Photosynthesis in Fescue

Abstract

Chloroplasts isolated from taDl fescue, Festuca arwudinacea Schreb., showed high rates of electron transport, comparable to rates observed for spinach chloroplasts.Chloroplasts were weDl coupled and rates of electron transport from water to methyl viologen (photosystem II and I) were increased two to five times when ADP and inorganic phosphate or methylamine (uncoupler) were added to the reaction mixture. Ratios of P:2e for photosystem II plus I were found to be near 1.2. Electron transport rates from water to pphenylenediamine or 2,6dichlorobenzoquinone (photosystem II) were over 300 micromoles 02 per hour per miligram chlorophyDl, while P:.2e ratios were found to be over 0.5. The highest rates of electron transport were found in electron flow from diaminodurene to methyl viologen (photosystem I) and P:2e ratios remained near 0.5.Light intensity saturation curves for photosystem II and I, as wel as the photosystems independently, resembled curves for spinach, with saturation of electron transport in photosystem I and photosystem II separately occurring at 35% of the available light intensity (6000 microeinsteins per square meter per second). Photosystem II and I in sequence were saturated at about half this light intensity.This report, as a preliminary study of the relationship between genome content and biochemical aspects of photosynthesis, presents a characterization of the photosynthetic electron transport system of the hexaploid tall fescue. Comparisons are made with the reported photosynthetic activities in isolated spinach chloroplasts and isolated maize tissue, two systems that have been examined extensively.Because ploidy level has been shown to affect leaf morphology (19), isolation of envelope-free chloroplasts can eliminate many variations due to physical differences; thus, direct comparison of genotypes can be made. The isolation procedure for fescue appeared difficult because the cell walls are highly silicated (27) and vegetative growth is coarse. Yet, when young, soft, actively growing tissue is harvested, little starch is isolated with the chloroplasts. Rates of electron transport and phosphorylation from this tissue are high and consistent.The results presented here show that optimal conditions for electron transport in fescue chloroplasts are similar to spinach chloroplasts. Measurements of changes in 02 concentration for PSII were 300+ tmol 02/h. mg Chl, for PSI were 1,000+ t,mol 02/h-mg Chl, and for both photosystems in sequence were 30+ (24,25) and results show increased nuclear chromosome number correlating with increased photosynthetic activity.

Photosynthesis in Fescue

“…Clones of selected tall fescue genotypes were vegetatively propagated from tillers and placed into 4-inch pots for growth chamber and greenhouse studies. Plant material grown in the growth chamber was kept at a 14-h (400 ,uE m 2 s-1), 25 was cut from young, fully expanded leaves as previously described (14). Chl content and Chl a to Chl b ratios were determined by extraction in 80%1o acetone, and absorption was measured on a Perkin-Elmer 552 spectrophotometer, as described by Arnon (2).…”

“…In our previous work (14), we have shown that isolated chloroplasts from hexaploid tall fescue can exhibit high rates of chloroplast electron transport and phosphorylation. Here, we compare the commonly cultivated hexaploid to a polyploid series of tall fescue with nuclear chromosome number of 14 in the diploid through chromosome number 70 in the decaploid.…”

Photosynthesis in Tall Fescue

“…was originally collected to study photosynthesis potential in wild tall fescue relatives varying in polyploidy (18, 22,26,28). We examined the light-driven reactions in the chloroplast thylakoids using this series (21,22). After screening many genotypes at all polyploid levels (2N = 2X = 14 chromosomes through 2N = lOX = 70 chromosomes), we observed no direct.effect on photosynthetic electron transport as chromosome number varied (22 P70.…”

“…was originally collected to study photosynthesis potential in wild tall fescue relatives varying in polyploidy (18,22,26,28). We examined the light-driven reactions in the chloroplast thylakoids using this series (21,22 …”

“…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.…”