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161.
Simulated swards of each of two selection lines of Lolium perennecv. S23 with fast and slow ratesof mature tissue respiration were establishedin growth rooms at 20/15 °C day/night temperatures and studiedover four successive regrowth periods of 46, 30, 26 and 53 daysduration. The slow line outyielded the fast,both in harvestable shoot (above a 5 cm cut) and in root andstubble. Its advantage increased over successive regrowth periodsto 23 per cent (total biomass). Gas analysis measurements onthe entire communities (including roots), during the final regrowthperiod, showed that the slow line had a 2234per cent lower rate of dark respiration per unit dry weight.This enabled it to maintain its greater mass of tissue for thesame cost in terms of CO2 efflux per unit ground area. Halfthe extra dry weight produced by the slow line,relative to the fast, could be attributed to itsmore economic use of carbon. The rest could be traced to a 25per cent greater tiller number which enabled the slowline to expand leaf area faster (though not at a greater rateper tiller), intercept more light and fix more carbon, earlyin the regrowth period. Lolium perenne L., ryegrass, respiration, maintenance respiration, tiller production, simulated swards, canopy photosynthesis, carbon economy 相似文献
162.
Measurements of CO2 exchange were used to construct a detailedaccount of the carbon economy of established simulated swardsof perennial ryegrass during 10 week periods in spring and autumn.Changes in sward dry weight estimated from gas exchange measurementsclosely matched observed changes in dry weight. In spring, light energy increased, the photosynthetic potentialof the canopy increased, and together these factors led to apattern of increasing photosynthetic uptake. In autumn, decreasinglight energy and decreasing canopy photosynthetic potentialled to decreasing photosynthetic uptake. During the periodsinvestigated, the changes in light energy receipt played themajor role in determining the pattern of photosynthetic uptake. A simple model of crop growth was used to illustrate the effectof such characteristic seasonal differences in the pattern ofphotosynthetic uptake on the subsequent loss of carbon duringrespiration and tissue death, and consequently on the productionof live tissue. The model describes how a reproductive cropin spring may accumulate more living dry matter than a vegetativecrop in autumn from the same total gross photosynthetic uptakeof carbon. Lolium perenne L., ryegrass, carbon economy, photosynthesis, respiration 相似文献
163.
164.
Shechinah Felice Choragudi Ganesh Kumar Veeramachaneni BV Raman Bondili JS 《Bioinformation》2014,10(8):507-511
Endo- β-N-acetylgucosaminidases (ENGases) are the enzymes that catalyze both hydrolysis and
transglycosylation reactions. It is of interest to study ENGases because of their ability to synthesize glycopeptides.
Homology models of Human, Arabidopsis thaliana and Sorghum ENGases were developed and their active sites
marked based on information available from Arthrobacter protophormiae (PDB ID: 3FHQ) ENGase. Further, these
models were docked with the natural substrate GlcNAc-Asn and the inhibitor Man3GlcNAc-thiazoline. The catalytic
triad of Asn, Glu and Tyr (N171, E173 and Y205 of bacteria) were found to be conserved across the phyla. The crucial
Y299F mutation showing 3 times higher transglycosylation activity than in wild type Endo-A is known. The hydrolytic
activity remained unchanged in bacteria, while the transglycosylation activity increased. This Y to F change is found
to be naturally evolved and should be attributing higher transglycosylation rates in human and Arabidopsis thaliana
ENGases. Ligand interactions Ligplots revealed the interaction of amino acids with hydrophobic side chains and polar
uncharged side chain amino acids. Thus, structure based molecular model-ligand interactions provide insights into
the catalytic mechanism of ENGases and assist in the rational engineering of ENGases. 相似文献
165.
We report here the isolation in the house sparrow Passer domesticus of a highly variable minisatellite locus. When used as a probe at high stringency, this minisatellite crosshybridizes to a specific and variable locus in many different species in the family Passeridae. Moreover, it also detects a variable locus in species belonging to several other families of passerines which suggests that this probe will be useful in at least one–third, and perhaps about one–half, of all bird species. 相似文献
166.
