Interactive effects of sodium chloride and calcium chloride on the accumulation of proline and glycinebetaine in peanut ( Arachis hypogaea L.)

Abstract

Many plants, including peanut ( Arachis hypogaea L.), when exposed to salinity stress produce the osmoticants: proline and glycinebetaine. Calcium ions also play a role in osmoprotection. During germination of peanut seeds subjected to NaCl salinity stress, proline and glycinebetaine concentrations in the embryonic axis increased continuously. A further increase in glycinebetaine concentration was observed with the addition of calcium chloride to the sodium chloride. The effects of sodium and calcium are thus additive in causing accumulation of glycinebetaine. Calcium appears to confer greater osmoprotection to the seedling exposed to salinity in this way. Two enzymes play an important role in controlling the level of proline. Proline oxidase catalyzes the conversion of proline to glutamate, thus reducing the concentration of proline. Another enzyme, γ-glutamyl kinase, plays an important role in the synthesis of proline. Addition of calcium chloride to NaCl-stressed seedlings lowered the proline concentration by increasing the level of proline oxidase and decreasing γ-glutamyl kinase activities. Salinity stress, in the absence of calcium, increased proline due to reduced proline oxidase activity and increased γ-glutamyl kinase activity both in the cotyledons and embryonic axis of peanut seedlings. Thus calcium ions increase glycinebetaine production but decrease proline levels in NaCl stressed peanut seedlings.