| 1. |
- HUNER, NPA, et al.
(författare)
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PHOTOSYNTHESIS, PHOTOINHIBITION AND LOW-TEMPERATURE ACCLIMATION IN COLD TOLERANT PLANTS
- 1993
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Ingår i: Photosynthesis Research. - 0166-8595. ; 37:1, s. 19-39
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Tidskriftsartikel (refereegranskat)abstract
- Cold acclimation requires adjustment to a combination of light and low temperature, conditions which are potentially photoinhibitory. The photosynthetic response of plants to low temperature is dependent upon time of exposure and the developmental history of the leaves. Exposure of fully expanded leaves of winter cereals to short-term, low temperature shifts inhibits whereas low temperature growth stimulates electron transport capacity and carbon assimilation. However, the photosynthetic response to low temperature is clearly species and cultivar dependent. Winter annuals and algae which actively grow and develop at low temperature and moderate irradiance acquire a resistance to irradiance 5- to 6-fold higher than their growth irradiance. Resistance to short-term photoinhibition (hours) in winter cereals is a reflection of the increased capacity to keep Q(A) oxidized under high light conditions and low temperature. This is due to an increased capacity for photosynthesis. These characteristics reflect photosynthetic acclimation to low growth temperature and can be used to predict the freezing tolerance of cereals. It is proposed that the enhanced photosynthetic capacity reflects an increased flux of fixed carbon through to sucrose in source tissue as a consequence of the combined effects of increased storage of carbohydrate as fructans in the vacuole of leaf mesophyll cells and an enhanced export to the crown due to its increased sink activity. Long-term exposure (months) of cereals to low temperature photoinhibition indicates that this reduction of photochemical efficiency of PS II represents a stable, long-term down regulation of PS II to match the energy requirements for CO2 fixation. Thus, photoinhibition in vivo should be viewed as the capacity of plants to adjust photosynthetically to the prevailing environmental conditions rather than a process which necessarily results in damage or injury to plants. Not all cold tolerant, herbaceous annuals use the same mechanism to acquire resistance to photoinhibition. In contrast to annuals and algae, overwintering evergreens become dormant during the cold hardening period and generally remain susceptible to photoinhibition. It is concluded that the photosynthetic response to low temperatures and susceptibility to photoinhibition are consequences of the overwintering strategy of the plant species.
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| 2. |
- HURRY, VM, 1960-, et al.
(författare)
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EFFECT OF LONG-TERM PHOTOINHIBITION ON GROWTH AND PHOTOSYNTHESIS OF COLD-HARDENED SPRING AND WINTER-WHEAT
- 1992
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Ingår i: Planta. - 0032-0935. ; 188:3, s. 369-375
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Tidskriftsartikel (refereegranskat)abstract
- The effect of repeated exposure to high light (1200 mumol . m-2 . s-1 photosynthetic photon flux density, PPFD) at 5-degrees-C was examined in attached leaves of cold-grown spring (cv. Katepwa) and winter (cv. Kharkov) wheat (Triticum aestivum L.) over an eight-week period. Under these conditions, Kharkov winter wheat exhibited a daily reduction of 24% in F(V)/F(M) (the ratio of variable to maximal fluorescence in the dark-adapted state), in contrast to 41% for cold-grown Katepwa spring wheat. Both cultivars were able to recover from this daily suppression of F(V)/F(M) such that the leaves exhibited an average morning F(V)/F(M) of 0.651 +/- 0.004. Fluorescence measurements made under steady-state conditions as a function of irradiance from 60 to 2000 mumol . m-2 . s-1 indicated that the yield of photosystem II (PSII) electron transport under light-saturating conditions was the same for photoinhibited and control cold-grown plants, regardless of cultivar. Repeated daily exposure to high light at low temperature did not increase resistance to short-term photoinhibition, although zeaxanthin levels increased by three- to fourfold. In addition, both cultivars increased the rate of dry-matter accumulation, relative to control plants maintained at 5-degrees-C and 250 mumol . m-2 . s-1 PPFD (10% and 28% for Katepwa and Kharkov, respectively), despite exhibiting suppressed F(V)/F(M) and reduced photon yields for O2 evolution following daily high-light treatments. Thus, although photosynthetic efficiency is suppressed by a long-term, photoinhibitory treatment, light-saturated rates of photosynthesis are sufficiently high during the high-light treatment to offset any reduction in photochemical efficiency of PSII. We suggest that in these cold-tolerant plants, photoinhibition of PSII may represent a long-term, stable, down-regulation of photochemistry to match the overall photosynthetic demand for ATP and reducing equivalents.
