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PubMed1977

Ribulose bisphosphate carboxylase: altered genetic expression in tall fescue.

A decaploid tall fescue (Festuca arundinacea Schreb) genotype has been found which exhibits net photosynthetic rates of 32 to 41 mg CO(2)/dm(2).hour as opposed to a mean of 22 mg CO(2)/dm(2).hour for 10 hexaploid genotypes. The decaploid genotype exhibited a ribulose 1,5-bisphosphate (RuBP) carboxylase specific activity 1.3- to 2-fold higher than typical tall fescue genotypes. Specific activities of photorespiratory enzymes and nitrate reduction enzymes were lower in the decaploid than the hexaploid genotypes. Results suggest that genetic expression of RuBP carboxylase activity may have been altered to increase the net photosynthesis rate in the decaploid genotype.

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PubMed1980

Photosynthesis in Grass Species Differing in Carbon Dioxide Fixation Pathways: III. OXYGEN RESPONSE AND ENZYME ACTIVITIES OF SPECIES IN THE LAXA GROUP OF PANICUM.

Measurements of CO(2) exchange at varying O(2) concentrations in seven grass species of the Laxa group of Panicum and activities of five photosynthetic enzymes were compared to values obtained for these characters in a cool season C(3) grass, tall fescue (Festuca arundinacea Schreb.) and a C(4) grass, P. maximum Jacq. Plants were divided into three groups on the basis of the inhibition of apparent photosynthesis by 21% O(2.) Rates of apparent photosynthesis in P. prionitis Griseb. and P. maximum were virtually unaffected by changes in O(2) concentration. In another group consisting of P. hylaeicum Mez., P. rivulare Trin., P. laxum Sw., and tall fescue apparent photosynthesis was inhibited by 28.2 to 36.0% at 21% O(2.) An intermediate inhibition of 20.6 to 23.3% at 21% O(2) was exhibited by P. milioides Nees ex Trin., P. schenckii Hack., and P. decipiens Nees ex Trin. The CO(2) compensation concentration for P. prionitis and P. maximum was low (</=6 microliters per liter CO(2) at 21% O(2)) and affected little by O(2), whereas values for P. hylaeicum, P. rivulare, P. laxum, and tall fescue were much greater, and increased almost linearly from 2 to 48% O(2.) Values for P. milioides, P. schenckii, and P. decipiens were intermediate to the other two groups. The effect of O(2) on total leaf conductance to CO(2) was similar to the C(3) grasses and the intermediate Panicums. However, estimates of photorespiration in the intermediate species were low and changed little with O(2) in comparison to estimates for the C(3) species which were higher and increased greatly with increased O(2.)Activities of phosphoenolpyruvate carboxylase were greatest in P. maximum and P. prionitis and one-fourth or less in the remaining species. Activity of ribulose bisphosphate carboxylase was 548 micromoles per mg chlorophyll per hour in tall fescue; activity in the remaining species was approximately one-fourth or less of that in tall fescue, with the exception of P. rivulare, in which it was 440 micromoles per milligram chlorphyll per hour. High activities of two C(4) decarboxylating enzymes, phosphoenolpyruvate carboxykinase and NADP-malic enzyme, were observed in P. maximum (1,988 micromoles per milligram chlorophyll per hour) and P. prionitis (125 micromoles per milligram chlorophyll per hour), respectively. Only minimal activities of decarboxylating enzymes were detected in the remaining species.

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PubMed1980

Photosynthesis of Grass Species Differing in Carbon Dioxide Fixation Pathways: IV. ANALYSIS OF REDUCED OXYGEN RESPONSE IN PANICUM MILIOIDES AND PANICUM SCHENCKII.

