The Study On The Role Of Salt Bladders In The Salt Tolerance Of Atriplex Canescens

Salinization is an important abiotic environmental factor that limits the development of agriculture and animal husbandry worldwide,and is one of the important causes of land degradation.Some plants have evolved a variety of salt tolerance mechanisms during their long-term adaptation to saline environments.The investigations of the mechanisms underlying salt tolerance will facilitate our understanding on the resources of halophyte species,and thus will have great significance for future ecological restoration and forage improvement.Atriplex canescens,a perennial C₄ semi-evergreen shrub belongs to Chenopodiaceae,is a typical recretohalophyte with an unique salt-secreting structure on leaf and stem surface:salt bladders.Our previous studies found that A.canescens possesses strong salt resistance,and the Na⁺concentration in its salt bladders significantly increased with the increase of NaCl treatment concentrations,indicating that the salt bladders may participate the process of A.canescens in response to saline environment.However,the specific role and its mechanism of salt bladders in salt tolerance of A.canescens are still unclear and need to further reveal.Based on the previous studies,therefore in this study,the morphological characteristics and dynamic changes of A.canescens's salt bladders were observed by scanning electron microscopy after salt treatment;the salt tolerance and ion accumulation patterns were analyzed in A.canescens plants of which salt bladders were brushed;finally,candidate genes related to trichomes development were cloned and their expression patterns were systematically analyzed.The main results of this study are as follows:1.The structure of salt bladders of A.canescens was similar to that of other species in Chenopodiaceae.The salt bladder was composed of large bladder cell,stalk cell and epidermal cells,and showed gradually rupture and degenerate with the increase of leaf age.The salt bladders of A.canescens are regenerative,and the time of their regeneration was about 3-4 days under normal conditions;NaCl treatment can significantly accelerated its regeneration and promote its volume increase and rupture.2.With the increase of NaCl concentration,the Na⁺concentration in salt bladders of A.canescens increased significantly,while the K⁺concentration decreased significantly.Moreover,the Na⁺and K⁺concentrations in salt bladders on the surface of mature leaves were higher than that of young leaves as well as old leaves.3.Salt bladders were closely related to salt tolerance of A.canescens.Under control conditions,there was no difference in physiological indexes between brushed and non-brushed plants,indicating that brushing salt bladders would not affect the normal growth of A.canescens.The removal of salt bladders significantly weakened the salt tolerance of A.canescens.As a result,the growth of A.canescens seedlings were reduced,and correspondingly,the plant height,leaf area,biomass,leaf relative water content as well as photosynthetic capacity decreased significantly,under salt treatment.4.Brushing the salt bladders significantly affected the ion accumulation patterns in A.canescens.Under salt treatment,the plant without salt bladders had to accumulate a large amount of Na⁺and Cl^-in metabolic organs such as leave since it failed to secrete above ions by salt bladders.Theses results further indicates that salt bladders can accumulated a large amount of Na⁺and Cl^-to maintain ion homeostasis in metabolic organs such as leaves,and reduced the damage of the saline environment to the plants.5.Three candidate genes,AcTTG1,AcGL2,AcGEM,that might be involved in development of salt bladders were screened from transcriptome data of A.canescens and cloned.AcTTG1 belongs to the WD40 transcription factor and encodes 341 amino acids;AcGL2 belongs to the HD-ZIP transcription factor and encodes 763 amino acids;AcGEM belongs to the GEM protein and encodes 293 amino acids.6.Expression pattern analysis showed that AcTTG1,AcGL2,and AcGEM were highly expressed in young leaves and mature leaves of A.canescens,and were significantly induced by salt and brush-salt bladders treatment,suggesting that these genes might be involved in regulating the development of salt bladders of A.canescens.