Alterations in hormonal and developmental characteristics in transgenic Populus conditioned by the rolC gene from Agrobacterium rhizogenes

One hybrid aspen (P. tremula L. x P. tremuloides Michx.) clone transgenic for different chimeric gene constructs has been used to determine hormonal levels in several plant tissues. Mainly, transgenic aspen carrying the rolC gene from Agrobacterium rhizogenes under control of the cauliflower-mosaic-virus 35S-promoter and the light inducible rbcS promoter from potato were compared with untransformed aspen. Determination of various hormones in different rolC transgenic plant tissues revealed changes in levels conditioned by 35S-rolC and rbcS-rolC transgenic aspens as compared with controls. These changes could be specific for a woody plant species. Measurements of hormones in predormant buds of 35S-rolC transgenics showed levels of abscisic acid of about half of the content as measured in predormant buds of untransformed controls. Two further determinations during the resting period (at the middle and at the end) confirmed the lower ABA level in 35S-rolC transgenics. In spring, these 35S-rolC transgenics starred to flush at least 2 weeks before the control plants. This possibly suggests the involvement of ABA in the process of maintenance of dormancy and break from it in this tree species. Tree-specific developmental characteristics are discussed in the light of varying hormone levels in aspen-Populus, a woody plant model system.