Protoplasma

, Volume 140, Issue 2–3, pp 141–150

Ultrastructure of the cytoskeleton in freeze-substituted pollen tubes ofNicotiana alata

  • S. A. Lancelle
  • M. Cresti
  • P. K. Hepler
Article

Summary

The ultrastructure of the cytoskeleton inNicotiana alata pollen tubes grownin vitro has been examined after rapid freeze fixation and freeze substitution (RF-FS). Whereas cytoplasmic microtubules (MTs) and especially microfilaments (MFs) are infrequently observed after conventional chemical fixation, they occur in all samples prepared by RF-FS. Cortical MTs are oriented parallel to the long axis of the pollen tube and usually appear evenly spaced around the circumference of the cell. They are always observed with other components in a structural complex that includes the following: 1. a system of MFs, in which individual elements are aligned along the sides of the MTs and crossbridged to them; 2. a system of cooriented tubular endoplasmic reticulum (ER) lying beneath the MTs, and 3. the plasma membrane (PM) to which the MTs appear to be extensively linked. The cortical cytoskeleton is thus structurally complex, and contains elements such as MFs and ER that must be considered together with the MTs in any attempt to elucidate cytoskeletal function. MTs are also observed within the vegetative cytoplasm either singly or in small groups. Observations reveal that some of these may be closely associated with the envelope of the vegetative nucleus. MTs of the generative cell, in contrast to those of the vegetative cytoplasm, occur tightly clustered in bundles and show extensive cross-bridging. These bundles, especially in the distal tail of the generative cell, are markedly undulated. MFs are observed commonly in the cytoplasm of the vegetative cell. They occur in bundles oriented predominantly parallel to the pollen tube axis. Although proof is not provided, we suggest that they are composed of actin and are responsible for generating the vigorous cytoplasmic streaming characteristic of living pollen tubes.

Keywords

Cytoskeleton Freeze substitution Nicotiana Pollen tubes Rapid freeze fixation 

Abbreviations

EGTA

ethylene glycol bis-(β-aminoethyl ether), N,N,N′,N′-tetraacetic acid

ER

endoplasmic reticulum

MF

microfilament

MT

microtubule

PEG

polyethylene glycol

PM

plasma membrane

RF-FS

rapid freeze fixation-freeze substitution

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Copyright information

© Springer-Verlag 1987

Authors and Affiliations

  • S. A. Lancelle
    • 2
  • M. Cresti
    • 1
  • P. K. Hepler
    • 2
  1. 1.Dipartimento di Biologia AmbientaleUniversita di SienaItaly
  2. 2.Botany DepartmentUniversity of MassachusettsAmherstUSA

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