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Photosynthesis and Formation of Fats in a Diatom

G. E. FOGG
Annals of Botany
New Series, Vol. 20, No. 78 (April 1956), pp. 265-285
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/42908546
Page Count: 21
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Photosynthesis and Formation of Fats in a Diatom
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Abstract

A study has been made, using C¹⁴ as a tracer, of the variations which occur according to the physiological condition of the cells in the distribution of carbon fixed, both in the light and in the dark, by the diatom Navicula pelliculosa (Bréb.) Hilse during periods of 30 to 300 seconds. Fixation into the following cell fractions was determined : (A) material soluble in 80 per cent, ethanol but insoluble in benzene, (B) material soluble both in 80 per cent. ethanol and in benzene, and (C) material insoluble in 80 per cent. ethanol. Carbon fixed in photosynthesis was incorporated, rapidly and in amounts representing up to 70 per cent. of the total fixation, into fractions B and C, as well as into fraction A. Considerable variation was found in the proportions of carbon entering the three fractions in the light; in actively growing cells the proportion entering fraction C preponderated over that in B, corresponding to the synthesis of protein, whereas in nitrogen-deficient cells fixation in B was the greater, corresponding to the synthesis of fat. These patterns changed only slowly, over periods of days, following the transfer of cells to altered conditions of nitrate supply. However, when ammonium nitrogen was supplied to nitrogen-deficient cells a marked change in distribution of carbon fixed occurred within 5 minutes, fixation in fraction B falling to a low value and that in A rising correspondingly. In cells subjected to prolonged nitrogen-deficiency, fixation in fraction B fell to a relatively low value but the proportion which this fraction formed of the total dry matter in the cells rose as a result of an increased rate of loss from the cells of constituents other than lipides. The distribution of carbon fixed was also dependent on light intensity. Fixation in fractions B and C rose relatively to that in A as light intensity was increased up to 100 foot-candles but fell again at the highest intensity used 2,000 foot-candles. These results are discussed with particular reference to the relationship between fat accumulation and photosynthesis in algae.

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