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1.
The responses to irradiance of photosynthetic CO 2 assimilation and photosystem 2 (PS2) electron transport were simultaneously studied by gas exchange and chlorophyll (Chl) fluorescence measurement in two-year-old apple tree leaves ( Malus pumila Mill. cv. Tengmu No.1/ Malus hupehensis Rehd). Net photosynthetic rate ( P
N) was saturated at photosynthetic photon flux density (PPFD) 600-1 100 (mol m -2 s -1, while the PS2 non-cyclic electron transport ( P-rate) showed a maximum at PPFD 800 mol m -2 s -1. With PPFD increasing, either leaf potential photosynthetic CO 2 assimilation activity (F d/F s) and PS2 maximal photochemical activity (F v/F m) decreased or the ratio of the inactive PS2 reaction centres (RC) [(F i – F o)/(F m – F o)] and the slow relaxing non-photochemical Chl fluorescence quenching (q s) increased from PPFD 1 200 mol m -2 s -1, but cyclic electron transport around photosystem 1 (RFp), irradiance induced PS2 RC closure [(F s – F o)/F m – F o)], and the fast and medium relaxing non-photochemical Chl fluorescence quenching (q f and q m) increased remarkably from PPFD 900 (mol m -2 s -1. Hence leaf photosynthesis of young apple leaves saturated at PPFD 800 mol m -2 s -1 and photoinhibition occurred above PPFD 900 mol m -2 s -1. During the photoinhibition at different irradiances, young apple tree leaves could dissipate excess photons mainly by energy quenching and state transition mechanisms at PPFD 900-1 100 mol m -2 s -1, but photosynthetic apparatus damage was unavoidable from PPFD 1 200 mol m -2 s -1. We propose that Chl fluorescence parameter P-rate is superior to the gas exchange parameter P
N and the Chl fluorescence parameter F v/F m as a definition of saturation irradiance and photoinhibition of plant leaves. 相似文献
2.
Rates of net photosynthesis ( P
N) and transpiration ( E), and leaf temperature (T L) of maintenance leaves of tea under plucking were affected by photosynthetic photon flux densities (PPFD) of 200–2 200 μmol
m −2 s −1. P
N gradually increased with the increase of PPFD from 200 to 1 200 μmol m −2 s −1 and thereafter sharply declined. Maximum P
N was 13.95 μmol m −2 s −1 at 1 200 μmol m −2 s −1 PPFD. There was no significant variation of P
N among PPFD at 1 400–1 800 μmol m −2 s −1. Significant drop of P
N occurred at 2 000 μmol m −2 s −1. PPFD at 2 200 μmol m −2 s −1 reduced photosynthesis to 6.92 μmol m −2 s −1. PPFD had a strong correlation with T L and E. Both T L and E linearly increased from 200 to 2 200 μmol m −2 s −1 PPFD. T L and E were highly correlated. The optimum T L for maximum P
N was 26.0 °C after which P
N declined significantly. E had a positive correlation with P
N. 相似文献
3.
African violet ( Saintpaulia ionantha H. Wendl) is one of the most easily and commonly tissue-cultured ornamental plants. Despite this, there are limited reports on photosynthetic capacity and its impact on the plant quality during acclimatization. Various growth, photosynthetic and biochemical parameters and activities of antioxidant enzymes and dehydrins of micropropagated plants were assessed under three light intensities (35, 70, and 100 µmol m ?2 s ?1 photosynthetic photon flux density – PPFD). Fresh and dry plant biomass, plant height, and leaf area were optimal with high irradiance (70–100 µmol m ?2 s ?1 PPFD). Chlorophyll and carotenoid contents and net photosynthesis were optimal in plants grown under 70 µmol m ?2 s ?1 PPFD. Stomatal resistance, malondialdehyde content, and Fv/ Fm values were highest at low light irradiance (35 µmol m ?2 s ?1 PPFD). The activities of three antioxidant enzymes, superoxide dismutase, catalase, and glutathione peroxidase, increased as light irradiance increased, signaling that high light irradiance was an abiotic stress. The accumulation of 55, 33, and 25 kDa dehydrins was observed with all light treatments although the expression levels were highest at 35 µmol m ?2 s ?1 PPFD. Irradiance at 70 µmol m ?2 s ?1 PPFD was suitable for the acclimatization of African violet plants. Both low and high irradiance levels (35 and 100 µmol m ?2 s ?1 PPFD) induced the accumulation of antioxidants and dehydrins in plants which reveals enhanced stress levels and measures to counter it. 相似文献
4.
