Correlation between the endogenous circadian rhythmicity in growth rate and fluctuations in oleic acid content in expanding stems of Chenopodium rubrum L.

Chenopodium rubrum L. plants exhibit an endogenous circadian rhythm in their instantaneous stem extension rate in continuous light (A. Lecharny and E. Wagner, 1984, Physiol. Plant. 60, 447–453). Stem extension rate and fatty-acid composition of two stem parts were measured in plants kept in continuous light for 90 h following a 12-h dark period. Fluctuations in the relative size of the oleic acid pool were evidenced in the stem tissues. The peaks (minima and maxima) of the oleic acid content occurred at the same times after the end of the 12-h dark periods as the peaks of the stem extension rate. This rhythmic behaviour ceased when growth was completed. No significant rhythmic changes were observed in any other fatty acid pools. Lipids in which the oleate content is rhythmically modified were exclusively phosphatidylcholine and phospha-tidylethanolamine. Thus, there was a specific correlation between the relative amount of oleic acid in phosphatidylcholine and phosphatidylethanolamine and the rate of instantaneous growth in the same tissue. The rhythmic variations in the oleic acid may be linked to the endomembrane flow in relation to the rate of growth.