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21.
Estimation of the effect of photoinhibition on the carbon gain in leaves of a willow canopy 总被引:21,自引:0,他引:21
The occurrence of photoinhibition of photosynthesis in leaves of a willow canopy was examined by measuring the chlorophyll-a fluorescence ratio of F
V/F
M (FM is the maximum fluorescence level of the induction curve, and FV is the variable fluorescence, F
V=F
M–F
0, where F0 is the minimal fluorescence). The majority of the leaves situated on the upper parts of peripheral shoots showed an afternoon inhibition of this ratio on clear days. This was the consequence of both a decrease in F
M and a rise in F
O. In the same leaves the diurnal variation in intercepted photosynthetic photon flux density (PPFD) was monitored using leaf-mounted sensors. Using the multivariate method, partial least squares in latent variables, it is shown that the dose of PPFD, integrated and linearly weighted over the last 6-h period, best predicts photoinhibition. Photoinhibition occurred even among leaves that did not intercept PPFDs above 1000 mol·m–2·s–1. Exposure of leaves to a standard photoinhibitory treatment demonstrated that the depression in the F
V/F
M ratio was paralleled by an equal depression in the maximal quantum yield of CO2 uptake and a nearly equal depression in the rate of bending (convexity) of the light-response curve of CO2 uptake. As a result, the rate of net photosynthesis is depressed over the whole natural range of PPFD. By simulating the daily course in the rate of net photosynthesis, it is estimated that in the order of one-tenth of the potential carbon gain of peripheral willow shoots is lost on clear days as a result of photoinhibition. This applies to conditions of optimal temperatures. Photoinhibition is even more pronounced at air temperatures below 23° C, as judged from measurements of the FV/FM ratio on clear days: the afternoon inhibition of this ratio increased in a curvilinear manner from 15% to 25% with a temperature decrease from 23° to 14° C.Abbreviations and Symbols FO
minimum fluorescence
- FV
variable fluorescence
- FM
maximum fluorescence
- PLS
partial least squares in latent variables
- PPFD
photosynthetic photon flux density
- VPD
water vapour-pressure deficit
This study was supported by the Swedish Natural Science Research Council. We are indebted to Dr. Jerry Leverenz (Department of Plant Physiology, University of Umeå, Sweden) for guidance with the modelling of the photosynthesis data. 相似文献
22.
In the last few years our knowledge of the structure and function of Photosystem II in oxygen-evolving organisms has increased significantly. The biochemical isolation and characterization of essential protein components and the comparative analysis from purple photosynthetic bacteria (Deisenhofer, Epp, Miki, Huber and Michel (1984) J Mol Biol 180: 385–398) have led to a more concise picture of Photosystem II organization. Thus, it is now generally accepted that the so-called D1 and D2 intrinsic proteins bind the primary reactants and the reducing-side components. Simultaneously, the nature and reaction kinetics of the major electron transfer components have been further clarified. For example, the radicals giving rise to the different forms of EPR Signal II have recently been assigned to oxidized tyrosine residues on the D1 and D2 proteins, while the so-called Q400 component has been assigned to the ferric form of the acceptor-side iron. The primary charge-separation has been meaured to take place in about 3 ps. However, despite all recent major efforts, the location of the manganese ions and the water-oxidation mechanism still remain largely unknown. Other topics which lately have received much attention include the organization of Photosystem II in the thylakoid membrane and the role of lipids and ionic cofactors like bicarbonate, calcium and chloride. This article attempts to give an overall update in this rapidly expanding field. 相似文献
23.
Sebahattin Özcan Cafer S. Sevimay Mustafa Yildiz Cengiz Sancak Murat Özgen 《Plant cell reports》1996,16(3-4):200-203
Summary Immature cotyledons and embryo axes of sainfoin were cultured on Murashige and Skoog (MS) media supplemented with various concentrations of 6-benzylaminopurine (BAP) and a-naphthaleneacetic acid (NAA) to induce adventitious shoot regeneration. The highest frequency of shoot regeneration occurred following an initial callus growth on a MS medium containing 0.5 mg/l BAP and 2 mg/l NAA. Immature embryo axes showed higher regeneration capacity than immature cotyledons, however, shoot elongation was best achieved on immature cotyledons. Regenerated shoots were excised and rooted in half strength MS medium with 1 mg/l indole-butyric acid (IBA) or 1 mg/l NAA. The rooted plantlets were finally transferred to compost. 相似文献
24.
