Physiological Responses Of Rice Seedlings Of Different Varieties To Short-term Salt Stress

The confliction between population and land source becomes severer in China,and per capita arable land area is gradually close to the lower limit of food security.Coastal salt-affected soil in eastern China can be reclaimed for agriculture use to mitigate the pressure derived from land shortage.However,salt-affected soil is usually characterized by high salt content,poor physical structure and low nutrient content,which limits the agricultural use of the land.Planting rice in salt-affected soil is beneficial both to the desalinization and to the use of salt-affected soil.Rice seedling is generally more sensitive to salt stress,and salt content in salt-affected soil can change due to the rainfall and fresh water irrigation.Therefore,deeper understanding of physiological responses of rice seedlings to short-term salt stress is of great importance in selection of salt-tolerant rice varieties and management of rice production in salt soil.In this study,four rice varieties(Guangyan、Guang 8、Yandao 12 and Xudao 9)were grown in hydroponics and treated with 50 mmol L’1 NaCl to investigate physiological responses of rice seedlings(including growth status,root morphological characters and activities,the contents of Na/K,proline,soluble sugar and MDA in seedlings,and the K+/Na+fluxes in root tips)to short-term salt stress.The results show that:(1)After 50 mmol L-1 NaCl stress,the shoot fresh weight and root activity of rice decreased significantly compared with the control,and the root growth was slowed down.The root length,root surface area,root diameter,root volume and root tip number of rice seedlings decreased significantly after salt stress,but the overall root growth status of salt-tolerant rice varieties was better than that of salt-sensitive rice varieties.The root activity of salt-sensitive rice varieties was lower than that of salt-tolerant rice varieties.(2)After 50 mmol L-1 NaCl stress,the contents of soluble sugar and proline in shoot of rice increased.Among the two indica rice varieties,the content of proline in salt tolerance rice Guangyan increased more than that in salt sensitive rice variety Guang 8,and the soluble sugar content of Guangyan was higher than that of salt sensitive rice variety Guang 8 after stress.Among the two japonica rice varieties,the soluble sugar content of shoot of salt-tolerant rice cultivar Yandao after stress was higher than that of salt-sensitive rice cultivar Xu 9.The response of MDA in seedlings to salt stress was similar with that of soluble sugar and proline.(3)Under different stress duration of 50 mmol L-1 NaCl,the content of Na+in shoot and root of rice increased significantly,and the rice showed a trend of Na+absorption.The Na+uptake rate of salt-tolerant rice varieties increased significantly after stress,but the Na+uptake rate of salt-sensitive rice varieties decreased significantly,and salt-tolerant rice materials could accumulate more Na+than salt-sensitive rice materials.(4)Under different stress duration of 50 mmol L-1 NaCl,K+content in shoot of rice showed a general trend of decrease,and K+content in root showed a trend of first decrease and then increase.Under 7 days of salt stress,the K+uptake of the two indica rice cultivars remained the trend after salt stress.The K+uptake rate of salt tolerant rice Guangyan increased after salt stress,but the K+uptake rate of salt sensitive rice Guang 8 decreased after salt stress.After salt stress,K+uptake of the two japonica rice varieties changed from the original trend to the efflux trend,but the efflux rate of salt-tolerant rice was less than that of salt-sensitive rice.Under 14 days of stress,the K+uptake rate of the rice Guangyan increased after salt stress,and the K+uptake rate of Guangyan was 1.41 times that of Guang 8.In the two japonica rice varieties,K+uptake of salt-tolerant rice salt rice changed from the original efflux trend to the trend of influx after salt stress,and K+uptake rate of salt-intolerant rice decreased after salt stress.The above results indicated that short-term salt stress can induce the physiological responses of rice seedlings of all varieties used in the study;The relative change of the tested physiological parameters was closely related with salt tolerance of the rice varieties and can be used as the potential references for the salt tolerance evaluation.