Deposition Of Wall Components Research Articles

Calcium/Calmodulin Regulated Cell Wall Regeneration in Zea mays Mesophyll Protoplasts

Abstract The composition of newly synthesized cell walls starting from enzymatically isolated Zea mays mesophyll protoplasts was studied. The contents of pectin, cellulose and hemicellulose in addition to the wall-associated proteins were followed in the presence of increasing con­centrations of calcium ions with or without the calcium channel blockers like lanthanum, lithium ions, verapamil, nifedipine and the calmodulin antagonist trifluperazine. Pectin accu­mulation was inhibited by all antagonists except lanthanum. Cellulose formation, however, was increased by organic antagonists trifluperazine, verapamil and maximally by nifedipine while it was not affected by the inorganic ions lanthanum or lithium. Hemicellulose accumu­ lated with nifedipine present but significantly decreased by all other antagonists. Added Ca2+ (5 -10 mᴍ) reversed most of the blockers-induced inhibition on pectin and hemicellulose. In the case of cellulose, however, calcium concentration which reversed the inhibitory action of these antagonists was dependent on the antagonist. Starch exhibited little alterations indicat­ ing its minor role in deposition of wall components. Cell wall-associated proteins were negatively affected by lanthanum and verapamil and positively by lithium and nifedipine. Gen­erally, this fraction was found in a negative correlation with pectin levels. Chlorophyll contents were lowered after growth for 48 h; this might be due to repeated cell division. These results are discussed in relation to the mechanism of antagonists and effects of calcium.

Xyloglucan in the cell walls of cotton fiber

Xyloglucans occur widely in the primary walls of higher plant cells where they are bound in close association with cellulose microfibrils. Evidence was recently presented that the polysaccharide functions in the organization of cellulose microfibril assembly by preventing the fasciation of the fibrils and could aid in spreading the fiber network over the cell surface’. In pea stems, auxin treatment induces the development of endo-(1+4)-/3-D-glucanase activities and these are responsible for xyloglucan turnover 2J. The integrity of xyloglucan could then control the ability of microfibrils to loosen, and of cells to elongate and expand during growth. Cotton fibers are highly elongated cells similar in shape to pollen tubes and root hairs. However, unlike these latter cell types, cotton fibers elongate not by tip growth, but by deposition of wall components and elongation throughout the length of the fiber”‘. During elongation, the fibers deposit a primary wall similar in composition to that of many other dicot species 5 that includes xyloglucan as one component6,7. We recently showed that xyloglucan deposition is restricted to the elongation phase of fiber development ‘. The mechanism by which cell shape is determined in cotton fibers is not understood, but the interaction of xyloglucan with cellulose microfibrils and the orientation of such tibrils might be expected to play some role. In this report, we have examined the fine structure of cotton fiber xyloglucan and compared its structure to that found in cell walls of other dicotyledonous plants. Cotton fiber cell wall polysaccharides were sequentially fractionated into hot water-soluble and 24% potassium hydroxide, and an insoluble fraction. Each fraction was analyzed by methylation analysis8 and the iodine-sodium sulfate method9 in order to determine the xyloglucan content. The results indicated that 95% of total xyloglucan was concentrated in the 24% potassium hydroxide extract.