The physiological ecology of Prasiola stipitata was examined in situ from two supralittoral sites in the Bay of Fundy (Nova Scotian, Canada) during November 2011, when the population was undergoing major expansion. Photosynthetic parameters (effective quantum yield, Φ PSII, maximum quantum yield, Fv/ Fm, and relative electron transport rate, rETR) were evaluated using chlorophyll fluorescence of PSII. A largely shaded and continuously moist population showed no change in Φ PSII from one hour after sunrise to sunset in which natural irradiance varied between 3 and 300 μmol photons m ?2 s ?1. High irradiance (up to 1800 μmol photons m ?2 s ?1) had no apparent negative impacts on either quantum yield or rETR, but high desiccation in the field reduced quantum yield to almost zero. When thalli were brought into the laboratory, no change in Fv/ Fm was observed up to 60% dehydration; however, there was a steep decline in Fv/ Fm between 60% and 85% dehydration. Thalli showed complete recovery of Fv/ Fm within one hour of reimmersion in seawater after 2 days of desiccation. After 15 days of desiccation full recovery required 24 h and after 30 days of desiccation thalli showed only partial recovery. These observations confirm the adaptation to photosynthesis in high irradiances and the rapid recovery following extreme desiccation observed in other Prasiola species. 相似文献
5.
Seedlings of five canopy species of tropical trees from Costa Rica and Puerto Rico were grown in full shade (midday range of photosynthetic photon flux density [PPFD], 100–140 μmol m ?2 s ?1), partial shade (midday PPFD, 400–600 μmol m ?2 s ?1) and full sun (midday PPFD, 1 500–1 800 μmol m ?2 s ?1) for 3 months. The species were Ochroma lagopus (Bombacaceae), a pioneer species; Inga edulis (Fabaceae), found in secondary forest; and Dipteryx panamensis (Fabaceae), Hampea appendiculata (Malvaceae), and Manilkara bidentata (Sapotaceae), three species characteristic of primary forest. After the plants were placed in the dark overnight, chlorophyll fluorescence characteristics were measured for recently expanded and mature leaves. The ratio of variable fluorescence to maximum fluorescence (F v/F m) was used to estimate the degree of chronic photoinhibition. Only individuals of one species, Dipteryx panamensis, showed significant depression of F v/F m after long-term exposure to full sun. The depression was highly correlated with quantum yield of O 2 evolution which also declined after exposure to full sun. The decline may have been related to foliar N concentration. Although all plants were supplied with ample nutrients, foliar N did not increase significantly for Dipteryx seedlings in full sun, whereas it did for Ochroma and Inga. Leaf age affected F v/F m only in the cases of Manilkara, where it was slightly lower in recently expanded leaves, and of Dipteryx where it interacted with the effects of light regime. We conclude that chronic photoinhibition is not common in seedlings of canopy trees of tropical rain forests except when availability of mineral nutrients may be limiting. 相似文献
6.
