Submitted to: Plant Cell and Environment
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/23/2004
Publication Date: 2/1/2005
Citation: Ebbert, V., Adams, W.W., Mattoo, A.K., Sokolenko, A., Demmig-Adams, B. 2005. Upregulation of a psii core protein phosphatase inhibitor and sustained d1 phosphorylation in zeaxanthin-retaining, photoinhibited needles of overwintering douglas fir. Plant Cell and Environment. 28:232-240. Interpretive Summary: Plant nutrient content and yield are both related to how well a plant converts sunlight into food through the process of photosynthesis. This so-called solar energy conversion (SEC) is reduced at extreme temperatures and also around noon when the plant is trying to protect itself from extreme environments. It is important to understand these processes in order to develop strategies that would enhance SEC for food production. A major site in photosynthesis intimately involved with these aspects is a protein complex called photosystem II (PSII). In this report, we took advantage of the existence in nature of sun-exposed evergreen species that stop growing under winter stress, a process that is characterized by decreased photosynthesis and increased protection. A key finding of this study is that decreased SEC is associated with higher incidence of protective processes and a sustained modification of the key PSII protein, D1 by phosphates. These findings are important to scientists interested in understanding the basic processes and factors that limit how a plant uses solar energy in photosynthesis.
Technical Abstract: Overwintering needles of the evergreen conifer Douglas fir exhibited an association between arrest of the xanthophyll cycle in the dissipating state (as zeaxanthin + antheraxanthin; Z+A) with a strongly elevated predawn phosphorylation state of the D1 protein of the photosystem II (PSII) core. Furthermore, the high predawn phosphorylation state of PSII core proteins was associated with strongly increased levels of TLP40, the cyclophilin-like inhibitor of PSII core protein phosphatase, in winter versus summer. In turn, decreases in predawn PSII efficiency, Fv/Fm, in winter were positively correlated with pronounced decreases in the non-phosphorylated from of D1. In contrast to PSII core proteins, the light-harvesting complex of photosystem II (LHCII) did not exhibit any nocturnally sustained phosphorylation. The total level of the D1 protein was found to be the same in summer and winter in Douglas fir when proteins were extracted in a single step from whole needles. In contrast, total D1 protein levels were lower in thylakoid preparations of overwintering needles versus needles collected in summer, indicating that D1 was lost during thylakoid preparation from overwintering Douglas fir needles. In contrast to total D1, the ratio of phosphorylated to non-phosphorylated D1 as well as the levels of the PsbS protein were similar in thylakoid versus whole needle preparations. The level of the PsbS protein, that is required for pH-dependent thermal dissipation, exhibited an increase in winter, while LHCII levels remained unchanged.