Embryo and endosperm development in wheat (Triticum aestivum L.) kernels subjected to drought stress

The aim of the present work was to reveal the histological alterations triggered in developing wheat kernels by soil drought stress during early seed development resulting in yield losses at harvest. For this purpose, observations were made on the effect of drought stress, applied in a controlled environment from the 5th to the 9th day after pollination, on the kernel morphology, starch content and grain yield of the drought-sensitive Cappelle Desprez and drought-tolerant Plainsman V winter wheat (Triticum aestivum L.) varieties. As a consequence of water withdrawal, there was a decrease in the size of the embryos and the number of A-type starch granules deposited in the endosperm, while the development of aleurone cells and the degradation of the cell layers surrounding the ovule were significantly accelerated in both genotypes. In addition, the number of B-type starch granules per cell was significantly reduced. Drought stress affected the rate of grain filling shortened the grain-filling and ripening period and severely reduced the yield. With respect to the recovery of vegetative tissues, seed set and yield, the drought-tolerant Plainsman V responded significantly better to drought stress than Cappelle Desprez. The reduction in the size of the mature embryos was significantly greater in the sensitive genotype. Compared to Plainsman V, the endosperm cells of Cappelle Desprez accumulated significantly fewer B-type starch granules. In stressed kernels of the tolerant genotype, the accumulation of protein bodies occurred significantly earlier than in the sensitive variety.     

Effect of drought on ear and flag leaf photosynthesis of two wheat cultivars differing in drought resistance

We investigated net photosynthetic rate (P_N) of ear and two uppermost (flag and penultimate) leaves of wheat cultivars Hongmangmai (drought resistant) and Haruhikari (drought sensitive) during post-anthesis under irrigated and non-irrigated field conditions. The P_Nof ear and flag leaf were significantly higher and less affected by drought in Hongmangmai than in Haruhikari. The rate of reduction in stomatal conductance (g_s) was similar for the two cultivars, but intercellular CO₂concentration (C_i) in the flag leaf of Hongmangmai was lower than that of Haruhikari in non-irrigated treatment. No differences were observed in leaf water potential (₁) and osmotic adjustment of the flag leaf of the cultivars. These results imply that differences in photosynthetic inhibition on the flag leaf at low leaf ₁between the cultivars were primarily due to non-stomatal effects. Hence the main physiological factor associated with yield stability of Hongmangmai under drought stress may be attributed to the capacity for chloroplast activity in the flag leaf, which apparently allows sustained P_Nof flag leaf during grain filling under drought stress. The higher P_Nof ear in Hongmangmai under drought could also be related to its drought resistance.This revised version was published online in March 2005 with corrections to the page numbers.     

Relationship between osmotic stress-induced abscisic acid accumulation,biomass production and plant growth in drought-tolerant and -sensitive wheat cultivars

The effects of increasing osmotic stress induced by 100–400 mOsm (−0.976 MPa) polyethylene glycol (PEG 6000) were investigated in a drought-tolerant (Triticum aestivum L. cv. Mv Emese) and drought-sensitive (cv. GK élet) wheat cultivar at the three-leaf stage. During osmotic stress, the decline of the water potential (ψ _w) was more significant in the leaves, while the abscisic acid (ABA) levels of the roots increased earlier and remained higher in the sensitive than in the tolerant variety. There was an increasing gradient of ABA content toward the youngest leaves in the drought-sensitive GK élet, while more ABA accumulated in the fully developed, older leaves of the tolerant cultivar Mv Emese. In accordance with the rapid and significant accumulation of ABA, the stomatal conductance decreased earlier in the tolerant cultivar. The effect of water stress on the PSII photochemistry was pronounced only 1 week after the exposure to PEG, as indicated by the earlier decrease of the net CO₂ fixation, the effective quantum yield (Φ_PSII) and the photochemical quenching (q _P) in light-adapted samples of the tolerant variety in 400 mOsm PEG 6000. The stress treatment caused more significant reductions in these parameters toward the end of the experiment in the sensitive cultivar. In spite of small differences in the photosynthetic characteristics, the net biomass production was not significantly altered by this osmotic stress. The accumulation of ABA controlled the distribution of the biomass between the shoot and root systems under osmotic stress, and contributed to the development of stronger and deeper roots in the drought-sensitive cultivar GK élet. However, the root elongation did not correlate with the drought sensitivity of these cultivars on the basis of crop yield.     

