To probe the role of xanthophylls in non-photochemical quenching (NPQ) and the compensatory acclimated photoprotection mechanisms, a tomato (Lycopersicon esculentum Mill. cv. Ailsa Craig) Xa mutant with deficit in lutein (L) and neoxanthin (N) contents was used. The Xa mutant showed lowered NPQ, an increased degree of de-epoxidation state [(A+Z)/(V+A+Z)], and decreases of photosystem 2 (PS2) antenna size. Although the Xa mutant had a CO2 assimilation rate similar to that of Ailsa Craig, it exhibited a much larger stomatal conductance (gs) than Ailsa Craig. Decreased electron flux in PS2 (J PS2) for the Xa mutant was associated with electron flux for photorespiratory carbon oxidation (Jo) and alternative electron flux in PS2 (Ja) while electron flux for photosynthetic carbon reduction (Jc) was not different from Ailsa Craig. Moreover, the Xa mutant also exhibited higher activities of antioxidant enzymes, higher contents of ascorbate and glutathione, and lower contents of reactive oxygen species. Hence some compensatory acclimated mechanisms of photoprotection operated properly in the lack of NPQ and xanthophylls. and Y. J. Wang ... [et al.].
Myrica cerifera L. (Myricaceae), the dominant woody species on many barrier islands along the southeastern coast of the United States, is expanding into grass-dominated, mesic, interdunal depressions where it forms dense thickets. Expansion may be attributed to a symbiotic nitrogen fixation with the bacterium Frankia, an evergreen leaf habit and, possibly, corticular photosynthesis (CP, i.e. refixation of respired CO2, %ref). We quantified seasonal variations in CP characteristics in first through fifth order branches of M. cerifera to determine the extent and relevance of CP to shrub expansion in coastal environments. Maximum mean %ref was 110±39 % of CO2 efflux in the dark (RD) in first order branches during winter. Minimum %ref was 18±3 % in fifth order branches during summer. Variations in %ref paralleled changes in incident photosynthetic photon flux density (PPFD). As incident PPFD attenuated with increasing branch order, %ref decreased. A less dense canopy in winter led to increased PPFD and increases in %ref. Total chlorophyll (Chl) content and Chl a/b ratios were consistent with shade acclimation as branch order increased. CP may be a mechanism to enhance M. cerifera shrub expansion because of the potential increase in whole plant carbon use efficiency and water use efficiency attributed to refixation of respired CO2. and J. K. Vick, D. R. Young.
Spring wheat plants were grown in pots at three CO2 concentrations (350, 550 and 700 ppm) and three soil water levels (40, 60 and 80% of field water capacity) in field open top chambers and were infested with bird cherry-oat aphids (Rhopalosiphum padi Linnaeus). Aphid population dynamics were recorded throughout the growing season and analysis of the chemical composition of spring wheat leaves was conducted at the same time. Results showed that: (1) Aphid populations increased with raised atmospheric CO2 concentrations. (2) The aphid populations showed different responses to different CO2 concentrations. The population size, population growth rate and population density found under the 350 ppm CO2 treatment was far less than those recorded under the 550 and 700 ppm CO2 treatments. The population size, population growth rate and population density recorded under the 700 ppm CO2 treatment was slightly higher than those recorded under the 550 ppm CO2 treatment. (3) The effect of CO2 concentration on the aphid population was correlated with soil water level. The highest aphid population size was achieved under the 60% soil water treatment. (4) Atmospheric CO2 and soil moisture had significant effects on the chemical composition of the wheat leaves. (5) Aphid population size correlated positively with the concentration of leaf water content, soluble proteins, soluble carbohydrates and starch, while correlating negatively with the concentration of DIMBOA and tannin.
In a field rain-fed trial with 15 cassava cultivars, leaf gas exchanges and carbon isotope discrimination (Δ) of the same leaves were determined to evaluate genotypic and within-canopy variations in these parameters. From 3 to 7 months after planting leaf gas exchange was measured on attached leaves from upper, middle, and lower canopy layers. All gas exchange parameters varied significantly among cultivars as well as canopy layers. Net photosynthetic rate (PN) decreased from top canopy to bottom indicating both shade and leaf age effects. The same trend, but in reverse, was found with respect to Δ, with the highest values in low canopy level and the lowest in upper canopy. There were very significant correlations, with moderate and low values, among almost all these parameters, with PN negatively associated with intercellular CO2 concentration (Ci), ratio of C i to ambient CO2 concentration C i/C a, and Δ. Across all measured leaves, Δ correlated negatively with leaf water use efficiency (WUE = photosynthesis/stomatal conductance, gs) and with gs, but positively with Ci and Ci/Ca. The later parameters negatively correlated with leaf WUE. Across cultivars, both PN and correlated positively with storage root yield. These results are in agreement with trends predicted by the carbon isotope discrimination model. and M. A. El-Sharkawy, S. M. de Tafur.