Lars Öhman Maria Alarcon Jan Ljunggren Anna-Karin Ramqvist Lena Häggström 《Biotechnology letters》1996,18(7):765-770
Summary
Spodoptera frugiperda (Sf-9) insect cells are fully capable of growth and proliferation in a glutamine, glutamate and aspartate-free medium, provided that ammonium ions are supplied. S. frugiperda (Sf-21) and Mamestra brassicae cells (IZD-MB-0503) also grow in glutamine-free media but not Trichoplusia ni cells (BTI-TN 5B1-4). The yield of -galactosidase in Sf-9 cells infected with a recombinant baculovirus under glutamine-free conditions was even higher than the yield obtained in glutamine containing cultures. 相似文献
25.
Since the exact mechanism of manganese (Mn)-induced learning disability is not known, we investigated the role of elevated
cholesterol in rats exposed daily to 357 and 714 μg Mn/kg for 30 d. Significant Mn accumulation was accompanied by increased
cholesterol content in the hippocampal region of Mn-treated rats. The learning, which is based on the time needed to reach
food placed at the exit of a T-maze after a 1-d training period, was significantly slower in exposed rats than in unexposed
rats. The rats receiving 357 and 714 μg Mn/kg reached the food in 104.5±13.8 and 113.3±25.7 s, respectively, on d 30, whereas
their untreated counterparts reached the food in 28.7±11.4 s. This delay was completely corrected to 29.3±7.8 and 30.7±6.0
s in rats with coadministration of an inhibitor of cholesterol biosynthesis with 357 and 714 μg/kg of Mn. The correction of
impaired learning was associated with the normalization of hippocampal cholesterol, but the Mn level in this region of the
brain was not influenced in rats treated with a drug that inhibits cholesterol biosynthesis. These results suggested that
Mn-induced hypercholesterolemia is involved in Mn-dependent learning disability. 相似文献
26.
Cold acclimation and photoinhibition of photosynthesis in Scots pine 总被引:13,自引:0,他引:13
Alla Krivosheeva Da-Li Tao Christina Ottander Gunnar Wingsle Sylvain L. Dube Gunnar Öquist 《Planta》1996,200(3):296-305
Cold acclimation of Scots pine did not affect the susceptibility of photosynthesis to photoinhibition. Cold acclimation did however cause a suppression of the rate of CO2 uptake, and at given light and temperature conditions a larger fraction of the photosystem II reaction centres were closed in cold-acclimated than in nonacclimated pine. Therefore, when assayed at the level of photosystem II reaction centres, i.e. in relation to the degree of photosystem closure, cold acclimation caused a significant increase in resistance to photoinhibition; at given levels of photosystem II closure the resistance to photoinhibition was higher after cold acclimation. This was particularly evident in measurements at 20° C. The amounts and activities of the majority of analyzed active oxygen scavengers were higher after cold acclimation. We suggest that this increase in protective enzymes and compounds, particularly Superoxide dismutase, ascorbate peroxidase, glutathione reductase and ascorbate of the chloroplasts, enables Scots pine to avoid excessive photoinhibition of photosynthesis despite partial suppression of photosynthesis upon cold acclimation. An increased capacity for light-induced de-epoxidation of violaxanthin to zeaxanthin upon cold acclimation may also be of significance.Abbreviations APX
ascorbate peroxidase
- DHA
dehydroascorbate
- DHAR
dehydroascorbate reductase
- Fm
maximal fluorescence when all reaction centres are closed
- Fv/Fm
maximum photochemical yield of PSII
- GR
glutathione reductase
- GSH
reduced glutathione
- Je
rate of photosynthetic electron transport
- MDAR
monodehydroascorbate reductase
- qN
nonphotochemical quenching of fluorescence
- qP
photochemical quenching of fluorescence
- SOD
superoxide dismutase
This work was supported by the Swedish Natural Science Research Council and the National Natural Science Foundation of China. 相似文献
27.