Photosynthetic Parameters at the Vegetative Stage and during Grain Development of Two Hexaploid Wheat Cultivars Differing in Salt Tolerance

Response of two spring wheat (Triticum aestivum L.) cultivars, salt tolerant SARC-I and salt sensitive Potohar, to different concentrations of NaCl was examined under glasshouse conditions. Eighteen-day-old plants of both the lines grown in sand culture were irrigated with 0 (control), 80, 160 or 240 mM NaCl in full strength Hoagland's nutrient solution. Shoot fresh and dry masses, and leaf area per plant of SARC-I at the vegetative stage, were significantly greater than those of cv. Potohar at higher salt concentrations, however, relative growth rate (RGR) of cv. Potohar was significantly higher than that of SARC-I. SARC-I had higher net photosynthetic rate (P_N), stomatal conductance (g_s) and transpiration rate (E) than cv. Potohar at the vegetative stage, but the cultivars did not differ significantly in water-use efficiency (P_N/E), intrinsic water use efficiency (P_N/g_s), and intercellular/ambient CO₂ concentration ratio. At the grain development stage, SARC-I had significantly higher P_N and g_s in the flag leaf than cv. Potohar under salinity. SARC-I was superior to cv. Potohar with respect to number of grains per spike, number of grains per spikelet, mean grain mass, and grain yield per plant at all NaCl concentrations.     

Selection of drought tolerant and sensitive genotypes from wheat DH population

Drought has significant effect on wheat production by decreasing grain yield. Phenotyping the populations is a useful tool for understanding the interactions between phenotype and genotype. 135 doubled haploid (DH) genotypes and their parental varieties Plainsman (Pl) and Cappelle Desprez (CD) were phenotyped in glasshouse under well-watered (WW) and drought-stress (DS) conditions. The response of plant height, heading time, aboveground biomass, grain yield, root dry mass harvest index (HI) under both conditions, and stress tolerance index (STI) and water consumption in WW conditions was studied. We found 20% decrease in the plant growth, 66% decrease in the aboveground biomass, and 77% decrease in the grain yield. Under WW conditions, high water consumption was not related to high yields, STI, and HI. The tolerant and the sensitive genotypes were selected. In the WW and water consumption treatment, the sensitive genotype group had better grain yield performance, but under DS, the tolerant group had higher grain yield. The average yield loss was 59% in the tolerant group compared to the WW treatment, and the sensitive yield loss was 68%. Correlation was found between the grain yield and root dry mass in the tolerant group. There was significant difference between the tolerant and sensitive groups on water consumption, as the sensitive genotypes had higher water need. We found strong positive correlation between the water consumption and the grain yield in the tolerant group. This study showed that the tolerant genotypes had improved water regulating efficiency.     

Root Respiration,Photosynthesis and Grain Yield of Two Spring Wheat in Response to Soil Drying

The effects of soil water regime and wheat cultivar, differing in drought tolerance with respect to root respiration and grain yield, were investigated in a greenhouse experiment. Two spring wheat (Triticum aestivum) cultivars, a drought sensitive (Longchun 8139-2) and drought tolerant (Dingxi 24) were grown in PVC tubes (120 cm in length and 10 cm in diameter) under an automatic rain-shelter. Plants were subjected to three soil moisture regimes: (1) well-watered control (85% field water capacity, FWC); (2) moderate drought stress (50% FWC) and (3) severe drought stress (30% FWC). The aim was to study the influence of root respiration on grain yield under soil drying conditions. In the experiment, severe drought stress significantly (p < 0.05) reduced shoot and root biomass, photosynthesis and root respiration rate for both cultivars, but the extent of the decreases was greater for Dingxi 24 compared to that for Longchun 8139-2. Compared with Dingxi 24, 0.04 and 0.07 mg glucose m⁻² s⁻¹ of additional energy, equivalent to 0.78 and 1.43 J m⁻² s⁻¹, was used for water absorption by Longchun 8139-2 under moderate and severe drought stress, respectively. Although the grain yield of both cultivars decreased with declining soil moisture, loss was greater in Longchun 8139-2 than in Dingxi 24, especially under severe drought stress. The drought tolerance cultivar (Dingxi 24), had a higher biomass and metabolic activity under severe drought stress compared to the sensitive cultivar (Longchun 8139-2), which resulted in further limitation of grain yield. Results show that root respiration, carbohydrates allocation (root:shoot ratio) and grain yield were closely related to soil water status and wheat cultivar. Reductions in root respiration and root biomass under severe soil drying can improve drought tolerant wheat growth and physiological activity during soil drying and improve grain yield, and hence should be advantageous over a drought sensitive cultivar in arid regions.     

