Hydroxyproline and proline content of cell walls of sunflower, peanut and cotton grown under salt stress

Proline and hydroxyproline content of the cell walls of peanut (Arachis hypogea L. cv. Shulamit), cotton (Gossypium hirsutum L. cv. sj) and sunflower (Helianthus annuus L. cv. Saffola SO222) were determined. Proline concentration in the leaves of all plants species tested was approximately 110 nmol · mg^-1 dry matter and higher than in the root and stem. Hydroxyproline concentration was highest in the root of all species tested and was between 30 and 60 nmol·mg^-1 dry matter. This was 5-10 times higher than the concentration in the stem and leaf. There was no significant effect of salt stress on proline and hydroxyproline concentration in "purified cell wall fraction" of sunflower. Salt stress (100 mmol·l^-1NaCl) reduced substantially plant growth of 53-day-old sunflowers, stem volume decreased from 21.3 ± 5.2 ml to 3.8 ± 1.6 ml, dry matter content of stem decreased from 719 ± 186 mg to 88±33 mg and the number of leaves per plant decreased from 18 to 13. These results suggest that inhibition of plant growth, by salt stress, was accompanied by inhibition of cell wall proteins (extensins) synthesis. Therefore, changes in the physicochemical properties of cell wall accompanying the osmotic adjustment should be sought in other posttranslational modifications of extensin(s), either glycosylation or inter-and/or intramolecular cross-linking in the cell wall.