We examined effects of late-season heat stress (L-SHS) on chlorophyll (Chl) fluorescence parameters and yield of bread wheat as well as roles of phosphate bio-fertilizer (PB-F) and Zn and B to compensate for the likely effects of heat stress. Factors were planting date (21 November and 5 January to coincide with grain filling to L-SHS) as the main factor, no inoculation (control) and inoculation of the seeds with PB-F as the sub-factor, and foliar application of water (control), Zn, B, and Zn + B as 3 L ha-1 as
sub-sub factor. Results revealed that L-SHS reduced maximal quantum yield of PSII photochemistry, effective quantum yield of PSII photochemistry, efficiency of PSII in the light-adapted state, and the grain yield. Moreover, L-SHS increased the nonphotochemical quenching. The PB-F mitigated the effects of L-SHS on Chl fluorescence, yield, and yield components. Among nutrients, the combined Zn + B was more effective in reducing the effects of L-SHS than that of Zn and B alone. Nevertheless, there was an interaction between foliar nutrients application and PB-F, suggesting that Zn application alone had a profound influence on improving Chl fluorescence parameters and increased yield in combination with PB-F., H. R. Eisvand, H. Kamaei, F. Nazarian., and Obsahuje bibliografii
In order to study the mechanisms of Se-mediated growth improvement as related to carbon (C) and nitrogen (N) metabolism, wheat plants were cultivated hydroponically with adequate (4 mM, Na) or low (1 mM, Nd) N supply and treated with 10 and 50 μM Na2SeO4 for six weeks. The Se supplementation enhanced plant biomass; it was significant for shoots of Na plants at 50 μM Se. Chlorophyll fluorescence parameters were significantly lowered under Nd conditions but restored completely by Se addition reaching values of those in Na plants. Net CO2 assimilation rate (PN) decreased only slightly by limited N availability, but it enhanced significantly in both Nd and Na plants equally by 10 and 50 μM Se. Effect of Se on PN in the Na plants occurred mainly due to the stomata opening, while it was related to both stomatal and nonstomatal mechanisms in the Nd plants. The Se treatment resulted in enhancement of nitrate reductase (NR) activity in both Na and Nd plants with an optimal response at 10 μM Se. Negative correlations between nitrate concentration and NR activity indicated a partial nitrate depletion in the roots following by elevated NR activity in Nd plants. In contrast, nitrite concentrations were higher in the Se treated plants. Higher amino acids and protein concentrations in the Se-treated plants might be an indication of a general upregulation of N metabolism. However, in Na plants, the stimulation of N metabolism was not observed at 50 μM Se which could not be attributed to lesser availability of C skeletons because of maintaning higher CO2 fixation under these conditions. It implies the function of some regulatory mechanisms that are responsible for coordination of C and N metabolism in whole plant., R. Hajiboland, N. Sadeghzade., and Obsahuje bibliografii
The changes in growth and photosynthetic performance of two wheat (Triticum aestivum L.) cultivars (Bolal-2973 and Atay-85) differing in their sensitivity to boron (B) toxicity were investigated under toxic B conditions. Eight-day old seedlings were exposed to highly toxic B concentrations (5, 7.5, and 10 mM H3BO3) for 5 and 9 days. Fast chlorophyll a fluorescence kinetics was determined and analysed using JIP test. Growth parameters, tissue B contents, and membrane damage were measured at two stress durations. The photochemical performance of PSII was hindered more in the sensitive cultivar (Atay-85) than that of the tolerant one (Bolal-2973) under B toxicity. The increase in the B concentration and stress duration caused membrane leakage in both cultivars. However, higher membrane damage was observed in Atay-85 compared to Bolal-2973. Additionally, significant reduction of growth parameters was observed in both cultivars at toxic B concentrations. The accumulation of B was higher in shoots than in roots of both cultivars. Nevertheless, Atay-85 translocated more B from roots to leaves compared to Bolal-2973. The advantages of certain JIP test parameters were demonstrated for evaluation of PSII activity in plants exposed to B stress. Evaluation of photosynthetic performance by JIP test as well as assessment of growth and tissue B content might be used to determine the effects of B toxicity in wheat. The results indicated lesser sensitivity to B toxicity in Bolal-2973 compared to Atay-85., M. T. Öz, Ö. Turan, C. Kayihan, F. Eyidoğan, Y. Ekmekçi, M. Yücel, H. A. Öktem., and Obsahuje bibliografii
