INDUCTION OF A PEA CELL-WALL INVERTASE GENE BY WOUNDING AND ITS LOCALIZED EXPRESSION IN PHLOEM

A full-length cell-wall invertase cDNA obtained from pea (Pisum sativu m L.) seedlings was cloned previously. The gene exhibits tissue-specif ic expression, and both its transcript and enzyme activities are abund ant only in root tissues. Mechanical wounding dramatically induced the accumulation of the cell-wall invertase mRNA in detached or intact le aves, stems, and roots. In both detached and intact tissues mRNA start ed to accumulate 3 h after wounding and in detached tissues (except ro ot tissues) was much stronger and lasted longer compared with that in intact pea plants. The induction of cell-wall invertase by wounding wa s not systemic, since no significant increase of transcript was found in the unwounded tissues remote from the site of wounding. Accumulatio n of this cell-wall invertase was induced by abscisic or jasmonic acid , and in situ hybridization studies show that this invertase mRNA is d ifferentially localized in wounded plant tissue, being most abundant i n the phloem. mRNA accumulation was limited mainly to the wounded area ; no significant increase was detected in the unwounded portions of th e wounded stem segments. The results suggest that, as part of the woun ding response, this cell-wall invertase may provide energy through hex ose availability to companion cells in the phloem.