Photosynthesis under salinity stress

Possibility of molecular protection of photosynthesis under salinity stress... 

The analysis of the assimilation as a function of intercellular COp partial pressure suggests a decline of photosynthetic capacity with increasing salinity. The A (p ) response curves of cotton plant grown under salinity condition showed a marked decline (Data not shown), both in the linear portion at low p and in the saturated region at high p. This would imply that non-stomatal limitations of photosynthesis also occur during salt stress, and they involve both rubisco activity and RuBP regeneration capacity (12). Non-stomatal inhibition of photosynthetic capacity has been reported for several salt sensitive species (2, 3, 6, 18). However, it could be possible that the salt induced depression of A(pi) curves is overestimated to an extent which depends on the distribution of open stomata over the leaf (8). 

A limitation in CO2 uptake during photosynthesis by plants subjected to water stress and salinity is a generally accepted phenomenon. Both environmental stress conditions result in a distinct decrease of leaf water potential, stomatal closure and a drop in leaf diffusive conductance, leading to a decrease in CO2 uptake. It was, however, shown that in spite of the decrease in intercellular C02 concentration under water stress, this was not the cause for the decrease in photosynthesis (1). The response of intact leaf photosynthesis to water and salt stresses were, however, found to be not so similar (2). Water stress inhibited CO2 fixation more drastically than an equivalent intensity of salt stress. 

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