The greening process in cress seedlings. II. Complexing agents and 5‐aminolevulinate inhibit accumulation of cab‐mRNA coding for the light‐harvesting chlorophyll a/b protein

Dark‐green cress seedlings were treated with 5‐aminolevulinate (ALA) or the metal complexing agents 2,2′‐bipyridyl and 8‐hydroxyquinoline. The subsequent induction of cab‐mRNA coding for the light‐harvesting chlorophyll a/b protein (LHCP) by white or far‐red light was investigated. Pretreatment with ALA 48 h after sowing yielded increased levels, the same pretreatment 72 or 96 h after sowing decreased levels of cab‐mRNA. The strongest inhibition of light induction of cab‐mRNA was found by pretreatment with 2,2′‐bipyridyl. Less inhibition was obtained by pretreatment with 8‐hydroxyquinoline. Steady‐state levels of transcripts which are not light‐regulated (actin, psbA) were only slightly decreased by pretreatment with ALA or the metal chelators, whereas no decrease was found for mRNA coding for NADPH: protochlorophyllide oxidoreductase. Run‐off transcription with isolated nuclei showed that the transcription rate was reduced by pretreatment of intact plants with the metal chelator 2,2′‐bipyridyl. The results are discussed in the context of current proposals for the role of transition metals. ALA, and chlorophyll precursors in light‐induction of gene expression.