Effects of Long-Term Fertilization on Leaf Photosynthetic Characteristics and Grain Yield in Winter Wheat

Based on a 20-year fertilization experiment with wheat-maize double cropping system, the effects of different long-term fertilization treatments on leaf photosynthetic characteristics and grain yield in different winter wheat (Triticum aestivum L.) cultivars were studied in the growing seasons of 2000–2001 and 2001–2002. A total of nine fertilization treatments were implemented, i.e. no fertilizer (CK), N fertilizer (N), N and P fertilizers (NP), N and K fertilizers (NK), N, P, and K fertilizers (NPK), only organic manure (M), organic manure and N fertilizer (MN), organic manure and N and P fertilizers (MNP), and organic manure and N, P, and K fertilizers (MNPK). With the treatments of combined organic manure and inorganic fertilizers (TMI), net photosynthetic rate (P _N), maximal activity of photosystem 2, PS2 (F_v/F_m), and chlorophyll content (SPAD value) of flag leaves and leaf area index (LAI) were much higher at the mid grain filling stage (20 or 23 d post anthesis, DPA), and exhibited slower declines at the late grain filling stage (30 DPA), compared with the treatments of only inorganic fertilizers (TI). The maximal canopy photosynthetic traits expressed as P _N×LAI and SPAD×LAI at the mid grain filling stage were also higher in TMI than those in TI, which resulted in different grain yields in TMI and TI. Among the treatments of TMI or among the treatments of TI, both flag leaf and canopy photosynthetic abilities and yield levels increased with the supplement of inorganic nutrients (N, P, and K fertilizers), except for the treatment of NK. Under NK, soil contents of N and K increased while that of P decreased. Hence the unbalanced nutrients in soil from the improper input of nutrients in NK treatment were probably responsible for the reduced flag leaf and canopy photosynthetic characteristics and LAI, and for the fast declining of flag leaf photosynthetic traits during grain filling, resulting in the reduced yield of NK similar to the level of CK.     

Comparison of resistance to drought of three bean cultivars

The aim of the present work was to evaluate oxidative stress and plant antioxidant system of three contrasting bean (Phaseolus vulgaris L.) genotypes in the response to drought. Drought was imposed 14 d after emergence, by withholding water, until leaf relative water content reached 65 %. Water stress increased lipid peroxidation (LPO), membrane injury index, H₂O₂ and OH^⋅ production in leaves of stressed plants. Activities of the antioxidative enzymes superoxide dismutase (SOD) and ascorbate peroxidase (APOX) increased significantly under water stress in all the studied cultivars, while catalase (CAT) increased in cvs. Plovdiv 10 and Prelom, but decreased in cv. Dobrudjanski ran. Furthermore cv. Plovdiv 10 which had the highest APOX and CAT activities also showed the lowest increase in H₂O₂ and OH^⋅ production and LPO while cv. Dobrudjanski ran showed the lowest increases (and often the lowest values) in the antioxidant enzyme activities and the highest increases of H₂O₂ and OH^⋅ production, and LPO. On the basis of the data obtained we could specify cv. Plovdiv 10 and cv. Prelom as drought tolerant and cv. Dobrudjanski ran as a drought sensitive.     

Effects of Soil Drought and Atmospheric Humidity on Yield,Gas Exchange,and Stable Carbon Isotope Composition of Barley

The combined effects of water status, vapour pressure deficit (VPD), and elevated temperature from heading to maturity were studied in barley. Plants growing at high VPD, either under well-watered or water deficit conditions, had higher grain yield and grain filling rate than plants growing at low VPD. By contrast, water stress decreased grain yield and individual grain dry matter at any VPD. Water regime and to a lesser extent VPD affected ¹³C of plant parts sampled at mid-grain filling and maturity. The differences between treatments were maximal in mature grains, where high VPD increased ¹³C for both water regimes. However, the total amount of water used by the plant during grain filling did not change as response to a higher VPD whereas transpiration efficiency (TE) decreased. The net photosynthetic rate (P _N) of the flag leaves decreased significantly under water stress at both VPD regimes. However, P _N of the ears was higher at high VPD than at low VPD, and did not decrease as response to water stress. The higher correlation of grain yield with P _N of the ear compared with that of the flag leaf support the role of ear as the main photosynthetic organ during grain filling under water deficit and high VPD. The deleterious effects of combined moderately high temperature and drought on yield were attenuated at high VPD.     

