The Physiological Roles Of Salt-secretion In Super Xerophyte Reaumuria Soongorica Responding To Salt And Drought

Drought and soil salinization are the two major abiotic stress factors for plants’ growth, since most of the crops are very sensitive to drought and salt. In the long evolutionary process, desert plants in northwest China have developed the unique adaptation mechanisms to harsh environments. Investigating the mechanisms underlying drought and salt tolerance of desert plants will provide the theoretical basis for the genetic improvement of important forages and crops. Reaumuria soongorica, a super xerophytic salt-secretion plant with a strong salt tolerance and drought resistance, is a main forage plant at desert steppe in northwest China, as well as an important species for windbreak and sand-fixation. It is a highlighted academic issue that the mechanisms of R. soongorica adapt to stress environments, but the physiological roles of salt-secretion in xerophyte responsing to salinity, especially arid habitats is not clear.In this study, we firstly invesigated the effects of 150 mmol·L-1 NaCl on growth,, salt-secretion, and the whole plant Na+ distribution pattern of R. soongorica, then further analyzed growth, salt-secretion, the concentration of Na+, K+, and osmotic potential of R. soongorica under different treatments, which involve salt treament(50 mmol·L-1 NaCl), osmotic stress (-0.5 MPa) and osmotic stress together with salt under the sand culture, and salt treatment (100 mmol·L-1 NaCl), drought stress (30% of field water holding capacity) and drought together with salt treatment under pot experiments on The main results are as follows:1. Under high concentration salinity condition (150 mmol·L-1 NaCl), R. soongorica is able to absorb a large amount of Na+, most of which were secreted through salt gland or accumulated in shoots, thus to alleviate the toxic effects of Na+ and maintain water status in plant, which contribute to stimulate the growth of plant. After exposed under 150 mmol·L-1 NaCl for 7 d, shoot fresh weight and dry weight of R. soongorica showed higher than control, but any significant changes of the tissue water content were not observed; the net Na+ uptake rate in root significantly increased for 44 times as that of control; correspondingly, the Na+ secretion and accumulation in shoots of R. soongorica exhibited significant enhancement which was 25 times and 2.1 time than that of control, respectively. The percentage of Na+ sectetion increased from 4.3% in the control to 35%, and the percentage of Na+ accumulation in shoots also was 43%.2. NaCl treatment stimulated the growth of R. soongorica, and significantly improved its drought resistance. In either sand culture experiment or pot experiment, NaCl treatment caused the shoot fresh weight increased significantly by 23%and 34%, respectively. Drought treatment inhibited the growth of plants, but the supplement of 50 or 100 mmol-L-1 NaCl significantly alleviated the adverse effects of drought on growth of R. soongorica:the shoot fresh weights were returned to the control level (sand culture experiment), and even higher than that of the control (pot experiment).3. The salt-secretion of R. soongorica is significantly induced by drought stress. Drought treatments significantly improve the amount of shoot Na+ secretion whether or not NaCl was supplied in medium. In sand culture experiment, shoot Na+ secretion was 2.2 times of the control under -0.5 MPa osmotic stress, and reached 4.3 times in the presence of 50 mmol-L-1 NaCl; a similar result was also observed in pot experiment:under drought treatment, though the only trace amounts of Na+ in the medium, the shoot Na+ secretion is still 1.6 times of the control.4. Salt-secretion might be an important way of R. soongorica to maintain the water balance under the osmotic stress. Under different treatments in sand culture experiments, tissue water contents always remain stable in R. soongorica plants, while osmotic potential contribution of Na+ and K+ accumulated in the shoots did not increase inspite of shoot osmotic potential is significantly decreased.5. Maintaining the stability of the shoot K+ level is another important strategy of R. soongorica to adapt to salt and drought stress. Under each treatment of the sand culture experiments and pot experiments, the shoot K+ concentration always show relatively stable.