Physio-Biochemiscal Responses Of Seed Germination And Seedling Of Sweet Pepper Under NaCl Stress

As an important way of cultivation of vegetables greenhouse cultivation has been rapidly developed around China. According to the statistical data of Shandong province in 2004, Shandong has become the largest greenhouse vegetable production base, which is leaded by sunlight greenhouse and coordinated with the low tunnel, medium tunnel and vinylhouse. However, secondary salinization problem of soil has been caused for many different reasons, and it has seriously affected the normal growth of vegetables. Using Capsicum annuum L. var. as research material, the seed germination and seedling growth stages under salt treatment and control condition was studied. Four NaCl concentration gradients (0,50,150 and 250 mmol·L-1 NaCl) were set and nutrients culture method was adopted in this study.The results were as followed:1. Seed germination condition under NaCl stresses:Germination energy was supreme with the treatment of 50 mmol·L-1 NaCl, which was above control. But it was lower than control with the treatment of 150 and 250 mmol·L-1 NaCl, and the higher the NaCl concentration, the lower the germination energy, germination rate, length of taproot and number of lateral root, which proved 50 mmol·L-1 NaCl can promote germination of sweet pepper in the initial stage and this effect could gradually disappear as the germination time prolonged. The rest would inhibit the process of seed germination. The germinating radicle of the 10th day were studied in this paper and its related physiological and biochemical indexes were determined. The results showed that with the rising of the concentrations of NaCl, root activity dropped; membrane lipid peroxidation produce MDA content and conductivity rised; antioxidant enzyme SOD activity declined; osmoregulation substance proline, soluble sugar and soluble protein content declined.2. Seedling growth condition under NaCl stresses: (1) agronomic trait:Agronomic traits were determined on the 18th day of salt treatment. except that 250 mmol-L"1 NaCl stress caused the seedling's death, the height,leaf area,fresh weight and dry weight of seedlings decreased under 50 mmol·L-1 and 150 mmol·L-1 NaCl stress relative to the controls. However, the root growth was promoted by 50 mmol·L-1 NaCl Stress. It indicated that 50 mmol·L-1 NaCl could promote root growth and inhibited growth of seedling of sweet pepper, however other salt concentrations significantly inhibited the growth of the whole plant.(2) physiological and biochemical characteristics:3-4 pieces of true leaf of sweet pepper were picked before and after treatment of 1,3,5,7 days, and its physiological and biochemical indexes were determined. The results showed that salt treatment of under 150 mmol-L"1 NaCl hadn't caused that plant chlorophyll was significantly decreased, as well as promoted the increasement of carotenoids. During 7days of salt treatment, euphyllas of sweet pepper responsed differently according to different concentrations. Under salt treatment of 50 and 150 mmol·L-1 NaCl, MDA content elevated with time prolonged and NaCl concentration increased. Under salt treatment of 250 mmol·L-1 NaCl, MDA content increased sharply and membrane lipid peroxidation was severity,the whole plant was more siginificantly hurt.(3) NaCl stress induce photoinhibition of seedling leaves of sweet pepper:The chlorophyll a fluorescence technique was considered as an effective tool of non-destructive leaf photosynthetic apparatus, and has been widely used in relevant studies. The JIP-test is a method to get a serials of biological parameters by analyzing the fluorescence transient induction curves to study response mechanisms of photosynthetic apparatus to environmental stress. In the present work, the responses of fluorescence in sweet pepper leaves to salt stress with different NaCl concentration were studied under high irradiance (1000μmol·m-2·s-1) stress. Our aims were to study effects of salt stress and high irradiance on photoinhibition of photosystem (PS)Ⅱand PSI in sweet pepper leaves. Relative to high irradiance stress, the chlorophyll a fluorescence induction curves changed greatly induced by NaCl stress under high irradiance stress, photoinhibition of photosystemⅡ(PSⅡ) was aggravated with apparent affect on PSⅡreaction centers and the acceptor side. At the same time, the donor side of PSⅡwas damaged by high NaCl concentration under high irradiance. Additionally, the activity of PSI reaction centers (P700+) was also inhibited by NaCl stress under high irradiance. These results showed that NaCl stress could aggravate photoinhibition of sweet pepper photosystems under high irradiance, and photoinhibition became more serious under higher NaCl concentration stress offered in the present work. However, PSI photoinhibition was less than PSⅡphotoinhibition. Additionally, high NaCl concentration could induce both damage to PSⅡdonor sides and PSI.