Abstract
In this investigation, the effect of salt stress on Portulaca oleracea L. was monitored at salinity levels of 100 and 300 mM NaCl. At a concentration of 100 mM NaCl there was a decrease in stomatal conductance (gs) simultaneously with an increase in CO2 assimilation (A) at the beginning of salt exposure (day 3). However, the leaf water potential (ψw), the substomatal concentration of CO2 (Ci), the maximum quantum yield of photosystem II (Fv/Fm), and the proline and malondialdehyde (MDA) content remained unchanged. Exposure to 300 mM NaCl caused a decrease in gs from day 3 and a decrease in water potential, CO2 assimilation, and Fv/Fm from day 9. There was a large increase in proline content and a significantly higher MDA concentration on days 6 and 9 of salt stress compared to the control group. After 22 days of exposure to 300 mM NaCl, there was a transition from the C4 cycle to crassulacean acid metabolism (CAM), manifested by a rapid increase in substomatal CO2 concentration and negative CO2 assimilation values. These results document the tolerance of P. oleracea to a lower level of salt stress and the possibility of its use in saline localities.
Highlights
Most crops are sensitive to high salt concentrations in the soil and salinization is one of the most serious environmental factors that can limit crop productivity [1,2]
The reduction in leaf water potential was observable from the sixth day of salt stress exposure and was statistically significant relative to control from the ninth day of salt treatment
The plants treated with the lower concentration of salt (100 mM NaCl), showed a higher assimilation of CO2 in the initial phases of salt stress (48% more than control), it is possible to observe a demonstrable decrease in stomatal conductance already in this phase of salt exposure
Summary
Most crops are sensitive to high salt concentrations in the soil and salinization is one of the most serious environmental factors that can limit crop productivity [1,2]. High concentrations of salt impose both osmotic and ionic stresses on plants [10]. Photosynthesis in all its phases is affected by stress factors, including salinity. The mechanism of photosynthesis involves several components and damage by a stress factor at any level may reduce a plant’s overall photosynthetic capacity [11]. Salt-induced osmotic effects can adversely affect the activities of a number of stomatal enzymes involved in carbon dioxide (CO2 ) reduction [13]. Increased levels of Na+ and Cl− in the non-stomatal leaf tissues can significantly affect metabolic processes that limit photosynthesis [16]
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