Influence of Salt Stress on Germination, Root Elongation and Carbohydrate Content of Five Salt Tolerant Taxa.

Abstract

Because salt stress can reduce photosynthesis and yields, as well as reducing crop value by damaging appearance, field, container, and greenhouse producers must manage salinity carefully to assure a profitable crop. Understanding plant responses to salt stress is key in managing this problem. A common protective response to salt stress is osmoregulation and/or osmoprotection via the accumulation of carbohydrates or compatible solutes such as the sugar alcohol mannitol. Various protective roles for these compatible solutes have been well documented in plants, cell cultures and maturing seeds. Less information is available on possible impacts of these compounds on protection against salt stress during the germination process itself. To specifically assess potential roles for sugars and sugar alcohols on germination, growth and carbohydrate metabolism, we selected seed from known mannitol and non-mannitol accumulating salt tolerant taxa and seed from known salt sensitive non-mannitol accumulating taxa, and germinated them in the presence of increasing concentrations of sodium chloride.

Seed of both salt tolerant and sensitive taxa showed varying degrees of decreased radical elongation as salt stress increased. Surprisingly, seed from taxa known to accumulate mannitol did not germinate better in saline environments than did seed from non-mannitol producing taxa. In fact, seed from non-mannitol taxa described as salt sensitive had somewhat higher germination and better growth under salt stress than seed of salt tolerant mannitol-containing plants. Analysis of soluble carbohydrates in seeds and seedlings incubated in the presence of increasing salt showed no overall correlation between mannitol content and germination or growth. However, accumulations of low molecular weight carbohydrates, especially sucrose, were observed at high levels of salt stress. Interestingly, this increase most often occurred after concentrations of salt were reached that totally inhibited germination, suggesting a potential role for carbohydrates in conditioning of seed during salt stress.