Protein phosphorylation and magnesium status regulate the degradation of the D1 reaction centre protein of Photosystem II

• Published in: Plant science (Limerick) 1996, Vol.115 (2), p.175-182
• Main Authors: Rintamäki, Eevi, Salo, Riitta, Koivuniemi, Antti, Aro, Eva-Mari
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Cell structures and functions; Chloroplast, photosynthetic membrane and photosynthesis; D1-specific proteinase; Fundamental and applied biological sciences. Psychology; Higher plants; Metabolism; Molecular and cellular biology; Moss Ceratodon purpureus; Photosynthesis, respiration. Anabolism, catabolism; Plant physiology and development; Regulation of D1 protein turnover; Thylakoid protein phosphorylation
• ISSN: 0168-9452; 1873-2259
• DOI: 10.1016/0168-9452(96)04343-9

Illumination of higher plant leaves (pumpkin, wheat and pea) at a photon flux density of 1200 μmol m −2 s −1 induced strong phosphorylation of the D1 reaction centre protein of photosystem II. Phosphorylation of D1 protein was not observed in a moss Ceratodon purpureus. To study the effect of protein phosphorylation on D1 degradation, thylakoids isolated from pumpkin leaves and Ceratodon were phosphorylated in vitro in the presence of ATP before being subjected to photoinhibitory illumination. The rate of photoinhibition of Photosystem II oxygen evolution was not influenced by phosphorylation conditions in pumpkin or Ceratodon thylakoids. D1 protein in its phosphorylated form in pumpkin thylakoids was degraded significantly more slowly whereas in Ceratodon the degradation of D1 protein occurred rapidly with or without the presence of ATP in the photoinhibitory medium. Depletion of Mg 2+ ions also blocked the degradation of unphosphorylated D1 protein in pumpkin thylakoid membranes. We conclude that degradation of the D1 protein in higher plants is regulated by phosphorylation on the substrate level and its optimal rate requires the presence of Mg 2+.