Linking changes in chlorophyll a fluorescence with drought stress susceptibility in mung bean [Vigna radiata (L.) Wilczek].

In the present study, the mung bean cv. NM-13-1 was selected as drought-tolerant and NM-54 as drought-sensitive. The effects of progressive drought (16 days) on the photosystem II (PSII) activity was assessed using OJIP and JIP-test in the selected two mung bean cultivars differing in drought tolerance. Drought stress reduced the relative water content to 70% (at threshold) and 62% (below the threshold) in cv.NM-13-1 and NM-54 , respectively. The greater reduction in quantum yield of PSII in cv.NM-54 due to drought stress was due to PSII photodamage. Raw OJIP induction curves and F and F normalised curves showed that significant changes in fluorescence occurred at the O, J, I and P steps only in cv. NM-54 . Double normalised differential kinetics indicated adverse effects at the antennae, oxygen-evolving complex and intersystem electron acceptors in cv.NM54 . Moreover, JIP-test analysis showed that drought stress caused a greater decrease in performance index (PI ) in cv.NM-54 as compared to that in cv. NM-13-1 , which is associated with an increase in V , rate of accumulation of closed reaction centres (M ), energy fluxes for absorption (ABS/RC), trapping (TR /RC), electron transport (ET /RC), and dissipation of absorbed energy as heat (DI /RC). In conclusion, two-week drought stress reduced the RWC below the threshold in cv.NM54 , which resulted in damages at the donor and acceptor sides of PSII. However, cv.NM-13-1 somehow maintained the RWC around the threshold and thus protected PSII. Of various JIP-test parameters, PI , F /F , V and M are key indicators of drought stress tolerance in mung bean cultivars.