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| 3. |
- KRUPA, Z, et al.
(författare)
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THE EFFECTS OF CADMIUM ON PHOTOSYNTHESIS OF PHASEOLUS-VULGARIS - A FLUORESCENCE ANALYSIS
- 1993
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Ingår i: Physiologia Plantarum : An International Journal for Plant Biology. - 0031-9317. ; 88:4, s. 626-630
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Tidskriftsartikel (refereegranskat)abstract
- Bean plants (Phaseolus vulgaris L. cv. Scarlett), germinated in darkness for 1 week, were transferred to light (200 mumol m-2 s-1) and cultivated for 1 week in a complete nutrient solution. After this period, cadmium ions in the form of CdSO4 were added at the concentrations of 0, 10, 20 and 50 muM. The effects of this metal on the properties of photosystem II photochemistry were studied by means of modulated fluorescence analysis. Steady state photochemical quenching, non-photochemical quenching and terminal fluorescence were determined in control and cadmium-treated plants. We postulate that, during short term exposure of plants to cadmium in the early stages of growth, the Calvin cycle reactions are more likely than photosystem II to be the primary target of the toxic influence of cadmium. The reduced demand for ATP and NADPH upon Calvin cycle inhibition causes a down-regulation of photosystem II photochemistry and of the yield of linear electron transport.
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| 4. |
- Oquist, Gunnar, 1941-, et al.
(författare)
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COLD-HARDENING-INDUCED RESISTANCE TO PHOTOINHIBITION OF PHOTOSYNTHESIS IN WINTER RYE IS DEPENDENT UPON AN INCREASED CAPACITY FOR PHOTOSYNTHESIS
- 1993
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Ingår i: Planta. - 0032-0935. ; 189:1, s. 150-156
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Tidskriftsartikel (refereegranskat)abstract
- Analyses of chlorophyll fluorescence and photosynthetic oxygen evolution were conducted to understand why cold-hardened winter rye (Secale cereale L.) is more resistant to photoinhibition of photosynthesis than is non-hardened winter rye. Under similar light and temperature conditions, leaves of cold-hardened rye were able to keep a larger fraction of the PS II reaction centres in an open configuration, i.e. a higher ratio of oxidized to reduced Q(A) (the primary, stable quinone acceptor of PSII), than leaves of non-hardened rye. Three fold-higher photon fluence rates were required for cold-hardened leaves than for non-hardened leaves in order to establish the same proportion of oxidized to reduced Q(A). This ability of cold-hardened rye fully accounted for its higher resistance to photoinhibition; under similar redox states of Q(A) cold-hardened and non-hardened leaves of winter rye exhibited similar sensitivities to photoinhibition. Under given light and temperature conditions, it was the higher capacity for light-saturated photosynthesis in cold-hardened than in non-hardened leaves, which was responsible for maintaining a higher proportion of oxidized to reduced Q(A). This higher capacity for photosynthesis of cold-hardened leaves also explained the increased resistance of photosynthesis to photoinhibition upon cold-hardening.
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| 5. |
- Oquist, Gunnar, 1941-, et al.
