Pectin's polygalacturonate single sugar chain helix visualized in Pt/C replicas

Abstract

Pectic polysaccarides are 34% by weight of tobacco cell wall materials, more than any other cell wall component (cellulose, 18.7%; hemicellulose, 11.4%; protein, 21.6%; lignin, 4.1%). During cell growth, the cell wall is loosened by acidification which then enables it to elongate by its own turgor pressure. It has been suggested that the primary action of acidification is the loosening of a calcium pectate gel which at 34% by weight must permeate the wall and bind the cell wall together. This same work suggests that minimum Ca2+binding occurs at pH 3 and lower and maximum Ca2+ binding occurs at pH 6 and that Ca2+ binding capacity is lost by treatment with polygalacturonase. If the capacity for acid-induced wall loosening Is switched on, which is dependent on protein not carbohydrate synthesis, then the rate of wall loosening is proportional to the pH between 5.7 and 4.5.