Reduced photorespiration has been reported in Panicum milioides on the basis of lower CO(2) compensation concentrations than in C(3) species, lower CO(2) evolution in the light, and less response of apparent photosynthesis to O(2) concentration. The lower response to O(2) in P. milioides could be due to reduced O(2) competition with CO(2) for reaction with ribulose 1,5-bisphosphate, to a reduced loss of CO(2), or to an initial fixation of CO(2) by phosphoenolpyruvate carboxylase. Experiments were carried out with Panicum maximum Jacq., a C(4) species having no apparent photorespiration; tall fescue (Festuca arundinacea Schreb.), a C(3) species; P. milioides Nees ex Trin.; and Panicum schenckii Hack. The latter two species are closely related and have low photorespiration rates. CO(2) exchange was measured at five CO(2) concentrations ranging from 0 to 260 microliters per liter at both 2 and 21% O(2). Mesophyll conductance or carboxylation efficiency was estimated by plotting substomatal CO(2) concentrations against apparent photosynthesis. In the C(4) species P. maximum, mesophyll conductance was 0.96 centimeters per second and was unaffected by O(2) concentration. At 21% O(2) mesophyll conductance of tall fescue was decreased 32% below the value at 2% O(2). Decreases in mesophyll conductance at 21% O(2) for P. milioides and P. schenckii were similar to that for tall fescue. On the other hand, loss of CO(2) in CO(2)-free air, estimated by extrapolating the CO(2) response curve to zero CO(2), was increased from 1.8 to 6.5 milligrams per square decimeter per hour in tall fescue as O(2) was raised from 2-21%. Loss of CO(2) was less than 1 milligram per square decimeter per hour for P. milioides and P. schenckii and was unaffected by O(2). The results suggest that the reduced O(2) response in P. milioides and P. schenckii is due to a lower loss of CO(2) in the light rather than less inhibition of carboxylation by O(2), since the decrease in carboxylation efficiency at 21% O(2) was similar for P. milioides, P. schenckii, and tall fescue. The inhibition of apparent photosynthesis by 21% O(2) in these three species at low light intensities was similar at 31 to 36% which also indicates similar O(2) effects on carboxylation. Apparent photosynthesis at high light intensity was inhibited less by 21% O(2) in P. milioides (16.8%) and P. schenckii (23.8%) than in tall fescue (28.4%). This lower inhibition in the Panicum species may have been due to a higher degree of recycling of photorespired CO(2) in these species than in tall fescue.

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PubMed1980

Photosynthesis of Grass Species Differing in Carbon Dioxide Fixation Pathways : VI. DIFFERENTIAL EFFECTS OF TEMPERATURE AND LIGHT INTENSITY ON PHOTORESPIRATION IN C(3), C(4), AND INTERMEDIATE SPECIES.

The effects of temperature and photosynthetically active radiation levels on photorespiration were investigated in Panicum milioides Nees ex Trin. and Panicum schenckii Hack., species known to have low photorespiration rates and other characteristics intermediate between C(3) and C(4) species. Comparisons were made with the C(3) grass species tall fescue (Festuca arundinacea Schreb.). An increase in temperature from 20 to 35 C raised photorespiration from 7.3 to 10.2 milligrams per square decimeter per hour in tall fescue, but the increase in P. schenckii was less than 1 milligram per square decimeter per hour. Increases in temperature caused much less change in CO(2) compensation concentration in P. milioides and P. schenckii than in tall fescue, values of 160 microliters per liter being obtained in tall fescue at 40 C compared to about 40 microliters per liter for P. milioides and P. schenckii. Photorespiration in P. schenckii increased by only about 1 milligram CO(2) per square decimeter per hour as the photosynthetically active radiation level was raised from 100 to 2,000 microEinsteins per square meter per second. Loss of CO(2) into CO(2)-free air actually decreased from 2.2 to 1.0 milligrams per square decimeter per hour as the radiation level was raised from 100 to 1,100 microEinsteins per square meter per second but tended to rise again at 2,000 microEinsteins per square meter per second. In contrast, photorespiration in tall fescue tripled with radiation level over the same range, reaching a maximum value of 7.2 milligrams per square decimeter per hour as determined by extrapolation of the CO(2) response curves to zero CO(2). The CO(2) compensation concentration in tall fescue was nearly insensitive to photosynthetically active radiation above 140 microEinsteins per square meter per second but, in P. milioides and P. schenckii, it decreased from values of 69 and 62 microliters per liter, respectively, to values of 21 and 16 as the radiation level was increased from 50 to 1075 microEinsteins per square meter per second. Interpolation of CO(2)-response curves showed that an increase in photosynthetically active radiation level from 100 to 2,000 microEinsteins per square meter per second reduced the CO(2) compensation value of P. schenckii from 38 to 19 microliters per liter. Data from these experiments indicate reduced photorespiration or a CO(2)-recycling mechanism in P. milioides and P. schenckii which causes apparent photorespiration to be nearly insensitive to temperature in the 20 to 35 C range and to decrease at high radiation intensities.

