Patterns of Protein Synthesis inLolium temulentum(L.)

Abstract

The course of amino-acid incorporation was followed during successive phases of leaf development in third and fifth leaves of Lolium temulentum(L.) growing under 8- and 16-h photoperiods. Three peak periods of protein synthesis were recognized during the life span of the leaf. The first coincided with leaf expansion and reflected the formation of photosynthetic enzymes while the second occurred in the fully expanded leaf and was associated with increases in alanine aminotransferase, malate dehydrogenase, and peroxidase. A third incorporation maximum coincided with the onset of senescence, possibly representing the elaboration or release of degradative enzymes. The positioning of the first and third protein-synthesis peaks was sensitive to photoperiod but the second maximum tended to occur at a fixed point after leaf emergence. Changes during the ‘greening-up’ of etiolated leaves are also described. An over-all correlation coefficient of +0.81 was obtained for the relationship between chlorophyll content and alanine aminotransferase activity. The data are discussed in relation to the existence of pre-programmed sequences in leaf development.