Almost four decades have passed since the new field of ecosystem simulation sprang into full force as an added tool for a sound research in an ever-advancing scientific front. The enormous advances and new discoveries that recently took place in the field of molecular biology and basic genetics added more effective tools, have strengthened and increased the efficiency of science outputs in various areas, particularly in basic biological sciences. Now, we are entering into a more promising stage in science, i.e. 'post-genomics', where both simulation modelling and molecular biology tools are integral parts of experimental research in agricultural sciences. I briefly review the history of simulation of crop/environment systems in the light of advances in molecular biology, and most importantly the essential role of experimental research in developing and constructing more meaningful and effective models and technologies. Such anticipated technologies are expected to lead into better management of natural resources in relation to crop communities in particular and plant ecosystems in general, that might enhance productivity faster. Emphasis is placed on developing new technologies to improve agricultural productivity under stressful environments and to ensure sustainable economic development. The latter is essential since available natural resources, particularly land and water, are increasingly limiting.
Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco; EC 4.1.1.39) is one of the key enzymes involved in assimilation of CO2 in chloroplasts. Phylloplane microfungi and their metabolites have been reported to affect the physiology of host plants, particularly, their photosynthesis. However, information is lacking on the effect of these microflora on the physiology of chloroplasts. The current study emphasized the impact of two dominant phylloplane fungi, Aspergillus niger and Fusarium oxysporum, on activity of Rubisco in tomato chloroplasts. Ergosterol, which is a component of only fungal cell membranes and is not synthesized by plants, have been demonstrated to elicit activity of Rubisco. In the present study, it was demonstrated through in silico, in vitro, and in vivo approaches. Results demonstrated that the fungal metabolites, which contained ergosterol, could double Rubisco activity. Maximum carboxylation rate of Rubisco increased also in ergosterol-treated plants. Michaelis-Menten constant of Rubisco was also slightly affected. Ergosterol was found also to influence and enhance the binding of CO2 and ribulose-1,5-bisphosphate to Rubisco. Therefore we can postulate that the physiology of the chloroplast is probably influenced by phylloplane microfungi., J. Mitra, P. Narad, P. K. Paul., and Obsahuje bibliografii
C3 photosynthesis at high light is often modeled by assuming limitation by the maximum capacity of Rubisco carboxylation (VCmax) at low CO2 concentrations, by electron transport capacity (Jmax) at higher CO2 concentrations, and sometimes by
triose-phosphate utilization rate at the highest CO2 concentrations. Net photosynthetic rate (PN) at lower light is often modeled simply by assuming that it becomes limited by electron transport (J). However, it is known that Rubisco can become deactivated at less than saturating light, and it is possible that PN at low light could be limited by the rate of Rubisco carboxylation (VC) rather than J. This could have important consequences for responses of PN to CO2 and temperature at low light. In this work, PN responses to CO2 concentration of common bean, quinoa, and soybean leaves measured over a wide range of temperatures and PPFDs were compared with rates modeled assuming either VC or J limitation at limiting light. In all cases, observed rates of PN were better predicted by assuming limitation by VC rather than J at limiting light both below and above the current ambient CO2. One manifestation of this plant response was that the relative stimulation of PN with increasing the ambient CO2 concentration from 380 to 570 µmol mol-1 did not decrease at less than saturating PPFDs. The ratio of VC to VCmax at each lower PPFD varied linearly with the ratio of PN at low PPFD to PN at high PPFD measured at 380 µmol(CO2) mol-1 in all cases. This modification of the standard C3 biochemical model was much better at reproducing observed responses of light-limited PN to CO2 concentrations from
pre-industrial to projected future atmospheric concentrations., J. A. Bunce., and Obsahuje bibliografii
