Changes in tubulin protein expression accompany reorganization of microtubular arrays during cell shaping in barley leaves

Barley (Hordeum vulgare L.) leaves grow from the base and thus exhibit a smooth developmental gradient. Developing mesophyll cells acquire their typical lobed shape synchronously along this gradient. Successive changes in the patterns of cortical microtubules are involved in the shaping process. The changes include formation and dispersal of band-like structures, the establishment of a random network and a dramatic loss of microtubules after completion of cell shaping. When the relative tubulin contents were determined in consecutive segments taken along the leaf, two tubulin maxima were found. They coincided with the establishment of the microtubular bands and the random network, respectively. Concomitantly, tubulin populations differing in the abundance of individual isotypes were found. The data indicate that the changes in the patterns of the cortical microtubules were not simply effected by shifting whole, stable microtubules, as may be inferred from immunofluorescence microscopy. Rather it appears that the formation of these patterns were accompanied by, or perhaps a result of, not only microtubule assembly and diassembly cycles, but also tubulin turnover.