Salinity-induced changes in leaf photosynthesis, chlorophyll, proline, hydrogen peroxide and malondialdehyde in loquat plants

The effect of high salinity on various physiological and biochemical parameters in loquat (Eriobotrya japonica Lindl.) leaves was investigated in the present study. For this purpose, three-year-old loquat seedlings were cultivated in an inert medium, consisting of sand and perlite (1/2, v/v), and fertigated thrice a week with a full strength Hoagland's nutrient solution containing either 0 mM NaCl (control treatment) or 80 mM NaCl (salinity treatment). Five plants (replicates) were used per treatment. After 81 days of exposure to salinity, leaf gas exchange parameters, i.e., photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO₂ concentration, were measured using a portable photosynthesis system. Leaf chlorophyll content was also measured using a portable chlorophyll meter. Furthermore, leaf samples were analyzed for proline (Pro), hydrogen peroxide (H₂O₂) and malondialdehyde (MDA). Based on the statistical analysis of the data, salinity caused significant reductions in photosynthetic rate, transpiration rate and stomatal conductance. There was no significant difference between control and salt-treated plants concerning the concentration of CO₂ in mesophyll. With regard to Pro, H₂O₂ and MDA, their concentrations in the leaves of plants treated with 80 mM NaCl were significantly higher than those of control plants. On the other hand, leaves of NaCl-treated plants had higher chlorophyll content compared to control plants. Overall, mainly stomatal but also non-stomatal factors were responsible for the reduction of photosynthetic rate in leaves of loquat plants grown under saline conditions.