THE CYCLIC REORIENTATION OF CORTICAL MICROTUBULES ON WALLS WITH A CROSSED POLYLAMELLATE STRUCTURE - EFFECTS OF PLANT HORMONES AND AN INHIBITOR OF PROTEIN-KINASES ON THE PROGRESSION OF THE CYCLE

The outer tangential wall (OTW) of epidermal cells of azuki bean epico tyls has a crossed polylamellate structure, in which lamellae of longi tudinal cellulose microfibrils alternate with lamellae of transverse c ellulose microfibrils. This implies that the cyclic reorientation of c ortical microtubules (MTs) from longitudinal to transverse and from tr ansverse to longitudinal occurs on the OTW. Treatment with a solution that contained no auxin caused the accumulation of cells with longitud inal MTs, suggesting that auxin is required for the reorientation of M Ts from longitudinal to transverse during the reorientation cycle. Tre atment with 6-dimethylaminopurine (DMAP), an inhibitor of protein kina ses that promoted the reorientation of MTs from transverse to longitud inal, resulted in the accumulation of cells with longitudinal MTs. Sub sequent treatment with auxin caused a marked increase in the percentag e of cells a with transverse MTs and then a decrease in the percentage , indicating that the reorientation of MTs from longitudinal to transv erse and then from transverse to longitudinal occurred during treatmen t with auxin. The percentage of cells with transverse MTs decreased mo re slowly in segments that had been pretreated with gibberellin A(3) ( GA) than in segments that had been pretreated without GA, suggesting t hat GA, in cooperation with auxin, caused the suppression of the reori entation of MTs from transverse to longitudinal.