AMELIORATION of SALINITY EFFECT in WHEAT PLANT by POLYAMINES

Abstract

Caryopses of a salt sensitive wheat cultivar (Triticum aestivum L. cv. Giza 163) were presoaked in various polyamines for 24 h (2.5 mM Put, 5 mM Spd or 2.5 rnM Spm) and then changes in growth para: 1eters: fresh mass (FM) ofboth shoot and root, relative growth rates of shoot and root ( RG R), root and shoot length and lea f area ratio (LAR) were measured. Mineral content of shoot and root (Na+, K +, Ca++ and Cr), endogenous polyamines of shoot (Put, Spd and Spm), ethy lene and proline l evel of shoot were determined. Pol yamine treatments si gnificantly alleviated the NaCI­

induced growth reduction. Polyamines were observed to increase FM and RGR of both shoot and root, but decreased Na+ and cr levels in shoot and root. The mitigating e ffect of PAs on plant growth was more pronoun ced by Put and Spd . Exogenous appli cation of polyamines also decreased the accumulation of ethyl ene and proline which was induced by NaCI. Polyamines also decreased polyamine/diamine ratio (increased by NaCl) which was related to salt tolerance (measured by growth parameters at vegetative stage). In present investigation al so studied the effect ofNaCI and polyamines on the lipid metabolism of the root plasma membrane

(total lipid, total and different classes of phospholipid, total and different classes of sterols) was also studied. Caryopses were presoaked in various polyamines for 24 h, then grmvn in MHS containing 150 mM NaCl for 15 days. The root plasma membrane was isolated by a two-phase partitioning system. The lipids of the pl asma membrane were extracted and characterized. Phosphatidylcholine, Phosphatidylethanolami ne and phosphatid yl gl ycerol were the major phospholipids \V ith lesser amount of phosphatidylinositol. phosphatid y l serine and diphosphatid yl gl ycerol. The major sterols were ca mpasterol and sti gm asterol \V ith a lessr amou nt of chol esterol and -s itosterol. Sodium Chloride at 1 50 mM signi flca ntl y decreased the total phospholipids. Salinity altered also th e rel ative distri bu ti on or phospholipids and sterol classes. Polyamines decreased the satu rated fatty acid s of tota l phospholipids and increased the unsaturated fatty acids, l eading to increase unsaturation/saturation ratio. The intluen ce of PAs on th e lipid metabolism of root pl asma membrane was consistent with their an1eliorating effect on the plant growth, where Put and Spd had the greatest effect on the induction of salt tolerance of the salt sensiti ve wheat cultivar used in this study. PAs-induced changes in the PM lipids seem to be in the direction to maintain the PM integrity under NaCl stress.

It can be concluded that PAs alleviated the deleterious effects of NaCI on the sensitive wheat cultivar used and, thereby enhancing i ts salt tolerance through: decreasing the level of toxic ions (Na+, Cr) and maintaining that of the beneficial ions (K+, Ca2) in the shoot and root decreasing ethylene and proline

prod uction, and PAs/diamine ratio. It is also through affecting the lipid metabolisn1 to alter rel ative abundance of different phospholipid and sterol classes to stabili ze the PM structure, and thus preserve its functions under salinity stress.