Changes in Molecular Weight of Cellulose in the Pea Epicotyl during Growth

Abstract

A procedure is described for preparing cellulose nitrate from pea tissues (Pisum sativum L. var. Alaska) in quantitative yield, undegraded and uncontaminated by other polysaccharides. The average degree of polymerization of this product, estimated from viscosity measurements, increased during cell growth and development from a value of about 5000 glucose units in the apical meristem (plumule plus hook) to values near 8000 in fully grown maturing tissues (>20 mm from apex). The cellulose content per cell also increased (approximately 10-fold) during growth in these tissues, as did particulate glucan synthetase activity (3-fold rise). Since the yield of soluble cellulase activity is known to decrease from high values in the meristem to barely detectable amounts in mature tissues, it is suggested that the relative levels and properties of these hydrolytic and synthetic enzyme activities control the amount and degree of polymerization of cellulose formed during cell expansion in the pea epicotyl.Degree of polymerization distribution patterns showed that a low molecular weight component of cellulose (degree of polymerization < 500) was prominent in young tissues whereas high molecular weight components (degree of polymerization > 7000) predominated in mature tissues. Also, cellulose which was formed from radioactive sucrose during 30 minutes of incubation showed a remarkably similar degree of polymerization distribution to cellulose which was present in the tissue at the time of synthesis. It is concluded that new and old parts of the epicotyl cellulose framework are subject to constant modification and equilibration by cellulose-metabolizing enzymes.