Effects Of Water Stress On Morphogenesis, Physiological Metabolism And Root Water Uptake Of Corn Seedlings

Water is the most important resourse limiting crop production in arid and semi-arid area.Moreover, seedlings establishment period is one of the critical phase in the life cycle of seedplant. The seedlings are prone to be damaged since they are too young to endure these adverseconditions. The establishment and survival of seedling would be impaired; furtherly cropproductivity was lowered greatly. In the practical theory of rain-fed agriculture, there are twosignificant points to ensure crop productivity: one is the physiological adaptive ability ofcrops; the other is water uptake ability of root. Therefore, corn seedlings were grownhydroponically, and drought stress simulated by PEG 6000 was imposed on these cornseedlings. The present study was mainly performed from those two aspects: response of cornto water stress during as its seedling stage; hydraulic properties of corn root under differentwater condition as well as techniques for hydraulic properties measuremens. The major resultsare as following:1. During the period of corn seedlings establishment, different parts of young seedlingsrespond differently to water stress. Coleoptile development of seedlings were greatly impairedby water stress, while the adverse effects of water stress on mesocotyl is the least, comparedto the other two parts (Coleoptile and root). It was notice-worthy that root developed betterthan control under mild water stress or under short duration of sever stress. It indicated thatmesocotyl and root growth were ensure priorly, because mesocotyl elongation is the drivingforce of seedling establishment, and root is the prime organ obtaining water and nutrients.Nevertheless, seedling establishment required longer time underwater stress.2. Water content, osmolates accumulation, reactive oxygen species, membrane lipidperoxidation and oxygen radicals scavenging systems of four parts of corn seedlings werestudied. The results showed water content of four parts declined, leaves water contentdecreased mostly under water stress; the content of proline, solubale sugar and soluble proteinin all four parts increased remarkably; ROS accumulated in the four parts with different extent;the content of MDA and relative membrane permeability increased significantly, theincrement of them were the greatest in leaves; protective enzyme activity and ROS scavengercontent increased to prevent seedlings from the damage of excess ROS. Therefore, cornseedling leaves were the most susceptible to water stress, followed with root system,mesocotyl and stem. 3. Corn young seedling stem is not appropriate to connect with RPP because air couldnot be completely removed from measurement system. Connecting RPP with mesocotyl ofcorn seedling can solve this problem. However, at least 2 cm mesocotyl is necessary to mounton RPP. Nevertheless, this method could not be used on corn seedlings that are older thanthree-four leaf stage, because the adventitious root will emerge on mesocotyl and the nodesbetween shoot and mesocotyl while plants grow. It indicated that hydraulic conductivity ofroot system of corn seedling could be measured by connecting mesocotyl with RPP. To someextent, it realizes the measurements of corn root system properties in situ, and providestechnical promotion for further studying on gramineous plant relations at different levels.4. Hydraulic conductivity for root systems of hydroponically corn seedlings with normaland drought conditions were measured using root pressure probe, high pressure flow meter,pressure chamber. The result showed drought simulated by PEG 6000 reduced hydraulicconductivity significantly. Moreover, three methods gave comparable results for those rootsystems of seedlings. Root pressure probe work best with such young seedlings before 2-3leaf-stage grown hydroponically or grown in pots; the requirements of seedling age duringmeasurements with pressure chamber was not strict, while HPFM can be used for plants at allage in the field5. The hydraulic conductance, the morphological and physiological parameters of cornroot system as well as photosynthetic parameters were investigated. The results showed undernormal water condition root water uptake ability increased gradually as seedling aging.However, water stress hampered the increasing of it, and the water uptake ability decreasedwith duration of water stress. This was resulted from the change of root morphology,physiological metabolism and photosynthesis capacity. With correlation analysis, it is foundthe decrease of root water uptake ability was mainly resulted from root vigor, root activesurface area and fresh weight. On the other hand, the correlation between hydraulicconductance and transpiration rate as well as stomatal conductance were not significant, itmight be due to seedling was too young, and growing fast, as well as the measuring rootsystem was exised from shoot.6. Hydraulic properties and solute transport parameters were studied at the level ofindividual root and whole root system by root pressure probe. It demonstrated water stressdecreased root pressure, root hydrdaulic conductivity and solute permeability of whole root system, and the decrease aggravated with duration of wate stress. In general, water stressinhibited parameters mentioned above in whole root system more than individual root.