Effects of phosphorus application on ion distribution in aloe seedlings under seawater stress
磷对海水胁迫下芦荟幼苗离子分布的影响

How to enhance plant salt tolerance has always been focus issue up to present.It has been reported that phosphorus application can increase plant tolerance to osmotic stress by elevating anti-dehydration of protoplast.Intracellular ion homeostasis is a fundamental process for keeping physiological activity of living cells and ion flux regulation is necessary for plant cells to exclude toxic ions and to accumulate essential ions to a proper level.The effects of exogenous phosphorus on ionic homeostasis of plant under salt stress might be important in exploring physiology and salt tolerance mechanism of plant under salt stress by studying.Xerophyte Aloe vera,a member of the Liliaceae plant family,is widely cultivated because of the high medical values.However few studies can be documented on effects of environmental factors on the growth of Xerophyte Aloe vera as well as its inner adaptive mechanisms related.Therefore,pot experiments were carried out to study the effects of exogenous P on dry matter accumulation,water content,Na~ ,Cl~-,K~ and Ca~(2 ) contents of aloe seedlings and their relative contents in various tissue cells under seawater stress by chemical analysis and X-ray electron probe microanalysis.Two P levels and two seawater concentrations used in this experiment were 0.5 mmol P L~(-1) and 1.5 mmol P L~(-1),and 0 and 30%,respectively.The results obtained were listed as follows.Exogenous P application increased dry weight and water content of aloe seedlings under seawater stress significantly.No significant differences of dry weights and water contents of aloe seedlings were found between high P and low P treatments on the condition of no seawater stress.Exogenous P application could decrease the relative contents of Na~ and Cl~-in various tissue cells of aloe seedling roots but could dramatically increased the relative contents of K~ and Ca~(2 ) in epidermis cells,phloem cells and xylem cells in aloe seedling roots exposing to seawater stress.The same trend could be summarized on Na~ ,Cl~-,K~ and Ca~(2 ) concentrations in aloe seedling leaves and roots from the chemical analysis.Supplement of P to the plant under seawater stress hardly decrease the relative contents of Na~ and Cl~-of aloe seedling leaves.However,exogenous P application could increase to a great extent the relative content of K~ in various tissue cells of aloe seedling leaves and relative content of Ca~(2 ) in epidermis cells,cortex cells and aqueous cells of aloe seedling leaves.At the same time,high K~ / Na~ and Ca~(2 )/ Na~ in leaves of aloe seedlings could be maintained under seawater stress by supplement of P,which indicated that application of P could improve selective absorption and transportation of K~ and Ca~(2 ) from root to shoot of aloe seedlings under the seawater stress condition.And this might be attributed to the enhanced tolerance of aloe seedlings to seawater by P application.