EXPRESSION OF AN ABA-INDUCED GENE OF TOMATO IN TRANSGENIC TOBACCO DURING PERIODS OF WATER-DEFICIT

The gene le25 is an abscisic acid (ABA)-induced gene of tomato which i s expressed both in wilted vegetative organs and developing seeds, Spa tial and temporal expression was analysed in tobacco plants transforme d with a chimeric gene in which 5'-upstream DNA sequences of le25 were fused to the E. coli uidA gene, which encodes beta-glucuronidase (GUS ), Histochemical staining revealed that GUS was expressed in all tissu es of vegetative organs in response to water deficit, Exogenous ABA in duced expression to a lesser extent, even though ABA content was the s ame as drought-stressed leaves, indicating a difference in response to endogenous ABA compared to exogenous ABA, Water-deficit-induced GUS e xpression in floral tissues was examined in pre-anthesis floral buds f rom four different stages (I-IV; 11, 16, 33, 49 mm bud length, respect ively), While non-stressed floral organs showed no GUS activity except in pollen at stages III and IV, GUS activity was water-deficit-induce d in sepals of all stages, petals of stage II, and stigmas of stage II and III, In seeds, GUS activity was detected in both the embryo and e ndosperm at 15 d post-anthesis, which coincided with a large increase in the concentration of ABA in the seed, In transgenic plants, the le2 5 5'-flanking DNA drove expression of GUS during water deficit in two modes: non-tissue-specific expression in vegetative organs, and tissue -specific expression in reproductive organs, The location of GUS activ ity indicated that ABA concentration is elevated throughout the tissue s of the leaf during periods of water deficit.