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PubMed1981

Photosynthesis in Fescue: I. HIGH RATE OF ELECTRON TRANSPORT AND PHOSPHORYLATION IN CHLOROPLASTS OF HEXAPLOID PLANTS.

Chloroplasts isolated from tall fescue, Festuca arundinacea Schreb., showed high rates of electron transport, comparable to rates observed for spinach chloroplasts.Chloroplasts were well 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 p-phenylenediamine or 2,6-dichlorobenzoquinone (photosystem II) were over 300 micromoles O(2) per hour per milligram chlorophyll, 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 well 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.

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PubMed1981

Ploidy effects on anatomy and gas exchange of tall fescue leaves.

A growth chamber study was designed to interpret differences in CO(2) exchange rate (CER) and leaf diffusive resistance among 4X, 6X, 8X, and 10X ploidy levels of tall fescue (Festuca arundinacea, Schreb). Mesophyll cell size, stomatal density, number of major and minor veins, and bundle cap size of leaf blades were evaluated. Diffusive resistance tended to decrease and CER to increase with increasing ploidy level. Mean stomatal density decreased from 43.6 per square millimeter to 30.6 per square millimeter as ploidy level increased from 4X to 8X. The 10X ploidy level exhibited the highest stomatal density, 47.2 per square millimeter. Major veins decreased from a mean of 14.2 to 10.2, and minor veins increased from a mean of 4.2 to 6.6, per leaf blade as ploidy increased from 4X to 10X. Total number of veins decreased significantly from a mean of 18.4 to 15.7 as ploidy increased from 4X to 8X.Length and width of mesophyll cells tended to increase as ploidy increased from 4X to 8X, but then decreased again at 10X. The number of cells in the bundle cap showed no trend among ploidy levels. Estimated volume of mesophyll cells increased six times between the 4X and the 6X level while chromosome number of nuclear DNA per cell increased only 50%. However, increases in estimated cell volume were proportional to chromosome number as ploidy increased from 6X to 8X. The relationship between cell volume and chromosome number at 10X was intermediate between that at 4X and 6X or 8X.Differences in stomatal density and diffusive resistance did not fully account for the ploidy effect on CER. Further mesophyll cell volume was positively related to CER, a factor contrary to earlier experiments.

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PubMed1981

Photosynthesis in Polyploid Tall Fescue : II. PHOTOSYNTHESIS AND RIBULOSE-1, 5-BISPHOSPHATE CARBOXYLASE OF POLYPLOID TALL FESCUE.

