Studies On Mechanisms Of Salt Tolerance In Grafted Tomato Seedlings

Soil secondary salinization has been a common phenomena in vegetable protected culture, mainly as a consequence of improper fertilizer application, unsuitable culture and management practices, less raining rinse and so on, leading to the progressive accumulation of salts in the soil, which inhibits vegetable growth and development, causes decline of yield and quality, brings a negative effect on sustainable development of vegetable production. It is showed that grafting can improve vegetable tolerance to environmental stresses, become an effective approach to overcome salt stress. Tomato (Lycopersicon esculentum Mill.) is one of the most important vegetables in protected culture, researchs on tomato grafting techniques, identification and the plant's response to disease and pest attack have been carried out, but few reports on physiological and biochemical mechanisms of grafted tomato in salt stress have been published. We use hydroponically-grown grafted and own-root tomato ( cvs.' Kagemusya' and ' Baoda 903' as rootstock and scion respectively ) seedlings as experimental materials, comparisons of physiological and biochemical changes were made between grafted and own-root tomato seedlings under 100 mM NaCl stress. There were 4 treatments (own-root, own-root +NaCl, grafted, grafted +NaCl).The following results were obtained. At the early stage of stress (2 d and 5 d), the Pn, Tr, Ci and Gs of own-root plant were significantly decreased, while Ls was significantly increased, the inhibition of photosynthesis of own-root plant was mainly caused by stomatal factor, water use efficiency (WUE) was significantly elevated, resulting from lower Pn. At the late stage of stress (10 d), the chlorophyll degradation of own-root was accelerated, salt ion destroyed chlorophyll photosynthetic structure, the Pn, Tr and Gs of own-root plant were still significantly decreased, Ci was significantly increased, while Ls was significantly decreased, WUE was significantly decreased because the decreasing extent of Pn was more obvious than Tr, leading to a poor water use. Non-stomatal limitation became the main factor to inhibit photosynthesis. Plant growth was significantly inhibited in own-root seedlings. Chlorophyll content was not significantly changed and photosynthesis of grafted plant was not inhibited significantly at the early stage of stress, the inhibition of photosynthesis was mainly caused by stomatal factor at the late stage of stress, and no...