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 inve rtase activity in adult maize leaves whereas cell wall invertase activity r emained constant. This response was closely related to the mRNA level for o nly one of the invertase gene (Ivr2), encoding a vacuolar isoform. In paral lel, four quantitative trait loci (QTLs) were detected for invertase activi ty under control and nine under stressful conditions. One QTL in control an d 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; s ome of them formed 'stress clusters'.