Consequences of salt stress on conductance to CO2 diffusion, Rubisco characteristics and anatomy of spinach leaves

Abstract

Spinach (Spinacia oleracea L.) leaves stressed by irrigation with water containing 1% (w/v) NaCl for 20 days had low conductance to CO2 diffusion both at the stomata and in the mesophyll. Mesophyll anatomy changed in salt-stressed leaves, which could have accounted for the decreased mesophyll conductance. Ribulose- 1,5-bisphosphate carboxylase/oxygenase in vitro activity and content were not affected by up to 20 days exposure to salinity but decreased when leaves were exposed to salt stress for longer than 20 days. Salt accumulation also caused a drop of Ca and Mg which might have decreased membrane stability and chlorophyll content, respectively. Measurements of chlorophyll fluorescence indicated that the 20-day-long salt stress did not directly affect photochemistry. We conclude that salinity reduces photosynthesis primarily by reducing the diffusion of CO2 to the chloroplast, both by stomatal closure and by changes in mesophyll structure which decreases the conductance to CO2 diffusion within the leaf. The capacity for carbon metabolism is eventually reduced but that occurs after substantial decreases in the conductance to CO2 diffusion.

Differences in photosynthetic performance and its correlation with growth among tomato cultivars in response to different salts

“…Nevertheless, patchy stomatal closure [6] and changes in cuticular [5] and g m [7] must be considered. There is an increasing body of evidence indicating that g m decreases in response to drought and salinity [11,13,20].…”

photosynthesis in the 7H Asakaze komugi/Manas wheat/barley addition line during salt stress

“…The decrease in photosynthesis during salt stress can be attributed to the reduced activity of primary photochemical processes (Kaiser et al, 1983) and to the inhibition of carbon dioxide fixation and assimilation (Flowers et al, 1977;Munns and Termaat, 1986;Khavari-Nejad and Mostofi, 1998;El-Shintinawy, 2000;Siler et al, 2007). The reduction in the CO 2 assimilation rate (A) caused by salt stress is mainly attributed to the decrease in stomatal conductance (g s ) and/or to the non-stomatal limitation (Bongi and Loreto, 1989;Brugnoli and Björkman, 1992;Delfine et al, 1999;Centritto et al, 2003) related to the processes of carbon fixation, such as the diffusion of CO 2 from the intercellular spaces to the chloroplasts, and to other important metabolic factors. According to some studies, salt stress has no effect on Photosystem II or primary photochemical processes (Robinson et al, 1983;Brugnoli and Björkmann, 1992;Morales et al, 1992), but the inhibition of carbon dioxide fixation is well known (Flowers et al, 1977;Munns and Termaat, 1986;Khavari-Nejad and Mostofi, 1998;El-Shintinawy, 2000;Siler et al, 2007).…”

Restrictions to Carbon Dioxide Conductance and Photosynthesis in Spinach Leaves Recovering from Salt Stress

“…On the other hand, salt accumulation caused a 25% reduction of the intercellular spaces in the mesophyll of spinach leaves with respect to the controls. This could have caused a more tortuous path for CO 2 directed toward the chloroplast and was suggested to be responsible for the observed photosynthesis reduction associated with low mesophyll conductance in salt-stressed leaves (Delfine et al, 1998).The objectives of this work were to understand, under conditions that do not affect relevantly the biochemical and photochemical capacity of salt-stressed leaves, and are not able to change leaf anatomy significantly: (a) whether the reduction of mesophyll conductance can be reversed by alleviating the salt stress, and (b) how important changes in mesophyll conductance are in determining photosynthesis limitation. …”