Contribution of Pre-Anthesis Assimilates and Current Photosynthesis to Grain Yield,and their Relationships to Drought Resistance in Wheat Cultivars Grown Under Different Soil Moisture

We investigated the relative importance of pre-anthesis assimilates stored in plant parts, mainly in the stem, and post-anthesis photosynthesis to drought resistance in wheat (Triticum aestivum L.) cultivars Hongwangmai (drought resistant) and Haruhikari (drought sensitive) subjected to two soil moisture regimes: irrigated and non-irrigated. In the irrigated treatment, soil moisture was maintained near field capacity throughout the growing season, while in the non-irrigated treatment water was withheld from 81 d after sowing until maturity. Drought stress reduced grain yield of Hongwangmai and Haruhikari by 41 and 60 %, respectively. Remobilization of pre-anthesis assimilates to the grain (remobilization) was reduced by drought in Hongwangmai but increased in Haruhikari. The contribution of pre-anthesis assimilates to the grain decreased under non-irrigated treatment in Hongwangmai. However, under water stress, Hongwangmai maintained a higher net photosynthetic rate in the flag leaf than Haruhikari. These results indicated that maintenance of post-anthesis photosynthetic rate was related to drought resistance in Hongwangmai rather than to remobilization under drought stress.     

Photosynthetic Characteristics of Non-Leaf Organs of Winter Wheat Cultivars Differing in Ear Type and their Relationship with Grain Mass Per Ear

Chlorophyll content, photosystem 2 functioning (F_v/F_m, F_v/F₀), activity of ribulose-1,5-bisphosphate carboxylase/oxygenase, and net photosynthetic rates (P _N) of flag leaf blade, sheath, peduncle, and ear organs were assessed in large-ear type (Pin 7) and small-ear type (ND93) wheat cultivars. Some differences were found in photosynthetic properties between different green plant parts, the values of all studied parameters in ear parts being higher in Pin7 than in ND93. Furthermore, ear surface areas and ear P _N in 26 wheat genotypes measured at anthesis showed highly significant positive correlation with grain mass per ear. Hence a greater capability of ear photosynthesis may result in a greater grain yield in large-ear type cultivars.     

The effect of drought stress on chlorophyll fluorescence in Lolium-Festuca hybrids

The effects of drought on photochemical efficiency of PSII in leaves of 22 hybrids of Festuca pratensis × Lolium multiflorum and Festuca pratensis × Lolium perenne and of Festuca pratensis cv. Skra were investigated. A significant decrease of electron transport efficiency (about 25%) in PSII (Φ_PSII) was not found before 9 days of seedling growth in hydroponics with water potential (Ψ_w) equal to −0.8 MPa (simulated “soil drought”). The decrease of Φ_PSII was similarly related to that of excitation energy capture by open PSII reaction centre (Fv’/Fm’) and also to the decrease of the proportion of oxidized to reduced Q_A (photochemical fluorescence quenching, q_p). According to the drought prolongation, variation of all parameters of fluorescence between genotypes significantly increased. The seedlings of some genotypes were able to recover electron transport efficiency in PSII after increasing water potential in nutrient solution (removing the “soil drought”). When plants grew in containers with soil and 4 genotypes with the highest sensitivity of electron transport to drought (S) as well as 4 genotypes with the highest tolerance (T) were compared 17 days after watering ceased, Ψ_w in leaves considerably decreased, but the differences between S and T genotypes were often not significant in this respect. The differences between S and T genotypes, as values of Fv/Fm were concerned, also appeared small (about 5%), similarly as that of Fv’/Fm’ (5%), q_p (12%) and Φ_PSII (about 15%). Drought stress increased non-photochemical quenching of chlorophyll fluorescence (NPQ) 15 to 47% and this could protect the PSII reaction centres from damages because of energy excess. The increase of NPQ was not closely connected with drought resistance of plants because it was similar in some genotypes tolerant to dehydration as well as in sensitive ones. The results of the experiments suggest that resources of genetic variability in Festulolium may be sufficient for revealing differences between genotypes on the basis of measurement of chlorophyll a fluorescence, as far as their tolerance to soil drought is concerned. As the tolerance of PSII against drought is high, the determinations of fluorescence should be performed rather under severe stress. Such methods seem to be useful for selection of genotypes with high drought tolerance as well as with the ability to at least partial repairing of PSII after drought.     

