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 sativum L.) seedlings was cloned previously. The gene exhibits tissue-specific expression, and both its transcript and enzyme activities are abundant only in root tissues. Mechanical wounding dramatically induced the accumulation of the cell-wall invertase mRNA in detached or intact leaves, stems, and roots. In both detached and intact tissues mRNA started to accumulate 3 h after wounding and in detached tissues (except root tissues) was much stronger and lasted longer compared with that in intact pea plants. The induction of cell-wall invertase by wounding was not systemic, since no significant increase of transcript was found in the unwounded tissues remote from the site of wounding. Accumulation of this cell-wall invertase was induced by abscisic or jasmonic acid, and in situ hybridization studies show that this invertase mRNA is differentially localized in wounded plant tissue, being most abundant in the phloem. mRNA accumulation was limited mainly to the wounded area; no significant increase was detected in the unwounded portions of the wounded stem segments. The results suggest that, as part of the wounding response, this cell-wall invertase may provide energy through hexose availability to companion cells in the phloem.