To determine whether freezing causes wide-spread cavitationin the xylem of freezing trees, pressure and temperature weremeasured inside freezing conifer sapwood blocks. Pressure risesof up to 3.3 MPa were recorded and average radial growth velocitiesof ice were between 1.75 and 2.3 µm sl. These growthvelocities of ice are less than the minimum growth velocityfor bubble nucleation during freezing. To complement this experimental study finite difference modelsof freezing in a single tracheid and freezing in an idealizedtree stem were constructed. The single tracheid model predictspressure rises similar to those measured experimentally. Thismodel also predicts that 5% to 8% of water in a tracheid lumenmigrates out of the tracheid during freezing. The tree stemmodel predicts growth velocities of ice three times faster thanthe values measured experimentally. These results are compared with previous contradictory theoriesof freezing in conifers. Key words: Freezing, xylem 相似文献
167.
168.
White clover (Trifolium repens L.) plants were grown from seedin perlite, inoculated with effective rhizobia and exposed tothe same concentration x days of 15N-labellednitrate in four contrasting patterns of doses. Acetylene reductionwas measured at intervals using an open, continuous-flow sytem.Mean dry weight per nodule and rates of acetylene reductionfell rapidly (23 d) during periods of exposure to highnitrate concentrations (> 7 mM N) and rose again, equallyrapidly, when nitrate was withdrawn or substantially reduced.The fall in mean dry weight per nodule (5066 per cent)was almost certainly too large to be accounted for by loss ofsoluble or storage carbohydrate only. No new nodules were formedduring periods of high nitrate availability. When nitrate wassupplied continuously at a moderate concentration (5.7 mM N)nodule numbers stabilised although existing nodules increasedin dry weight by almost four-fold over the 30 d measurementperiod. Treatment had no effect on the percentage nitrogen in planttissues although there were large differences in the proportionsderived from nitrate and N2-fixation. Plants exposed continuouslyor frequently to small doses of nitrate took up more nitrate,and hence relied less heavily on N2-fixation, than those exposedto larger doses less often. Increased reliance on nitrate broughtwith it increased total dry weight and shoot: root ratios. Possiblemechanisms involved in bringing about these differences in nitrogennutrition and growth are discussed. White clover, Trifolium repens, nitrate, N2-fixation, nodule, acetylene reduction, 15N 相似文献
169.
The leaf growth, tiller production, light interception, anddry weight increase of a simulated sward of S24 perennial ryegrass(Lolium perenne) were followed during the development of thesward from a collection of two-leaved seedlings to a closedcanopy with an LAI of 23, of which 15 consisted of green leaflaminae. The dry weight of live shoots increased exponentiallyat first, but then entered a long linear phase of increase.This was equivalent to a crop growth rate of 200 Kg ha1day1 and a conversion efficiency of radiant energy (400700nm) of 7.2 per cent. Towards the end of the growth period therate of increase of live shoots declined rapidly to zero anda ceiling yield was reached equivalent to 10 metric tons ha1.Leaf growth continued at a high rate, but was equalled by therate of leaf death, so that the weight of live leaf tissue remainedconstant. By this time the swards had achieved a stable tillerpopulation (about 1 cm1), each tiller bore a constantnumber of live leaves (about three), and the length of eachnewly expanded leaf equalled the length of the old leaf it replaced(about 70 cm). The swards were grown in Perlite so that in theabsence of soil fauna dead leaves accumulated at the base ofthe sward where, after 12 weeks, they accounted for 19 per centof the total weight of dry matter produced. 相似文献
170.
Normal ciliary ultrastructure is thought to be necessary for effective function. There has been little or no attempt to quantify ultrastructural abnormalities in nasal disease and assess their significance. In this study we measured nasal ciliary function and examined ciliary ultrastructure in nasal brushings from 35 patients with perennial nasal symptoms refractory to treatment. Ultrastructural defects included microtubular abnormalities, compound cilia and ciliary ‘blebs’. the incidence of abnormal cilia was 16.7%, compared with 9% in controls, but there was only a poor correlation between ultrastructural defects and ciliary beat frequency. One patient had primary ciliary dyskinesia (PCD) with a typical clinical history and immotile cilia. However, only secondary ultrastructural abnormalities were seen. We have been unable to show that ciliary ultrastructural defects form the basis of impaired function. In patients with suspected PCD, nasal brushings should be taken for functional and ultrastructural studies; ideally, a further sample should be obtained for examination of possible primary ultrastructural abnormalities. 相似文献