Acclimation of clusterbean cotyledon to UV-B radiation in the presence of UV-A: partial restoration of photosynthetic energy balance and redox homeostasis

The photosynthetic responses of clusterbean (Cyamopsis tetraganoloba) cotyledons exposed to UV-A, UV-B or UV-A + UV-B radiation for 1 h daily until day 10 have been compared. The loss in the rate of O2 evolution and CO2 assimilation (Pn) are incommensurate with each other in both UV-A and UV-B exposed samples indicating the occurrence of loss in photostasis of photosynthesis by these two radiation bands. The alteration in redox status of QA further suggests about a loss in redox homeostasis in the photosynthetic electron transport chain. However, both photochemical efficiency of PS II and Pn are well maintained in UV-A + UV-B exposed cotyledons in spite of reduction in water-use efficiency. The acclimatization of clusterbean cotyledon to UV-B radiation in the presence of UV-A has been attributed to accumulation of flavonoids, increase in stomatal conductance (gs) and reduction in functional size of PS II.

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