(författare)
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EFFECTS OF COLD-ACCLIMATION ON THE SUSCEPTIBILITY OF PHOTOSYNTHESIS TO PHOTOINHIBITION IN SCOTS PINE AND IN WINTER AND SPRING CEREALS - A FLUORESCENCE ANALYSIS
- 1991
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Ingår i: Functional Ecology. - 0269-8463. ; 5:1, s. 91-100
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Tidskriftsartikel (refereegranskat)abstract
- Winter and spring varieties of cereals and seedlings of Scots pine were exposed to a low temperature regime of 4-5-degrees-C for the induction of frost hardiness. The effect of cold acclimation on the susceptibility of photosynthesis to photoinhibition was analysed using variable chlorophyll fluorescence. Winter rye responded with an increased resistance to photoinhibition upon cold hardening, whereas low temperature acclimated spring barley and Scots pine showed no increase in resistance to photoinhibition. In the case of winter rye, the leaves had to develop at low temperature in order to acquire increased resistance to photoinhibition. It is suggested that resistance to photoinhibition of photosynthesis under low temperature acclimation of cereals is important for the induction of frost hardiness. The importance of leaf orientation for the susceptibility of photosynthesis to photoinhibition at low temperatures was demonstrated; horizontal leaves were more photoinhibited than were vertical leaves (light coming from above). Most species and cultivars studied exhibited some photoinhibition during cold acclimation. Even weak light of a PPFD of 50-mu-mol m-2 s-1 under long day conditions and 5-degrees-C can induce photoinhibition of Scots pine. It is concluded that photoinhibition of photosynthesis under low temperature conditions no longer should be considered only as a high light response and that light probably is a much more significant stress factor under low temperature regimes than previously thought. The inability of the evergreen Scots pine to acquire an increased resistance to photoinhibition is discussed in relation to its natural habitat, where low temperatures and high light often occur together during winter. It is suggested that photoinhibition of photosynthesis under conditions when overall photosynthesis is limited by temperature provides a means for controlled dissipation of excessive excitation as heat. In this view photoinhibition is a naturally occurring phenomenon of significant physiological and ecological importance for evergreen species in cold, temperate climates.
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| 6. |
- Oquist, Gunnar, 1941-, et al.
(författare)
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LOW-TEMPERATURE EFFECTS ON PHOTOSYNTHESIS AND CORRELATION WITH FREEZING TOLERANCE IN SPRING AND WINTER CULTIVARS OF WHEAT AND RYE
- 1993
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Ingår i: Plant Physiology. - 0032-0889. ; 101:1, s. 245-250
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Tidskriftsartikel (refereegranskat)abstract
- Winter cultivars of rye (Secale cereale L., cv Musketeer) and wheat (Triticum aestivum L. cvs Kharkov and Monopol), but not a spring cultivar of wheat (Glenlea), grown at cold-hardening temperatures showed, at high irradiances, a higher proportion of oxidized to reduced primary, stable quinone receptor (Q(A)) than did the same cultivars grown under nonhardening conditions. In addition, there was a positive correlation between the effects of low-growth temperature on this increased proportion of oxidized Q(A), and a concomitant increase in the capacity for photosynthesis, and LT50, the temperature at which 50% of the seedlings are killed, in cultivars showing different freezing tolerances. This suggests that low-temperature modulation of the photosynthetic apparatus may be an important factor during the induction of freezing resistance in cereals. Finally, the control of photosystem II photochemistry by nonphotochemical quenching of excitation energy was identical for nonhardened and cold-hardened winter rye. However, examination of measuring temperature effects per se revealed that, irrespective of growth temperature, nonphotochemical quenching exerted a stronger control on photosystem II photochemistry at 10-degrees-C rather than at 20-degrees-C.
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| 7. |
- Oquist, Gunnar, 1941-, et al.
