Abstract
The growth reduction observed in many plants caused by salinity is often associated with a decrease in their photosynthetic capacity. This effect could be associated with the partial stomatal closure and/or the non-stomatal limitation which involves the decrease in ribulose-1,5-bisphosphate carboxylase oxygenase (RUBISCO) activity. The objective of this study was to explore the mechanisms of inhibited photosynthesis in Arabidopsis thaliana (Pa-1 accession) under salt stress. Pa-1 seeds grown on a solid substrate for 25 days on standard medium were challenged with 50 mM NaCl for 15 days. Harvests were carried out every five days by separating the rosette leaves and roots. Salt stress reduced growth by limiting the number of the rosette leaves and not their biomass. Accumulation of Na+ and Cl- increased during the treatment period, whereas K+ and Ca2+ accumulation were reduced in salt treatment. RUBISCO and phosphoenolpyruvate carboxylase (PEPC) activities were increased with the age of the leaves to a maximum after 10 days of treatment then later decreased. We concluded that the sensitivity of Pa-1 to salinity may be due to a reduction in number of leaves, in the photosynthetic assimilation with stomatal closure and damage of the RUBISCO and PEPC activities. Key words: Arabidopsis thaliana, photosynthetic parameters, salinity, ribulose-1,5-bisphosphate carboxylase oxygenase (RUBISCO), phosphoenolpyruvate carboxylase (PEPC).
Highlights
Excessive soil salinity is an important constraint limiting the distribution of plants in natural habitats, and an increasingly severe agricultural problem in arid and semiarid regions (Flowers, 2004)
We concluded that the sensitivity of Pa-1 to salinity may be due to a reduction in number of leaves, in the photosynthetic assimilation with stomatal closure and damage of the RUBISCO and phosphoenolpyruvate carboxylase (PEPC) activities
The reduction was greater after long term salinity treatment (15 days) and it was more pronounced for leaf area parameter
Summary
Excessive soil salinity is an important constraint limiting the distribution of plants in natural habitats, and an increasingly severe agricultural problem in arid and semiarid regions (Flowers, 2004). Plants have evolved complex mechanisms allowing for adaptation to osmotic and ionic stress caused by high salinity. These mechanisms include osmotic adjustment by accumulation of compatible solutes (Bohnert et al, 1999; Yeo, 1998) and lowering the toxic concentration of ions in the cytoplasm by restriction of Na+ influx or its sequestration into the vacuole and/or its extrusion (Binzel et al, 1988; Hajibagheri et al, 1987). Plant growth under salinity is significantly reduced due to the inhibition of leaf expansion and a decrease in photosynthesis (Lips, 1998). The decrease in photosynthetic rate has been attributed mainly to stomatal closure (Kaiser, 1987) but could be at least partially a consequence of feedback inhibition due to the increase of sucrose in source leaves
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