Control of chlorophyll synthesis by phytochrome : I. The effect of phytochrome on the formation of 5-aminolevulinate in mustard seedlings.

Treatment of mustard (Sinapis alba L.) seedlings with levulinate leads to the inhibition of chlorophyll synthesis and causes the accumulation of 5-aminolevulinate which is only formed in light. A stoichiometric relationship exists between the extent of inhibition of chlorophyll synthesis and 5-aminolevulinate accumulation. The formation of 5-aminolevulinate in continuous white light is increased by pre-irradiation. The effect of the preirradiation can be fully attributed to phytochrome. Under various light conditions the rate of 5-aminolevulinate formation in levulinate-treated seedlings is similar to the rate of chlorophyll accumulation in seedlings not treated with levulinate. This result supports the hypothesis that the phytochrome-controlled chlorophyll accumulation is regulated at the level of the formation of 5-aminolevulinate.