Photosynthesis in Tall Fescue : IV. Carbon Assimilation Pattern in two Genotypes of Tall Fescue Differing in Net Photosynthesis Rates

Physiological variation in populations of Ranunculus repens L. (creeping buttercup) from the temporary limestone lakes (turloughs) in the west of Ireland

A dissected-leaved form of Ranunculus repens L. occurs in the temporary limestone lakes (turloughs) across the west of Ireland. Turloughs fill with groundwater for up to 8 months of the year. Under experimental conditions, these turlough populations demonstrated a higher rate of aerial and submerged photosynthesis than populations of the more typical broad-leaved ruderal form. The turlough populations also had higher rates of stomatal conductance and exhibited a higher stomatal index on the upper leaf surface and a lower index on the lower leaf surface than the ruderal populations. Neither population could utilize bicarbonate to any great extent, with rates of photosynthesis under submerged conditions being only 5 % of aerial rates. Respiration under submerged conditions was significantly higher in the turlough populations than in ruderal populations, and it is hypothesized that the more dissected leaf shape of the turlough population may have a thinner boundary layer and thus enhance gas exchange in submerged conditions.

Photosynthate partitioning in Basal zones of tall fescue leaf blades

Elongating grass leaves have successive zones of cell division, cell elongation, and cell maturation in the basal portion of the blade and are a strong sink for photosynthate. Our objective was to determine dry matter (DM) deposition and partitioning in basal zones of elongating tall fescue (Festuca arundinacea Schreb.) leaf blades. Vegetative tall fescue plants were grown in continuous light (350 micromoles per square meter per second photosynthetic photon flux density) to obtain a constant spatial distribution of elongation growth with time. Content and net deposition rates of water-soluble carbohydrates (WSC) and DM along elongating leaf blades were determined. These data were compared with accumulation of (14)C in the basal zones following leaf-labeling with (14)CO(2). Net deposition of DM was highest in the active cell elongation zone, due mainly to deposition of WSC. The maturation zone, just distal to the elongation zone, accounted for 22% of total net deposition of DM in elongating leaves. However, the spatial profile of (14)C accumulation suggested that the elongation zone and the maturation zone were sinks of equal strength. WSC-free DM accounted for 55% of the total net DM deposition in elongating leaf blades, but only 10% of incoming (14)C-photosynthate accumulated in the water-insoluble fraction (WIF approximately WSC-free DM) after 2 hours. In the maturation zone, more WSC was used for synthesis of WSC-free DM than was imported as recent photosynthate.

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

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.