P. Nick et al., A MICROTUBULE-ASSOCIATED PROTEIN IN MAIZE IS EXPRESSED DURING PHYTOCHROME-INDUCED CELL ELONGATION, Plant journal, 8(6), 1995, pp. 835-844
Plants can adapt their shape to environmental stimuli. This response i
s mediated by the reorganization of cortical microtubules, a unique el
ement of the cytoskeleton. However, the molecular base of this respons
e has remained obscure so far. In an attempt to solve this problem, si
gnal-dependent changes in the pattern of microtubule-binding proteins
were analysed during coleoptile elongation in maize, that is, under th
e control of the plant photoreceptor phytochrome. Two putative MAPs of
100 kDa (P-100) and 50 kDa apparent molecular weights were identified
in cytosolic extracts from non-elongating and elongating cells. Both
proteins co-assembled with endogenous tubulin, bound to neurotubules a
nd were immunologically related to the neural MAP tau: the P-100 prote
in, depending on the physiological situation, was manifest as a double
band and was always found to be heat-stable. In contrast, the 50 kDa
MAP was heat-stable only for particular tissues and physiological trea
tments. The P-100 protein was present in all tissues, however in a red
uced amount in elongating coleoptiles. The 50 kDa MAP was expressed ex
clusively upon induction of phytochrome-dependent cell elongation. As
shown by immunofluorescence double-staining, an epitope shared by both
proteins colocalized with cortical microtubules in situ, but exclusiv
ely in elongating cells. In non-elongating cells, only the nuclei were
stained. Partially purified nuclei from elongating cells were enriche
d in P-100, whereas the 50 kDa MAP became enriched in a partially puri
fied plasma membrane fraction.