Cotton (Gossypium hirsutum) seed trichomes expand via diffuse growing mechanism

Abstract

The ultrastructure of cotton (Gossypium hirsutum) seed trichomes was investigated to obtain insight into their growth behavior during the phase of rapid cell elongation. A mold and cast method of scanning electron microscopy was used to record the morphological changes in the ovular surface during the initiation and elongation of trichomes. A rapid freeze-fixation and freeze-substitution protocol was used to study the cytological features of trichomes at 2 days after anthesis. At the cytological level, attention was primarily focused on determining whether the seed trichomes display features that are characteristic of other tip-growing plant cells, including organelle zonation, polarized deposition of cell wall, axial orientation of microtubules, and microfilament meshwork at the cell apex. Our results show that cotton seed trichomes do not share any ultrastructural characteristic with other tip-growing plant cells. Rather, they show all the characteristics of cells that undergo diffuse growth. The roles of actin microfilaments and microtubules were also investigated through an in vitro administration of cytochalasin D and colchicine. Although the disruption of actin filaments did not stop trichome growth, disruption of microtubules did prevent polarized cell expansion. Based on these results, cotton seed trichomes are not tip-growing cells but expand via diffuse growth. Key words: cytoskeleton, freeze-fixation, freeze-substitution, Gossypium hirsutum, lint fibers, tip growth, trichomes.

Intrusive growth of flax phloem fibers is of intercalary type

“…In the intrusively elongating flax fiber, the microtubules in the subapex, on the contrary, were either aligned transversally to the long axis of the cell, or they had a helical orientation. Such orientations are typical for diffusely elongating cells (Tiwari and Wilkins 1995;Wasteneys and Galway 2003).…”

The Control of Single-Celled Cotton Fiber Elongation by Developmentally Reversible Gating of Plasmodesmata and Coordinated Expression of Sucrose and K+ Transporters and Expansin

“…Each cotton fiber is a single cell and elongates from 10 to 15 m up to 2.5 to 3.0 cm by ‫ف‬ 16 days after anthesis (DAA) before it switches to secondary cell wall cellulose synthesis (Basra and Malik, 1984;Tiwari and Wilkins, 1995). The rate of fiber elongation and the final length attained are well above that commonly seen for plant cells (Cosgrove, 1997) and render it perhaps the longest single cell in higher plants.…”

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