Studies On Mechanism Of Salt Ions Transportation And Distribution In Hibiscus Hamabo Sieb.et Zucc.

Ion balance is essential to the growth of plant under salt stress. Salt tolerance of plant depends largely on the choice of roots on salt and the distribution of salt in organs, tissues and cells. In this dissertation, the growth, the ions transportation and distribution mechanism of Hibiscus hamabo Sieb.et Zucc. were investigated with its seeds and seedlings being treated with NaCl and KCl solutions with different concentrations. The structure and development process of the resembling salt glands on the leaf surface of Hibiscus hamabo Sieb.et Zucc. were discovered for the first time by using the scanning microscope and the paraffin section.Generally, the seeds are very sensitive to salt stress when they were in the germinating period, and the activity of seeds embryo are the basis of their survival under salt stress. The seeds of Hibiscus hamabo Sieb.et Zucc. were treated with NaCl and KCl solutions with different concentrations and the mixture of the two with equivalent molarity. The ion contents in the seed coat and embryo were determined and the activities of superoxide dismutase (SOD), peroxide catalase (CAT), and peroxidase (POD) in the embryo were measured as well. It was found that the seed coat can inhibit the Na+ and K+ entering the inside of the seeds under salt stress and that both the seed coat and embryo have higher absorption of Na+ than K+ with the embryo has a high K+ content. The accumulations of Na+ in seed coat and K~+ in the embryo results in a maintenance of low Na~+/K~+ ratio to adapt the high salt stress. At the same time, the activities of SOD, CAT, and POD in the embryos showed increasing firstly and then decreasing with the salt concentrations, that is, the activities were strengthened under low concentrations to start the protection mechanism, while they were inhibited under high-salt concentrations, but the antioxidant enzymes can work in concert and harmony.The annual seedlings of Hibiscus hamabo Sieb.et Zucc. were treated with different concentrations of NaCl solutions, when the NaCl concentration was 50 mmol/L, the photosynthetic rate, plant height and plant fresh and dry weight reached the maximum and they are higher than the control, then they showed a downward trend as the salt concentration increased. The growth of seedlings needed certain salt but its salt resistance was limited. Its growth and development would be inhibited under the salty environments.It was found that both the NaCl and KCl solutions with the concentrations being 100, 200, and 300 mmol/L all had restrained effects on the annual seedlings's growth with the effects of NaCl solutions being stronger. As to the root-shoot ratio, the fresh weight ratio was higher than the dry weight ratio, indicating that the roots absorb large amounts of water to alleviate the toxicity of salt on plants.Also it was found that the roots and lower leaves of the annual seedlings of Hibiscus hamabo Sieb.et Zucc. accumulated higher contents of Na~+, K~+, Cl- when it treated with different concentrations of NaCl and KCl solutions. The ratio of Na~+/K~+ in roots reached the highest level when it was treated with NaCl solutions. At different leaf position, the lower leaves had a higher Na~+/K~+ ratio, while the upper leaves had the smallest Na~+/K~+ ratio. Under the KCl treatment, the ratio of K~+/Na~+ in upper leaves was always in the highest levels, which might be due to the high affinity transport system for K~+ (K~+-HATS) to increase the root's K~+ absorption. So transported K~+ to the shoot selectively in order to maintain high K~+/Na~+ in the leaves. The salt ions'detention within the roots and the accumulation in the lower leaves decreased the ion transportation and distribution to the active growth parts of the aerial part, thus reduced the salt injury to the plant.Salt glands were the most notable structure of the recretohalphyte, which can excrete the excessive salt to enhance the plant's salt tolerance. The resembling salt glands on the leaf surface of Hibiscus hamabo Sieb.et Zucc. were discovered by using the scanning electron microscope and paraffin section. Further, we explored the morphological structure of resembling salt gland and salt secretion. This structure is originated from epidermal cells of leaf and it finally develops into mature structure with eight cells on the basis of basal cell. The results of ions contents in the leaf secretion showed that the resembling salt gland executed the function of salt secretion. The secretion rate of Na~+ and K~+ reached the maximum when the salt concentration was 200 mmol/L. Furthermore, Hibiscus hamabo Sieb.et Zucc. has a series of structures adapted to the saline environment, such as stellate hairs and crystal cells.