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1.
Summary Temporary immersion bioreactors are an efficient tool for plant mass propagation because they increase multiplication rate
and plant quality. Little knowledge is available on the ecosystem and physiological behavior of plantlets when using this
new culture technique. In order to evaluate the effects of the conditions on physiological change of pineapple plantlets,
a factorial experiment was conducted, where axillary clusters were cultured under two levels of photosynthetic photon flux
(PPF): 30 μmol m−2s−1 (low) and 225 μmol m−2s−1 (high), using two culture methods (conventional micropropagation in liquid medium and a temporary immersion bioreactor) during
the elongation phase. CO2 concentration in the headspace volume container was measured during a whole cycle of temporary immersion (3h). At the time
before the next immersion period, the levels of CO2 increased significantly to 14171 μmol mol−1 at high PPF. The maximal photosynthetic rate as well as the maximum quantum yield of photosystem II were low for plantlets
cultivated in the femporary immersion bioreactor at high PPF. However, these plantlets showed large increases in sugar and
nitrogen uptake and also increases in dry weight and foliar area. These results indicate that shoot growth did not totally
depend on the photosynthesis process. In vitro pineapple plantlets appeared to use more nutrients in the culture medium than those from photosynthesis. In summary, temporary
immersion bioreactor-derived plantlets showed remarkable nutrient uptake, indicating a higher photo-mixotrophic metabolism. 相似文献
2.
Summary
In vitro banana (Musa spp.) shoots were cultured under photomixotrophic (30 gl−1 sucrose and 0.2 h−1 number of air exchanges of culture vessels) and photoautotrophic (0 gl−1 sucrose and 3.9 h−1 number of air exchanges) conditions for 28 d in 370 cm3 Magenta boxes (GA7-type) containing 70 ml of half-strength Murashige and Skoog (MS) medium with 22.2 μM N6-benzyladenine (BA). The effects of varying CO2 concentration (475 or 1340 μmol mol−1) and light intensity (photosynthetic photon flux (PPF) of 100 or 200 μmol m−2 s−1) were investigated. Fresh and dry weights of banana shoots grown photomixotrophically were significantly greater on day 28
than those grown photoautotrophically. Photoautorophic shoots had a larger number of unfolded leaves and greater leaf area
than photomixotrophic plants by days 14 and 28, regardless of CO2 concentration. The shoot fresh and dry weights on day 14 in photoautotrophic conditions were significantly greater at PPF
of 200 μmol m−2 s−1 than at 100 μmol m−2 s−1. The increase in net photosynthetic rate of photoautotrophic banana shoots was significant compared with photomixotrophic
shoots. The multiplication ratio of in vitro banana shoots grown photoautotrophically in a 28-d culture period was the greatest at 100 μmol m−2 s−1 PPF and 475 μmol mol−1 CO2. 相似文献
3.
Photosynthetic Response of Carrots to Varying Irradiances 总被引:7,自引:3,他引:4
Response to irradiance of leaf net photosynthetic rates (P
N) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled
environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 μmol m−2 s−1 at 20 °C and 350 μmol (CO2) mol−1(air). The values of P
N were fitted to a rectangular hyperbolic nonlinear regression model. P
N for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher P
N than CC. None of the cultivars reached saturation at 1 000 μmol m−2 s−1. The predicted P
N at saturation (P
Nmax) for Cascade, CC, Oranza, and RCC were 19.78, 16.40, 19.79, and 18.11 μmol (CO2) m−2 s−1, respectively. The compensation irradiance (I
c) occurred at 54 μmol m−2 s−1 for Cascade, 36 μmol m−2 s−1 for CC, 45 μmol m−2 s−1 for Oranza, and 25 μmol m−2 s−1 for RCC. The quantum yield among the cultivars ranged between 0.057–0.033 mol(CO2) mol−1(PAR) and did not differ. Dark respiration varied from 2.66 μmol m−2 s−1 for Cascade to 0.85 μmol m−2 s−1 for RCC. As P
N increased with PAR, intercellular CO2 decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between
600 and 800 μmol m−2 s−1 followed by a steep decline resulting in sharp increases in water use efficiency.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
4.
