Hormonal content and sensitivity of transgenic tobacco and potato plants expressing single rol genes of Agrobacterium rhizogenes T‐DNA

Abstract

SummaryThe expression of single rol genes of the TL‐DNA of Agrobacterium rhizogenes strain A4 in transgenic tobacco (Nicotiana tabacum L.) and potato (Solanum tuberosum L.) plants alters the internal concentrations of, and the sensitivity to, several plant hormones. The levels of immunoreactive cytokinins, abscisic acid, gibberellins and indole‐3‐acetic acid were analysed in tissues of the apical shoots, stems, leaves, roots and undifferentiated callus tissue. The addition of the dominant and morphogenetically active rolA, rolB, or rolC genes resulted in alterations in the content of several hormones. rolC overexpression in particular led to an up to fourfold increase in the content of isopentenyladenosine, dihydrozeatin riboside and trans‐zeatin riboside‐type cytokinins in potato plants. This increase correlated well with different levels of expression of the rolC gene in different transgenic plants. Furthermore it was shown that the dwarfism of P35s‐rolC transgenic tobacco and potato plants is correlated with a 28–60% reduction of gibberellic acid A1 concentration in apical shoots. Exogenous addition of gibberellic acid completely restored stem elongation in P35s‐rolC transgenic plants. Apical shoots of dwarf rolA transgenic tobacco plants also contained 22% less gibberellic acid A1 than control plants, but growth cannot be restored completely by exogenously added gibberellic acid. Similarly, the sensitivity of transgenic tobacco seedlings or callus tissues towards different phytohormone concentrations can be altered by the expression of single rol genes. The overexpression of the rolC gene in seedlings led to an altered response to auxins, cytokinins, abscisic acid, gibberellic acid and the ethylene precursor 1‐aminocyclopropane‐carboxylic acid. The overexpression of the rolB gene in tobacco calli led to necrosis at lower auxin concentrations than in the wild‐type, while other parameters of auxin action, like the induction of cell growth, remained unchanged.