Responses of salt-stressed citrus plants to foliar-applied proline

Abstract

In this study, one-year old grapefruit trees grafted onto sour Orange (SO) and C22 rootstocks were exposed to NaCl-induced salinity (approx. 6 dS m-1) in pot culture for two months under greenhouse conditions. The experiment was laid out in a randomized block design with eight replicates. The trees were irrigated with saline solution containing 0.1% liquid fertilizer "Miracle-Gro Liqua Feed 9-4-9" (N-P2O5-K2O) enriched with micronutrients. The experimental treatments consisted of three levels (4 mM, 8 mM, 12 mM) of foliar applied proline along with control application. Distilled water served as the control. During the experiment the seedlings were sprayed totally five times with ten days intervals. At the end of the treatment physiologically mature leaves, free of damage or defects, were sampled. Dried and ground leaf samples were used for chemical (Na and Cl) and biochemical (DPPH scavenging activity, reducing power, total phenolic content, proline) analysis. Spesific leaf area, leaf water relations and leaf gas exchange of the plants were also determined. Foliar PRO application decreased Na and Cl concentrations of the leaves, and improved spesific leaf area in the final dose. Water leaf relations, photosynthetic activity and biochemical parameters were affected positively even though some differences were determined between the cultivars.