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 rootstockswere exposed to NaCl-induced salinity (approx. 6 dS m-1) in pot culture for two months undergreenhouse conditions. The experiment was laid out in a randomized block design with eightreplicates. The trees were irrigated with saline solution containing 0.1% liquid fertilizer“Miracle-Gro Liqua Feed 9-4-9” $(N-P_2O_5-K_2O)$ enriched with micronutrients. Theexperimental treatments consisted of three levels (4 mM, 8 mM, 12 mM) of foliar appliedproline along with control application. Distilled water served as the control. During theexperiment the seedlings were sprayed totally five times with ten days intervals. At the endof 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 (DPPHscavenging activity, reducing power, total phenolic content, proline) analysis. Spesific leafarea, leaf water relations and leaf gas exchange of the plants were also determined. FoliarPRO application decreased Na and Cl concentrations of the leaves, and improved spesific leafarea in the final dose. Water leaf relations, photosynthetic activity and biochemicalparameters were affected positively even though some differences were determined betweenthe cultivars.