Örjan Totland 《American journal of botany》1996,83(4):452-458
Some plants in arctic and alpine habitats have heliotropic flowers that track the sun. This results in a heating of the flower's interior, which may improve the possibilities for insect pollination and seed production. Here, I examine whether flower heliotropism in an alpine population of the self-incompatible Ranunculus acris L. (Ranunculaceae) enhances pollinator visitation and seed production. Flowers of Ranunculus acris tracked the sun during the day. Tracking accuracy was greatest during the middle of the day. The temperature elevation in flowers was negatively correlated with the flower's angle of deviation from the sun. Despite the increased temperature, insects did not discriminate among flowers on the basis of their angle of deviation from the sun, or tend to stay longer in the flowers aligned closest towards the sun. A tethering experiment was conducted on three groups of plants flowering at different times in the 1993 season and on one group the following season. Manipulation plants were constrained not to track the sun, whereas control plants tracked the sun naturally. Solar tracking had no effect on seed:ovule ratio, seed mass, or abortion rate in any of the groups. There is probably a very narrow range of weather conditions (cold, sunny, and calm) where flower heliotropism may enhance visitation rate to flowers and their seed production. 相似文献
28.
Silica biomorphs are inorganic self-organized precipitates resulting from a crystal aggregation process controlled by a metal silicate membrane. They display morphological and symmetric properties of living organisms and form under physico-chemical conditions similar to some geochemical conditions suggested for the chemical precipitation of Precambrian chert precursors. In consequence, these inorganic precipitates are proposed as an alternative interpretation to be considered when trying to decipher the biogenicity of putative Precambrian microbiotas. 相似文献
29.
A. J. Soitamo G. Zhou A. K. Clarke G. Öquist E-M. Aro P. Gustafsson 《Plant molecular biology》1994,26(2):709-721
The unicellular cyanobacterium Synechococcus sp. PCC 7942 has three psbA genes encoding two different forms of the photosystem II reaction centre protein D1 (D1:1 and D1:2). The level of expression of these psbA genes and the synthesis of D1:1 and D1:2 are strongly regulated under varying light conditions. In order to better understand the regulatory mechanisms underlying these processes, we have constructed a strain of Synechococcus sp. PCC 7942 capable of over-producing psbA mRNA and D1 protein. In this study, we describe the over-expression of D1:1 using a tac-hybrid promoter in front of the psbAI gene in combination with lacI
Q
repressor system. Over-production of D1:1 was induced by growing cells for 12 h at 50 mol photons m-2 s-1 in the presence of 40 or 80 g/ml IPTG. The amount of psbAI mRNA and that of D1:1 protein in cells grown with IPTG was three times and two times higher, respectively. A higher concentration of IPTG (i.e., 150 g/ml) did not further increase the production of the psbAI message or D1:1. The over-production of D1:1 caused a decrease in the level of D1:2 synthesised, resulting in most PSII reaction centres containing D1:1. However, the over-production of D1:1 had no effect on the pigment composition (chlorophyll a or phycocyanin/number of cells) or the light-saturated rate of photosynthesis. This and the fact that the total amounts of D1 and D2 proteins were not affected by IPTG suggest that the number of PSII centres within the membranes remained unchanged. From these results, we conclude that expression of psbAI can be regulated by using the tac promoter and lacI
Q
system. However, the accumulation of D1:1 protein into the membrane is regulated by the number of PSII centres. 相似文献
30.
Production and properties of inulinase from Aspergillus niger 总被引:5,自引:0,他引:5
Summary A thermostable inulinase was identified in a strain of A. niger. The highest activity was observed at 50 °C (50 Lml–1) and 77% and 34% of this was retained at 60° and 65°C, respectively. pH stability, the effect of thermal stabilizers such as Propylene glycol (10%) and Sorbitol (10%) and effects of different cations were investigated. It was found that the activity was completely inhibited by Ag+ and Hg2+, while Na+ had an activator effect. 相似文献