TOMATO ASR1 MESSENGER-RNA AND PROTEIN ARE TRANSIENTLY EXPRESSED FOLLOWING SALT STRESS, OSMOTIC-STRESS AND TREATMENT WITH ABSCISIC-ACID

The Asr1 cDNA clone was isolated by differential screening of tomato (Lycopersicon esculentum Mill., cv. Ailsa Craig) ripening fruit cDNA library with cDNA prepared from RNA isolated from leaves of water-stressed vs. irrigated tomato seedlings. In this study the steady state levels of tomato Asr1 mRNA and protein were further investigated. Low levels of mRNA and protein were detected in the roots and shoots of hydroponically grown tomato plants. Application of NaCl or PEG to the growth medium resulted in an elevation of the steady state levels of both Asr1 mRNA and protein, This increase was transient, reaching a maximum 12-24 h after the application of the stress. The extent of the increase correlated with the severity of the stress. The similarity between the response of mRNA and protein to the stress suggests that the Asr1 gene is regulated mainly by RNA transcription or RNA stability. The response of Asr1 to water and salt stresses could be mimicked by treatment of the seedlings with ABA, suggesting that this hormone is involved in the mechanism of activation of the Asr1 gene by these abiotic stresses.