The response of barley (Hordeum vulgare L. cv. Akcent) to various photosynthetic photon flux densities (PPFDs) and elevated [CO2] [700 μmol (CO2) mol−1; EC] was studied by gas exchange, chlorophyll (Chl) a fluorescence, and pigment analysis. In comparison with barley grown under ambient [CO2] [350 μmol (CO2) mol−1; AC] the EC acclimation resulted in a decrease in photosynthetic capacity, reduced stomatal conductance, and decreased total
Chl content. The extent of acclimation depression of photosynthesis, the most pronounced for the plants grown at 730 μmol
m−2 s−1 (PPFD730), may be related to the degree of sink-limitation. The increased non-radiative dissipation of absorbed photon energy for
all EC plants corresponded to the higher de-epoxidation state of xanthophylls only for PPFD730 barley. Further, a pronounced decrease in photosystem 2 (PS2) photochemical efficiency (given as FV/FM) for EC plants grown at 730 and 1 200 μmol m−2 s−1 in comparison with AC barley was related to the reduced epoxidation of antheraxanthin and zeaxanthin back to violaxanthin
in darkness. Thus the EC conditions sensitise the photosynthetic apparatus of high-irradiance acclimated barley plants (particularly
PPFD730) to the photoinactivation of PS2.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
Hemant Lata Suman Chandra Ikhlas Khan Mahmoud A. ElSohly 《In vitro cellular & developmental biology. Plant》2009,45(1):12-19
Induction of high-frequency shoot regeneration using nodal segments containing axillary buds from a 1-yr-old mother plants
of Cannabis sativa was achieved on Murashige and Skoog (MS) medium containing 0.05–5.0 μM thidiazuron. The quality and quantity of regenerants
were better with thidiazuron (0.5 μM thidiazuron) than with benzyladenine or kinetin. Adding 7.0 μM of gibberellic acid into
a medium containing 0.5 μM thidiazuron slightly increased shoot growth. Elongated shoots when transferred to half-strength
MS medium supplemented with 500 mg l−1 activated charcoal and 2.5 μM indole-3-butyric acid resulted in 95% rooting. The rooted plants were successfully acclimatized
in soil. Following acclimatization, growth performance of 4-mo-old in vitro propagated plants was compared with ex vitro vegetatively grown plants of the same age. The photosynthesis and transpiration characteristics were studied under different
light levels (0, 500, 1,000, 1,500, or 2,000 μmol m−2 s−1). An increase in photosynthesis was observed with increase in the light intensity up to 1,500 μmol m−2 s−1 and then decreased subsequently at higher light levels in both types of plants. However, the increase was more pronounced
at lower light intensities below 500 μmol m−2 s−1. Stomatal conductance and transpiration increased with light intensity up to highest level (2000 μmol m−2 s−1) tested. Intercellular CO2 concentration (C
i) and the ratio of intercellular CO2 concentration to ambient CO2 (C
i/C
a) decreased with the increase in light intensity in both in vitro as well as ex vitro raised plants. The results show that in vitro propagated and hardened plants were functionally comparable to ex vitro plants of same age in terms of gas and water vapor exchange characteristics, within the limits of this study. 相似文献
6.
Huguette Sallanon Monique Berger Catherine Genoud Alain Coudret 《In vitro cellular & developmental biology. Plant》1998,34(2):169-172
Summary MicropropagatedRosa hybrida plantlets were simultaneously rooted and acclimatized under 100 and 200 μmol m−2 s−1 light for 2 wk. At the end of the first week of acclimatization, the plantlets were transferred onto a low water potential
medium (from −0.06 MPa to −0.3 MPa). Dry weight was decreased by increased hight and low water potential. Photoinhibition
of photosynthesis, expressed as a decrease in Fv/Fm ratio and ΦPSII and an increase in 1 −qp, occurred in plants grown under
200 μmol m−2 s−1. When high light (200 μmol m−2 s−1) and water stress were applied simultaneously, their effects on chlorophyll fluorescence parameters depended on stress duration;
after 1 d of water stress, photoinhibition was more pronounced; after 7 d of stress, Fv/Fm ratio and ΦPSII were higher than
after 1 d of stress; photoinhibition was reduced. This suggests that after a 1-d stress, the effect of water stress alone
included a superimposed effect of photoinhibition to which the water-stressed plants were sensitized; after 7 d, plantlets
had adapted to water stress. The photoprotective effects under high light might result in energy dissipative mechanisms linked
to photochemical and nonphotochemical quenching other than CO2 fixation. 相似文献
7.
