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81.
82.
83.
Physiological effects of five months exposure to low concentrations of O3 and NH3 on Douglas fir (Pseudotsuga menziesii) 总被引:2,自引:0,他引:2
Three years old seedlings of Douglas fir (Pseudotsuga menziesii) were exposed lo filtered air, O3 (day and night concentrations of 78 and 30 μgm?3: respectively). NH3 (54 μg m?3) and to a mixture of NH3+O3 (day and night concentrations of 49 + 83 and 49 + 44 μg m?3 respectively), for 5 months in fumigation chambers. Both gas exchange and chlorophyll fluorescence were measured on shoots which had sprouted at the beginning of the exposure period. After 4. 8, 10 and 20 weeks of exposure, light response curves of electron transport rate (J) were determined, in which J was deduced from chlorophyll fluorescence. Net CO2 assimiialion was measured at maximum light intensity of 560) μmol m?2 S?1 (Pn.560). After 8 and 10 weeks of exposure also light response curves of CO2 assimilation were assessed. Shoots exposed to O3 showed a reduction in net CO2 assimilation as compared to the control shoots during the entire exposure period. The reduction was related lo a lower chlorophyll content and a lower electron transport rate, whereas no effect on quantum yield efficiency (qy) was observed. In contrast, shoots exposed to NH3 showed a positive effect on photosynthesis. Shoots exposed to NH3. + O3 showed a rapid increase in Pn.560, in the period between 4 and 8 weeks to a level equal of that of the NH3-treatment. After this period a decline in Pn.560 was observed. After 10 weeks of exposure shoots exposed to O3 showed an increased transpiration rate in the dark as compared to the control shoots. In addition, water use efficiency (WUE) declined as a result of an increase in leaf conductance. Both observations indicate that the stomatal apparatus was affected by O3. A high transpiration rate in the dark was also found for shoots esposed to NHX. However, shoots exposed to NH3+ O3 showed neither an effect on WUE, nor an effect on transpiration rate in the dark. The possibility that NH3 delayed the O3 induced effects on photosynthesis and stomatal conductance is discussed. 相似文献
84.
Changes in in vivo fluorescence quenching in rye and barley as a function of reduced PSII light harvesting antenna size 总被引:1,自引:0,他引:1
Stefan Falk Marianna Krol Denis P. Maxwell David A. Rezansoff Gordon R. Gray Norman P. A. Huner 《Physiologia plantarum》1994,91(4):551-558
The relationship between the size of the light harvesting antenna to photosystem II (LHCII) and quenching of non-photochemical and dark level fluorescence was studied in wild-type rye (Secale cereale L. cv. Musketeer) and barley (Hordeum vulgare L. cv. Gunilla) as well as in the barley chlorophyll b-less chlorina F2 mutant (H. vulgare L. cv. Dornaria, chlorina-F2). Exposure for 10 min to an irradiance of 500 μmol m?2 s?1 resulted in a strong (0.71–0.73) non-photochemical (qs) quenching of the fluorescence yield in wild-type (WT) material, while the barley chlorina F2-mutant was quenched to 75% of this level. Relaxation of qs in darkness revealed a fast initial decay, related to relaxation of the high-energy-state dependent (qE) part of qs. Etiolated seedlings of rye and barley exposed to intermittent light (IML) for 36 cycles of 2 min light and 118 min darkness had suppressed Chl b and LHCII-production in both WT rye and barley, while the barley chlorina F2-mutant became totally devoid of all LHCII-polypeptides. It was found that the levels of qs and qs were similar in control grown barley chlorina F2 and IML-grown WT rye and barley, but qs was reduced by 30 to 35% and qs by 50 to 65%, respectively, as compared to control-grown. WT plants. No significant qs could be detected in IML-grown barley chlorina F2. It is clear, from these changes in in vivo fluorescence quenching in rye and barley that a significant level of qs is detectable even in the absence of LHCII. Only when the proximal antennae are totally absent, does qE completely disappear. We conclude that the presence of LHCII is not an absolute requirement for qE-quenching and suggest that distal as well as proximal antenna may contribute to qE in vivo. 相似文献
85.
86.