The responses of photochemical efficiency to desiccation and salinity gradients in an intertidal edible brown macroalga, Sargassum fusiforme (Harvey) Setchell (Sargassaceae, Fucales), were determined using a pulse amplitude modulation (PAM)-chlorophyll fluorometer. The effective quantum yields ( ΔF/ Fm'; = ΦPSII) of photosystem II (PSII) dropped to zero after 360-min aerial exposure under low irradiance (20 μmol photons m −2 s −1) and 120-min exposure under high irradiance (700 μmol photons m −2 s −1) for this species at 20°C and 50% relative humidity. Under these conditions, ΔF/ Fm' failed to recover to initial levels even after 1-day rehydration in seawater. In general, ΔF/ Fm' decreased as desiccation reduced the absolute water content (AWC, %). Nevertheless, when AWC was above ca. 20%, ΔF/ Fm' was mostly restored to initial levels after 1-day rehydration in seawater, suggesting strong tolerance to dehydration. Furthermore, S. fusiforme appeared to tolerate a broad range of salinity (i.e. 15–50 psu) during six days of culture; however, ΔF/ Fm' declined when salinity was <10 and 60 psu. Strong tolerance to dehydration and salinity stress likely provides S. fusiforme an advantage that allows it to flourish in the intertidal habitat. 相似文献
7.
Photosynthetic rates of green leaves (GL) and green flower petals (GFP) of the CAM plant Dendrobium cv. Burana Jade and their sensitivities to different growth irradiances were studied in shade-grown plants over a period
of 4 weeks. Maximal photosynthetic O 2 evolution rates and CAM acidities [dawn/dusk fluctuations in titratable acidity] were higher in leaves exposed to intermediate
sunlight [a maximal photosynthetic photon flux density (PPFD) of 500–600 μmol m −2 s −1] than in leaves grown under full sunlight (a maximal PPFD of 1 000–1 200 μmol m −2 s −1) and shade (a maximal PPFD of 200–250 μmol m −2 s −1). However, these two parameters of GFP were highest in plants grown under the shade and lowest in full sun-grown plants.
Both GL and GFP of plants exposed to full sunlight had lower predawn F v/F m [dark adapted ratio of variable to maximal fluorescence (the maximal photosystem 2 yield without actinic irradiation)] than
those of shade-grown plants. When exposed to intermediate sunlight, however, there were no significant changes in predawn
F v/F m in GL whereas a significant decrease in predawn F v/F m was found in GFP of the same plant. GFP exposed to full sunlight exhibited a greater decrease in predawn F v/F m compared to those exposed to intermediate sunlight. The patterns of changes in total chlorophyll (Chl) content of GL and
GFP were similar to those of F v/F m. Although midday F v/F m fluctuated with prevailing irradiance, changes of midday F v/F m after exposure to different growth irradiances were similar to those of predawn F v/F m in both GL and GFP. The decreases in predawn and midday F v/F m were much more pronounced in GFP than in GL under full sunlight, indicating greater sensitivity in GFP to high irradiance
(HI). In the laboratory, electron transport rate and photochemical and non-photochemical quenching of Chl fluorescence were
also determined under different irradiances. All results indicated that GFP are more susceptible to HI than GL. Although the
GFP of Dendrobium cv. Burana Jade require a lower amount of radiant energy for photosynthesis and this plant is usually grown in the shade,
is not necessarily a shade plant. 相似文献
8.
We compared the responses of sun and shade acclimated saplings of Picea abies and Pinus cembra to excess photosynthetic photon flux density (PPFD) equivalently exceeding the level for saturating net photosynthetic rate
( P
N). Exposure for 2 h up to 2000 μmol(photon) m −2 s −1 did not affect radiant energy saturated P
N. Photoinhibition of photosynthesis was indicated by a small (10 %) reduction of the potential efficiency of photosystem 2
as derived from measurements of chlorophyll fluorescence (F V/F M). However, the extent of F V/F M reduction and half-time for recovery were similar in sun and shade acclimated saplings of both species. Furthermore, the
effect on F V/F M was not stronger when the plants were exposed to excess PPFD at 5 °C instead of 15 °C. Frost-hardening of plants increased
slightly their resistance to excess PPFD. Establishment of these conifer saplings usually acclimated to shade in their natural
habitat may hardly be endangered by a sudden increase of PPFD, e.g., by gap formation.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
9.
