Developmental changes in sub-plastidic distribution of chlorophyll biosynthetic intermediates in cucumber (Cucumis...

Four-day-old etiolated cucumber seedlings (Cucumis sativus L.) were transferred to cool-white-fluorescent light (15 mumol m-2 s-1) for 1 h and 24 hours and etiochloroplasts and chloroplasts were isolated from developing cotyledons. Plastids were fractionated to stroma, envelope and thylakoid or inner membranes and the pigment contents of all these different fractions were analysed. In intact cucumber chloroplast protochlorophylide 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 protochlorophylide pool 1.0% was partitioned to envelope membranes and 99.0% was partitioned to thylakoids. Stroma had only trace amounts of protochlorophylide. In contrast to chloroplasts, etiochloroplasts had, besides protochlorophylide, 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-protoporphyrin 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.