Elucidation of Mechanisms of Salinity Tolerance in Zoysia matrella Cultivars: A Study of Structure and Function of Salt Glands

摘要

Salt glands are important structural adaptations in some plant and animal species that are involved in the excretion of excess salts. Zoysia matrella is a highly salt tolerant turf grass that has salt glands. Two cultivars of Z. matrella, ?Diamond? and ?Cavalier?, were examined in this study to look for salt gland related factors responsible for the differences in their degree of salt tolerance. In addition to the adaxial salt gland density being higher in ?Diamond?, the salt glands in salt treated (300 mM NaCl) plants of this cultivar were bigger than the ones in ?Cavalier?. ?Diamond?, as well as some of the ?Diamond? x ?Cavalier? hybrid lines, showed a significant induction in salt gland density in response to salt treatment. Examination of salt gland density in ?Diamond? x ?Cavalier? hybrid lines showed that salt gland density was a highly heritable trait in the salt-treated population. Ultrastructural modifications in the salt glands observed with Transmission Electron Microscopy (TEM), coupled with Cl- localization studies, suggested a preference for symplastic transport of saline ions in Z. matrella.Salt glands have been studied in several plant species; however, no studies have tried to associate the role of ion transporters with the functioning of salt glands in plants. RNA in situ studies with Na+ transporters showed localization of ZmatHKT1 transcripts in the adaxial salt glands, leaf mesophyll and bundle sheath cells for both cultivars. ZmatSOS1 expression was observed in the xylem parenchyma cells for leaves from both cultivars, but the expression was markedly different around the cells bordering the vascular tissue. The strongest expression of ZmatSOS1 for ?Diamond? was seen in the bundle sheath cells and the phloem, while for ?Cavalier? the signal was strongest in the mestome sheath cells and in cells surrounding the phloem. No expression of ZmatSOS1 was seen in the salt glands for either cultivars. ZmatNHX1 expression in both cultivars was very low, and observed in the salt glands and neighboring epidermal cells. Three alleles of ZmatNHX1 were identified in Z. matrella, along with three alternatively-spliced forms of ZmatNHX1, the expression of which were cultivar and treatment specific. Together, these results provide a model for salt transport in Z. matrella and signify potential roles of salt glands and select ion transporters in the salt tolerance of this species.