French bean (Phaseolus vulgaris L.) cotyledons lost most of their reserve substances during several early days of germination and turned green. In cotyledon mesophyll cells of one-week-old seedlings, plastids were represented predominantly by amyloplasts (starch grains) and chloroamyloplasts, and the cells appeared to be metabolically highly active. Cell heterogeneity associated with distance of the cells from cotyledon vascular bundles was evident. Only mesophyll cells near to the bundles were rich in plastids. In two-weeks-old intact bean plants, the cotyledons were yellow and shrunken, and their cells were nearly "empty". The plastids in them were represented by senescent plastids (gerontoplasts) only. In the gerontoplasts as well as freely in cytosol, fluorescent lipoid inclusions were accumulated. This cotyledon development was more or less independent of irradiance. In "decapitated" bean plants, senescence of mesophyll cells and plastids was slowed down considerably, and the life span of the cotyledons was prolonged. and J. Kutík, N. Wilhelmová, J. Snopek.
We examined the effects of foliar application of various nitrogen (urea) concentrations on gas-exchange and chlorophyll (Chl) fluorescence characteristics in bean plants treated by heat stress (42/30°C, day/night temperatures). Heat stress caused reductions in contents of Chl a, Chl b, and in maximum photochemical efficiency of PSII by 13, 20, and 27%, respectively, regardless of the N treatment. However, N fertilization caused significant increases in these parameters, especially at higher N concentrations. The net photosynthetic rate and stomatal conductance were enhanced by 32, 60, and 69% and by 25, 88, and 100% due to addition of 5, 10, and 15 mM N, respectively. However, gas-exchange parameters were reduced by 24% due to heat stress. N fertilization alleviated adverse effects of heat stress., I. A. Hassan, H. M. Abou Zeid, W. Taia, N. S. Haiba, A. Zahran, R. H. Badr, R. A. El Dakak, E. A. Shalaby., and Obsahuje bibliografii
Primary leaves of young plants of common bean (Phaseolus vulgaris cv. Carioca and Negro Huasteco) and cowpea (Vigna unguiculata Walp cv. Epace 10) were exposed to high irradiance (HI) of 2 000 µmol m-2 s-1 for 10, 20, and 30 min. The initial fluorescence (F0) was nearly constant in response to HI in each genotype except for Carioca. A distinct reduction of maximum fluorescence (Fm) was clearly observed in stressed genotypes of beans after 20 min followed by a slight recovery for the longer stress times. In common bean, the maximum quantum yield (Fv/Fm) was reduced slowly from 10 to 30 min of HI. In cowpea, only a slight reduction of Fv/Fm was observed at 20 min followed by recovery to normal values at 30 min. HI resulted in changes in the photochemical (qP) and non-photochemical (qN) quenching in both species, but to a different extent. In cowpea plants, more efficiency in the use of the absorbed energy under photoinhibitory conditions was related to increase in qP and decrease in qN. In addition, lipid peroxidation changed significantly in common bean genotypes with an evident increase after 20 min of HI. Hence the photosynthetic apparatus of cowpea was more tolerant to HI than that of common bean and the integrity of cowpea cell membranes was apparently maintained under HI. and L. C. S. Ferreira ... [et al.].