Imbalances of D1 Protein Turnover during Stress Induced Chlorosis of a Declining Spruce Tree

Abstract

Development of chlorosis and loss of PSII activity were compared in a declining spruce from the Schollkopf site (Freudenstadt, Black Forest, Germany) during two vegetation periods. As a control tree, an apparently healthy, green tree was used. Loss of leaf chl content in the declining tree occurred during the development of the new flush in the second year needles. It preceded clearly any permanent functional inhibition of PSII as detected by changes in the chl fluorescence parameter F v /F m . The degradation of the photosynthetic apparatus was due to changes in thylakoid protein turnover, especially of the PSII D1 protein. Together with the loss of chl, an increase in D1 protein synthesis per chl determined by radioactive labelling was observed. It was up to 5 times higher than measured before the onset of chlorosis and more than 2 times higher than in the green control. Immunological determination by Western-blotting revealed that D1 protein content per chl decreased to 30% of the green control. Thus, D1 protein degradation was even more stimulated than its synthesis. The loss of the D1 protein was accompanied by a comparable loss of CP 47 showing that polypeptides of both the PSII reaction centre and its inner antennae were lost by degradation. This process probably prevented a large accumulation of inactivated PSII. However, together with other factors, it might initiate the breakdown of the other polypeptides, especially of LHCII, resulting in the observed chlorosis.