Photosynthesis in Tall Fescue : V. Analysis of High PSI Activity in a Decaploid Genotype

Abstract

Previous work in our laboratory (Krueger, Miles 1981 Plant Physiol 68: 1110-1114) indicated that a decaploid genotype (I-16-2) of tall fescue (Festuca arundinacea Schreb.) which exhibits unusually high net photosynthesis rates also had high potential rates of photosynthetic electron transport through photosystem I (PSI) compared to the typical hexaploid genotype (V6-802). Analysis of electron transport activity revealed that the oxidizing side of PSI as the major site of difference. Examination of the whole thylakoids and subchloroplast particle protein components of the common hexaploid and the decaploid genotypes had major polypeptide differences at 30, 21, and 12.5 kilodaltons. These differences could not be assigned to a specific physiological function in PSI. The decaploid had increased P(700) and plastocyanin content on a chlorophyll basis. Antibodies raised against fescue plastocyanin were used to quantitate plastocyanin in crude (Triton X-100) solubilized extracts of plant material. Results showed that the decaploid had 16% and 40% more plastocyanin on a weight and area basis, respectively. The antibodies did not inhibit electron transport (diaminodiurene to methyl viologen) in isolated thylakoids strengthening the hypothesis of plastocyanin as an internal mobile electron shuttle. The trend of inhibition of plastocyanin by KCN was similar in the two genotypes but the decaploid had 15 to 20% higher rates of electron flow under nearly all inhibiting conditions.