Light effects on phenylalanine ammonia-lyase substrate levels and turnover rates in maize seedlings

Abstract

If extracted phenylalanine ammonia-lyase (PAL) activity reflects in vivo activity, there should be a correlation between light-induced changes in extracted PAL activity and light-induced changes in PAL substrate turnover rates. Light-induced increases in levels of extracted PAL activity from dark- grown maize seedlings exposed to continuous white light are accompanied by corresponding decreases in free pools of phenylalanine and tyrosine, the two substrates of PAL in maize. Evidence is presented which indicates that these changes are not the result of changes in protein synthesis. The light-induced change in turnover rate of phenylalanine, is shown to be strongly correlated with light-induced PAL activity in roots of maize seedlings, indicating extracted PAL activity reflects in vivo activity.