Patterns of syntheses during internodal growth of Pisum stems

Abstract

The sequential (correlative) growth of the internodes of etiolated Pisum plants has been studied by determinations of the deposition of organic and inorganic matter, comprising 4 cell wall fractions, 5 N-fractions, and 7 mineral nutrient elements during 4 days for the first 4 internodes and the buds. The S-shaped internode growth curve can be derived from the simpler time courses of meristem activity and cell elongation which must be considered separately. Pectin synthesis has a sharp maximum during the cell divisions, lignification also starts early. Cellulose and protein syntheses are maximal during the most rapid internode elongation, which means when maximal number of cell units are elongating simultaneously. RNA-synthesis and breakdown are closely related to cell divisions and cessation of cell elongation respectively, leading to a net loss when cell divisions have ceased. There is practically no net synthesis of RNA during the mentioned period of most rapid internode elongation. Not further identified hemicellulose and rest-N are accumulated nearly up to the cessation of internode elongation, indicating that there is no nutrient deficiency. There is a small loss of only soluble α-amino-N when growth ceases. Factors limiting cell elongation and internode elongation are discussed. Protoxylem is very early differentiated through the meristem. Studies on the transport mechanism are in progress.