Net photosynthesis on a leaf area and leaf weight basis increased significantly with ploidy in a 4X, 6X, 8X and 10X allopolyploid series of tail fescue (Festuca arundinacea Schreb.). Total protein did not increase significantly with ploidy. Rocket immunoelectrophoresis was used to quantitate ribulose-1, 5-bisphosphate carboxylase (RuBPCase) protein. RuBPCase content, expressed on both a concentration basis and as a percentage of total protein increased significantly with ploidy in both field and greenhouse experiments. The range of RuBPCase content was 16 to 73% of total protein and 2.8 and 6.5 mg/ml of extract. Specific activity of RuBPCase did not increase significantly with ploidy. Chlorophyll concentration increased as a quadratic function of ploidy, with the mean for 8X genotypes representing maximal chlorophyll content. Evidence is presented that increasing concentrations of RuBPCase are associated with higher net photosynthesis rates in tall fescue. This suggests that RuBPCase may represent a marker for increased net photosynthesis. RuBPCase was extracted in a partially active state or inhibited state and must be fully activated by Mg(2+) and HCO(3) (-) to measure maximal activities. Polyploidization appeared to increase selectively the allocation of total protein for synthesis of RuBPCase; however, there was also a range for carboxylase content among the genotypes within a given ploidy level.

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PubMed1981

Photosynthesis in Fescue : III. RATES OF ELECTRON TRANSPORT IN A POLYPLOID SERIES OF TALL FESCUE PLANTS.

Photosystem I electron transport activity has been found to be considerably higher in a decaploid tall fescue (Festuca arundinacea Schreb.) genotype as compared to a common hexaploid genotype. The decaploid genotype also displayed a higher photosystem whole chain (Photosystem II plus Photosystem I uncoupled) activity, suggesting a connection between polyploidy and increased electron transport activity. However, when a polyploidy series of tall fescue, ranging from diploid to decaploid with several different genetic isolates at each ploidy level, was examined in natural growth conditions, no effect of increasing genome content on electron transport and photophosphorylation was found. These results suggest that a gene component of one of the genomes involved may be responsible for the increased activity rather than simply the total chromosome content.

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PubMed1983

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

We previously reported that the net photosynthetic rate of a decaploid genotype (I-16-2) of tall fescue (Festuca arundinacea Schreb.) was 32 to 41 versus 22 milligrams CO(2) per square decimeter per hour in a hexaploid genotype (V6-802) (Randall, Nelson, Asay Plant Physiol 59: 38-41). The high rate was later correlated with increases in total ribulose 1,5-bisphosphate carboxylase protein (17%) and activity (27%) (Joseph, Randall, Nelson Plant Physiol 68: 894-898). This report characterizes photosynthesis with respect to light saturation and early products of photosynthesis in an attempt to identify regulatory metabolic site(s) in these two genotypes. Analysis of the early products of photosynthesis indicated that both genotypes fixed CO(2) via the Calvin-Benson cycle with phosphoglyceric acid as the initial primary product. Both genotypes had similar (14)C-labeled intermediates. Sucrose was the primary sink of (14)CO(2) assimilation. After 10 min of (14)CO(2) assimilation with attached leaves, sucrose accounted for 89% (decaploid) and 81% (hexaploid) of the total (14)C incorporated. In 10 min, this amounted to 1.3 (decaploid) and 0.8 (hexaploid) mumol [(14)C]sucrose formed g fresh weight(-1) and reflected the observed differences in photosynthetic rates. There was limited labeling of starch (1%) and fructan (1%). Results of total nonstructural carbohydrates and P(i) analysis also demonstrated sucrose was the predominant carbohydrate in fescue leaves. Quantitative differences in sucrose and P(i) between the two genotypes may reflect changes in partitioning and this possibility is discussed.

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PubMed1984

Carbohydrate metabolism in leaf meristems of tall fescue : I. Relationship to genetically altered leaf elongation rates.