The concept of using higher plants to maintain a sustainable life support system for humans during long-duration space missions is dependent upon photosynthesis. The effects of extended exposure to microgravity on the development and functioning of photosynthesis at the leaf and stand levels were examined onboard the International Space Station (ISS). The PESTO (Photosynthesis Experiment Systems Testing and Operations) experiment was the first long-term replicated test to obtain direct measurements of canopy photosynthesis from space under well-controlled conditions. The PESTO experiment consisted of a series of 21–24 day growth cycles of Triticum aestivum L. cv. USU Apogee onboard ISS. Single leaf measurements showed no differences in photosynthetic activity at the moderate (up to 600 μmol m−2 s−1) light levels, but reductions in whole chain electron transport, PSII, and PSI activities were measured under saturating light (>2,000 μmol m−2 s−1) and CO2 (4000 μmol mol−1) conditions in the microgravity-grown plants. Canopy level photosynthetic rates of plants developing in microgravity at ∼280 μmol m−2 s−1 were not different from ground controls. The wheat canopy had apparently adapted to the microgravity environment since the CO2 compensation (121 vs. 118 μmol mol−1) and PPF compensation (85 vs. 81 μmol m−2 s−1) of the flight and ground treatments were similar. The reduction in whole chain electron transport (13%), PSII (13%), and PSI (16%) activities observed under saturating light conditions suggests that microgravity-induced responses at the canopy level may occur at higher PPF intensity. 相似文献
8.
This work describes the long-term acclimation of the halotolerant microalga Dunaliella viridis to different photon irradiance, ranging from darkness to 1500 μmol m−2 s−1. In order to assess the effects of long-term photoinhibition, changes in oxygen production rate, pigment composition, xanthophyll
cycle and in vivo chlorophyll fluorescence using the saturating pulse method were measured. Growth rate was maximal at intermediate irradiance
(250 and 700 μmol m−2 s−1). The increase in growth irradiance from 700 to 1500 μmol m−2 s−1 did not lead to further significant changes in pigment composition or EPS, indicating saturation in the pigment response
to high light. Changes in Photosystem II optimum quantum yield (Fv/Fm) evidenced photoinhibition at 700 and especially at 1500 μmol m−2 s−1. The relation between photosynthetic electron flow rate and photosyntetic O2 evolution was linear for cultures in darkness shifting to curvilinear as growth irradiance increased, suggesting the interference
of the energy dissipation processes in oxygen evolution. Carbon assimilation efficiencies were studied in relation to changes
in growth rate, internal carbon and nitrogen composition, and organic carbon released to the external medium. All illuminated
cultures showed a high capability to maintain a C:N ratio between 6 and 7. The percentage of organic carbon released to the
external medium increased to its maximum under high irradiance (1500 μmol m−2 s−1). These results suggest that the release of organic carbon could act as a secondary dissipation process when the xanthophyll
cycle is saturated.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
9.
Photosynthetic properties of carnivorous plants have not been well characterized and the extent to which photosynthesis contributes
to carbon gain in most carnivorous plants is also largely unknown. We investigated the photosynthetic light response in three
carnivorous plant species, Drosera rotundifolia L. (sundew; circumpolar and native to northern British Columbia, Canada), Sarracenia leucophylla Rafin. (‘pitcher-plant’; S.E. United States), and D. capensis L. (sundew; Cape Peninsula, South Africa), using portable gas-exchange systems to explore the capacity for photosynthetic
carbon gain in carnivorous plant species. Maximal photosynthetic rates (1.32–2.22 μmol m−2 s−1 on a leaf area basis) and saturating light intensities (100 to 200 μmol PAR m−2 s−1) were both low in all species and comparable to shade plants. Field or greenhouse-grown D. rotundifolia had the highest rates of photosynthesis among the three species examined. Dark respiration, ranging from −1.44 (S. leucophylla) to −3.32 (D. rotundifolia) μmol m−2 s−1 was high in comparison to photosynthesis in the species examined. Across greenhouse-grown plants, photosynthetic light compensation
points scaled with light-saturated photosynthetic rates. An analysis of gas-exchange and growth data for greenhouse-grown
D. capensis plants suggests that photosynthesis can account for all plant carbon gain in this species. 相似文献
10.
In an experimental site for reforestation of degraded area, three-year-old plants of Bertholletia excelsa Humb. & Bonpl. were subjected to different fertilization treatments: T0 = unfertilized control, T1 = green fertilization
(branches and leaves) and T2 = chemical fertilization. Higher net photosynthetic rates (P
N) were observed in T1 [13.2±1.0 μmol(CO2) m−2 s−1] compared to T2 [8.0±1.8 μmol(CO2) m−2 s−1] and T0 [4.8±1.3 μmol(CO2) m−2 s−1]. Stomatal conductance (g
s), transpiration rate (E) and water use efficiency (WUE) of individuals of T1 and T2 did not differ significantly, however, they were by 88, 55 and
63%, respectively, higher in T1 than in the control. The mean values of variable fluorescence (Fv), performance index (P.I.) and total chlorophyll [Chl (a+b)] were higher in T1. Our results indicate that green fertilization improves photosynthetic structure and function in plants
of B. excelsa in young phase. 相似文献
11.