The ability of photosynthesis and CAM to acclimate to low (220 µmol m ?2 s ?1; LL) and relatively high (550 µmol m ?2 s ?1; HL) photosynthetic photon flux densities (PPFD) was investigated in the CAM-cycling species Delosperma tradescantioides by means of CO 2 gas exchange and chlorophyll fluorescence analysis. Furthermore, the influence of short-term drought on malic acid accumulation and the activity of photosystem II (PSII) was studied to assess the possible interactions between drought and the prevailing PPFD in this species. HL plants showed features of sun versus shade acclimation relative to LL plants. Nocturnal malic acid accumulation (Δ-malate) and leaf water content also tended to be higher in HL plants. Irrespective of the PPFD during growth, the weak Δ-malate doubled within 3 days of drought. Despite largely restricted CO 2 uptake, photosynthetic activity as estimated from fluorescence analysis declined only ca 5%. After 7 days of drought, when plants showed CAM-idling and Δ-malate had decreased again, potential carbon assimilation was still ca 84% of that in well-watered plants and remained relatively constant throughout the day. Decarboxylation of malic acid accounted for ca 23% of potential assimilation assuming total oxidation of a maximum portion of this organic acid. Drought did not affect predawn maximum photochemical efficiency (F v/F m). Nonphotochemical quenching (qN) increased (24%) in response to desiccation and resulted in a more or less constant reduction state of PSII. This increase in qN resulted mainly from the change in its fast-relaxing component (qNF), while the slow component (qNS) was significant only at or above saturating PPFD in both HL and LL plants. The photon response characteristics of PSII, which differed between LL and HL plants, were unaffected by short-term drought. Photon harvesting and photon use were always adjusted to guarantee a low reduction state of PSII. Results suggest that in both LL and HL plants CAM-cycling may help to stabilize photosynthesis but to a large extent by other means than simply providing internally derived CO 2. 相似文献
10.
A simple and inexpensive feedback control system that provides continuous and precise control of photosynthetic photon flux density (PPFD) in a whole plant cuvette is described. A ‘Plexiglass’ tank is interposed between a light source and cuvette and PPFD changed by varying the level of dyed liquid in the tank. The amount of liquid pumped into or drained from the tank is a function of the difference (error) between a defined set point value of PPFD and that measured in the cuvette. The set point can be varied as a function of time, can follow the output of a quantum sensor measuring ambient PPFD or can be driven by values of PPFD read from a data file. Within the 0.4 to 0.64 μm waveband, the dye acts as a neutral density filter so that there is no change in spectral distribution with PPFD. Photosynthetic photon flux density in the cuvette was controlled to better than 20 μmol m −2s −1 when the set point was varied from 200 to 1100 μmol m −2s −1 over 3 min. When the set point was held constant or changed less rapidly, errors did not exceed 5 μmol m −2s −1. Net photosynthesis of Western redcedar ( Thuja plicata Donn.) seedlings held at 18 °C closely followed rapid changes in PPFD. 相似文献
11.
Diurnal changes of photosynthesis in the leaves of grapevine ( Vitis vinifera × V. labrusca) cultivars Campbell Early and Kyoho grown in the field were compared with respect to gas exchanges and actual quantum yield
of photosystem 2 (Φ PS2) in late May. Net photosynthetic rate (P N) of the two cultivars rapidly increased in the morning, saturated at photosynthetic photon flux density (PPFD) from 1200
to 1500 μmol m −2 s −1 between 10:00 and 12:00 and slowly decreased after midday. Maximum P N was 13.7 and 12.5 μmol m −2 s −1 in Campbell Early and Kyoho, respectively. The stomatal conductance (g s) and transpiration rate changed in parallel with P N, indicating that P N was greatly affected by g s. However, the decrease in P N after midday under saturating PPFD was also associated with the observed depression of Φ PS2 at high PPFD. The substantial increase in the leaf to air vapour pressure deficit after midday might also contribute to decline
of g s and P N. 相似文献
12.
