Relationship of Lipid Metabolism to the Respiration and Growth of Pea Stem Sections

Abstract

Lipids active in increasing the growth of red-light grown seedling pea stem sections did so within 3 hours; at the same time respiration increased and growth rate was greater than that of the intact plant. The greater final length of the intact internode was due to a longer growth period. Both active and inactive lipids were taken up rapidly into all major metabolic fractions; among centrifugal fractions, methyl oleate tended to label those that contained metabolically active membranes. It is concluded that lipids active in the bioassay are probably the effective molecules at the subcellular site of action. No direct effect of lipids on isolated mitochondria could be shown. The respiration of stem tissue was not influenced by dinitrophenol or carbonyl cyano m-chlorophenyl hydrazone, although dinitrophenol inhibited growth. Lipid-induced respiration was sensitive to these agents as well as to cyanide, indicating cytochrome oxidase probably was involved. The promotion of growth and respiration by lipids is not linked to protein synthesis, since actinomycin D, puromycin, and cycloheximide failed to inhibit the respiratory increase even though strongly limiting amino-acid incorporation into protein. Lipids are thought to increase growth by promoting respiration.