The physiological bases for genetic differences in leaf growth rates were examined in two genotypes of tall fescue (Festuca arundinacea Schreb.) selected for a 50% difference in leaf elongation rate. Genotypes had similar dark respiration rates and concentrations of carbohydrate fractions in the leaf meristem and in each daily growth segment above the meristem. Dark respiration rates and concentrations of nonreducing sugars, fructans, and takadiastase-soluble carbohydrates were highest in leaf intercalary meristems and declined acropetally with tissue age. Concentrations of reducing sugars were 1.0% of dry weight in leaf meristems, 3.7% of dry weight in tissue adjacent to the meristem, then decreased progressively with distance from the meristem. Glucose, fructose, and myo-inositol comprised over 90% of the monosaccharides present in leaf meristems. Soluble protein concentration was 9.7 milligrams per gram fresh weight in leaf meristems, 5.5 milligrams per gram in tissues immediately above the meristem and, thereafter, increased linearly with distance from the meristem.Leaf meristems of the genotype exhibiting rapid leaf elongation contained 30% more soluble protein than those of the genotype selected for slow leaf elongation. The 4-fold difference in size of the leaf meristem appeared to be more important in influencing leaf elongation than were other characteristics examined.

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PubMed1984

Carbohydrate Metabolism in Leaf Meristems of Tall Fescue : II. Relationship to Leaf Elongation Rates Modified by Nitrogen Fertilization.

Our objective was to examine alterations in carbohydrate status of leaf meristems that are associated with nitrogen-induced changes in leaf elongation rates of tall fescue (Festuca arundinacea Schreb.). Dark respiration rates, concentrations of nonstructural carbohydrates, and soluble proteins were measured in leaf intercalary meristems and adjacent segments of elongating leaves. The two genotypes used differed by 43% in leaf elongation rate. Application of high nitrogen (336 kilograms per hectare) resulted in 140% higher leaf elongation rate when compared to plants receiving low nitrogen (22 kilograms per hectare). Leaf meristems of plants receiving high and low nitrogen had dark respiration rates of 5.4 and 2.9 microliters O(2) consumed per milligram structural dry weight per hour, respectively. Concentrations of soluble proteins were lower while concentrations of fructan tended to be slightly higher in leaf meristems of low-nitrogen plants when compared to high-nitrogen plants. Concentrations of reducing sugars, nonreducing sugars, and takadiastase-soluble carbohydrate of leaf meristems were not affected by nitrogen treatment. Total nonstructural carbohydrates of leaf meristems averaged 44 and 39% of dry weight for low- and high-nitrogen plants, respectively. Within the leaf meristem, approximately 74 and 34% of the pool of total nonstructural carbohydrate could be consumed per day in high- and low-nitrogen plants, respectively, assuming no carbohydrate import to the meristem occurred. Plants were able to maintain high concentrations of nonstructural carbohydrates in leaf meristems despite a 3-fold range in leaf elongation rates, suggesting that carbohydrate synthesis and transport to leaf intercalary meristems may not limit leaf growth of these genotypes.

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PubMed1984

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.

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PubMed1987

Changes in k, rb, and na transport to shoots after anoxia.

The effect of anoxia on subsequent uptake and transport of K, Rb, and Na was examined with seedlings of barley (Hordeum vulgare L.), corn (Zea mays L.), and tall fescue (Lolium x Festuca hybrid derivative) to further our understanding of xylem loading. Roots were incubated in solutions depleted of O(2) by flushing with N(2) gas. After 1 hour exposure, plants were returned to aerated solutions for 16 hours prior to measuring uptake and transport. For each species, anoxia pretreatment significantly enhanced Na transport to the shoot. The rate of Na accumulation into roots, however, was not affected. There was no enhancement of either K or Rb accumulation in shoots, indicating specificity for Na transport. A minimum exposure to anoxia of 30 minutes and a minimum of 12 hours elapsed time was necessary to achieve the maximum rate of Na transport to the shoot in barley seedlings. Accumulation of Na in the shoot of both the control and anoxia pretreated barley plants was inhibited by anoxia and by addition of the proline analog, l-azetidine-2-carboxylic acid, during the uptake period. Enhancement of Na transport was associated with a proportional increase in the rate of synthesis of a membrane bound protein with a molecular weight of 78,000 daltons.

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PubMed1987

Assessment of spatial distribution of growth in the elongation zone of grass leaf blades.