Severely yellowed ten-year-old spruce trees growing in the Vosges Mountains on an acidic soil were fertilised with Magnesium lime during the spring of 1990. The effects of this treatment were assessed 18 months later. A very significant improvement of the mineral status of the trees was detected, with increasing Mg contents in the needles, and as a consequence, reduced yellowing and improved chlorophyll content. Only slight differences with control trees were observed for height increase. Effects of this improved nutrition on photosynthesis were tested measuring net CO2 assimilation rates and chlorophyll a fluorescence. Light-saturated net assimilation rates of current-year needles were high, reaching 5.3 mol m–2 s–1 on a total needle area basis. The improvement in chlorophyll and Mg content had no significant effect on net assimilation rates or on any parameter describing photochemical functions of both current-and previous-year needles. Despite the strong inter-individual variability in needle chlorophyll and Mg contents (ranging from 0.2 to 0.8 mg g–1 fresh weight, and 0.05 to 0.5 mg g-1 dry weight respectively), photochemical efficiency of PS II under limiting irradiance only decreased significantly on older needles displaying Mg contents below 0.1 mg g–1. It is concluded from these results that spruce trees exhibit a high degree of plasticity with regard to Mg deficiency on acidic soils, and that improved Mg nutrition and increased chlorophyll content do not necessarily improve photosynthesis and height growth.Abbreviations A
light-saturated net CO2 assimilation rate (mol m–2 s–1)
- gw
light-saturated needle conductance to water vapour (mmol m–2 s–1)
- wp and wm
pre-dawn and mid-day needle water potential (MPa)
-
osmotic potential of sap expressed from needles (MPa)
- PFD
photosynthetic photon flux density (mol m–2 s–1)
- Fv/Fm
photochemical efficiency of PS II after 20 min dark adaptation
- F/Fm
'
photochemical efficiency of PS II reaction centres after 10 min at a PFD of 220 mol m–2 s–1 相似文献
87.
Gas exchange and dry-weight production in Opuntia ficus-indica, a CAM species cultivated worldwide for its fruit and cladodes, were studied in 370 and 750 μmol mol−1 CO2 at three photosynthetic photon flux densities (PPFD: 5, 13 and 20 mol m−2 d−1). Elevated CO2 and PPFD enhanced the growth of basal cladodes and roots during the 12-week study. A rise in the PPFD increased the growth of daughter cladodes; elevated CO2 enhanced the growth of first-daughter cladodes but decreased the growth of the second-daughter cladodes produced on them. CO2 enrichment enhanced daily net CO2 uptake during the initial 8 weeks after planting for both basal and first-daughter cladodes. Water vapour conductance was 9 to 15% lower in 750 than in 370 μmol mol−1 CO2. Cladode chlorophyll content was lower in elevated CO2 and at higher PPFD. Soluble sugar and starch contents increased with time and were higher in elevated CO2 and at higher PPFD. The total plant nitrogen content was lower in elevated CO2. The effect of elevated CO2 on net CO2 uptake disappeared at 12 weeks after planting, possibly due to acclimation or feedback inhibition, which in turn could reflect decreases in the sink strength of roots. Despite this decreased effect on net CO2 uptake, the total plant dry weight at 12 weeks averaged 32% higher in 750 than in 370 μmol mol−1 CO2. Averaged for the two CO2 treatments, the total plant dry weight increased by 66% from low to medium PPFD and by 37% from medium to high PPFD. 相似文献
88.
Chlorophyll loss in leaves of cut flowers of alstroemeria (Alstroemeria pelegrina L. cv. Westland) was rapid in darkness and counteracted by irradiation and treatment of the flowers with gibberellic acid (GA3). The mechanism of the effect of GA3 under dark conditions was investigated. The content of various carbohydrates in the leaves under dark conditions rapidly decreased; this was not influenced by treatment with GA3. indicating that the loss of carbohydrates in the leaves did not induce the loss of chlorophyll. Placing the cut flowers in various solutions of organic and inorganic nutrients exhibited no significant effect on the retention of chlorophyll in leaves of dark-senescing flowers. The total nitrogen content in leaves of dark-senescing cut flowers decreased with time. Leaves of GA3-treated flowers retained more nitrogen. In contrast, the buds of GA3-treated flowers retained less nitrogen during senescence in the dark than control buds. To investigate whether GA3 affects export of assimilates from the leaf to various parts of control and GA3-treated flowers, we labelled one leaf with radioactive carbon dioxide. 14C-assimilates accumulated preferentially in the flowers, in which the relative specific activity of the youngest floral buds was highest. No significant differences were observed in the distribution of 14C-labelled compounds between the buds of control and GA3-treated flowers. To establish the importance of source-sink relations for the loss of leaf chlorophyll we removed the flower buds (i. e. the strongest sink) from the cut flowers. This removal only slightly delayed chlorophyll loss as compared to the large delay caused by GA3-treatment. In addition, detached leaf tips exhibited chlorophyll loss in the dark, which was delayed by GA3-treatment in a fashion comparable with that in flowers. Together these data demonstrate that interactions of the leaves with other plant organs are not essential for chlorophyll loss during senescence in the dark. Additionally, we have found no evidence that GA3 delays the loss of chlorophyll by affecting the transport of nutrients within the cut flowers. 相似文献
89.