Dissemination of cassava tissue culture plantlets is difficult in the arid tropics due to low eux vitro survival rates. Increased in vitro light intensity has been reported to induce high ex vitro survival rates. The results from earlier experiments suggested that it would be worthwhile to analyse the separate effects of in vitro light and of temperature on the in vitro growth pattern as well as differentiate its relation to ex vitro survival. Accordingly, analysis of a range of in vitro light intensities from 0 to 369 μmol ?1 m ?2 photosynthetic photon flux density (PPFD) was conducted both with and without fans to control the heat. Temperature proved stable at low PPFD levels but increased above 204 μmol s ?1 m ?2 when no fans were used. Increased PPFD levels induced larger fresh and dry masses as well as stem thickness. PPFD levels affected the developmental index (senescent leaf numbers) in vitro when it rose above 204 μmol s ?1 m ?2 PPFD. Raised temperature ranges increased the multiplication index (node numbers) in vitro and ex vitro. It increased root number and leaf development (lobe anatomy). As in vitro temperatures of up to 40°C improve multiplication rates and PPFD levels above 101 μmol s ?1 m ?2 were detrimental for ex vitro survival (as low as 60%), it is suggested that simpler and less costly laboratories with low light levels and a wide range of temperature tolerance could be successfully established in the tropics for in vitro cleaning and rapidly multiplying crops like cassava. 相似文献
13.
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 F v/F m and F v/F 0 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. 相似文献
14.
The effects of temperature, irradiance, and desiccation on the photosynthesis of a cultivated Japanese green alga Caulerpa lentillifera (Caulerpaceae) were determined by a pulse amplitude modulation (PAM)-chlorophyll fluorometer and dissolved oxygen sensors. The photochemical efficiency in the photosystem II (Fv/Fm and ΔF/Fm') during the 72-h temperature exposures (8, 12, 16, 20, 24, 28, 32, 36, and 40°C) was generally stable at 16–32°C but quickly dropped at lower and higher temperatures. The photosynthesis–temperature curve at 200 μmol photons m?2 s?1 also revealed that the maximum gross photosynthesis (GPmax) occurred at 30.7°C (30.5–30.9, 95% highest density credible intervals). Photosynthesis–irradiance curves at 16, 24, and 32°C quickly saturated, then expressed photoinhibition, and revealed that the maximum net photosynthetic rates (NPmax) and saturation irradiance (Ek) were highest at 32°C and lowest at 16°C. Continuous 6-h exposure to irradiances of 200 (low) and 400 (high) μmol photons m?2 s?1 at 16, 24, and 32°C expressed greater declines in their ΔF/Fm' at 16°C, revealing chronic chilling-light stress. The response to continuous desiccation (~480 min) under 50% humidity at 24°C showed that ΔF/Fm' dropped to zero at 480-min aerial exposure, and the treatments of more than 60-min desiccation did not return to the initial level even after 24-h subsequent rehydration in seawater. Likewise, ΔF/Fm' fell when the absolute water content (AWC) of the frond dropped below AWC of 90% and mostly did not return to the initial level even after 24-h subsequent rehydration in seawater, signifying a low tolerance to desiccation. 相似文献
15.
In the field, photosynthesis of Acer saccharum seedlings was rarely light saturated, even though light saturation occurs at about 100 mol quanta m -2 s -1 photosynthetic photon flux density (PPFD). PPFD during more than 75% of the daylight period was 50 mol m -2 s -1 or less. At these low PPFD's there is a marked interaction of PPFD with the initial slope (CE) of the CO 2 response. At PPFD-saturation CE was 0.018 mol m -2 s -1/(l/l). The apparent quantum efficiency (incident PPFD) at saturating CO 2 was 0.05–0.08 mol/mol.
