A maize vacuolar invertase, IVR2, is induced by water stress. Organ/tissuespecificity and diurnal modulation of expression

The expression of invertases was analyzed in vegetative organs of well-wate red and water-stressed maize (Zea mays) plants. Early changes in sucrose me tabolism and in acid soluble invertase expression were observed in vegetati ve sink and source organs under mild water stress. The organ-specific induc tion of acid invertase activity was correlated with an increase in the Ivr2 gene transcripts and in the vacuolar invertase proteins. In addition diurn al changes in activity and Ivr2 transcripts for vacuolar invertase were not ed in shoots. Hexoses (glucose and fructose) accumulated in all organs exam ined from water-stressed plants. In situ localization studies showed that g lucose accumulation, vacuolar invertase activity, invertase protein, and th e Ivr2 transcripts colocalized specifically in bundle sheath and vascular t issue cells of mature stressed leaf; in primary roots the stress-induced in crease of Ivr2 transcripts was detected only in root tips. Based on these r esults different regulatory roles are proposed in sink and source organs fo r the stress induced Ivr2 vacuolar invertase.