice seedlings under different NH4＋ /NO3- ratio and different water condition. [Method] Under the hydroponic condition in laboratory, 3 NH4＋/NO3- ratios （0/100, 50/50 and 100/0） and 2 water conditions （＋PEG,-PEG） were designed for Fengliangyou 7203. [Result] The root-canopy ratio of rice seedlings increased under any of the NH4＋/NO3- ratios and water conditions. Under water stress, the root-canopy ratio of rice seedlings changed most greatly at the NH4＋/NO3- ratio of 0/ 100; the overall water potential of rice seedlings reached the lowest at the NH4＋/ NO3- ratio of 100/0; and the changes of water potential and xylem flow pH were relatively stable at the NH4＋/NO3- ratio of 50/50. Under the condition of no water stress, the growth of rice seedlings was best at the NH4＋/NO3- ratio of 50/50, followed by the NH4＋/NO3- ratios of 0/100 and 100/0. [Conclusion] This study will pro- vide a basis for understanding the relationship between water potential and xylem flow.