Transient Nature of a (1 --> 3), (1 --> 4)-beta-d-Glucan in Zea mays Coleoptile Cell Walls.

Excised Zea mays L. embryos were cultured on Linsmaier and Skoog medium. Coleoptiles were sampled at regular intervals and the length, fresh weight, cell wall weight, and cell wall neutral sugar composition were determined. A specific beta-d-glucanase from Bacillus subtilis was used to determine the content of a (1 --> 3),(1 --> 4)-beta-d-glucan.Coleoptiles elongated through the 5th day following imbibition with the most rapid elongation occurring between days 3 and 4. The greatest net rate of incorporation of cell wall per coleoptile occurred between the 2nd and 3rd days when deposition of approximately one-third of the maximum net glucan level was observed. By day 5, the amount of glucan present had increased 34-fold from the 6 micrograms per coleoptile on day 1 and accounted for about 14% of the cell wall (w/w). Thereafter, the glucan content declined until only 3.3% (w/w) remained by day 10. In this 10-day interval, xylose increased 32% and cellulose content doubled, while proportions of other neutral sugars changed less dramatically.These results are consistent with a possible role for the beta-d-glucan in elongation of the Zea coleoptile. Moreover, changes in the quantity of this wall component clearly reflect the dynamic nature of plant cell wall polysaccharides. An evaluation of glucan dynamics in vivo suggests that in vitro autolysis studies employing Zea coleoptile walls may overestimate the actual rate of glucan turnover in the intact tissue.