Salt stress differentially regulates mobilisation of carbon and nitrogen reserves during seedling establishment of Pityrocarpa moniliformis.

Abstract

Seedling establishment is a critical step in environment colonisation by higher plants that frequently occurs under adverse conditions. Thus, we carried out an integrated analysis of seedling growth, water status, ion accumulation, reserve mobilisation, metabolite partitioning and hydrolase activity during seedling establishment of the native Caatinga species Piptadenia moniliformis (Benth.) Luckow & R.W. Jobson under salinity. Two-day-old seedlings were cultivated in vitro for 4days in water agar (control) or supplemented with 50 or 100mm NaCl. Biochemical determinations were performed according to standard spectrophotometric protocols. We found that 100mm NaCl stimulated starch degradation, amylase activity and soluble sugar accumulation, but limited storage protein hydrolysis in the cotyledons of P.moniliformis seedlings. Although Na+ accumulation in the seedling affected K+ partitioning between different organs, it was not possible to associate the salt-induced changes in reserve mobilisation with Na+ toxicity, or water status, in the cotyledons. Remarkably, we found that starch content increased in the roots of P.moniliformis seedlings under 100mm NaCl, probably in response to the toxic effects of Na+ . The mobilisation of carbon and nitrogen reserves is independently regulated in P.moniliformis seedlings under salt stress. The salt-induced delay in seedling establishment and the resulting changes in the source-sink relationship may lead to storage protein retention in the cotyledons. Possibly, the intensification of starch mobilisation in the cotyledons supported starch accumulation in the root as a potential mechanism to mitigate Na+ toxicity.