Correlation between 5-aminolaevulinate accumulation and protochlorophyll photoconversion.

A 1-min light pulse delivered to mustard seedlings (Sinapis alba L.) 60 h after sowing initiates the release of cotyledonary 5-aminolaevulinate (ALA) accumulation which continues for at least 2 h in the dark. Phytochrome (P fr) increases the rate of ALA accumulation after a 24-h red light pretreatment but is not the trigger for this release. It is shown that the rate of ALA accumulation varies with the wave-length and fluence rate of the 1-min light pulse and can be predicted from the degree of protochlorophyll-(ide) photoconversion. There is a linear correlation between the rate of ALA accumulation and the degree of protochlorophyll(ide) (PChl)→chlorophyll(ide) a (Chl a) photoconversion in etiolated seedlings. In seedlings pretreated with red light this correlation is non-linear and the rate increases more rapidly with increasing degrees of PChl→Chl a photoconversion. It is suggested that there may exist an interaction between P fr and PChl→Chl a photoconversion in controlling ALA accumulation.