Microfilaments are thin threads of actin

Microtubules are hollow & composed of tubulin

Actin & tubulin are proteins

The cytoskeleton is comprised of a system of non-membranous long thin proteinaceous threads distributed in the cytosol. Two types of cytoskeletal elements are found in plants: microfilaments composed of the protein actin, and microtubules composed of the protein tubulin.

Microfilaments are solid strands approximately 5-7 nm in thickness, and microtubules are hollow structures about 25 nm in thickness. Except in mitosis or meiosis, plant microtubules are usually in close association with the plasma membrane as shown in the electron micrographs at the upper left, and in the lower panel illustrating radish root rhizodermis (Raphanus sativus). They appear both in cross-sectional (lower micrograph, arrows) and longitudinal views (arrows).

The upper right-hand micrograph shows a rather unusual situation in which microtubules are associated with the tonoplast (epidermal cell from growing leaf of mullein Verbascum thapsus).