Studies On Eco-physiology And Molecular Function Of Plants Between Root Signals Or Leaf Cuticle And Drought Tolerance

Drought is one of the most important constraints limiting the growth of plants andecosystem productivity around the world. Plant responses to water deficit are complex andencompass many aspects, including stress sensing and signaling, changes in growth andbiomass allocation patterns, water status homeostasis, decreased stomatal conductance andCO2 assimilation, osmoregulation, and detoxification processes. In this study, relationshipbetween root chemical signal or leaf epicuticular and drought tolerance was investigated byusing eco-physiology and molecular biology method. In eco-physiology level, we are mainlyfocused on the soil water threshold range of chemical signals and drought tolerance wasmediated by reactive oxygen species (ROS) homeostasis. In molecular level, we screenedsome mutants in response to abiotic stress in Arabidopsis. Also, we used map-based cloningto map the gene BDG1 and functional analysis of cuticle pathway which has important role inabiotic stress.A pot experiment was used to investigate the homeostasis between ROS and antioxidantdefense at five harvest dates, and its role in the correlation between soil-water threshold rangeof chemical signals and drought tolerance in three wheat (Triticum aestivum) cultivars duringprogressive soil drying. The cultivars were bred at different periods, cv. BM1 (old), cv.Xiaoyan6 (recent) and cv. Shah229 (modem). They were treated with progressive soil drying.Shoot biomass was affected by drought imposed by two water treatments (90 and 55% fieldwater capacity). The modern wheat cultivar had a lower ROS content and higherROS-scavenging antioxidant capacity with greater soil drying (68-25% soil water content)compared with the older cultivar. The modern cultivar also had excellent adaptation todrought, with a longer survival of 22.7 d and less reduction in shoot biomass of 20.9%, due toearly chemical signals and better balance between ROS production and antioxidants. Theolder cultivar had survival of 15.3 d and 37.3% reduction of shoot biomass. Wider soil-waterthreshold range of chemical signals was positively correlated with improved droughttolerance and better ROS homeostasis. These results suggest that ROS homeostasis acts as a regulator in relationships between soil-water threshold range of chemical signals and droughttolerance.The endogenous ABA level plays a key role in various stress responses including theregulation of these processes is partially mediated by change of de novo ABA biosynthesis.However, regulation of NCED3 gene was not fully elucidated until now. We used a luciferasereporter system to screen a lot of mutants in response to various abiotic stresses. One ofmutant, name red1, was reduced ABA content and decreased NCED3 expression level. Stressphenotype analysis showed that redl was sensitive to osmotic stress, ABA, salt treatment ingermination and post germination growth. Northern blot analysis of stress-responsive genesshowed thatRD29A, RD22, COR15a, COR47, KIN1, P5CS1å’ŒRAB18 was reduced inred1 mutant plants under osmotic stress treatment. Furthermore, red1 mutant plants have fasttranspiration water loss and reduced drought resistance to drought. Map-based cloning of red1shows that it is a new allele of BDG1, which has a role in the formation of cuticle. Furtherstudies on the redl mutant plants showed that it impairs the osmotic stress regulation of ABAbiosynthesis and ABA signaling genes by RNA gel blot and microarry analysis. In addition,genetic analysis of other cuticle mutants showed that all of these mutants were sensitivity toosmotic stress, and RNA gel blot analysis indicated that these mutants also impair the osmoticstress regulation of ABA biosynthesis and ABA signaling genes. In conclusion, we identifieda novel pathway that it could regulate the ABA biosynthesis and ABA signaling pathwayunder osmotic stress treatment.