The effect of drought hardening and chilling on ABA content in xylem sap and ABA - delivery rate from root of tomato plant

This paper is a continuation of our studies related to the response of two tomato cultivars: Robin and New Yorker to chilling: the later is more tolerant to chilling than the former one (Starck et al. 1994). The concentration of ABA in the xylem sap and ABA delivery rate (calculated as the amount of ABA exuded in 2h from the cut stump, following shoot removal) were estimated by ELISA. The relative water content (RWC) of the leaf blades and stomatal resistance (RS) were also measured. Tomato plants were grown in a greenhouse, under noncontrolled conditions. Before chilling some of the plants were drought hardened for 10 days (H). As an consequence of water deficit only New Yorker growth slightly decreased. Plants were chilled to 2–5 °C during three consecutive, 16-h nights, preceded by warm days, which caused a decrease in the RWC of leaf blades. Chilling did not decreased leaf blade hydration significantly, but drastically increased the concentration of ABA in the xylem sap in more chilling tolerant cv. New Yorker only. The delivery rate of ABA was markedly enhanced in both cultivars, but much more in New Yorker. Drought hardening increased ABA delivery rate in cv. Robin only, especially after chilling. The lack of correlation between changes in the RWC of leaf blades after low temperature treatment and the concentration of ABA in the xylem sap as well as its delivery rate suggest, that in both tomato cultivars chilling increased ABA level directly, not as an secondery effect of temperature-induced water deficit.     

Effect of the carmine spider mite (Acarida: Tetranychidae) infestation and mechanical injury on the level of ABA in tomato plants

The aim of this study was to determine the changes in the abscisic acid (ABA) content in tomato leaves infested by the carmine spider mite (CSM) (Tetranychus cinnabarinus Boidsuval) and in leaves that were mechanically injured. It was also investigated whether signalling from stressed to non-stressed organs occurred. Tomato plants (Lycopersicon esculentum Mill.) cvs. Romatos and Slonka (with various susceptibility to CSM) were stressed at the stage of first cluster flowering by either CSM feeding (72 hours) or by mechanical puncturing simulated feeding injury by CSM (18 hours). It was found that under control condition the level of ABA differed significantly between cultivars, being always higher in plants of the susceptible cv. Romatos. In response to CSM feeding, the content of ABA in infested organs of the more tolerant plant (cv. Slonka) increased by 95 % but in the susceptible one by 11 % only. ABA content in the organs non-stressed by CSM feeding either increased (Slonka cv.) or decreased (Romatos cv.). In response to mechanical wounding, ABA content in directly injured organs increased but to a lower degree (49 %) and only in Slonka cv.. The same was true for ABA content in non-injured organs of damaged plants of this cultivar. Observed changes in ABA level in non-stressed organs are probably the results of signalling from stressed organs. Plant response measured by changes in ABA level to the stress generated by CSM feeding, was much stronger than merely by mechanical injury.     

Comparison of Hexaploid and Tetraploid Wheat Cultivars in their Responses to Water Stress

We studied the effect of water stress imposed at anthesis and pre-anthesis stages on oxidative stress and antioxidant activity in four wheat cultivars, two hexaploid Triticum aestivum cultivars, drought resistant cv. C 306 and drought susceptible cv. Hira, and two tetraploid cultivars, T. durum cv. A 9-30-1 and T. dicoccum cv. HW 24. Water stress decreased relative water content (RWC), membrane stability index (MSI), and increased H₂O₂ and malondialdehyde (MDA) contents as well as activity of superoxide dismutase (SOD), catalase (Cat) and peroxidase (POX) in all the genotypes at all the stages. Both the tetraploid cultivars showed higher RWC, MSI and SOD activity, and lower H₂O₂ and MDA contents under water stress than hexaploid ones. Cat and POX activities were highest in C 306.     

Heat Stress and Spermidine: Effect on Chlorophyll Fluorescence in Tomato Plants

Two tomato (Lycopersicon esculentum L.) cultivars: Robin (tolerant) and Roma (sensitive to heat stress) were studied. Chlorophyll fluorescence induction parameters (F_v/F_p, A_max, and Rfd) at 25 °C showed that the PS2 activity was similar for both cultivars. The parameters, measured at 38 °C, decreased in both cultivars, but more in cv. Roma. Exogenous application of 4 mM spermidine improved the plant heat-resistance in both cultivars, and especially in cv. Roma. Analysis of chlorophyll fluorescence changes during linear increase in temperature showed that cv. Robin plants have higher ability to hardening and higher resistance to thermal damage of the pigment-protein complexes structure and the activity of PS2 than cv. Roma.     

