Developmental changes in sub-plastidic distribution of chlorophyll biosynthetic intermediates in Cucumber (Cucumis sativus L.)

Four-day-old etiolated cucumber seedlings (Cucumis sativusL.) were transferred to cool-white-fluorescent light (15 μmol m−2s−1)for 1 h and 24 hours and etiochloroplasts and chloroplasts were isolated from developing cotyledons. Plastids were fractionated to stroma, envelope and thylakoid orinner membranes and the pigment contents of all these different fractions were analysed. In intact cucumber chloroplast protochlorophyllide was present in significant amounts whereas protoporphyrin IX and Mg-protoporphyrin plus its monoester were present only in very small quantities. Out of the total chloroplastic protochlorophyllide pool 1.0 % was partitioned to envelope membranes and 99.0 % was partitioned to thylakoids. Stroma had only trace amounts of protochlorophyllide. In contrast to chloroplasts, etiochloroplasts had, besides protochlorophyllide, significant amounts of other chlorophyll biosynthetic intermediates. In etiochloroplasts, protoporphyrin IX primarily partitioned to inner membranes (59.1 %) followed by stroma (37.7 %) and envelope (3.21 %). The content of Mg-pro toporphyrin IX plus its monoester in different subplastidic fractions was 74.4 % for inner membranes, 22.58 % for stroma and 3.02 % for envelope. Protochlorophyllide primarily partitioned to inner membranes (95.79 %), followed by envelope (4.15 %) and, to a negligible extent (0.06 %), into stroma. The sub-plastidic distribution of chlorophyll biosynthetic intermediates in etiochloroplasts was, therefore, different than that of chloroplasts. The significance of differential distribution of chlorophyll biosynthetic intermediates among thylakoids, envelope and stroma in developing and mature plastids is discussed in relation to chloroplast biogenesis.