Rapid photosynthetic adaptation to heat stress triggered in potato leaves by moderately elevated temperatures 总被引:17,自引:7,他引:10
M. HAVAUX 《Plant, cell & environment》1993,16(4):461-467
Photosystem II (PSII) is considered to be one of the most thermolabile aspects of photosynthesis. In vivo measurements of chlorophyll fluorescence and photosynthetic oxygen evolution in 25°C-grown potato leaves (cv. Haig) indicated that the threshold temperature Tc above which PSII denatures was indeed rather low–about 38°C–with temperatures higher than Tc causing a rapid and irreversible loss of PSII activity. The present study demonstrates the existence of adaptive processes which rapidly adjust the in vivo thermal stability of PSII in response to temperature increase. Transfer of potato leaves from 25°C to temperatures slightly lower than Tc (between 30 and 35°C) was observed to cause an upward shift of the Tc value without any appreciable loss of PSII activity. This increase in PSII thermotolerance was substantial (around +5°C in the Haig cultivar), rapid (with a half-time of ~20 min) and slowly reversible at 25°C (>24h). As a consequence, high temperatures (e.g. 40°C) which caused a complete and irreversible inhibition of the PSII function had very little effect in 35°C-treated leaves, thus suggesting that the above-described PSII changes could be of prime importance for the plant's behaviour in the field. Accordingly, the rise in Tc at 35°C was much larger (+8°C) in Sahel, a stress-resistant potato variety, than in the heat-sensitive Haig cultivar. 相似文献
90.
In vivo photosynthetic electron transport does not limit photosynthetic capacity in phosphate-deficient sunflower and maize leaves 总被引:8,自引:0,他引:8
The effects of extreme phosphate (Pi) deficiency during growth on the contents of adenylates and pyridine nucleotides and the in vivo photochemical activity of photosystem II (PSII) were determined in leaves of Helianthus annuus and Zea mays grown under controlled environmental conditions. Phosphate deficiency decreased the amounts of ATP and ADP per unit leaf area and the adenylate energy charge of leaves. The amounts of oxidized pyridine nucleotides per unit leaf area decreased with Pi deficiency, but not those of reduced pyridine nucleotides. This resulted in an increase in the ratio of reduced to oxidized pyridine nucleotides in Pi-deficient leaves. Analysis of chlorophyll a fluorescence at room temperature showed that Pi deficiency decreased the efficiency of excitation capture by open PSII reaction centres (φe), the in vivo quantum yield of PSII photochemistry (φPSII) and the photochemical quenching co-efficient (qP), and increased the non-photochemical quenching co-efficient (qN) indicating possible photoinhibitory damage to PSII. Supplying Pi to Pi-deficient sunflower leaves reversed the long-term effects of Pi-deficiency on PSII photochemistry. Feeding Pi-sufficient sunflower leaves with mannose or FCCP rapidly produced effects on chlorophyll a fluorescence similar to long-term Pi-deficiency. Our results suggest a direct role of Pi and photophosphorylation on PSII photochemistry in both long-and short-term responses of photosynthetic machinery to Pi deficiency. The relationship between φPSII and the apparent quantum yield of CO2 assimilation determined at varying light intensity and 21 kPa O2 and 35 Pa CO2 partial pressures in the ambient air was linear in Pi-sufficient and Pi-deficient leaves of sunflower and maize. Calculations show that there was relatively more PSII activity per mole of CO2 assimilated by the Pi-deficient leaves. This indicates that in these leaves a greater proportion of photosynthetic electrons transported across PSII was used for processes other than CO2 reduction. Therefore, we conclude that in vivo photosynthetic electron transport through PSII did not limit photosynthesis in Pi-deficient leaves of sunflower and maize and that the decreased CO2 assimilation was a consequence of a smaller ATP content and lower energy charge which restricted production of ribulose, 1-5, bisphosphate, the acceptor for CO2. 相似文献