Wheat plants grown in controlled growth chambers were exposed to drought stress (DS) and high temperature (HT) singly and in combination (DS+HT). The effects of these two stresses on net photosynthetic rate (PN), stomatal conductance (gs), intercellular CO2 concentration (Ci), quantum efficiency of photosystem 2 (ΦPS2), variable to maximum chlorophyll (Chl) fluorescence (Fv/Fm), photochemical (qp) and non-photochemical (NPQ) Chl fluorescence, and yield were investigated. Grain yield was decreased by 21 % due to DS, while it was increased by 26 % due to HT. PN, g s, Ci, and Chl fluorescence were dramatically reduced to DS, HT, and their interaction, except NPQ which showed an increase due to HT.
Field experiments were conducted under rain-fed conditions to study the growth and photosynthetic efficiency of transgenic Bt cotton hybrids during 2002-03 and 2003-04 seasons. Three Bt cotton hybrids (Bollgard 1) and their non-Bt (NBt) counterparts viz. MECH 12, MECH 162, and MECH 184 were grown along with a local hybrid NHH44. Growth parameters such as plant height, main-stem nodes, biomass accumulation, and physiological processes like stomatal conductance (gs), and rates of transpiration (E) and photosynthesis (PN) did not differ significantly between Bt and NBt hybrids up to 80 DAS (d after sowing). Squaring commenced at 50 DAS both in Bt and NBt. The loss of young fruiting forms by the entomological factors was three times less in Bt than NBt. As a consequence, Bt had more early formed bolls on the lower canopy which contributed to higher biomass and seed cotton yield. On the other hand, bolls distributed intermittently in NBt. Heavy boll load altered the growth and physiological processes, and as a result Bt had higher gs, E, and PN than NBt. Since developing bolls (sink) divert the saccharides and nutrients from other organs, Bt plants with heavy boll load senesced early and stopped the production of new squares and bolls. Thus, the boll load influenced the change in growth and physiological processes of Bt from NBt. and K. B. Hebbar, N. K. Perumal, B. M. Khadi.
Physiological responses of two wheat (Triticum aestivum L.) genotypes (salt-tolerant DK961 and salt-sensitive JN17) to increased salt concentrations (50, 100, 150 mM NaCl: NaCl50, NaCl100, NaCl150) were studied. Photosynthetic capacity, irradiance response curves, contents of soluble sugars, proteins, and chlorophyll (Chl), K+/Na+ ratio, and activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) in flag leaves were measured on 7 d after anthesis. In control (NaCl0) plants, non-significant (p>0.05) differences were found in gas exchange and saturation irradiance (SI) between salt-tolerant (ST) and salt-sensitive (SS) wheat genotypes. However, we found higher soluble sugar and protein contents, K+/Na+ ratio, and antioxidant enzyme activities, but lower Chl content and yield in ST wheat. Salinity stresses remarkably increased soluble sugar and protein contents and the antioxidant activities, but decreased K+/Na+ ratio, Chl contents, SI, photosynthetic capacities, and yield, the extent being considerably larger in JN17 than DK961. Although the soluble sugar and protein contents and the antioxidant activities of JN17 elevated more evidently under salt stresses, those variables never reached the high levels of DK961. The antioxidant enzyme activities of SS wheat increased in NaCl50 and NaCl100, but decreased rapidly when the NaCl concentration reached 150 mM. Thus the ST wheat could maintain higher grain yield than the SS one by remaining higher osmoregulation and antioxidative abilities, which led to higher photosynthetic capacity. Hence the ST wheat could harmonize the relationship between CO2 assimilation (source) and the grain yield (sink) under the experimental conditions. and Y. H. Zheng ... [et al.].
In the field, supplemental application of N fertilizer to rice (Oryza sativa) shortly before the beginning of heading stage increases leaf N content and enhances photosynthesis during the grain-filling period. In search of varietal differences in leaf gas exchange in response to supplemental N application, we examined 13 rice varieties grown in the field during two successive years. The varieties included japonica and indica varieties, both of which are widely grown in Japan. The response to supplemental N application could not be separated clearly between variety groups; some of the japonica varieties, but none of the indica varieties, exhibited significant increase in stomatal conductance (gs) after supplemental N application. Supplemental N was more effective to increase stomatal aperture in the varieties with inherently lower gs. Varieties that showed greater response of g s to supplemental N application might be able to adjust their stomatal aperture with appropriate N control. Although the internal-to-ambient CO2 mole fraction ratio and the leaf carbon isotopic composition (δ13C) differed among varieties as a result of variations in stomatal aperture and the CO2 requirement of mesophyll, supplemental N application barely influenced these parameters, because it only moderately affected stomatal aperture. Since δ13C tended to increase with increasing number of days from transplantation to heading stage in japonica varieties, δ13C values were more sensitive to differences in growth rate between years than to N application., S. Shimoda, A. Maruyama., and Obsahuje bibliografii