Knowledge about the spatial distribution of growth is essential for understanding the leaf growth process. In grasses the elongation zone is located at the base of the leaf blade and is enclosed by sheaths of older leaves. Assessment of spatial growth distribution, therefore, necessitates use of a destructive method. We used a fine needle to make holes through bases of tillers at the location of the leaf elongation zone of tall fescue (Festuca arundinacea Schreb.), then measured the displacement of the holes after a 6 or 24 h interval. Needle holes caused a 22 to 41% decrease in daily leaf elongation so experiments were conducted to investigate if the spatial distribution of growth in the elongation zone was altered. Leaf elongation rate was reduced similarly when needle holes were made within or above the zone where cell elongation occurs. Distribution of elongation within the zone was the same when estimated by displacement of needle holes or ink marks placed on the epidermis of the elongation zone after surrounding tissue had been removed. Making holes at different locations within the elongation zone did not differentially affect the relative contribution of the damaged or undamaged parts to leaf elongation. These findings demonstrate that needle holes or ink marks in paired leaves can be used to estimate the relative distribution of growth in the elongation zone of undamaged tall fescue leaf blades.

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PubMed1988

Diurnal Growth of Tall Fescue Leaf Blades : II. Dry Matter Partitioning and Carbohydrate Metabolism in the Elongation Zone and Adjacent Expanded Tissue.

The spatial distributions of net deposition rates of water soluble carbohydrate-free dry matter (WSC-free DM) and WSC were evaluated within and above the elongation zone of tall fescue (Festuca arundinacea Schreb.) leaf blades during light and darkness. Imported DM used for WSC-free DM synthesis during darkness (67% of the total in experiment I and 59% in experiment II) was greater than during light (47% in both experiments), suggesting that the 65% higher leaf elongation rate during darkness was accompanied by higher rates of synthesis of cellular structural components. Deposition rates of WSC in the basal and central part of the elongation zone (0-20 mm from the ligule) were similar during light and darkness, but above 20 millimeters WSC deposition occurred during light and WSC loss occurred during darkness. WSC deposition and loss throughout the elongation zone and the recently expanded tissue were mostly due to net synthesis and degradation of fructan. Fructan was predominantly low molecular weight and contributed about 50% of the total osmotic partial pressure of WSC. In the most actively growing region, where fructan synthesis was most rapid, no diurnal change occurred in molecular weight distribution of fructan. WSC solute concentrations were diluted in the most actively growing tissue during darkness because net monosaccharide and fructan deposition were unaltered and sucrose deposition was decreased, but growth-associated water deposition was increased by 77%. Net rates of fructan synthesis and degradation were not related to tissue sucrose concentration, but appeared to respond to the balance between assimilate import and assimilate use in synthesis of cellular structural components (i.e. WSC-free DM) and deposition of monosaccharides. Fructan synthesized in tissue during most active elongation was degraded when the respective tissue reached the distal limit of the elongation zone where assimilate import in darkness was insufficient to maintain synthetic processes associated with further differentiation of cells.

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PubMed1988

Characterization of fructan from mature leaf blades and elongation zones of developing leaf blades of wheat, tall fescue, and timothy.

Water-soluble carbohydrate composition of mature (ceased expanding) leaf blades and the elongation zone of developing leaf blades was characterized in wheat (Triticum aestivum L.), tall fescue (Festuca arundinacea Schreb.), and timothy (Phleum pratense L.). These species were chosen because they differ in mean degree of polymerization (DP) of fructan in the mature leaf blade. Our objective was to compare the nature and DP of the fructan. Vegetative plants were grown with a 14-hour photoperiod and constant 21 degrees C at the leaf base. Gel permeation chromatography of leaf blade extracts showed that the apparent mean fructan DP increased in the order wheat < tall fescue < timothy. Apparent mean DP of elongation zone fructan was higher than that of leaf blade fructan in wheat and timothy, but the reverse occurred for tall fescue. Low DP (</=10) and high DP (>10) pools were found in both tissues of tall fescue and wheat, but concentration of low DP fructan was very low in either tissue of timothy. All three species have high DP fructan. Comigration with standards on thin-layer chromotography showed that wheat contained 1-kestose and a noninulin fructan oligomer series. Tall fescue contained neokestose, 1-kestose and higher oligosaccharides that comigrated with neokestose-based compounds and inulins. Thin-layer chromatography showed that small amounts of fructose-containing oligosaccharides were present in timothy.

