EXPRESSION OF A WOUND-INDUCIBLE CYTOKININ BIOSYNTHESIS GENE IN TRANSGENIC TOBACCO - CORRELATION OF ROOT EXPRESSION WITH INDUCTION OF CYTOKININ EFFECTS

The Agrobacterium-derived cytokinin-biosynthesis gene ipt was fused to the wound-inducible proteinase-inhibitor-IIK gene promoter from potato and introduced into Nicotiana plumbaginifolia and N. tabacum. Maximum accumulation of ipt transcripts in the leaves of transgenic plants was observed within 3-24 h after leaf wounding. Root and stem ipt messages were not detected in unwounded transgenic N. plumbaginifolia PI-II-ipt seedlings until after the plants bolted whereas in N. tabacum, a relatively low level of root and stem expression was evident only prior to stem elongation and not detected after the plants bolted. Atypical cytokinin effects were observed with the N. plumbagini-folia but not N. tabacum transformants. Transgenic N. plumbaginifolia plants bolted sooner, were taller than control plants and had larger leaves with lower specific fresh weights and chlorophyll content. At flowering, the emergence of numerous lateral shoots from lower stem sections and basal leaf greening followed the moderate increase in root ipt transcripts and corresponded to a greater than 100-fold increase in zeatin and zeatinriboside cytokinin concentrations. The expression pattern of the PI-II-ipt gene followed that of the PI-IIK gene and, when expressed in the root, corresponded with induction of characteristic cytokinin effects.