| 1. |
- Greer, DH, et al.
(författare)
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Photoinhibition and recovery of photosynthesis in intact barley leaves at 5 and 20°C
- 1991
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Ingår i: Physiologia Plantarum. - : Wiley. - 0031-9317 .- 1399-3054. ; 81:2, s. 203-210
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Tidskriftsartikel (refereegranskat)abstract
- Photoinhibition of photosynthesis and its recovery were studied in intact barley (Hordeum vulgare L. cv. Gunilla) leaves grown in a controlled environment by exposing them to two temperatures, 5 and 20-degrees-C, and a range of photon flux densities in excess of that during growth. Additionally, photoinhibition was examined in the presence of chloramphenicol (CAP, an inhibitor of chloroplast protein synthesis) and of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Susceptibility to photoinhibition was much higher at 5 than at 20-degrees-C. Furthermore, at 20-degrees-C CAP exacerbated photoinhibition strongly, whereas CAP had little additional effect (10%) at 5-degrees-C. These results support the model that net photoinhibition is the difference between the inactivation and repair of photosystem II (PSII); i.e. the degradation and synthesis of the reaction centre protein, D1. Furthermore, the steady-state extent of photoinhibition was strongly dependent on temperature and the results indicated this was manifested through the effects of temperature on the repair process of PSII. We propose that the continuous repair of PSII at 20-degrees-C conferred at least some protection from photoinhibition. At 5-degrees-C the repair process was largely inhibited, with increased photoinhibition as a consequence. However, we suggest where repair is inhibited by low temperature, some protection is alternatively conferred by the photoinhibited reaction centres. Providing they are not degraded, such centres could still dissipate excitation energy non-radiatively, thereby conferring protection of remaining photochemically active centres under steady-state conditions. A fraction of PS II centres were capable of resisting photoinhibition when the repair process was inhibited by CAP. This is discussed in relation to PS II heterogeneity. Furthermore, the repair process was not apparently activated within 3 h when barley leaves were transferred to photoinhibitory light conditions at 20-degrees-C.
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| 2. |
- Hurry, Vaughan, 1960-, et al.
(författare)
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Effects of a short-term shift to low-temperature and of long-term cold hardening on photosynthesis and ribulose-1,5-bisphosphate carboxylase oxygenase and sucrose-phosphate synthase activity in leabves of winter rye (Secale-Cereale L)
- 1994
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Ingår i: Plant Physiology. - 0032-0889 .- 1532-2548. ; 106:3, s. 983-990
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Tidskriftsartikel (refereegranskat)abstract
- The effect of a short-term (hours) shift to low temperature (5 degrees C) and long-term (months) cold hardening on photosynthesis and carbon metabolism was studied in winter rye (Secale cereale L. cv Musketeer), Cold-hardened plants grown at 5 degrees C exhibited 25% higher in situ CO2 exchange rates than nonhardened plants grown at 24 degrees C. Cold-hardened plants maintained these high rates throughout the day, in contrast to nonhardened plants, which showed a gradual decline in photosynthesis after 3 h. Associated with the increase in photosynthetic capacity following cold hardening was an increase in ribulose-1,5-bisphosphate carboxylase/oxygenase and sucrose phosphate synthase activity and 3- to 4-fold increases in the pools of associated metabolites. Leaves of nonhardened plants shifted overnight to 5 degrees C required 9 h in the light at 5 degrees C before maximum rates of photosynthesis were reached. The gradual increase in photosynthesis in leaves shifted to 5 degrees C was correlated with a sharp decline in the 3-phosphoglycerate/triose phosphate ratio and by an increase in the ribulose bisphosphate/3-phosphoglycerate ratio, indicating the gradual easing of aninorganic phosphate-mediated feedback inhibition on photo-synthesis. We suggest that the strong recovery of photosynthesis in winter rye following cold hardening indicates that the buildup of photosynthetic enzymes, as well as those involved in sucrose synthesis, is an adaptive response that enables these plants to maximize the production of sugars that have both cryoprotective and storage functions that are critical to the performance of these cultivars during over-wintering.
