The greening process in cress seedlings. V. Possible interference of chlorophyll precursors, accumulated after thujaplicin treatment, with light-regulated expression of Lhc genes

Abstract

Dark-grown cress seedlings were treated with β-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 monomethylester (MgPPMe). Other porphyrins accumulated only in 48-h-old seedlings but not in 72-h-old seedlings. Levels of several mRNAs were differentially affected by pretreatment. The level of psbA and POR transcripts 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 partly 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 induction in the water controls. In contrast, the Lhc mRNA level in 72-h-old seedlings was slightly decreased by thujaplicin and the subsequent light induction was inhibited by about 50%. This inhibition of light induction was found for all investigated single Lhc genes. Differential interference by Chl precursors other than Pchlide with Lhc gene expression is discussed.