and PPFD-saturated CO 2 exchange was 6–8 mol m -2 s -1. The ratio of internal CO 2 concentration to external ( C
i
/ C
a
) was 0.7 to 0.8 except during sunflecks when it decreased to 0.5. The decrease in C
i
/ C
a
during sunflecks was the result of the slow response of stomates to increased PPFD compared to the response of net photosynthesis. An empirical model, which included the above parameters was used to simulate the measured CO 2 exchange rate for portions of two days. Parameter values for the model were determined in experiments separate from the daily time courses being sumulated. Analysis of the field data, partly through the use of simulations, indicate that the elimination of sunflecks would reduce net carbon gain by 5–10%.List of symbols
A
measured photosynthetic rate under any set of conditions (mol m -2 s -1)
-
A
m
(atm)
measured photosynthetic rate at saturating PPFD, 350 l/l CO 2 and 21% (v/v) O 2 (mol m -2 s -1)
-
C
constant in equation of Smith (1937, 1938)
-
C
a
CO 2 concentration in the air (l/l)
-
C
i
CO 2 concentration in the intercellular air space (l/l)
-
C
i
/*
C
i
corrected for CO 2 compensation point, i.e., C
i
- I
*, (l/l)
- CE
initial slope of the CO 2 response of photosynthesis (mol m -2 s -1/(l/l))
- CEM
CE at PPFD saturation
-
E
transpiration rate (mmol m -2 s -1)
-
F
predicted photosynthetic rate (mol m -2 s -1)
-
G
leaf conductance to H 2O (mol m -2 s -1)
-
I
photosynthetic photon flux density (mol m -2 s -1)
-
N
number of data points
-
P
m
predicted photosynthetic rate at saturating CO 2 and given PPFD (mol m -2 s -1)
-
P
ml
predicted photosynthetic rate at saturating CO 2 and PPFD (mol m -2 s -1)
-
R
d
residual respiratory rate (mol m -2 s -1)
-
T
a
air temperature (°C)
-
T
l
leaf temperature (°C)
-
V
reaction velocity in equation of Smith (1937, 1938)
-
V
max
saturated reaction velocity in equation of Smith (1937, 1938)
- VPA
vapor pressure of water in the air (mbar/bar)
- VPD
vapor pressure difference between leaf and air (mbar/bar)
-
X
substrate concentration in equation of Smith (1937, 1938)
-
initial slope of the PPFD response of photosynthesis at saturating CO 2 (mol CO 2/mol quanta)
- (atm)
initial slope of the PPFD response of photosynthesis at 340 l/l CO 2 and 21% (v/v) O 2 (mol CO 2/mol quanta)
-
I
*
CO 2 compensation point after correction for residual respiration (l/l)
-
PPFD compensation point (mol m -2 s -1) 相似文献
16.
Hylocereus undatus (Haworth) Britton and Rose growing in controlled environment chambers at 370 and 740 μmol CO 2 mol ?1 air showed a Crassulacean acid metabolism (CAM) pattern of CO 2 uptake, with 34% more total daily CO 2 uptake under the doubled CO 2 concentration and most of the increase occurring in the late afternoon. For both CO 2 concentrations, 90% of the maximal daily CO 2 uptake occurred at a total daily photosynthetic photon flux density (PPFD) of only 10 mol m ?2 day ?1 and the best day/night air temperatures were 25/15°C. Enhancement of the daily net CO 2 uptake by doubling the CO 2 concentration was greater under the highest PPFD (30 mol m ?2 day ?1) and extreme day/night air temperatures (15/5 and 45/35°C). After 24 days of drought, daily CO 2 uptake under 370 μmol CO 2 mol ?1 was 25% of that under 740 μmol CO 2 mol ?1. The ratio of variable to maximal chlorophyll fluorescence (F y/F m) decreased as the PPFD was raised above 5 mol m ?2 day ?1, at extreme day/night temperatures and during drought, suggesting that stress occurred under these conditions. F v/F m was higher under the doubled CO 2 concentration, indicating that the current CO 2 concentration was apparently limiting for photosynthesis. Thus net CO 2 uptake by the shade-tolerant H. undatus, the photosynthetic efficiency of which was greatest at low PPFDs. showed a positive response to doubling the CO 2 concentration, especially under stressful environmental conditions. 相似文献
17.
