Ivr2, a candidate gene for a QTL of vacuolar invertase activity in maize leaves. Gene-specific expression under water stress.

Water shortage produced an early and large stimulation of acid-soluble invertase activity in adult maize leaves whereas cell wall invertase activity remained constant. This response was closely related to the mRNA level for only one of the invertase gene (Ivr2), encoding a vacuolar isoform. In parallel, four quantitative trait loci (QTLs) were detected for invertase activity under control and nine under stressful conditions. One QTL in control and one in stressed plants was located near to the Ivr2 gene on chromosome 5. Other QTLs for invertase activity were found close to carbohydrate QTLs; some of them formed 'stress clusters'.