Factors Associated with the Synthesis of Chlorophyll in the Dark in Seedlings of Pinus jeffreyi

Abstract

1. Chlorophyll formation in the dark and certain relationships between megagametophyte and sporophyte were studied in germinating seeds and excised seedlings of Pinus jeffreyi. Certain aspects of chlorophyll synthesis in light and darkness were also compared. 2. Embryos excised from ungerminated seeds did not form chlorophyll when grown in darkness on various extracts of megagametophytic tissues or on certain synthetic media. The chlorophyll pigments formed in light and darkness were spectroscopically similar. This is a confirmation and extension of some of Schmidt's data. 3. Seedlings separated from megagametophytes during the first few days after germination continued to form chlorophyll in the dark for a limited time, but at a slower rate than those remaining in contact with megagametophytes. 4. Seedlings separated from megagametophytes after 6 days in the dark and exposed to light of about 60 foot-candles during the following 2 days synthesized chlorophyll about four times more rapidly than similar seedlings kept in the dark, but at about the same rate as seedlings remaining in contact with their megagametophytes in the dark. 5. The increase in chlorophyll exhibited by seedlings grown in the dark in contact with megagametophytes appears to follow the curves for increase in total magnesium and dry weight. The total magnesium in ungerminated embryos, however, exceeded the amount present in the chlorophyll of the oldest plants examined. 6. Seedlings excised from megagametophytes 6 days after germination in the dark and then grown in Loo's medium in the dark increased in dry weight and total magnesium content, but they synthesized chlorophyll at the same rate and in the same quantity as similar excised seedlings grown on a medium of washed agar and Pyrex-distilled water. 7. Total ether-soluble magnesium in seedlings grown in the dark in contact with their megagametophytes increased during germination, but more slowly than magnesium incorporated in chlorophyll. Four days after the beginning of the experiment 2.5% of the total ethersoluble magnesium was attributed to that in chlorophyll; 6 days later this value was 35.2%. In seedlings separated from megagametophytes 6 days after germination and continued in the dark on Loo's medium the maximum value was 22%. 8. The rate of chlorophyll synthesis and the maximum amount formed in the dark by seedlings separated from megagametophytes and grown in the dark varies with the duration of contact of these two seed components during germination and preceding separation. 9. The temperature coefficient for chlorophyll production in the dark by seedlings separated on the sixth day after commencement of germination was estimated to be 1.69 in the temperature interval 11⚬-23.5⚬ C. Chlorophyll accumulation at 34⚬ C. and at 37⚬ C. was considerably below that at 23.5⚬ C. 10. The possibility that different, or fewer, steps in the synthesis of chlorophyll are photochemical in P. jeffreyi than have been described for etiolated angiosperm seedlings is discussed.