Fast changes in soluble carbohydrates and proline contents in tomato seedlings in response to ionic and non-ionic iso-osmotic stresses

Qualitative and quantitative changes in soluble carbohydrates and proline contents were studied in young plants of two tomato cultivars (Lycopersicon esculentum L. Mill.) differing in their salt-tolerance (cvs. Pera and Volgogradskij). Seedlings were treated for 24 h with ionic (300 mmol L-1) and non-ionic isoosmotic (380 g kg(-1) polyethylene glycol MW 6000) stresses. Salinity provoked a decrease in the hexose contents and it also dramatically enhanced sucrose accumulation in all organs of the plants, and to a greater extent in the salt-sensitive cv. Volgogradskij. The PEG iso-osmotic stress, compared with saline conditions, only affected the hexose contents in a similar way to salinity in the cv. Volgogradskij, while it increased the sucrose content 2.5 and 4 times in the roots of Pera and Volgogradskij, respectively. Proline accumulation was more important in the salt-sensitive cultivar under both conditions. The contribution of these solutes to the osmotic potential was up to -0.3 MPa under non-ionic stress, but they had little influence under salinity compared with control plants. The fast changes observed in soluble carbohydrates and proline composition are discussed in relation to the osmotic adjustment under saline and non-permeant iso-osmotic stresses.