Recovery from 60 min of photoinhibitory treatment at photosynthetic photon flux densities of 500, 1400 and 2200 μMmol m ?2 s ? was followed in cells of the green alga Chlamydomonas reinhardtii grown at 125 μMmol m ?2 s ?1. These light treatments represent photoregulation, moderate photoinhibition and strong photoinhibition, respectively. Treatment in photoregulatory light resulted in an increased maximal rate of oxygen evolution (P max) and an increased quantum yield (Φ), but a 15% decrease in F v/F M. Treatment at moderately photoinhibitory light resulted in a 30% decrease in F v/F M and an approximately equal decrease in Φ. Recovery in dim light restored F v/F M within 15 and 45 min after high light treatment at 500 and 1400 μMmol m ?2 s ?1, respectively. Convexity (Θ), a measure of the extent of co-limitation between PS II turnover and whole-chain electron transport, and Φ approached, but did not reach the control level during recovery after exposure to 1400 μMmol m ?2 s ?1, whereas P max increased above the control. Treatment at 2200 μMmol m ?2 s ?1 resulted in a strong reduction of the modeled parameters Φ, Θ and P max. Subsequent recovery was initially rapid but the rate decreased, and a complete recovery was not reached within 120 min. Based on the results, it is hypothesized that exposure to high light results in two phenomena. The first, expressed at all three light intensities, involves redistribution within the different aspects of PS II heterogeneity rather than a photoinhibitory destruction of PS II reaction centers. The second, most strongly expressed at 2200 μmol m ?2 s ?1, is a physical damage to PS II shown as an almost total loss of PS II α and PS II Q B-reducing centers. Thus recovery displayed two phase, the first was rapid and the only visible phase in algae exposed to 500 and 1400 μmol m ?2 s ?1. The second phase was slow and visible only in the later part of recovery in cells exposed to 2200 μmol m ?2 s ?1. 相似文献
18.
Independent short-term effects of photosynthetic photon flux density (PPFD) of 50–400 μmol m −2 s −1, external CO 2 concentration ( C
a) of 85–850 cm 3 m −3, and vapor pressure deficit (VPD) of 0.9–2.2 kPa on net photosynthetic rate ( P
N), stomatal conductance ( g
s), leaf internal CO 2 concentration ( C
i), and transpiration rates ( E) were investigated in three cacao genotypes. In all these genotypes, increasing PPFD from 50 to 400 μmol m −2 s −1 increased P
N by about 50 %, but further increases in PPFD up to 1 500 μmol m −2 s −1 had no effect on P
N. Increasing C
a significantly increased P
N and C
i while g
s and E decreased more strongly than in most trees that have been studied. In all genotypes, increasing VPD reduced P
N, but the slight decrease in g
s and the slight increase in C
i with increasing VPD were non-significant. Increasing VPD significantly increased E and this may have caused the reduction in P
N. The unusually small response of g
s to VPD could limit the ability of cacao to grow where VPD is high. There were no significant differences in gas exchange
characteristics ( g
s, C
i, E) among the three cacao genotypes under any measurement conditions. 相似文献
19.
Genetically modified potato ( Solanum tuberosum L. cv. Desiree) and tobacco ( Nicotiana tabacum cv. Samsun N.N.) plants were used to analyze the effects exerted by the chloroplastic (cp) fructose- 1,6-bisphosphatase (FBPase) on the regulation of light energy discrimination at the level of photosystem II. The cp-FBPase activity was progressively inhibited by an mRNA antisense to this FBPase. The chlorophyll fluorescence quenching parameters of these transgenic plants were compared to those of wild-type and transgenic plants that were acclimated to low temperatures. In particular various lines of the transgenic potato and tobacco plants were exposed to a temperature treatment of 10 and 20°C for 10 days. Light intensities were kept low to reduce photoinhibition so that we could analyze exclusively the effects of a modification in the carbon fixation cycle on the chlorophyll fluorescence quenching parameters. The photon flux densities (PFDs) employed at the level of the middle leaves of all plants were set to two different values of 10 μmol m ?2 s ?1 and 50 μmol m ?2 s ?1. Subsequent to this 10-day acclimation the chlorophyll-fluorescence parameters of all plants were measured. Photoinhibition as expressed by the F y/F m ratio was minor in plants subjected to a PFD of 10 μmol m ?2 s ?1. Higher photon fluence rates of 50 μmol m ?2 s ?1 at temperatures of 10°C gave rise to a significant reduction in the F y/F m ratios obtained from the transgenic plants which were characterized by a restriction in cp-FBPase capacity to 20% of normal activity. Furthermore, a progressive inhibition of the cp-FBPase activity induced an amplified nonphotochemical quenching of chlorophyll fluorescence with in the genetically manipulated species (except at 10°C and 50 μmol m ?2 s ?1). The increase in nonphotochemical quenching depended upon light and temperature. Photochemical quenching of light quanta within the antisense plants declined relative to that in the wild type. To further characterize the mechanisms producing higher levels of nonphotochemical fluorescence quenching. we analyzed several of the xanthophyll cycle pigments. The deepoxidation state of the xanthophyll cycle pigments in potato plants increased with attenuating FBPase activities under all conditions. For tobacco plants, this elevation of the deepoxidation state was only observed at a PFD of 50 μmol m ?2 s ?1. 相似文献
20.
