Acclimation to freezing temperatures in perennial ryegrass (Lolium perenne)

The increasing demands being placed on natural grasslands in the era following the appearance of Bovine Spongiform Encephalitis require that forage crops provide a reliable extended season of growth, combined with good winter survival to ensure sward longevity. The ability to tolerate sub-zero temperatures is integral to the survival of perennial forages. Since the development of freezing tolerance is crucial to the survival and productivity of over-wintering crops, forage breeding programmes require an improved understanding of the individual characteristics that contribute to tolerance to sub-zero temperatures. Photosynthesis, carbohydrate content and changes in protein composition were investigated in two varieties of Lolium perenne which differ in their response to growth at low temperature.     

Absorption of nitrate and ammonium ions by Lolium perenne from flowing solution cultures at low root temperatures

Lolium perenne L. cv. 23 (perennial ryegrass) plants were grown in flowing solution culture and acclimatized over 49 d to low root temperature (5°C) prior to treatment at root temperatures of 3, 5, 7 and 9°C for 41 d with common air temperature of 20/15°C day/night and solution pH 5·0. The effects of root temperature on growth, uptake and assimilation of N were compared with N supplied as either NH₄ or NO3 at 10 mmol m^?3. At any given temperature, the relative growth rate (RGR) of roots exceeded that of shoots, thus the root fraction (Rf) increased with time. These effects were found in plants grown with the two N sources. Plants grown at 3 and 5°C had very high dry matter contents as reflected by the fresh weight: freeze-dried weight ratio. This ratio increased sharply, especially in roots at 7 and 9°C. Expressed on a fresh weight basis, there was no major effect of root temperature on the [N] of plants receiving NHJ but at any given temperature, the [N] in plants grown with NHJ was significantly greater than in those grown with NO₃. The specific absorption rate (SAR) of NH⁺₄ was greater at all temperatures than SAR-NO₃. In plants grown with NH⁺, 3–5% of the total N was recovered as NH⁺₄, whereas in those grown with NO^?₃ the unassimilated NO^?₃ rose sharply between 7 and 9°C to become 14 and 28% of the total N in shoots and roots, respectively. The greater assimilation of NH⁺₄ lead to concentrations of insoluble reduced N (= protein) which were 125 and 20% greater, in roots and shoots, respectively, than in NO^?₃-grown plants. Plants grown with NH⁺₄ had very much greater glutamine and asparagine concentrations in both roots and shoots, although other amino acids were more similar in Concentration to those in NO^?₃ grown plants. It is concluded that slow growth at low root temperature is not caused by restriction of the absorption or assimilation of either NH⁺₄ or NO^?₃. The additional residual N (protein) in NH⁺₄ grown plants may serve as a labile store of N which could support growth when external N supply becomes deficient.     

Cytogenetics of Lolium perenne

Summary A number of diploid inbred lines of Lolium perenne were treated with colchicine at the early seedling stage to induce chromosome doubling. In each inbred line the colchicine-treated undoubled diploids were kept as controls, as well as the normal untreated diploids. Comparisons of vegetative growth and development, involving the three treatments within each line, revealed that colchicine treatment of seedlings has long-lasting effects upon plant growth and development independent of chromosome doubling, and that for certain characteristics the effects of chromosome doubling are confounded with other effects of the treatment used to produce tetraploids. This colchicine induced variation in the diploids is transmitted through the seed generations in at least one of the inbred lines. The variation appears to be non-random and also shows a strong genotypic component. In so far as the effects of chromosome doubling could be determined, they showed the usual gigas response but were again strongly influenced by genotype.     

Cytogenetics of Lolium perenne

Summary A number of inbred lines of Lolium perenne have been developed as far as the fifth inbred generation and are being used for basic studies on the cytogenetics of the species. An analysis on variation in the pattern of chiasma frequency and distribution, including the parent plants and all generations down to the S5, reveals that the effect of inbreeding is to reduce chiasma frequency and to increase both the cell and bivalent variances. Evidence is presented for a genetic basis of polygenic control of chiasma formation and distribution, and a model is suggested for control over the three related components of variation which involves a two-stage level of regulation.     

