PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Chromium (VI) promotes Photosystem II activity in Brassica juncea. SHIPRA GUPTA^*,1, SWATI SRIVASTAVA¹, P. PARDHA SARADHI¹, ¹ Department of Environmental Biology, Delhi, India

ABSTRACT- Investigations carried out to evaluate probable alterations caused to the photosynthetic machinery upon the exposure of seven-day-old seedlings of Brassica juncea to various levels of chromium (VI) revealed that chromium promotes photosystem II (PSII) mediated photoreactions. The extent of increase in photosystem II activity, in the presence of uncoupler (5 mM NH₄Cl) was relatively higher in the thylakoids from chromium treated seedlings in comparison to those from the control. The latter results revealed that chromium enhanced PS II activity is certainly not due to uncoupling of electron transport from photophosphorylation. Light saturation kinetics revealed that the PS II activity of thylakoids from chromium stressed seedlings was significantly higher at almost all light intensities in comparison to those for controls. Interestingly, PS II activity of thylakoids from chromium treated plants at 25% of the saturating light intensity was in par with the PS II activity of the thylakoids from control plants at saturating light intensity indicating that thylakoids from chromium treated seedlings were more potent in using the trapped light energy. Thylakoids from both control and chromium treated seedlings exhibited maximum PS II activity at pH 7.5. Interestingly, the PS II activity of thylakoids from chromium exposed plants was even higher at pH 8.0 as well as 8.5, demonstrating chromium promotes tolerance of PS II mediated photoreactions to alkaline pH. These investigations revealed for the first time that chromium has a role to play in promoting PS II activity atleast in Brassica juncea.

KEY WORDS: Chromium (VI), Brassica juncea, Photosystem II, Light saturation curve