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Title: HETEROGENEITY OF PHOTOSYSTEM II DURING THE CELL CYCLE OF THE GREEN ALGA SCENEDESMUS QUADRICAUDA PLANT PHYSIOLOGY (J) VOL. 120 PP. 433-441

Author
item KAFTAN, D - PLANT BIOLOGY UOFI URBANA
item MESZAROS, T - PLANT BIOLOGY UOFI URBANA
item NEDBAL, L - PLANT BIOLOGY UOFI URBANA
item WHITMARSH, CLIFFORD

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/1/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: Photosynthesis is the driving force for plant growth and productivity. The factors that limit photosynthetic performance, particularly the rate and efficiency of photosynthesis, are poorly understood. The first stage of photosynthesis involves light harvesting and electron transport and depends on metal containing protein complexes known as photosystem II and photosystem I. In earlier work we showed that as many as one-third of the photosystem II complexes do not work properly, and as a result do not contribute to photosynthesis. We are trying to understand why plants devote energy and resources for the construction and maintenance of photosystem II complexes that appear to be wasteful. In this study we measured the performance of different forms of the photosystem II complex during the cell development. Our results show that just prior to and during cell division that the photosystem II complex appears to limit overall photosynthesis, but is not limiting at the peak of photosynthetic activity. This information furthers our understanding of the role of photosystem II in controlling photosynthetic performance.

Technical Abstract: The photosynthetic activity of the green alga Scenedesmus quadricauda was investigated during synchronous growth in light/dark cycles. The rate of photosynthesis varied more than twofold during the cell cycle. To assess the role of photosystem II in modulating overall photosynthesis we measured two types of photosystem II heterogeneity - one based on electron transport activity, which identifies inactive photosystem, II centers, and one based on antenna size. The results show that at the time of the maximum photosynthetic capacity, there are no photosystem II beta centers, the antenna size of active photosystem II active centers is at a minimum, and the proportion of inactive photosystem II centers is the same as detected at the onset of the light period. The minimum photosynthetic activity coincided with a substantial increase in the proportion of inactive photosystem II centers, and with an increase in stacking of the thylakoid membranes. These data indicate photosystem II does not limit photosynthetic activity during the first half of the light period. However, the low photosynthetic activity observed prior to and during cell division can be accounted for by a limited capacity of photosystem II, which corresponded to an increase in proportion of inactive photosystem II centers.