Research On Germination Under Stress Conditions And Methods Of Improving Plant Tolerance

Soil salinization is a serious worldwide problem and getting more and more serious. More than 800 million hectares of land throughout the world are salt affected. NaCl is the most soluble and widespread salt, which is limits plant gowth and yield greatly. Seed germination and seedling growth is the crucial phases in plant life cycle. Understanding the germination characteristic and mechanism of salt tolerance at this phase will provide theoretical basis for improving plant salt tolerance. In the past few decades, plant breeders in seeking a reliable and low-cost screening method to improve plant salt tolerance.This study used NaCl as the main stress factor, surveyed the response of seed germination under stress condition; and probed into several potential methods for improving germplasm salt resistance. We described the effects of salinity and temperature on seed germination, and discussed the double effects of salinity, viz osmotic and ionic on germination. We determined how salinity, exposure time and low salt concentration influence seed germination recovery and to get a whole knowledge seed germination strategy under constant changes’edaphic condition. We tested pre-sowing seed treatment as a shotgun approach to impove germination ability——seed priming,including selecting reagents which most effectively and low-cost; modeling the priming effect by thermal time model and hydrotime model and simulated emergence on the field. We also explored the method for screening salt tolerance germplasm at early seedlings. We researched on model species to explore the mechanism of salt tolerance, which could provide theoretical basis for genetic engineering.We obtained the important results and conclusions as follows.Temperature and salinity and their interaction influenced seed germination performance. High temperatures inhibited germination severly; Low water potential could improve germination; in most case, the osmotic effect of salinity plays a role. The increased salinity‘pre-treatment’raised the recovery percentage. As the exposure duration extended, the recovery percentage obviously decreased. Seed could recovery under non- or slight NaCl solutions, however, after seeds emerged in 400mM NaCl for 20d, the recovery ability under 100mM was remarkable lower than in 0 and 50mM NaCl. It is concluded that exposure to hyper-saline condition for short-time can stimulate germination in this species, and prolonged time can inhibit germination recovery.The four priming regents all accelerated seed imbibition; 10%PEG is the best osmoticum for seedling and biomass is highest; Water as the priming regent was low-cost and more convenience, and also took account of seed yield.Priming decreased the thermal requirement of all the tested crops; The simulated priming effect was maximized during the cooler conditions in early spring; The root system of primed seeds developed in advanced, and indicated that the seedlings were more tolerant to drought.Priming decreased hydrotime constant, the priming effect more significant at low temperature.If the environmental water potential fixed, then the primed seed could germinate earlier. This gave indirect evidence that priming can improve the drought tolerance in seed.The results indicated that the radicle of early seedlings (7 day age) is the most sensitive organ to salt stress, and can be used for screening a large number of salt tolerance genotypes. The method is simple and save time. The Root re-growth method could be applicable to screening salt tolerance germplasm inter- and intra- species.Quinoa already proven value as a seed crop for human consumption makes quinoa a prime candidate for becoming a‘model’species for the elucidation of the genetics and physiology of salt tolerance in plants.When quinoa plants are exposed to high levels of NaCl (400 mM), the plants show a suite of morphological and physiological changes that are indicative of mechanisms and strategies used by dicotyledonous halophytes to combat the dual affects of alinity, these being osmotic stress and ion toxicity. These changes include an increased amounts of Na+ in the shoot , with preferential accumulation of Na+ in old versus young leaves; a significant increase in K+ loading into the xylem with a resulting increased accumulation of K+ in leaf tissues; better osmoprotection of young developing leaves against associated oxidative stress; a significant reduction in the number of stomata per leaf area, as well as a concomitant decrease in the number of pavement cells; and a reduction in measured stomatal conductance that was less pronounced in salt tolerant varieties. Collectively, these traits contribute to the remarkable salinity tolerance of quinoa; a species that can complete its life cycle in NaCl concentrations equivalent of seawater.