Cab mRNA is primarily produced when needed ie. In other words, phytochrome affects the amplitude , but not the period of cab gene expression 3. Phenylpropanoid biosynthesis genes are also activated before dawn. Enzymes in the phenylpropanoid pathway govern the production of a wide range of phenolic compounds. Included in these are flavonoid pigments, many of which absorb UV light, thereby protecting plants from UV damage.
Genes implicated in cell elongation are circadian-regulated.
C. Inputs other than light can set the circadian clock. Imbibition, but not release from stratification, sets the circadian clock in Arabidopsis seedlings.