Studies On Response Of Root Cellular Ion Homeostasis To Drought And Its Physiological Mechanisms In Barley

Drought stress is the most widely-occurring,severe and complicated environmental constraint resulting in the marked loss of crop yield worldwide.Developing drought-tolerant crop varieties and improving drought-tolerant agronomic practices are economical and effective strategies to fight against drought stress.Understanding the mechanisms underlying crop drought tolerance is the precondition and can provide theoretical support for drought-tolerant breeding and cultivation.In this dissertation,a series of barley genotypes contrasting in drought tolerance were firstly identified,and the role of the ability for K~+uptake and translocation regulation in drought tolerance was then clarified.Moreover,the difference in responses of root apex and mature zone to drought stress was investigated through transcriptomic analysis and small RNA sequencing.Finally,a genome-wide analysis and identification of barley HAK/KUP/KT transporters were conducted,and drought-inducible HvHAK13 and HvHAK1.1 were cloned for further analysis.The main results are as follows:1.Barley genotypes differing greatly in drought tolerance were identified and thetraits suitable for evaluating drought tolerance were determined.Totally 237 cultivated and 190 wild barley genotypes were grown in vermiculite and evaluated for their drought tolerance under water-limited drought and 20%PEG8000-stimulated drought.There was a dramatic difference in drought tolerance among the two barley populations,with wild barley showing higher drought tolerance than cultivated barley.No significant difference was observed in the effects of water-limited drought and 20%PEG8000-stimulated drought on barley growth,and the effects of these drought treatments on the inhibition of barley growth were significantly and positively correlated.The correlation and PLS-DA analysis indicated that relative water content and sap osmolality of the youngest fully-expanded leaf were the ideal selection criteria for evaluating drought tolerance at seedling stage in barley.2.The ability to regulate K~+uptake and translocation and drought tolerance areclosely related in barleyDrought stress significantly affected the expression of genes coding K~+channels and transporters responsible for K~+uptake and translocation as well as genes coding plasma membrane-localized proton pumps(time-and genotype-dependent),leading to massive uptake of K~+and efflux of H~+.The ability to regulate K~+uptake and H~+efflux is closely related to the maintenance of K~+content in tissues and the alleviation of growth inhibition by drought stress.The greater the ability is,the higher drought tolerance it is in barley.3.There is a distinct difference in response patterns of root apex and mature zoneto drought stressRoot apex and mature zone in barley differed greatly in sensitivity,response patterns and magnitude to drought stress in terms of physiology,transcriptomics and small RNA sequencing.In comparison with mature zone of root,root apex took in more K~+,accumulated more ROS,had more differentially expressed genes and miRNAs,and more complicated miRNA-mRNA regulatory network.4.The two genes HvHAK13 and HvHAK1.1 belonging to barley HAK/KUP/KTfamily was cloned and their expression patterns analyzed.There are 24 HAK/KUP/KT genes in barley and they were unevenly distributed on7 chromosomes,with chromosome 2 having the most genes.HAK/KUP/KT family in barley could be classified into 4 clusters,with cluster I and II containing more members.The expression of these HAK/KUP/KT genes was affected by drought stress and differed between root apex and mature zone.Drought-inducible HvHAK13 and HvHAK1.1 are both localized on plasma membrane.HvHAK13 was mainly expressed in roots,and was induced after drought treatment of 6 h and inhibited after 3 d treatment;And HvHAK13 was also induced in stem.While HvHAK1.1 was mainly expressed in roots,and was inhibited and induced after drought treatment of 6 h and 3 d,respectively.No obvious currents were detected in Xenopus laevis oocytes heterologously expressing HvHAK13 and HvHAK1.1.