Effects Of ABA On Root Cortex Cell Hydraulics Of Arabidopsis Thaliana

In north of China， shortage of water is terrible, and this situation has gonefrom bad to worse. On this condition, it is important to build up water-savingagriculture, cultivate new varieties of drought-tolerant and so on. Water deficitproblems are inevitable in the process of plant growth, so improve the ability ofwater uptake by plant roots is vital to promote growth of plants and increaseproduction of crops.Cell pressure probe is the only instrument which was used to determine singlecell turgor pressure （P） of high plant in-situ. Improved pressure probe can be directlymeasured, such as half time of water exchange (T^w_1/2), volumetric elastic modulus ofcells （ε） and hydraulic conductivity （Lp） and so on.Nowdays, ABA has become the most widely studied kind of phytohormone.The relationship between ABA and root warter uptake has long been reported,but itstill remains controversial.By using hydroponic culture, the plant materials in this research include twowild-type Arabidopsis thaliana （Col and Ler） and a mutant （Qm）. In this research,we use cell-pressure probe to investigate the effects of exogenous ABA and waterstress on different Arabidopsis thaliana hydraulic properties, including turgorpressure （P）, half time of water exchange (T^w_1/2), elastic modulus （ε） and hydraulicconductivity （Lp）; explore the early signal about the influence of ABA on hydraulicsof Arabidopsis thaliana root cortex cell in the level of molecular genetics. Provide atheoretical basis for the ABA on plant water relations, expect to combine exogenousABA treatment with agricultural production, improving agricultural production.The results of this study are listed as follows: 1. Exogenous ABA treatments have different effects on hydraulics properties inroot cortical cells of wild-type （Col） and （Ler）. First, we found that, P remained thesame as the exogenous ABA treatments went on. Meanwhile, the variation of εcorrelated with the changing of ABA concentration and treatment time, but therewere not remarkable variation. However, exogenous ABA has significant effects onhalf-time of water exchange (T^w_1/2) and hydraulic conductivity （Lp）. Specifically,half-time of water exchange (T^w_1/2) of wild-type （Col） and （Ler） gradually decreaseas ABA concentration and treatment period rise. Results show that T^w_1/2reaches theminimum when plants are treated for60min at concentration of1000nmol·L-1,while Lp reached the maximum value, under the same condition, then the value ofT^w_1/2and Lp recovered to the value of control after2h. It means that exogenousABA has instantaneous effect on root cortex cells’ hydraulics. Comparing withwild species, exogenous ABA do not have significant influence on T^w_1/2and Lp ofQm which is a quadruple （pyr1;pyl1;pyl2;pyl4） mutant. The evidances reveal thatABA can improve the root cortex cells’ hydraulic ability of Arabidopsis thaliana andthe signal transduction pathway mediated by ABA receptor PYR/PYL/RCAR getsinvolved in the ABA-induced effects of water uptake.2. Comparing hydraulic properties under well-water and water stress wassimulated with PEG^-6000, The results demonstrated that ε and T^w_1/2increasedsignificantly, P and Lp of three different genotypes Arabidopsis reducedsignificantly. By comparison, the difference of all of this hydraulic parameters ofQm is most pronounced, probably because Qm is insensitive to endogenous ABA,which is produced under stress condition in plant. Aquaporin is the major way tomaintain water uptake at cell level under water stress environment, and ABA canincrease the activity and expression of aquaporin. Qm, a quadruple（pyr1;pyl1;pyl2;pyl4） mutant, is insensitive to endogenous ABA, caused the biggestdecrease of hydraulic conductivity. The result reveal that endogenous ABA may improve the root cortex cells’hydraulic ability of Arabidopsis thaliana and the signal transduction pathwaymediated by ABA receptor PYR/PYL/RCAR gets involved in the ABA-inducedeffects of water uptake.