Physicochemical characterization of cellulose from perennial ryegrass leaves (Lolium perenne)

In this study, we investigated the physicochemical properties of the cellulosic preparations obtained from both untreated perennial ryegrass leaves and de-juiced leaves. It was found that treatment at 22 degrees C with 18% NaOH and 18% KOH for 2h, and 10% NaOH and 10% KOH for 16 h yielded 28.2%, 28.8%, 22.7%, 23.4%, respectively, of 'cellulose' residue from untreated ryegrass leaves and 35.7%, 36.8%, 32.8% and 34.6%, respectively, from the de-juiced leaves. For each cellulosic fraction, the glucose content was 71.6%, 69.6%, 67.8%, 66.7%, 69.7%, 68.6%, 63.9% and 61.7%, respectively. The structure of the cellulose samples was examined using FTIR and CP/MAS (13)C NMR spectroscopy and X-ray diffraction. The cellulosic preparations were free of bound lignin except for noticeable amounts of residual hemicelluloses (28.4-38.3%), and had intrinsic viscosities between 275.1 and 361.0 mL/g, along with molecular weights from 144,130 to 194,930 g/mol. This study found that the cellulose samples isolated from both de-juiced ryegrass leaves and the untreated leaves had a much lower percent crystallinity (33.0-38.6%) than that from wood-based fibres (60-70%) and had much shorter fibres (0.35-0.49 mm) than those of either cereal straws, bagasse or wood. In addition, a partial disruption of the hydrogen bonds and microfibrils may occur during the de-juicing process by mechanical activity, which results in a decreased cellulose crystallinity and fibre length. These findings are significant in relation to hydrolysing ryegrass cellulose for bio-ethanol production.     

Submicroscopic morphology of trichophyton mentagrophytes grown at different temperatures

Several modifications were observed in Trichophyton mentagrophytes cultivated at 19° and 37 °C, i.e. nine degrees below and above the optimum of 28 °C. The phenomena included inhibition of the growth rate, changes in the gross aspects of the cultures as well as of the microscopic and submicroscopic morphology of the hyphal cells. At the ultrastructural level, in particular, it was shown that, at the suboptimal temperature, although the organelle structure in both young and aged hyphal cells remained nearly unchanged, unusual bodies of probable storage significance and plasmalemmasomes were formed.At the supraoptimal temperature, the youngest cells showed a normal organization but were richer in glycogen clusters and enveloped by a cell wall thicker than the ones at the optimal condition. In the cells far from the apex, the endomembrane integrity was lost and consequently an autolytic activity occurred. Degradation phenomena were detectable also at cell wall level. The cytological changes observed were tentatively correlated with a possible different sensitivity of the membrane system at the experimented temperature conditions.Investigation supported by a grant from Consiglio Nazionale delle Ricerche of Italy (Contract No. 7500536).     

Photosynthesis and Photorespiration in Lolium multiflorum and Lolium perenne

The response of net photosynthesis to changing light-flux densityby leaves of Lolium multiflorum (S. 22) and L. perenne (S. 321)is more adequately described by current models when a term allowingfor photorespiration is included. The magnitude of this termwas determined from the changes in the slope of the light-responsecurves for net photosynthesis. A pseudo first-order rate-constantfor photorespiration, and a pseudo second-order rate-constantfor photosynthesis calculated by this technique for L. multiflorumwere found to be similar to corresponding parameters calculatedfrom light-compensation-point measurements using a simple modeldescribed by Brown (1969). The relative magnitudes of respirationand photosynthesis at light saturation for both Lolium specieswere similar to reported values for other temperate species(Lake, 1967). Two selection lines of L. perenne (S. 321) with contrastingdry-matter yields were found to have the same parameters forrespiration and photosynthesis.     

Buoyancy regulation in Microcystis aeruginosa grown at different temperatures

Abstract The buoyancy regulation in light-limited cultures of the gas vacuolate cyanobacterium Microcystis aeruginosa AK1 was studied at three temperatures, 15, 20 and 28°C. At the two highest temperatures the organism remained buoyant during the entire light period, whereas at the lowest temperature the buoyancy was reduced at the start of the light period. With this temperature the buoyancy was lost during the light period. This reduced buoyancy was caused by an increase in ballast and a decrease in the gas vesicle volume. Buoyancy changes during a transient state with slow changes in temperatures, i.e., 1°C per day, were caused by changes in polysaccharide ballast. The gas vesicle volume showed no significant change during the transient state.
The maximal photosynthetic rate was dependent upon the growth and incubation temperature, whereas the light harvesting efficiency was independent of the temperature. The results are discussed in an ecological context.     

