Abstract
Changes in morphology of chloroplast nuclei (cp-nuclei), total cp-DNA content,number of cp-nuclei, oxygen-evolution activity and chlorophyll (a and b) content wereexamined during the degeneration and development of chloroplasts, usin Chlamydomonasgreinhardii cells which had been incubated on solid medium for various periods.Under 4'-6-diamidino-2-phenylindole (DAPI) epifluorescence microscopy, eachcell that had been incubated for 7 days had one cell nucleus, one cup-shaped chloroplastand abou 1t 0 small, dispersed cp-nuclei in the chloroplast. One day after incubationof these cells on fresh medium, the cell volume and cp-nuclei increased in size 2-3 fold,but rapidly decreased in size after cell division. Afte 7 days orf abou incubationt , cellsceased to divide and cp-nuclei began to associate with each other. At about 20 daysthey formed a ring-shaped structure surrounding the pyrenoid, followed by condensationinto one cp-nuclear particle near the pyrenoid. When 41-day-old cells, having only onecp-nucleus, were reinoculated on fresh solid medium, the cp-nucleus increased in size2-3 fold, divided into several cp-nuclear particles and then dispersed into the chloroplast,forming a bead-like structure, before cell division. From microscopic fluorometry,a 4-fold increase in total cp-DNA content per chloroplast, without an increase in thenumber of cp-nuclear particles per chloroplast, occurred one day after the start of theexperiment and one day after reinoculation of 41-day-old cells onto fresh medium. Theprocess of condensation of dispersed cp-nuclear particles into one cp-nucleus duringdegeneration of the chloroplast was not accompanied by any change in total cp-DNAcontent per chloroplast. A large peak of oxygen-evolution (0.6-0.9 pmoles/cell/hour)was seen one day after inoculation and reinoculation of the cells. The chlorophyllcontent (a+b) was high (1.2-2.2 pg/cell) during the first week of incubation, after whichit gradually decreased.Key words: Chlamydomonas — Chloroplast degeneration — Chloroplast development— Cp-DNA — Cp-nucleus — Oxygen evolution.
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