Use of mutants and transformed plants to study the action of auxins

Barbier-Brygoo, H.; Maurel, C.; Shen, W.H.; Ephritikhine, G.; Delbarre, A.; Guern, J.

Symposia of the Society for Experimental Biology 44: 67-77

1990


ISSN/ISBN: 0081-1386
PMID: 2130519
Document Number: 366918
Results of a comparison of the properties of several plant genotypes differing in their reaction to auxins are described. The hormonal response used to compare the genotypes was the auxin-induced variation of the transplasmalemma electrical potential difference ( Delta Em) exhibited by protoplasts isolated from leaves of root tips. Using this membrane response, it was shown that large variations in the sensitivity to auxins can be induced either by mutagenesis in tobacco or by transformation of various materials by Agrobacterium rhizogenes. Tobacco protoplasts isolated from an auxin resistant mutant, when compared to protoplasts from the control genotype, displayed an auxin-induced hyperpolarization with a 10-fold decrease in their sensitivity to the hormone. Conversely, protoplasts isolated from root tips of various plants transformed by A. rhizogenes or from the leaves of tobacco plants regenerated from transformed roots, exhibited a 100 to 1000-fold increase in their sensitivity to auxins. The single gene, rolB, from the Ri plasmid harboured by A. rhizogenes was able to induce the dramatic modification in the sensitivity to auxins of tobacco protoplasts. The auxin-induced hyperpolarization of tobacco protoplasts was inhibited by antibodies directed against an auxin-binding protein (ABP) purified from maize coleoptile membranes. Immunotitrations of ABP antigens at the external surface of tobacco protoplasts suggested that transformed protoplasts have more surface receptors than protoplasts from the normal genotype, whereas protoplasts isolated from the auxin-tolerant mutant have less receptors than their wild-type counterpart. The results suggested that the sensitivity of tobacco protoplasts to auxin could be dependent on the number of functional receptors exposed at the outer surface of the plasmalemma.

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