Effects of elevated CO2 concentration and climate-warming on photosynthesis during winter in Lolium perenne

Long-term effects of atmospheric carbon dioxide concentration(ambient or 700 µmol mol^–1) and air temperature(simulation of field conditions or + 4 C) on leaf photosyntheticrate were examined in Lolium perenne L. cv. Vigor, exposed tonatural illumination during winter. Photosynthetic capacitywas compared over a range of air temperatures and photon fluxdensities of photosynthetically active radiation which wererepresentative of winter climate (5–15 C and 0–500µmol m^–2s^–1), with CO₂ level during measurementsimilar to that during the experimental period. Long-term exposureto increased air temperature reduced leaf CO₂ fixation capacityby 23% (averaged over all measurement conditions), resultingfrom a decline in lightsaturated uptake rate, but not in incident-lightquantum efficiency. CO₂- stimulation was largely absent in plantsgrown in ambient temperature, but pronounced in plants grownunder +4 C, where it compensated for two-thirds of the 23%drop. This enhancing effect of elevated CO₂ level on leaf CO₂uptake rate observed in the warmer treatment, was strongly dependenton measurement temperature, increasing from 5% at 5 C, to upto 32% at 15 C. Measurements of chlorophyll fluorescence anddry matter corresponded with the observed changes in assimilationcapacity, which could not be attributed to a deteriorated nitrogenstatus of the leaves as there was a similar N content on anarea basis. Several hypotheses are considered to explain theobserved CO₂-temperature interactions. Key words: Acclimation, chlorophyll fluorescence, elevated CO₂ level, global warming, low temperature     

Catalase activity in arctic microfungi grown at different temperatures

The total of 98 strains of moulds were isolated from soils collected in arctic tundra (Spitzbergen). Among these strains Penicillium cyclopium 1, the most effective for production of catalase, was selected by the method of test-tube microculture. The time course of growth and catalase production by this strain showed the intracellular activity of this enzyme to be about 3-fold higher than its extracellular level Some properties of crude catalase preparation, isolated from postculture liquids by lyophilization, were also examined. Catalase activity showed its maximum at 15 degrees C, indicating adaptation of the enzyme to lower temperatures of the arctic environment.     

Leaf photosynthesis in pure swards of two grasses (Lolium perenne and Lolium multiflorum) subjected to contrasting intensities of defoliation

Photosynthetic rates were measured on light saturated, fully-expanded leaves in pure swards of Lolium perenne and Lolium multiflorum during late summer using 14-carbon dioxide. These swards were defoliated by cutting at three heights of 3, 6 and 9 cm above the ground. The photosynthetic rates of leaves on tillers in swards cut constantly 3 cm above ground level were higher than those of leaves in swards cut constantly 9 cm above ground level. Additional treatments with various sequences of cuts 3, 6 and 9 cm above ground level were designed to reduce damage to the growing points of tillers whilst ensuring satisfactory harvesting of the shoots. The photosynthetic rates of leaves on tillers cut to various heights above ground level at successive harvests were intermediate between those of similar leaves in the constantly low and high cut swards. The rates of photosynthesis of Italian ryegrass leaves were higher than those of perennial ryegrass leaves for a short time after defoliation of the constantly high cut swards. However, these perennial ryegrass leaves quickly adapted their rates of photosynthesis to the higher irradiances they received after cutting. Thus grass species differing in morphology adjust to management practices by the use of different photosynthetic strategies.     

Models for mesophyll cell arrangement in leaves of ryegrass (Lolium perenne L.)

Summary Three models for mesophyll cell arrangement in leaves of Lolium perenne L. are described. It is shown that mesophyll cells may be represented as spheres packed in a tetragonal lattice. The need to quantify mesophyll cell arrangement is discussed in relation to leaf photosynthesis.The variation on measurements of some anatomical features of leaves is examined and discussed.     

Regulation of photosynthesis and antioxidant metabolism in maize leaves at optimal and chilling temperatures: review

Maize (Zea mays L.) is a chilling (below 15 °C) sensitive plant that shows little capacity to acclimate to low growth temperatures. Maize leaves are extremely sensitive to chilling injury, which usually results in premature leaf senescence. Leaves exposed to temperatures below 10 °C in the light show substantial inhibition of CO₂ assimilation and down-regulation of photosynthetic electron transport. However, the intrinsic relationships between the quantum efficiencies of photosystems I and II are not modified by chilling. Moreover, the integral relationships between non-cyclic electron transport and CO₂ fixation are similar in chilled and unchilled leaves. In this review we examine the roles and importance of photosynthetic regulation, carbon metabolism and antioxidant metabolism in determining the sensitivity of maize leaf photosynthesis to chilling. The distinct cellular localisation patterns of antioxidant enzymes such as glutathione reductase (EC 1.6.4.2) and dehydroascorbate reductase (EC 1.8.5.1) can restrict the recycling of antioxidants associated with photosynthesis during chilling. Disruption of circadian regulation of metabolism and insufficient antioxidant defence are postulated to cause chilling sensitivity.     

