Linkage between leaf development and photosynthetic response at hyperosmotic salinity in the C-4 grass Panicum antidotale

Abstract

This study aimed at elucidating the impact of salinity on the differential responses of the photosynthetic apparatus at different stages of leaf development in the C4 perennial grass Panicum antidotale. Plants were grown for a period of 15 days at hyper-osmotic salinity (up to 400 mM NaCl) or at control conditions (no addition of NaCl to the culture medium). Each day plants were harvested and salt stress effect on biomass production (fresh and dry weight) was recorded. In parallel leaves were divided from leaf tip to leaf base in five segments for analysis of stress effects on the following parameters: chlorophyll fluorescence parameters (Fv/Fm, ΦPSII, ETR), MDA (an indicator of peroxidation of membrane lipids), and ion leakage.A direct correlation between membrane lipid peroxidation and (i) membrane integrity as well as (ii) inhibition of PSII function was found under salinity. In monocots the leaf meristem is located at the base and mature parenchymatic cells preferentially are found at the leaf tip. This may explain our finding that the degree of salt mediated inhibition of photosynthetic activity (ETRcontrol/ETRstressed) was 20-fold higher at leaf tip than at leaf base. Thus, we discuss observed variance in apparent salt resistance in terms of heterogeneity of the photosynthetic apparatus (due to difference in spatial and temporal development) along the leaf lamina.