Growth kinetics, polyamine pattern and biosynthesis in hairy root lines of Nicotiana tabacum

Publisher Website
Google Scholar
Abstract
The possibility of a relation between the expression of root inducing (Ri) T‐DNA genes of Agrobacterium rhizogenes and changes in polyamine metabolism has been explored in fast‐growing tobacco hairy roots. Transformed root cultures have been established on hormone‐fee medium; they came from transgenic plants of Nicotiana tabacum L. cv. Xanthi with different altered phenotypes, designated transformed (T) and supertransformed (T'). T and especially T′ roots developed more rapidly both by elongation and lateral branching, and showed a higher growth rate than the untransformed control. After 3 weeks in culture, normal roots showed a very reduced meristematic zone, and flow cytometric analysis indicated that 2C nuclei were predominant in the apical parts in contrast to T and T′ roots, in which endopolyploidisation also appeared. Putrescine, spermidine and traces of spermine were present in all the samples, both in free and in conjugated forms. Putrescine was the major polyamine detected in controls and in transformed roots. At the time of excision, the polyamine levels were similar in normal, T and T′ roots. Significant differences were found during the progression of growth, particularly in the TCA‐insoluble fraction in which polyamines varied differently according to the type of roots, increasing considerably in T roots on day 8, then decreasing. The lower polyamine contents found in growing transformed roots were concomitant to low arginine (EC 4.1.1.19) and ornithine (EC 4.1.1.17) decarboxylase activities. It is suggested that polyamine levels and related enzyme activities are linked to growth kinetics rather than being a consequence of foreign gene expression.