Ben-Hayyim, G., Volcani Center, Inst. of Horticulture, P. O. Box 6, Bet-Dagan, 50-250, Israel Martin-Tanguy, J., Laboratoire de Physioparasitologie, Station Amelioration des Plantes, INRA, BV 1540, F-21034 Dijon Cedex, France Tepfer, D., Lab. de Biol. de la Rhizosphere, Inst. Natl. de la Rech. Agronomique, F-78026 Versailles Cedex, France
The effects of rolA on root and shoot architecture have been ascribed to a deficiency in gibberellic acid (GA3) and to changes in polyamine metabolism. Using tobacco, we examined interactions among GA3, a polyamine accumulation inhibitor (a-DL-difluoromethylornithine or DFMO) and the rolA gene controlled by the 35S CaMV promoter. We measured the effects of these three agents on architecture and polyamine accumulation in excised roots and whole plants grown in vitro. Previous work showed that DFMO or genetic transformation with the rolA gene from Agrobacterium rhizogenes, controlled by the 35S promoter (P35s-rolA), caused excised tobacco roots to grow faster with altered root system architecture. We show that gibberellic acid (GA3) reversed the effects of DFMO on the architecture of excised root systems, but neither reversed the effects of DFMO on growth, nor the changes in growth and architecture associated with P35S-rolA. GA3 treatment alone resulted in increased agmatine levels, suggesting that the inhibition of the effects of DFMO on architecture was through a stimulation of the arginine decarboxylase (ADC) pathway. GA3 alone also inhibited the accumulation of putrescine and tyramine conjugates in excised roots. In tobacco plants growing in vitro DFMO and P35S-rolA were associated with reduced shoot height which was partially restored by GA3 treatment; however, GA3 also stimulated shoot height in the controls. GA3 did not lessen the leaf wrinkling associated with P35S-rolA P35S-rolA increased root number in young seedlings in vitro, and increased root system length in seedlings grown in soil. As in excised roots, the developmental changes linked to DFMO and P35S-rolA were accompanied by reductions in putrescine titers. GA3 treatment stimulated putrescine accumulation in stems and leaves, and partially reversed the negative effects of DFMO and P35S-rolA on putrescine accumulation in roots, stems and leaves. Again, the restoration of putrescine pools appeared to be through a stimulation of the ADC pathway, since agmatine accumulated in plants exposed to GA3. In general, the effects of DFMO and P35S-rolA on phenotype and polyamine metabolism were coordinated, and in many cases these effects were similarly modulated by GA3, reinforcing the previous conclusion that the phenotypic effects of rolA in roots and shoots occur through interference with polyamine metabolism and that the putrescine conjugates are particularly important in regulating root system growth and architecture. We were unable, however, to discern consistent evidence for a direct role for GA3 in establishing the RolA phenotype.
Changing root and shoot architecture with the rolA gene from Agrobacterium rhizogenes: Interactions with gibberellic acid and polyamine metabolism
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Ben-Hayyim, G., Volcani Center, Inst. of Horticulture, P. O. Box 6, Bet-Dagan, 50-250, Israel Martin-Tanguy, J., Laboratoire de Physioparasitologie, Station Amelioration des Plantes, INRA, BV 1540, F-21034 Dijon Cedex, France Tepfer, D., Lab. de Biol. de la Rhizosphere, Inst. Natl. de la Rech. Agronomique, F-78026 Versailles Cedex, France
Changing root and shoot architecture with the rolA gene from Agrobacterium rhizogenes: Interactions with gibberellic acid and polyamine metabolism
The effects of rolA on root and shoot architecture have been ascribed to a deficiency in gibberellic acid (GA3) and to changes in polyamine metabolism. Using tobacco, we examined interactions among GA3, a polyamine accumulation inhibitor (a-DL-difluoromethylornithine or DFMO) and the rolA gene controlled by the 35S CaMV promoter. We measured the effects of these three agents on architecture and polyamine accumulation in excised roots and whole plants grown in vitro. Previous work showed that DFMO or genetic transformation with the rolA gene from Agrobacterium rhizogenes, controlled by the 35S promoter (P35s-rolA), caused excised tobacco roots to grow faster with altered root system architecture. We show that gibberellic acid (GA3) reversed the effects of DFMO on the architecture of excised root systems, but neither reversed the effects of DFMO on growth, nor the changes in growth and architecture associated with P35S-rolA. GA3 treatment alone resulted in increased agmatine levels, suggesting that the inhibition of the effects of DFMO on architecture was through a stimulation of the arginine decarboxylase (ADC) pathway. GA3 alone also inhibited the accumulation of putrescine and tyramine conjugates in excised roots. In tobacco plants growing in vitro DFMO and P35S-rolA were associated with reduced shoot height which was partially restored by GA3 treatment; however, GA3 also stimulated shoot height in the controls. GA3 did not lessen the leaf wrinkling associated with P35S-rolA P35S-rolA increased root number in young seedlings in vitro, and increased root system length in seedlings grown in soil. As in excised roots, the developmental changes linked to DFMO and P35S-rolA were accompanied by reductions in putrescine titers. GA3 treatment stimulated putrescine accumulation in stems and leaves, and partially reversed the negative effects of DFMO and P35S-rolA on putrescine accumulation in roots, stems and leaves. Again, the restoration of putrescine pools appeared to be through a stimulation of the ADC pathway, since agmatine accumulated in plants exposed to GA3. In general, the effects of DFMO and P35S-rolA on phenotype and polyamine metabolism were coordinated, and in many cases these effects were similarly modulated by GA3, reinforcing the previous conclusion that the phenotypic effects of rolA in roots and shoots occur through interference with polyamine metabolism and that the putrescine conjugates are particularly important in regulating root system growth and architecture. We were unable, however, to discern consistent evidence for a direct role for GA3 in establishing the RolA phenotype.