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| 3. |
- Hurry, V.M., et al.
(författare)
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Effects of growth at cold hardening temperatures and temperature shifts on resistance to photoinhibition
- 1993
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Ingår i: Advances in plant cold hardiness. - Boca Raton : CRC Press. - 9781351069526 - 0849349508 ; , s. 103-112
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Bokkapitel (refereegranskat)abstract
- This chapter presents a summary of results that illustrate the photosynthetic responses of cold-tolerant cereals, spinach, and pine to low temperature-induced photoinhibition. Pre Exposure to a low temperature regime induces a cold-hardened state that imparts a certain level of freezing resistance and enhances the winter survival of the seedlings under natural conditions. Photosynthesis provides the energy for this cold hardening process. The phenomenon of resistance to photoinhibition was examined at several levels of cellular organization in winter rye: isolated thylakoids; isolated, intact mesophyll cells; and leaf segments. In contrast to the herbaceous cold-tolerant plants, Scots pine exposed to cold hardening conditions exhibited the same susceptibility to low temperature-induced photoinhibition as nonhardened Scots pine. To attain maximum cold hardiness, the herbaceous plants grow and develop at low temperatures and, as a consequence, develop a resistance to low temperature photoinhibition. The capacity to down-regulate PSII through photoinhibition may be an important characteristic that separates cold-tolerant from chilling-sensitive plant species.
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| 4. |
- Ottander, Christina, 1962-, et al.
(författare)
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Photosystem II reaction centres stay intact during low temperature photoinhibition
- 1993
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Ingår i: Photosynthesis Research. - 0166-8595 .- 1573-5079. ; 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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| 5. |
- Ottander, Christina, 1962-, et al.
(författare)
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Recovery of photosynthesis in winter-stressed Scots pine
- 1991
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Ingår i: Plant, Cell and Environment. - : Wiley. - 0140-7791 .- 1365-3040. ; 14:3, s. 345-349
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Tidskriftsartikel (refereegranskat)abstract
- Winter-induced inhibition of photosynthesis in Scots pine (Pinus sylvestris L.) is caused by the combined effects of light and freezing temperatures; light causes photoinhibition of photosystem 11 (Strand & Oquist, 1985b, Physiologia Plantarum, 65, 117-123), whereas frost causes inhibition of enzymatic steps of photosynthesis (Strand & Oquist, 1988, Plant, Cell & Environment, 11, 231-238). To reveal limiting steps during recovery from winter stress, the potential of photosynthesis to recover and the actual recovery outdoors during spring, were studied in Scots pine. Studies of light dependent O2-evolution under saturating CO2 and recordings of room temperature fluorescence induction kinetics were used. When branches of pine, in February and March, were brought into the laboratory and kept at 18-degrees-C and 100-mu-mol m-2 s-1, light saturated rates and apparent quantum yields of photosynthetic O2-evolution recovered fully within approximately 48 h. The photochemical efficiency of photosystem II, as measured by Fv/Fm ratios, recovered fully within 24h after an initial lag-phase of 2-3 h. Under natural winter conditions, the Fv/Fm ratio decreased more in exposed than in shaded pine, whereas the efficiency of photosynthesis was similarly inhibited in exposed and shaded pine. However, when recovery from winter stress occurred during spring, the Fv/Fm ratios of both shaded and exposed pine recovered well before photosynthesis. It is concluded that the light-induced photoinhibition component of winter stress in photosynthesis of pine recovers well before the frost induced component(s) of winter stress. In this context, reversible photoinhibition of photosynthesis in evergreen conifers is considered as a dynamic down-regulation of photosystem II to prevent more severe photodynamic damage of the thylakoid membrane when photosynthesis is inhibited by frost.
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