Reorganization of the microtubule and actin cytoskeleton in root cells of Triticum aestivum L. during low temperature and abscisic acid treatments

Information on the effects of low temperatures and abscisic acid (ABA) on the structural organization of MTs and MFs is scarce and contradictory (Chu et al., 1993; Eun and Lee, 1997; Jiang et al., 1996; PihakaskiMaunsbach and Puhakainen, 1995; Rikin et al., 1983; Sakiyama and Shibaoka, 1990). Nothing is known about the interaction of these components on the cold acclimation of plants. Seedling roots of winter wheat cultivars differing in their frost resistance—Bezostaya 1 (low frost resistant), Mironovskaya 808 (moderately frost resistant) and Albidum 114 (highly frost resistant)—were the objects of the investigation. The plants were grown in hydroculture at an illumination of 100 W/m and with a photoperiod of 12 h. Nonacclimated plants were grown at 23 (C for 5 or 9 days. ABA (30 μM) was added to the 7-day-old plant roots and the plants were grown in ABA solution for 3 days. For cold acclimation, 8-day-old plants were transferred to 3 (C for 7 days. In treatments, in which the effect of ABA was studied together with cold acclimation, ABA was added 1 day before the beginning of acclimation. The visualization of the cytoskeleton was conducted by indirect immunofluorescent microscopy using monoclonal tubulin and actin antibodies (Baluska et al., 1997). In the cold-acclimated and ABA-treated winter wheat plants, the comparative investigation of the state (localization, orientation, structure) and the stability of actin and microtubule cytoskeleton have been done in the cells of different root zones. Cold acclimation caused the aggregation of MTs; it increased the fluorescence and stability of microfilaments (MFs) and MTs mainly in the zone of root differentiation. This could testify to the strengthening of the contacts between MTs and MFs. The stability of MTs was estimated by their response to the depolymerizing action of oryzalin. The roots were incubated in a solution of oryzalin (10 μM) for 3 h. To define the stability of MTs in cells of the differentiation zone, a quantitative approach was used. For each of the four variants (without acclimation, cold acclimation, ABA without acclimation, ABA with acclimation), 25 sections of several roots were investigated, and the number of sections, containing intact MTs in differentiating cells, was calculated. As in cold acclimation, ABA induced the formation of MT bunches, but in cells of the meristem and the elongation zones only. However, in the zone of differentiation, an increase in the stability of MT structures correlated with a decrease in the content, the degree of aggregation and the immunofluorescence of MTs and with the complete depolymerization of MFs. It was shown that the stabilizing effect of ABA on MTs depended on the degree of plant frost resistance (Fig. 1). For this reason, the ABA-induced increase of MT stability may be used as a diagnostic marker of frost resistance in different winter wheat cultivars. It was revealed that plant cold acclimation removed the effect of hormone on the structural organization of MTs and MFs in the zone of differentiation. It is suggested that such processes as depolymerization of MTs, a decrease of the number of unstable MT populations and an increase in the number of stable ones cause the slowing down of the growth of ABAtreated plants or plants at the initial stage of cold acclimation. At the end of the plant cold acclimation, the induction of plant growth is evidently determined by an increase of the number of dynamic/unstable populations of MTs and by an increase of polymerization of MFs. * Corresponding author. Tel.: +7-8432-32-51-45; fax: +7-8432-38-74-18. E-mail address: olga.olinevich@ksu.ru (L.P. Khokhlova). Cell Biology International 27 (2003) 211–212 Cell Biology International