(författare)
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THE TEMPERATURE-DEPENDENCE OF THE REDOX STATE OF Q(A) AND SUSCEPTIBILITY OF PHOTOSYNTHESIS TO PHOTOINHIBITION
- 1993
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Ingår i: Plant physiology and biochemistry (Paris). - 0981-9428. ; 31:5, s. 683-691
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Tidskriftsartikel (refereegranskat)abstract
- The relationship between the redox state of primary, stable quinone acceptor of photosystem II (Q(A)) and the susceptibility of photosynthesis to photoinhibition at different temperatures was investigated. Non-hardened and cold-hardened seedlings of winter rye, and of winter and spring cultivars of wheat, were obtained by growth at either 20/16-degrees-C (day/night) or 5/5-degrees-C (day/night), respectively. A single, curvi-linear relationship was established between the steady-state redox level Of Q(A) and the susceptibility of photosynthesis to short-term (8 h) photoinhibition at 5 or 25-degrees-C when spring and winter cultivars of rye and wheat, in non-hardened or cold-hardened states, were plotted together. Furthermore, irrespective of temperature (0 to 25-degrees-C) or state of cold-hardiness, the susceptibility of photosynthesis to photoinhibition was controlled fully in winter rye by the redox state Of Q(A); e.g. similar susceptibilities to photoinhibition were obtained at 0, 5 and 25-degrees-C provided that the photon fluence rate at the different temperatures was adjusted to keep 50% of the photosystem II reaction centres in a closed state under steady-state illumination. Our results suggest that the primary reason plants become prone to photoinhibition at low temperatures is that the proportion of closed reaction centres increases due to the low temperature imposed constraints on photosynthesis. Thus, we propose that low temperature sensitized photoinhibition results from low temperature inhibition of photosynthesis rather than from low temperature inhibition of the photosystem II repair cycle.
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| 8. |
- OTTANDER, C, et al.
(författare)
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PHOTOSYSTEM-II REACTION CENTERS STAY INTACT DURING LOW-TEMPERATURE PHOTOINHIBITION
- 1993
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Ingår i: Photosynthesis Research. - 0166-8595. ; 35:2, s. 191-200
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Tidskriftsartikel (refereegranskat)abstract
- Photoinhibition of photosynthesis was studied in intact barley leaves at 5 and 20-degrees-C, to reveal if Photosystem II becomes predisposed to photoinhibition at low temperature by 1) creation of excessive excitation of Photosystem II or, 2) inhibition of the repair process of Photosystem II. The light and temperature dependence of the reduction state of Q(A) was measured by modulated fluorescence. Photon flux densities giving 60% of Q(A) in a reduced state at steady-state photosynthesis (300 mu mol m-2 s-1 at 5-degrees-C and 1200 mumol m-2 s-1 at 20-degrees-C) resulted in a depression of the photochemical efficiency of Photosystem II (F(v)/F(m)) at both 5 and 20-degrees-C. Inhibition of F(v)/F(m) occurred with initially similar kinetics at the two temperatures. After 6 h, F(v)/F(m), was inhibited by 30% and had reached steady-state at 20-degrees-C. However, at 5-degrees-C, F(v)/F(m) continued to decrease and after 10 h, F(v)/F(m) was depressed to 55% of control. The light response of the reduction state of Q(A) did not change during photoinhibition at 20-degrees-C, whereas after photoinhibition at 5-degrees-C, the proportion of closed reaction centres at a given photon flux density was 10-20% lower than before photoinhibition. Changes in the D1-content were measured by immunoblotting and by the atrazine binding capacity during photoinhibition at high and low temperatures, with and without the addition of chloramphenicol to block chloroplast encoded protein synthesis. At 20-degrees-C, there was a close correlation between the amount of D1-protein and the photochemical efficiency of photosystem II, both in the presence or in the absence of an active repair cycle. At 5-degrees-C, an accumulation of inactive reaction centres occurred, since the photochemical efficiency of Photosystem II was much more depressed than the loss of D1-protein. Furthermore, at 5-degrees-C the repair cycle was largely inhibited as concluded from the finding that blockage of chloroplast encoded protein synthesis did not enhance the susceptibility to photoinihibition at 5-degrees-C. It is concluded that, the kinetics of the initial decrease of F(v)/F(m) was determined by the reduction state of the primary electron acceptor Q(A), at both temperatures. However, the further suppression of F(v)/F(m) at 5-degrees-C after several hours of photoinhibition implies that the inhibited repair cycle started to have an effect in determining the photochemical efficiency of Photosystem II.
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