Phase separations in membranes of Anacystis nidulans grown at different temperatures

Freeze fracture electron microscopy studies were performed on samples of Anacystis nidulans quenched from different temperatures. Membrane lipid phase separations were observed to take place over the ranges 15–30°C, 5–25°C and –5–15°C for cultures grown at 38, 28 and 18°C, respectively. Differential scanning calorimetry heating curves showed endotherms which coincided with these temperature ranges. Variations of phase separation temperatures with growth temperature, and hysteresis effects in the calorimetric measurements, were related to changes in the fatty acid composition of membrane lipids.     

Growth, photosynthesis and assimilate partitioning in Lolium temulentum exposed to chilling temperatures

Vegetative plants of Lolium temulentum L, grown at 20°C with an 8 h photoperiod were transferred to either 5 or 2°C (8 h photoperiod) at 4th leaf maturity. Measurement of dry weight gain indicated a marked decline in relative growth rate below 5°C, with growth being reduced as much between 5 and 2°C as between 20 and 5°C. This reduction was not associated with increased mortality and was reversible if plants were returned to 20°C. Tissue explants from cold-treated plants retained the ability to extend if returned to 20°C Rates of extension in explants were less temperature sensitive than the relative growth rates observed in intact plants. Measurements of photosynthetic capacity, and of the patterns of accumulation of reserve carbohydrate in plants exposed to different temperatures, suggested that the inhibition of growth caused by chilling is not caused by an inability of the plants to fix sufficient carbon.     

Immunochemistry of Yersinia enterocolitica O3 grown at different temperatures.

Comparative agglutinations of homogeneous stable suspensions prepared with Yersinia enterocolitica growth at 37 degrees C and at 25 degrees C were performed with anti-sera prepared in rabbits with the bacteria grown at both these temperatures. Sera prepared with live Y. enterocolitica grown at 37 degrees C agglutinated both suspensions at a much lower titre than the sera prepared with formaldehyde-treated bacteria is grown at 25 degrees C. All the sera in which strongly precipitating antibodies were induced reacted, in agar-gel, against native and heated proteins. The small amounts of antipolysaccharides induced in all the sera reacted only in the ring test against the bacterial polysaccharides. The absorption of the sera prepared with live Y. enterocolitica grown at 37 degrees C, with antigens synthesized at 25 degrees C did not remove all the homologous antibodies; apparently, some determinants are specific for the bacteria grown at 37 degrees C. Morphological changes of the small rods to elongated bacilli and filamentous forms were observed in most cultures of the Y. enterocolitica grown at 37 degrees C; these changes coincided with a low yield of proteins and point to an inhibitory effect of the 37 degrees C temperature.     

Effect of S-methylmethionine on the photosynthesis in maize at different chilling temperatures

The effect of the natural compound S-methylmethionine (SMM) on the functioning of the photosynthetic apparatus, the efficiency of photosynthesis and the synthesis of stress-induced phenoloids and anthocyanins involved in defence was investigated in young maize plants exposed to moderate and severe chilling stress. Damage to PSII was observed as a reduction in the value of variable fluorescence (Fv/Fm) which could be detected even after few hours of mild chilling stress. At temperatures below 10°C, the reduction in Fv/Fm was more pronounced. Changes in the value of net photosynthesis exhibited a similar tendency. SMM has a moderating effect on this reduction and its protective effect was more pronounced under long-lasting chilling stress and at the lowest temperatures. Monitoring of fluorescence intensities and ratios correlated with the levels of stress defence compounds. The fluorescence intensities were found to increase over the course of chilling stress in response to SMM, with the highest values being recorded in plants exposed to the longest period of stress. A similar tendency was observed for the quantity of anthocyanins. The results confirm the complex role of SMM, which is manifested both in preserving the ability of the photosynthetic apparatus to function and in stimulating the synthesis of metabolites involved in stress defence.