This paper reports on the fast fluorescence responses of Gardenia jasminoides Ellis plantlets, at two successive stages (shoot multiplication and root induction) of culture in vitro. We test whether plantlets in vitro suffer photoinhibition during culture and whether the degree of photoautotrophy of these mixotrophic plantlets has any effect on the extent of photoinhibitory impairment. In this regard the effects of different sucrose levels in the medium and PPFD during growth on the development of photoautotrophy and the extent of photoinhibition were evaluated. Plantlets were grown under low, intermediate, and high (50, 100, and 300 mol m -2 s -1) PPFD, and at 3 different sucrose concentrations (0.5, 1.5, and 3.0%, w/v) in the medium, during shoot multiplication. During root induction the same growth conditions were assayed except for the high PPFD. The development of photoautotrophy was assessed via the difference between the stable carbon isotope composition of sucrose used as heterotrophic carbon source and that of leaflets grown in vitro. Plantlets from root induction showed more developed photoautotrophy than those from shoot multiplication. For both stages the low-sucrose medium stimulated the photoautotrophy of plantlets in vitro. In addition, intermediate PPFD induced photoautotrophy during shoot multiplication. For plantlets of both culture stages at the lowest PPFD no photoinhibition occurred irrespective of the sucrose concentration in media. However, during the shoot multiplication stage chlorophyll fluorescence measurements showed a decrease in F
v
/F
m
and in t
1/2 as growing PPFD increased, indicating photoinhibitory damage. The decline of F
v
/F
m
was caused mostly by an increase in F
o
, indicating the inactivation of PSII reaction centers. However plantlets growing under low sucrose showed reduced susceptibility to photoinhibition. During root induction, only plantlets cultured with high sucrose showed a decrease in F
v
/F
m
as PPFD increased, although t
1/2 remained unchanged. In this case, the decline of F
v
/F
m
was mostly due to a decrease in F
m
, which indicates increased photoprotection rather than occurrence of photodamage. Therefore, growth in low-sucrose media had a protective effect on the resistance of PSII to light stress. In addition, plantlets were more resistant to photoinhibition during root induction than during shoot multiplication. Results suggest that increased photoautotrophy of plantlets reduces susceptibility to photoinhibition during gardenia culture in vitro.Abbreviations AP
apparent photosynthesis
- Chl
total chlorophyll content
- Chl a/b
chlorophyll a-to-b ratio
- Chl/Car
total chlorophyll-to-carotenoids ratio
- 13C
ratio of 13C/ 12C relative to PeeDee belemnite standard
- F
m
maximum chlorophyll fluorescence
- F
o
fluorescence emission when all reaction centres are open and the photochemical quenching is minimal
- F
v
variable chlorophyll fluorescence (F
m
-F
o
)
- F
v
/F
m
the ratio of variable to maximum chlorophyll fluorescence, indicator photochemical efficiency of PSII
- MS medium
Murashige and Skoog (1962) medium
- PPFD
photosynthetic photon flux density
- Rd
dark respiration, t
1/2 the half-time of the increase from F
o
to F
m
- IAA
indole butyric acid 相似文献
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