Effect Of Nitrogen Forms And Water Station On The Root Aerenchyma Formation And Water Uptake Of Rice Seedlings

In China,the water consumption of rice is the largest among the food crops,which take more than 70%of the total agricultural water consumption each year.In traditional flooded rice cultivation,the utilization of water resources is extremely low.In addition,China is one of the most water-scarce countries in the word.Therefore,improve the traditional rice cultivation patterns and develop water saving cultivation of rice has become one of the focus in the study of rice production in China.Meanwhile,the cultivation of rice on dry seedbed with its water and fertilizer management techniques also received more and more attention,which could save water but also improved the stress resistance of rice seedlings.Compared with traditional flooded cultivation,nitrogen form in non-flooded cultivation is transferred from ammonium-based to nitrate-based or the mixture of nitrate and ammonium.Therefore,it is important to study the influence of different nitrogen forms on growth of rice seedlings for enhances the tolerance of rice seedlings to water stress.In our previous studies,we have demonstrated that water stress accelerated aerenchyma formation in rice seedlings fed with nitrate nutrition,which inhibit water uptake,resulting to the lower tolerance of rice seedlings fed with nitrate nutrition to drought stress,comparing to rice seedlings fed with ammonium nutrition.To study the mechanism of aerenchyma formation in rice seedlings fed with nitrate nutrition,hydroponic experiments supplied with different nitrogen forms and water stress simulated by adding 10%(w/v)polyethylene glycol 6000 were conducted in different rice cultivars(cv.'Shanyou 63' hybrid indica and cv.'Yangdao 6' indica,China).We investigated the influence of different nitrogen forms on growth of rice seedlings,nitrogen metabolism,root morphology and anatomical structure of rice roots,and the absorption of water and nutrients under simulated water stress conditions.We try to illuminate how nitrogen forms and water deficit regulated aerenchyma formation,and how ammonium improve the tolerance to simulated water stress.The results showed as follows:1.Compared with normal water conditions,water stress significantly increased root growth in two nitrogen forms and inhibited the shoot biomass of rice seedlings fed with nitrate nutrition,however,had no effect on rice plants fed with ammonium nutrition.Water stress decreased the absorption and accumulation of nitrogen,phosphorus and potassiumin rice seedlings fed with nitrate nutrition,meanwhile,it also inhibited the ability of nitrogen assimilation,which resulting the lower protein content,comparing with rice seedlings fed with ammonium nutrition.2.Simulated water stress significantly accelerated root length,surface area and volume,especially in rice seedlings fed with nitrate nutrition.Compared with nitrate nutrition,ammonium nutrition reduced the rice root diameter and improved root activity,which enhanced the ability of rice to water uptake and nutrients absorption.Under water stress conditions,the root aerenchyma formation in rice seedlings fed with nitrate nutrition was earlier than that fed with ammonium nutrition,and its area was directly proportional to the distance from the root tip.3.Under water stress conditions,the change of root morphology and the larger aerenchyma formation decreased root xylem sap rate,water potential and relative water content of leaf,and water transport in rice seedlings fed with nitrate nutrition.Meanwhile,compared with ammonium nutrition,the lower proline content and increased MDA content,leading to cellular oxidative damage and cell death of root in rice seedlings fed with nitrate nutrition.4.Water stress significantly enhanced root respiration,and decreased the root reactive oxygen species(ROS)scavenging enzymes activity,such as superoxide dismutase(SOD),catalase,peroxidase(POD),which resulting accumulation of superoxide anion in rice seedlings fed with nitrate nutrition,when compared with rice seedlings fed with ammonium nutrition.Consequently,the decreased antioxidant capability and accumulation of ROS owing to ROS scavenging enzymes system imbalance resulting in greater aerenchyma formation in root of rice seedlings fed with nitrate nutrition under water stress conditions.