Intracellulair Organization: A Prerequisite for Root Hair Elongation and Cell Wall Deposition

Cell growth requires not only production of matter, but in addition, the targeting, transport, and delivery of this matter to the site of cell expansion. Thus, a proper organization of cell structure, the cytoarchitecture, is a necessity for cell elongation. The actual process of cell growth in a cell under turgor pressure is Golgi vesicle membrane insertion into the existing cell wall at the site of wall expansion. If one of these prerequisites is missing, growth will not occur. Thus, the Golgi vesicle is the unit of cell growth. The tip-growing cell with robust cell expansion at a defined site is a model system " par excellence" to study this process. In this chapter, we discuss the so-called tip-growth unit, i.e., the assemblage of nucleus, endoplasmic reticulum, polysomes, Golgi bodies, Golgi vesicles, exocytosis machinery, clathringcoated vesicles, endosomes, and mitochondria that specifically accumulate in the (sub)apical region of tip-growing root hairs, all working in concert to enable apical growth. The last paragraph of this chapter reviews methods used for the visualization of cellulose microfibrils