Patterns of Protein Synthesis in Lolium temulentum (L.): I. CHANGES OCCURRING DURING LEAF DEVELOPMENT

The course of amino-acid incorporation was followed during successivephases of leaf development in third and fifth leaves of Loliumtemulentum(L.) growing under 8- and 16-h photoperiods. Threepeak periods of protein synthesis were recognized during thelife span of the leaf. The first coincided with leaf expansionand reflected the formation of photosynthetic enzymes whilethe second occurred in the fully expanded leaf and was associatedwith increases in alanine aminotransferase, malate dehydrogenase,and peroxidase. A third incorporation maximum coincided withthe onset of senescence, possibly representing the elaborationor release of degradative enzymes. The positioning of the firstand third protein-synthesis peaks was sensitive to photoperiodbut the second maximum tended to occur at a fixed point afterleaf emergence. Changes during the ‘greening-up’of etiolated leaves are also described. An over-all correlation coefficient of +0.81 was obtained forthe relationship between chlorophyll content and alanine aminotransferaseactivity. The data are discussed in relation to the existenceof pre-programmed sequences in leaf development.