Fusicoccin affects cortical microtubule orientation in the isolated epidermis of sunflower hypocotyls

Abstract

Epidermal peels isolated from sunflower hypocotyls provide a convenient model to study the relationship between cortical microtubule orientation and strain rate. Extension of peels can be modulated using chemical treatment and mechanical stress, i.e., by adding a chemical to the incubation medium and applying a load exceeding the yield threshold for irreversible (plastic) strain. In this study, peels were pre-incubated for ca. 12 h (long-term pre-incubation) or for 1 h (short-term pre-incubation). In the long-term pre-incubated peels, fusicoccin applied to the medium neither enhanced the rate of longitudinal plastic strain of loaded peels, nor affected microtubule orientation. However, fusicoccin increased the strain rate of short-term, pre-incubated peels and affected microtubule orientation in both extending (loaded) and non-extending (unloaded) peels. Without fusicoccin, microtubule orientation was generally longitudinal or steep, whereas in fusicoccin-treated unloaded peels it was transverse and oblique microtubules in peel portions corresponding to the apical part of the hypocotyl. Although the frequency of transverse orientation was increased through loading, there was no strong correlation between the rate of fusicoccin-induced strain and microtubule orientation. It is hypothesized that the insensitivity of long-term pre-incubated peels to fusicoccin with respect to strain rate is due to a lack of active plasma membrane H(+) -ATPases. Thus, the sensitivity of short-term, pre-incubated, unloaded (non-extending) peels to fusicoccin, with respect to microtubule orientation, indicates that orientation might be affected by electric currents resulting from fusicoccin stimulation of H(+) -ATPases.

A model for leaf initiation: Determination of phyllotaxis by waves in the generative circle

“…In contrast, control by one sort of often-asymmetric cytoskeleton can be ruled out: the microtubule bundle system. For some time this system has been studied in elongate easier-to-image cells of seedling shoot axes, where spiraling patterns of peripheral microtubules set the pattern for spiraling cellulose deposition in the wall where see especially Paredez et al 72,73 Gutierrez et al 74 note also demonstrations by Chan et al 75 of shifts in pattern during development and see Burian and Hejnowics, 52,53 for new biophysical studies of microtubule orientation in a simple system). More recently, disposition of microtubules has been studied at the shoot apex, 49 where interesting correlations with distributions of auxin transporters of phyllotactic patterning have been identified but causal correlations have been ruled out.…”

“…Consistent with but not uniquely specified by models in which mechanical stress and strain play a critical or even the decisive patterning role, 9,10,21,22,49,50 microtubules can be aligned by mechanical stress. 49,[51][52][53] However, there is no reason to believe that auxin transporters are controlled by microtubules; for example, the evidence from years of experimentation on polarization during gravitropism indicates that effects of auxin distribution control microtubules and not vice versa. 54 Moreover, recent experiments on the shoot apex show that distribution of one auxin transporter, PIN1, can be correlated with while not controlled by microtubules.…”

Global Compression Reorients Cortical Microtubules in Arabidopsis Hypocotyl Epidermis and Promotes Growth

“…They also reoriented when compressed under a glass slide or Petri dish [34,35]. Reorientations were not observed in sunflower epidermal peels loaded with 5 g [36]; when loaded with 1 g (0.01 N), the microtubules reoriented away from the longitudinal in situ orientation, and when loaded with 10 g (0.1 N) became more aligned in the longitudinal direction [25]. The response thus depends upon the tissue, the amount of force, and the direction in which it is applied.…”

In Memoriam: Zygmunt Hejnowicz (1929–2016)

“…Between 2005 (the year of Zygmunt's retirement) and 2011, Zygmunt published a series of papers on dynamics of cortical microtubules, most of them together with his last PhD student, Agata Burian. [34][35] In 2005, based on observations of immunolabelled microtubule arrays in fixed specimen, Zygmunt postulated autonomous rotational changes of microtubule arrays; this was confirmed afterwards by other authors on the basis of in vivo observations.…”