Effect of Daylength on Phenol Metabolism in the Leaves of Salvia occidentalis

A method of phenol determination in plant leaves has been developed which is based on the in situ oxidation of these compounds in an atmosphere containing ammonia, followed by difference spectrophotometry. The development of the phenol pattern has been studied in each separate leaf of a Salvia occidentalis plant grown in short and in long days. During the light period the phenol content (mainly chlorogenic acid and isochlorogenic acids) increases in proportion to the length of this period, whereas during the subsequent dark period the phenol content decreases. This decrease does not continue during the second part of a dark period if that period is interrupted by a light break with red light. Instead a small increase is observed. This effect of red light can be reversed with far red light. It is argued that a correlation with flower induction in this short day plant can be construed if it is assumed that the continuous presence of certain o-dihydroxyphenols in the cytoplasm of leaf cells inhibits the synthesis or the transport of a flowering hormone.