Substrate Specificity of Chlorophyll(ide) <i>b</i> Reductase in Etioplasts of Barley (<i>Hordeurn Vulgare</i> L.)

Abstract

Enzyme activity of chlorophyll(ide) b reductase is present in etioplasts. Recently the conversion of chlorophyllide b to chlorophyll a via 7 1 ‐hydroxychlorophyll a was demonstrated in barley etioplasts. We used zinc pheophorbide b for a detailed investigation of the reduction of the 7‐formyl group to the 7 l ‐hydroxy compound in intact barley etioplasts. The reaction proceeded likewise before esterification and after esterification with phytyl diphosphate. The metal‐free pheophorbide b , that is not accepted by chlorophyll synthase for esterification, is reduced to 7 1 ‐hydroxypheophorbide a to a small extent. The zinc (13 2 S )‐pheophorbide b is at least equally well accepted for reduction as the epimer with the 13 2 R configuration of natural chlorophyll b. The reaction requires NADPH or NADH, although the latter is less effective. ATP is not required for the first step to the 7 1 ‐hydroxy compound. The significance of chlorophyll b reduction for acclimation from shade to sun leaves and for chlorophyll degradation is discussed.