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 celiulase 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.The microfibrillar network of cellulose which encloses the protoplasts of plant cells is extensive and interwoven even in the youngest meristematic cells, and it becomes more massive and complex during growth and maturation (24). The wall framework appears to be so restrictive that biochemical reactions which have the potentiality for controlling its deposition and "loosening" have often been proposed as regulators for cell expansion (12,15,25). The problem has been to identify critical reactions and define circumstances under which they are growth limiting. In the present study, estimates were made of the amount and degree of polymerization and the DP3 distribution of cellulose in pea epicotyl tissues at different stages of development. Assays were taken or are available of levels of cellulase and cellulose synthetase activities in enzyme preparations from these same tissues. The intention was to look for evidence, i.e.. correlations, to help assess the likelihood that hydrolytic and synthetic enzymes actually operate in vivo to control the mass and chain lengths of the cellulose deposited during growth. Such correlations have been observed in Acetobacter xylinlum cultures (11). In the pea epicotyl, it is established (2,23,26) that enzymes that use activated glucose donors to form glucan which is f8-l ,4-linked and alkali-insoluble are localized in membranes. Th...

Incorporation of UDP-[14C]Glucose into Xyloglucan by Pea Membranes

“…In primary cell walls of pea stem, cellulose ranges in size from Dp2 5000 to 8000 (17), whereas xyloglucan has a mol wt of 250,000 to 350,000, i.e. a glucose backbone of approximately DP 1000 (4,10).…”

“…Such potential precursors have also been detected in vivo (1,17). Whether they represent nascent cellulose or xyloglucan is not clear (12,14).…”

Change in Molecular Size of Cellulose during Regeneration of Cell Wall on Carrot Protoplasts

“…The residue on a glass filter was washed thoroughly with petroleum ether and was stored in vacuo over CaClj and P2O5, Nitration and fractionation of cellulose. Nitration of cellulose was carried out as described by Spencer and Maclachlan (1972), Dried crude wall preparation was nitrated in a mixture of HNOj-HjPOj-PjO; (64:26; 10, w/w) for 5 h at 5°C, The nitrated product was washed on a sintered glass filter with cold 50% (v/v) acetic acid and with a copious amount of water. The residue was suspended in water and neutralized with saturated NaHCO^, then washed with water and methanol.…”

“…Nitrated cellulose was separated into a number of fractions according to the differences in solubility in acetonewater (Spencer and Maclachlan 1972), About 1 g of cellulose nitrate was dissolved in 820 ml of anhydrous acetone and 180 ml of acetone-water (1 ; 1, v/v) were added to the solution with stirring. The precipitate of the cellulose nitrate formed after 1 h was removed by centrifugation at 8000 g for 20 min, then the acetone content of the supernatant was reduced by evaporation to yield the next fraction.…”

“…They suggested that such an uncoordinate assembly of the cell wall components may occur in general in protoplast culture. Spencer and Maclachlan (1972) have studied the DP distribution pattern of cellulose in pea epicotyl and found that the average molecular weight of cellulose increased significantly during the growth. In the apical section of pea epicotyl, low molecular weight cellulose with a DP below 500 was the major component, whereas high molecular weight cellulose (DP > 7000) predominated in basal tissue sections.…”