Regulation Of Stomatal Development On The Abaxial Epidermis Of Cotyledon By Ethylene In Arabidopsis

Stomata are ports for gas and water vapor exchange between plants and their environment.Stomatal development is strictly regulated by endogenous signals and environmental cues.Ethylene is an important signal that regulates multiple physiological processes in plants;however,its function in stomatal development remains largely unknown.Cell biology analysis of stomata phenotype of ethylene mutants,combined with phamautically treatment and marker gene expression comparison,was used to explore how ethylene regulates stomatal development in Arabidopsis.The main results are as follows:(1)Ehylene and its signaling pathway regulate stomatal development at least in three aspects.Firstly,ethylene and its signaling transduction positively regulate stomatal initiation and development;Secondly,ACC promote symmetric division of GMC;finally,ethylene and its signal modulate GC differentiation and affect its size and shape.(2)Exogenous ACC and ethphon treatment increased while block of ACC and ethylene biosynthesis by AVG and AIB/Co2+decreased the stomatal density on the adaxial epidermis of wild type.Block of ACC biosynthesis genetically resulted in small stomatal density in acs2,acs26 and acs8 mutants,while ACC accumulation in etol-1 was companied by increased stomatal density.In addition,block of ethylene signaling also dampen the stomatal initiation as stomatal density in ein2 and ein3eill were decreased compared with wild type(3)SGCs were found on the epidermis of acs8 cotylendons owing to defect in GMC symmetric division.ACC treatment can rescue this defect and diminish the SGC formation,while AVG treatment resulted in more SGCs.These results indicated that SGC formation is owing to the defect in ACC biosynthesis.Nevertheness,block of ACC biosynthesis by AVG or/and block of signaling by AgNO3 induced the formation of SGCs in wild type seedlings,further proved the positive function of ACC in GMC division.(4)Enlarge GCs were found in all the mutants checked in this study,and defect in GC symmetry and distorted GCs were found in some of them,which indicated that disruption of either biosynthesis or signaling of ethylene has efect on GC differentiation and norphogenesis and cause abnormal GC size and shape.This also proved the importance for the plant to maintain ethylene biosynthesis and signaling strictly in a steady status during growth and development.(5)The promotion of ethylene on asymmetric division of stomatal lineage precursor cells might founction by interaction with TMM and its partenors,which involved in the regulation of stomatal density and patterning on the epidermis by exocellular signals and their receptors on the membrane system.Since the overproduction of stoma in tmm-1 did not response to the inhibition by AVG,it might be possible that AVG's inhibition of stomatal development in wild type was at least partially dependant on function of TMM and its partenor(6)Not only the normal divison of GMC in wild type but also the abnormal excessive division of GMC in flp background could be diminished by AVG treatment.A result further proved that the promotion effect of ACC on GMC division and indicated that block of GMC division by ACC deficient is independent on FLP function.In addition,SGC formation and it ratio were promoted by ACC treatment and inhibited by AVG treatment in cyca2;234 triple mutant just like in wild type,but not in cdkb1;11;2 double mutant.The resistance of SGC formation and ratio change to ACC and AVG treatment indicated that the function of ACC on GMC division is at least partially dependant on CDKBl's function but not CYCA2's.The effect of exogenous ACC and AVG on pCDKB1;1-GFP and pCDKB1;1:CDKB1;1-GFP expression was further confirmed by this possibility.Altoghether,our results showed the effect of ethylene on stomatal development in Arabidopsis:promotion of asymmetric division of precursor cells,promotion of symmetric division of GMC,and regulation of GC size and shape.And there is difference between ethylene and its precursor ACC in regulation of stomatal development.These results will help to understand the molecular mechanism of ethylene on regulation of cell division and differentiation in stomatal development,and the flexibility of stomatal development under variable environments,which lay foundation for the adaptation of plants to versatile stress conditions by establishing optimal stoma density and distribution on epidermis and high water use efficiency.