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.].
Of the four tested sweet potato cultivars having different features in growth and yield, cv. Koganesengan (KOG) was sustainable in photosynthetic activity through young to aged leaves under drought. One of the causes for this phenomenon may be stomatal conductance (g s) of this cultivar that was relatively high in both aged and drought-imposed leaves. In these leaves the non-photochemical quenching (NPQ) was low and the quantum yield of photosystem 2 (Φe) was high, compared to those of the other cultivars. This helps to prevent excessive accumulation of chemical energy in leaves and a decrease in photoinhibition damage to the photosynthetic function, by which KOG sustains a relatively high photosynthetic activity under the drought and alleviates functional deterioration caused by leaf age. and Haimeirong, F. Kubota.
In spring and winter cultivars of oilseed rape (Brassica napus var. oleifera), acclimation of photosynthetic apparatus to cold was connected with the increase in activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) and sucrose-phosphate synthase (SPS). Conversely, cold de-acclimation entailed the decline of RuBPCO and SPS activities. The rate of this photosynthetic de-acclimation might depend on day temperature. On the other hand, temperature rise during de-acclimation (identical during the day and night) resulted in the improvement of photosynthetic activity measured by means of chlorophyll fluorescence. An increase in SPS activity (and even transitory increase in RuBPCO activity) was observed when the elongation growth rate (EGR) accelerated during de-acclimation. Throughout re-acclimation, plants with high EGR were unable to maintain or recover higher photosynthetic capacity, despite the fact that SPS activity remained high or even increased during re-acclimation. and M. Rapacz, K. Hura.