Grain zinc, iron and protein concentrations and zinc-efficiency in wild emmer wheat under contrasting irrigation regimes

Micronutrient malnutrition, and particularly deficiency in zinc (Zn) and iron (Fe), afflicts over three billion people worldwide, and nearly half of the world’s cereal-growing area is affected by soil Zn deficiency. Wild emmer wheat [Triticum turgidum ssp. dicoccoides (Körn.) Thell.], the progenitor of domesticated durum wheat and bread wheat, offers a valuable source of economically important genetic diversity including grain mineral concentrations. Twenty two wild emmer wheat accessions, representing a wide range of drought resistance capacity, as well as two durum wheat cultivars were examined under two contrasting irrigation regimes (well-watered control and water-limited), for grain yield, total biomass production and grain Zn, Fe and protein concentrations. The wild emmer accessions exhibited high genetic diversity for yield and grain Zn, Fe and protein concentrations under both irrigation regimes, with a considerable potential for improvement of the cultivated wheat. Grain Zn, Fe and protein concentrations were positively correlated with one another. Although irrigation regime significantly affected ranking of genotypes, a few wild emmer accessions were identified for their advantage over durum wheat, having consistently higher grain Zn (e.g., 125 mg kg^?1), Fe (85 mg kg^?1) and protein (250 g kg^?1) concentrations and high yield capacity. Plants grown from seeds originated from both irrigation regimes were also examined for Zn efficiency (Zn deficiency tolerance) on a Zn-deficient calcareous soil. Zinc efficiency, expressed as the ratio of shoot dry matter production under Zn deficiency to Zn fertilization, showed large genetic variation among the genotypes tested. The source of seeds from maternal plants grown under both irrigation regimes had very little effect on Zn efficiency. Several wild emmer accessions revealed combination of high Zn efficiency and drought stress resistance. The results indicate high genetic potential of wild emmer wheat to improve grain Zn, Fe and protein concentrations, Zn deficiency tolerance and drought resistance in cultivated wheat.     

Relationships of endogenous plant hormones to accumulation of grain protein and starch in winter wheat under different post-anthesis soil water statusses

Accumulation of protein and starch in grain is a key process determining grain yield and quality in wheat. Under drought or waterlogging, endogenous plant hormone levels will change and may have an impact on the yield and quality of wheat. In a greenhouse experiment, four winter wheat (Triticum aestivum L.) varieties differing in grain protein content, Heimai 76, Wanmai 38, Yangmai 10 and Yangmai 9, were subjected to drought (SRWC = 4550%, DR), waterlogging (WL) and moderate water supply (SRWC = 7580%, CK), beginning from 4 days post-anthesis (DPA) to maturity. On the 10 (grain enlargement stage) and 20 (grain filling stage) DPA, endogenous abscisic acid (ABA), gibberellins (GA₁₊₃), indole-3-acetic acid (IAA) and zeatin riboside (ZR) were determined in sink and source organs of wheat plants by enzyme linked immunosorbent assay (ELISA). The patterns of hormonal changes were similar in four varieties. The ABA levels were much higher under DR and WL than under CK. Compared with CK, GA₁₊₃ levels in whole-plant under DR and WL changed a little at 10 DPA, but markedly decreased under DR and WL at 20 DPA. Changes of endogenous IAA level under DR and WL exhibited a complicated pattern, depending on organs and growth stages. Particularly at the 20 DPA, the mean levels of IAA in roots, leaves and grains decreased significantly under DR and WL. In comparison with CK, ZR levels in all organs significantly decreased under DR and WL at both stages. The correlation analyses between yields and contents of starch and protein in grains and levels and ratios of four hormones in source and sink organs indicated that the changes in yield and content of grain starch and protein under DR and WL were associated with the reduced IAA, ZR and GA₁₊₃ levels and elevated ABA level in plants, especially in grains. It was proposed that the changed levels of endogenous hormones under post-anthesis DR and WL might indirectly affect protein and starch accumulation in grains by influencing the regulatory enzymes and processes.