Regulation in some vital physiological attributes and antioxidative defense system in carrot (<em>Daucus carota</em> L.) under saline stress

Abstract

Regulation of some key metabolic phenomena including antioxidative defense system involved in plant salt tolerance is of great concern. Changes in chlorophyll pigments, chlorophyll fl uorescence and leaf gas exchange characteristics, glycinebetaine and proline contents, and enzymatic and non-enzymatic antioxidants was assessed in two carrot (Daucus carota L.) cultivars, DC-4 and T-29 under saline stress in a greenhouse study. Application of different saline regimes (0, 50, 100 and 150 mM NaCl) to the growth medium considerably reduced the shoot and root fresh and dry weights, shoot and root lengths, chlorophyll b contents, leaf water potential (Ψ_w), leaf osmotic potential (Ψ_s), photosynthetic rate (A), water-use effi ciency, sub-stomatal CO₂ concentration (C_i), stomatal conductance (gs), transpiration rate (E), C_i/C_a ratio, leaf and root K⁺ and Ca²⁺ contents, leaf MDA, total phenolics, total soluble proteins, and activities of CAT, SOD and POD enzymes, while a marked increase was observed in leaf turgor potential (Ψ_p), leaf and root Na⁺ and Cl^- contents, leaf proline, glycinebetaine (GB), ascorbic acid (AsA) and H₂O₂ contents in both cultivars. Of both carrot cultivars, cultivar T-29 was relatively higher in shoot and root fresh weights, root Na⁺, leaf and root Ca²⁺, leaf proline, MDA, total phenolics, soluble proteins and activity of SOD enzyme. In contrast, cultivar DC-4 was relatively higher in leaf Ψ_w and Ψ_s, leaf K⁺, root Ca²⁺ and leaf GB as compared to those in the other cultivar. The relatively better growth of cultivar T-29 was found to be correlated with improved leaf water potential, leaf Ca²⁺, proline, phenolics, and activity of SOD enzyme under saline conditions.