Drought stress limits wheat growth and productivity. The response of wheat (Triticum aestivum L.) to different water supply conditions (well-watered and drought-stressed) and exogenous methyl jasmonate (MeJA; 0 and 0.25 μM) was studied. The application of MeJA enhanced wheat adaptability to drought stress by physiological and metabolic adjustments. Drought stress reduced net photosynthetic rate (PN), stomatal conductance (gs), transpiration rate (E), and water-use efficiency (WUE) in wheat. The application of exogenous MeJA decreased also gs and E, but stimulated WUE. Meanwhile, MeJA mitigated the decline of PN, gs, and WUE induced by drought stress and midday depression by 6-183%. Both drought stress and exogenous MeJA induced stomatal closure, which improved water status and delayed plant senescence. MeJA enhanced the activities of superoxide dismutase, peroxidase, catalase, and reduced malondialdehyde content. PN-PAR response curves showed that MeJA mitigated the decline of maximum PN, apparent quantum yield, and saturation irradiance, and the increase of compensation irradiance. Drought stress and exogenous MeJA increased dark respiration rate and showed an additive effect. These results indicated that 0.25 μM MeJA enhanced the photosynthesis under drought stress mainly by improving the water status and antioxidant capacity of wheat., C. Ma, Z. Q. Wang, L. T. Zhang, M. M. Sun, T. B. Lin., and Obsahuje bibliografii
Understanding distribution and transport of carbon assimilates and photosynthesis contribution to grain yield in wheat spike is important in assessing the photosynthetic process under stress conditions. In this study, photosynthetic characteristics were evaluated in a pot experiment. Transport of spike photosynthates to grain was demonstrated using 14C isotope tracer technique. Yield and key enzyme activities of C3 and C4 pathways were examined after anthesis in wheat cultivars of different drought resistance. The ear net photosynthetic rate, chlorophyll content of the spike bracts (glume, lemma, and palea), and relative water content slightly decreased under water deficit in drought resistant variety Pubing 143 (Pub) during the grain filling stage, whereas all parameters decreased significantly in drought sensitive variety Zhengyin 1 (Zhe). Grain 14C-photosynthate distribution rate fell by 3.8% in Pub and increased by 3.9% in Zhe. After harvest, the water-use efficiency of Zhe dropped by 18.7% under water deficit. Rubisco activity in ear organs declined significantly under water deficit, whereas activity of C4 pathway enzymes was significantly enhanced, especially that of phosphoenolpyruvate carboxylase and NADP-malate dehydrogenase. Water deficit exerted lesser influence on spike photosynthesis in Pub. Ear organs exhibited delayed senescence. Accumulation of photosynthetic carbon assimilates in ear bracts occurred mainly during the early grain filling and photosynthates were transported in the middle of grain filling. C4 pathway enzymes seem to play an important function in ear photosynthesis. We speculate that the high enzyme activity of the C4 pathway and the increased capacity of photosynthetic carbon assimilate transport were the reasons for the drought tolerance characteristics of ears., S. Jia, J. Lv, S. Jiang, T. Liang, C. Liu, Z. Jing., and Obsahuje bibliografii
Physiological traits, which are positively associated with yield under salt-stress conditions, can be useful selection criteria in screening for salt tolerance. We examined whether chlorophyll (Chl) content can be used as screening criterion in wheat. Our study involved 5 wheat genotypes under both saline and nonsaline field conditions as well as in a sand-culture experiment. Salt stress reduced significantly biomass, grain yield, total Chl and both Chl a and b in all genotypes. In the sand-culture experiment, Chl accumulation was higher in PF70354/BOW, Ghods, and H499.71A/JUP genotypes at nonsaline control, moderate, and high salt concentrations, respectively. In the field experiment, genotype H499.71A/JUP belonged to those with the highest Chl density. The SPAD (Soil Plant Analysis Development) meter readings were linearly related to Chl content both in the sand-culture and in the field experiment. However, salt stress affected the calibration of SPAD meter. Therefore, separate Chl-SPAD equations were suggested for saline and nonsaline conditions. The correlation coefficients between the grain yield and SPAD were positive and significant both in the sand culture and in the field experiment. These findings suggested that SPAD readings could be used as a tool for rapid assessment of relative Chl content in wheat genotypes. It could be used for the indirect selection of high-yielding genotypes of wheat under saline condition in sand-culture and field experiments., A. Kiani-Pouya, F. Rasouli., and Obsahuje bibliografii