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Plant Physiology 51:1117-1126 (1973)
© 1973 American Society of Plant Biologists

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Articles

Development of Photochemical Activity and the Appearance of the High Potential Form of Cytochrome b-559 in Greening Barley Seedlings

Knud W. Henningsen1 and N. K. Boardman

a Division of Plant Industry, Commonwealth Scientific and Industrial Research Organization, Canberra 2601, Australia

The development of photochemical activity during the greening of dark-grown barley seedlings (Hordeum vulgare L. cv. Svalöfs Bonus) was studied in relation to the formation of the high potential form of cytochrome b-559 (cytochrome b-559HP). Photosynthetic oxygen evolution from leaves was detected at 30 minutes of illumination. The rate of oxygen evolution per gram fresh weight of leaf was as high at 2 to 2.5 hours of greening as at 24 hours or in fully greened leaves. On a chlorophyll basis, the photosynthetic rate at 90 minutes of greening was 80-fold greater than the rate at 45 hours. It is concluded that the majority of photosynthetic units are functional at an early stage of greening, and that chlorophyll synthesis during greening serves to increase the size of the units.

Plastids showed substantial photochemical oxygen evolution after a seedling greening time of 1 hour. However, a comparison of the relative activity of leaves and plastids at 2 hours and 24 hours of greening suggests that there was some inactivation of greening plastids during isolation. Appreciable photosystem I activity was observed as early as 15 minutes of greening.

The synthesis of cytochrome b-559HP during greening does not correlate with the onset of oxygen evolution. Cytochrome b-559HP was absent from etioplasts and in most preparations of 2-hour plastids. The average amount of cytochrome b-559HP at 2 hours of greening was well below the level needed to provide 1 molecule of the carrier for each functional photosynthetic chain. The results suggest that cytochrome b-559HP is not essential for oxygen evolution. Cytochrome f, cytochrome b6, and the low potential form of cytochrome b-559 were present in the etioplast. There was little increase in the levels of these cytochromes during 24 hours of greening.

1 Permanent address: Institute of Genetics, University of Copenhagen, Denmark.






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Copyright © 1973 by the American Society of Plant Biologists