THE GREENING PROCESS IN CRESS SEEDLINGS .5. POSSIBLE INTERFERENCE OF CHLOROPHYLL PRECURSORS, ACCUMULATED AFTER THUJAPLICIN TREATMENT, WITH LIGHT-REGULATED EXPRESSION OF LHC GENES

Dark-grown cress seedlings were treated with beta-thujaplicin alone or in combination with 5-aminolevulinate (ALA). This treatment induced a nearly complete inhibition of protochlorophyllide (Pchlide) synthesis and a significant accumulation of magnesium protoporphyrin monomethyl ester (MgPPMe). Other porphyrins accumulated only in 48-h-old seedling s but not in 72-h-old seedlings. Levels of several mRNAs were differen tially affected by the pretreatment. The level of psbA and FOR transcr ipts was either not affected in the dark (48-h-old seedlings) or only slightly decreased (72-h-old seedlings) by thujaplicin treatment. The moderate increase of the psbA transcript level by farred light was par tly inhibited by thujaplicin in 48-h and 72-h-old seedlings. The level of the Lhc mRNA was increased by thujaplicin treatment in the dark in 48-h-old seedlings, comparable with the level achieved by light induc tion in the water controls. In contrast, the Lhc mRNA level in 72-h-ol d seedlings was slightly decreased by thujaplicin and the subsequent l ight induction was inhibited by about 50%. This inhibition of light in duction was found for all investigated single Lhc genes. Differential interference by Chl precursors other than Pchlide with Lhc gene expres sion is discussed.