Cm. Duckett et Cw. Lloyd, GIBBERELLIC ACID-INDUCED MICROTUBULE REORIENTATION IN DWARF PEAS IS ACCOMPANIED BY RAPID MODIFICATION OF AN ALPHA-TUBULIN ISOTYPE, Plant journal, 5(3), 1994, pp. 363-372
To test whether shifts induced in microtubule orientation by gibberell
ic acid (GA(3)) involved changes in tubulin isotypes, pea stem cells w
ere examined when elongation had been enhanced by GA(3). The behaviour
of a dwarf recessive mutation (le), with very low endogenous levels o
f gibberellin, was compared with the tall (Le) plant. Two hours after
adding GA(3), cells were measurably longer than controls and this coin
cided with a net shift of microtubule orientation from longitudinal an
d oblique to transverse - an effect that was more pronounced in the dw
arf. There were always more cells with net-transverse microtubules in
GA(3)-treated tissue than in controls, but as growth ceased, the major
orientation of the microtubule arrays became oblique in both samples.
Microtubule reorientation was rapid and was closely correlated with t
he growth of the cells. Although changes in orientation and isotype we
re monitored over a 40 h period, immunoblotting 2D gels with the well
characterized antibodies YL1/2 and YOL1/34 confirmed that alterations
to the alpha-tubulin constellation could be detected as early as the 2
h time point. Again the effect was especially pronounced in dwarf pla
nts. In the presence of added GA(3), one alpha-tubulin isotype (design
ated alpha 1) retained its position in the alpha-tubulin constellation
(as determined by total protein staining and with YOL1/34 that recogn
izes detyrosinated as well as tyrosinated tubulin). It was no longer r
ecognized, however, by the anti-tyrosinated alpha-tubulin antibody YL1
/2. This indicates that as GA(3) begins to cause a reorientation of th
e cortical microtubules (and to enhance the rate of cell elongation) t
he alpha 1 isotype is rapidly changed, probably by post-translational
modification.