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PubMed1989

Effects of nitrogen on mesophyll cell division and epidermal cell elongation in tall fescue leaf blades.

Leaf elongation rate (LER) in grasses is dependent on epidermal cell supply (number) and on rate and duration of epidermal cell elongation. Nitrogen (N) fertilization increases LER. Longitudinal sections from two genotypes of tall fescue (Festuca arundinacea Schreb.), which differ by 50% in LER, were used to quantify the effects of N on the components of epidermal cell elongation and on mesophyll cell division. Rate and duration of epidermal cell elongation were determined by using a relationship between cell length and displacement velocity derived from the continuity equation. Rate of epidermal cell elongation was exponential. Relative rates of epidermal cell elongation increased by 9% with high N, even though high N increased LER by 89%. Duration of cell elongation was approximately 20 h longer in the high- than in the low-LER genotype regardless of N treatment. The percentage of mesophyll cells in division was greater in the high- than in the low-LER genotype. This increased with high N in both genotypes, indicating that LER increased with cell supply. Division of mesophyll cells adjacent to abaxial epidermal cells continued after epidermal cell division stopped, until epidermal cells had elongated to a mean length of 40 micrometers in the high-LER and a mean length of 50 micrometers in the low-LER genotype. The cell cycle length for mesophyll cells was calculated to be 12 to 13 hours. Nitrogen increased mesophyll cell number more than epidermal cell number: in both genotypes, the final number of mesophyll cells adjacent to each abaxial epidermal cell was 10 with low N and 14 with high N. A spatial model is used to describe three cell development processes relevant to leaf growth. It illustrates the overlap of mesophyll cell division and epidermal cell elongation, and the transition from epidermal cell elongation to secondary cell wall deposition.

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PubMed1989

Environmental Effects on Photorespiration of C(3)-C(4) Species : I. Influence of CO(2) and O(2) during Growth on Photorespiratory Characteristics and Leaf Anatomy.

The possibility of altering CO(2) exchange of C(3)-C(4) species by growing them under various CO(2) and O(2) concentrations was examined. Growth under CO(2) concentrations of 100, 350, and 750 micromoles per mole had no significant effect on CO(2) exchange characteristics or leaf anatomy of Flaveria pringlei (C(3)), Flaveria floridana (C(3)-C(4)), or Flaveria trinervia (C(4)). Carboxylation efficiency and CO(2) compensation concentrations in leaves of F. floridana developed under the different CO(2) concentrations were intermediate to F. pringlei and F. trinervia. When grown for 12 days at an O(2) concentration of 20 millimoles per mole, apparent photosynthesis was strongly inhibited in Panicum milioides (C(3)-C(4)) and to a lesser degree in Panicum laxum (C(3)). In P. milioides, acute starch buildup was observed microscopically in both mesophyll and bundle sheath cells. Even after only 4 days exposure to 20 millimoles per mole O(2), the presence of starch was more pronounced in leaf cross-sections of P. milioides compared to those at 100 and 210 millimoles per mole. Even though this observation suggests that P. milioides has a different response to low O(2) with respect to translocation of photosynthate or sink activity than C(3) species, the concentration of total available carbohydrate increased in shoots of all species by 33% or more when grown at low O(2). This accumulation occurred even though relative growth rates of Festuca arundinacea (C(3)) and P. milioides grown for 4 days at 210 millimoles per mole O(2), were inhibited 83 and 37%, respectively, when compared to plants grown at 20 millimoles per mole O(2).

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