The effects of elevated growth temperature (ambient + 3.5°C) and CO2 (700 μmol mol-1) on leaf photosynthesis, pigments and chlorophyll fluorescence of a boreal perennial grass (Phalaris arundinacea L.) under different water regimes (well watered to water shortage) were investigated. Layer-specific measurements were conducted on the top (younger leaf) and low (older leaf) canopy positions of the plants after anthesis. During the early development stages, elevated temperature enhanced the maximum rate of photosynthesis (Pmax) of the top layer leaves and the aboveground biomass, which resulted in earlier senescence and lower photosynthesis and biomass at the later periods. At the stage of plant maturity, the content of chlorophyll (Chl), leaf nitrogen (NL), and light response of effective photochemical efficiency (ΦPSII) and electron transport rate (ETR) was significantly lower under elevated temperature than ambient temperature in leaves at both layers. CO2 enrichment enhanced the photosynthesis but led to a decline of NL and Chl content, as well as lower fluorescence parameters of ΦPSII and ETR in leaves at both layers. In addition, the down-regulation by CO2 elevation was significant at the low canopy position. Regardless of climate treatment, the water shortage had a strongly negative effect on the photosynthesis, biomass growth, and fluorescence parameters, particularly in the leaves from the low canopy position. Elevated temperature exacerbated the impact of water shortage, while CO2 enrichment slightly alleviated the drought-induced adverse effects on P max. We suggest that the light response of ΦPSII and ETR, being more sensitive to leaf-age classes, reflect the photosynthetic responses to climatic treatments and drought stress better than the fluorescence parameters under dark adaptation. and Z.-M. Ge ... [et al.].
We tested the effect of growing conditions during micropropagation on the fast kinetics of chlorophyll (Chl) fluorescence of Gardenia jasminoides Ellis plantlets during a 4-week acclimation to ex vitro. We studied whether photoautotrophic growing in vitro produced plantlets with less photoinhibition impairment during acclimation. Of the growing conditions stimulating photoautotrophy in vitro, only loose tube caps had a positive effect, whereas low sucrose or sucrose-free content in the medium and high PPFD showed a negative effect. Thus, plantlets cultured with 3 % (m/v) of sucrose were subsequently less photoinhibited throughout acclimation than those cultured with low sucrose (0.5 %) or sucrose-free media. Moreover, at the end of acclimation the former plantlets showed Fv/Fm and Fv/F0 ratios typical of unstressed ex vitro plants as well as a higher Chl content and ratio of Chls to carotenoids. Plantlets cultured at a photosynthetic photon fluence density (PPFD) of 50 µmol m-2 s-1 also showed a better performance at the end of acclimation than those cultured at a higher (110 µmol m-2 s-1) PPFD. Thus except in the case of loose-tube closure, gardenia plantlets cultured in vitro under conventional sucrose concentration and PPFD are the least photoinhibited during acclimation. Nevertheless, significant interactions between the in vitro growing factors were observed at the end of acclimation. and M. D. Serret, M. I. Trillas, J. L. Araus.
Carbon dioxide interacts both with reactive nitrogen species and reactive oxygen species. In the presence of superoxide, NO reacts to form peroxynitrite that reacts with CO2 to give nitrosoperoxycarbonate. This compound rearranges to nitrocarbonate which is prone to further reactions. In an aqueous environment, the most probable reaction is hydrolysis producing carbonate and nitrate. Thus the net effect of CO2 is scavenging of peroxynitrite and prevention of nitration and oxidative damage. However, in a nonpolar environment of membranes, nitrocarbonate undergoes other reactions leading to nitration of proteins and oxidative damage. When NO reacts with oxygen in the absence of superoxide, a nitrating species N2O3 is formed. CO2 interacts with N2O3 to produce a nitrosyl compound that, under physiological pH, is hydrolyzed to nitrous and carbonic acid. In this way, CO2 also prevents nitration reactions. CO2 protects superoxide dismutase against oxidative damage induced by hydrogen peroxide. However, in this reaction carbonate radicals are formed which can propagate the oxidative damage. It was found that hypercapnia in vivo protects against the damaging effects of ischemia or hypoxia. Several mechanisms have been suggested to explain the protective role of CO2 in vivo. The most significant appears to be stabilization of the iron-transferrin complex which prevents the involvement of iron ions in the initiation of free radical reactions., A. Veselá, J. Wilhelm., and Obsahuje bibliografii