title: The Variability of the Photosynthetic Unit in Chlorella II. The Effect of Light Intensity and Cell Development on Photosynthesis, P-700 and Cytochrome f in Homocontinuous and Synchronous Cultures of Chlorella.
abstract: The effect of light intensity of steady state photosynthesis, the contents of P-700 and cytochrome f was studied in homocontinuously grown Chlorella cells. The adaptation to higher light intensities drastically provokes the decrease of chlorophylls per dry weight, per packed cell volume and per cell. The light saturating curves show that high light grown cells produce threefold more oxygen per chlorophyll, whereas the oxygen evolution per cell is reduced by half. The rates of saturated photosynthesis per chlorophyll are directly correlated with increasing light intensities. The content of P-700 is slightly altered by light intensity. On the other hand, cytochrome f is changed in very strict accordance with the alterations of biomass productivity and photosynthetic capacity. The mathematical equation for the relationship between maximal photosynthesis and cytochrome f concentration is found to be linear with a correlation coefficient of 0.96. In addition to the results of homocontinuously grown Chlorella cells, the relationship between photosynthesis and the content of cytochrome f was analyzed in synchronous cultures. After the onset of light the photosynthetic activity rises as well as the content of cytochrome f. During the dark period, however, when the photosynthetic capacity is low, there still remains a high amount of cytochrome f. The results are discussed on the basis of the variability of the photosynthetic unit and the in-tactness of the thylakoid membrane. It is proposed to introduce the term of the «physiological photosynthetic unit» defined by the ratio of chlorophyll to cytochrome f. Its size is proved to be used as an indicator of the rate limiting step in the photosynthetic electron transport.
authors.affiliation: Institut für Allgemeine Botanik der Universität, Saarstr. 21, D-6500 Mainz, Federal Republic of Germany.
authors.forename: C
authors.initials: C
authors.lastname: Wilhelm
authors.forename: A
authors.initials: A
authors.lastname: Wild