photosynthesis, nitrogen metabolism and antioxidant defense system in b-deficient tea (camellia sinensis (l.) o. kuntze) plants

response of tea plants to b deficiency was studied in hydroponic medium under environmentally controlled conditions. plants height, number of leaves and dry matter production of shoot and root were significantly decreased by b deficiency. concentration of chlorophyll, carotenoids, anthocyanins and flavonoids was not affected by b deficiency in the young leaf, while a significant reduction of chl a/b ratio and increase of carotenoids concentration was detected in the old leaf. among leaf chlorophyll fluorescence parameters, only non-photochemical quenching (qn) increased in parallel to increase of carotenoids in the old leaves of b-deficient plants. net assimilation (a) and transpiration (e) rate and stomatal conductance (gs) were decreased significantly under b deficiency conditions only in the young leaf. activity of nitrate reductase increased in the young and decreased in the old leaf slightly, but was not influenced by b deficiency in the roots. nitrate concentration diminished while nitrite concentration increased in the young leaf under b starvation. data of antioxidant enzymes activity implied that ascorbate peroxidase was likely important for the protection of old leaf and peroxidase for roots, while superoxide dismutade contributed to the protection of all three organs against oxidative stress provoked by b deficiency conditions. h2o2 content of leaves and roots did not increase or even decreased under b deficiency conditions, that was associated with accumulation of proline. our evidences suggest a protective role for proline against free radicals that may contribute significantly to the higher tolerance of tea plants to b deficiency.