Abstract

Light and developmental processes affect the cortical microtubule (cMT) orientation. The cMT orientation with a special regard to its chirality was analyzed under the outer epidermal cell walls in different regions of sunflower hypocotyls kept in darkness and after irradiation with blue and red light. The results show that the cMT orientation depends on the cell position along hypocotyl, but generally cMTs are oblique. The oblique orientation has defined chirality: either of Z-form (right-handed) or S-form (left-handed). In the lower region of hypocotyls the Z-form dominates. After irradiation of hypocotyls with blue light this domination has been maintained and appeared also in the upper region. In contrast, after irradiation with red light the Z-form domination has not been apparent. It is proposed that in darkness, variations of cMT orientations in the epidermis along the hypocotyl are due to developmental processes, while blue and red light affect the cMT orientation via "shifting" these processes backward and forward, respectively.

Highlights

  • Cytoskeleton plays an important role in plant morphogenesis

  • The cortical microtubule (cMT) orientation histograms for hypocotyls in each series were to some extent variable

  • A tendency to decrease the frequency of transverse orientation and to increase the histogram asymmetry is apparent along the hypocotyl basipetally (Fig. 2a-c, 3a-c)

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Summary

Introduction

The array of cortical microtubules (cMTs), i.e. microtubules underlying the plasma membrane during interphase, is thought to determine the direction of cell growth by influencing the orientation of cellulose microfibrils (Wymer and Lloyd 1996; Baskin 2001). The relationship between cMTs and cellulose microfibrils is still controversial (Emons et al 1992; Ketelaar and Emons 2001). They exhibit periods of growth, pausing and shortening. In Arabidopsis the cMT migration occurs by means of the so called hybrid treadmilling mechanism (Shaw et al 2003), in which the cMT migration is the net result of polymerization-biased dynamic instability at the leading (plus) ends and slow intermittent depolymerization at the lagging (minus) ends

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