Protein content, antioxidant activity, carbohydrates and photosynthesis in leaves of girdled stems of four olive cultivars

Girdling practice gained attention as a mean to increase crop yields particularly for alternate bearing plants. Data published for ligneous are controversial and mechanisms by which girdling regulates plant growth and photosynthesis for olive tree are still not well elucidated. The physiological modifications induced by shoots girdling, and their effects on the mobilization of assimilates, on the gas exchanges and on antioxidant activity were studied in olive leaves of Meski, Picholine, Chetoui and Koroneiki cultivars. From each ‘ON’ and ‘OFF’ trees, six shoots were selected, 3 of them were girdled and 3 were used as control. Total carbohydrates, alcoholic (Mannitol) and soluble (Glucose, Fructose and Sucrose) sugars, photosynthesis parameters, total protein and antioxidant activities in leaves of ‘ON’ and ‘OFF’ trees were analyzed. In girdled shoots a reduction of photosynthetic rate and a greater accumulation of both carbohydrates and antioxidant activities were observed. Girdling, breaking off the phloematic flow, caused a store of elaborated sap in leaves that inhibited the photosynthetic activity inducing an oxidative stress. Our results confirmed fluctuations in carbohydrates, gas exchanges and antioxidant activities as a direct consequence of girdling and of presence or absence of fruits, and showed clearly how each olive cultivar responds differently to girdling evidencing that the girdling effects are cultivar dependent