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

Biologically active lipids increase the growth of pea stem sections within 3 hours at the same time their respiration is increased and their growth rate is more than that of the intact plant. The greater final length of the intact internode is due to a longer growth period. Both active and inactive lipids are rapidly taken up and enter all major metabolic fractions; among centrifugal fractions methyl oleate tends to label those that contain 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 and 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 is probably 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. It is most likely that the effect of lipids on growth is due to their promotion of respiration.