Effect of Sodium Chloride on Primary Photochemical Activities in Cotyledonary Leaves of Brassica juncea

The effect of varying concentrations of sodium chloride (NaCl) (0, 100, 150 and 200 mM) on seedling growth, pigment composition and the primary photochemical activities in cotyledonary leaves of Brassica juncea cv. DIRA 367 was investigated. NaCl-stress resulted in a considerable decrease in growth of the seedlings without causing any significant change in dry weight. While, chlorophyll a content was higher in cotyledonary leaves of seedlings raised in high salt containing media, chlorophyll b content did not show any significant variation till 11th day of growth. Thus the high Chl a/Chl b ratio in NaCl treatments reflects changes in the photosynthetic antenna size. The carotenoid content in 11 day old cotyledonary leaves, on the other hand, was much reduced at high concentrations of NaCl. NaCl treatments caused an increase in water oxidation capacity, as measured through H₂O → MV (whole chain) or H₂O → PD_OX (PS II) photoreactions, by 1.2 to 2.0 fold. But, PS I mediated photochemical activities showed no or only a minor increase by NaCl treatment. The enhancement in photochemical activities noted even in presence of uncouplers (NH₄Cl and methyl amine) suggest that the NaCl induced enhancement of primary photochemical activity is not linked to the uncoupling of electron transport from photophosphorylation.

Also, the studies on the interactive effect of in vivo ageing and salinity on the pigment composition and primary photochemical activities suggest that ageing and NaCI-stress result in partly independent and partly interactive changes in the pigment composition and photochemical activities.