Summary
Caustis blakei is an attractive cut foliage plant harvested from the wild in Australia and marketed under the name of koala fern. Previous
attempts to propagate large numbers of this plant have been unsuccessful. The effect of four light irradiances on organogenesis
from compact and friable callus of C. blakei was studied for 21 wk. Both callus types produced numerous primordial shoots but many failed to develop into green plantlets.
However, significantly more primordial shoots and green plantlets developed on the friable callus than on the compact callus,
and significantly more green plantlets were regenerated under the higher photon irradiances of 200 and 300 μmol m−2s−1 than under the lower irradiances of 100 and 150 μmol m−2s−1. The compact callus produced its maximum number of green plantlets early in the experiment (after 9 wk), while the friable
callus continued to produce primordial shoots and green plantelets throughout the period of the experiment, and reached its
maximum production of green plantlets at 21 wk under the irradiance of 300 μmol m−2s−1. Organogenesis from friable callus under high irradiance (300 μmol m−2s−1) offers an efficient propagation method for C. blakei. 相似文献
12.
Nuphar lutea is an amphibious plant with submerged and aerial foliage, which raises the question how do both leaf types perform photosynthetically
in two different environments. We found that the aerial leaves function like terrestrial sun-leaves in that their photosynthetic
capability was high and saturated under high irradiance (ca. 1,500 μmol photons m−2 s−1). We show that stomatal opening and Rubisco activity in these leaves co-limited photosynthesis at saturating irradiance fluctuating
in a daily rhythm. In the morning, sunlight stimulated stomatal opening, Rubisco synthesis, and the neutralization of a night-accumulated
Rubisco inhibitor. Consequently, the light-saturated quantum efficiency and rate of photosynthesis increased 10-fold by midday.
During the afternoon, gradual closure of the stomata and a decrease in Rubisco content reduced the light-saturated photosynthetic
rate. However, at limited irradiance, stomatal behavior and Rubisco content had only a marginal effect on the photosynthetic
rate, which did not change during the day. In contrast to the aerial leaves, the photosynthesis rate of the submerged leaves,
adapted to a shaded environment, was saturated under lower irradiance. The light-saturated quantum efficiency of these leaves
was much lower and did not change during the day. Due to their low photosynthetic affinity for CO2 (35 μM) and inability to utilize other inorganic carbon species, their photosynthetic rate at air-equilibrated water was
CO2-limited. These results reveal differences in the photosynthetic performance of the two types of Nuphar leaves and unravel how photosynthetic daily rhythm in the aerial leaves is controlled. 相似文献
13.
In three tropical rain forest light environments in Sabah, Malaysia, we compared photosynthesis in seedlings of ten climax
tree species with putatively differing shade tolerances. The objectives of the study were (a) to characterise the range of
photosynthetic responses in ten species of the Dipterocarpaceae and (b) to elucidate those photosynthetic characteristics
that might provide a basis for niche partitioning. Seedlings were acclimated (c. 7 months) in three light environments; understorey, partial shade and a gap (140 m2). The light environments represented a gradation in median diurnal (0630–1830 hours) photon flux density (PFD) ranging from
understorey (4.7 μmol m−2 s−1), through partial shade (21.2 μmol m−2 s−1) to gap (113.7 μmol m−2 s−1). Integrated diurnal PFD were in the sequence gap > partial shade > understorey (15.2, 4.7, 1.3 mol m−2 day−1, respectively). In gap-acclimated plants, species differed in the photosynthetic light-response variables apparent quantum
yield, dark respiration rate, light compensation point, net saturated leaf assimilation rate (A
sat), and in stomatal conductance (g
s sat) when assimilation rate (A) was saturated. A light-demanding pioneer species (Macaranga hypoleuca) and a shade-demanding understorey species (Begonia sp.) had, respectively, higher and lower A
sat and g
s sat than the dipterocarp species. In high-light conditions A
sat and g
s sat were strongly positively correlated in dipterocarp species. Differing photosynthetic characteristics of gap-acclimated plants
suggest that, in these dipterocarp species, different rates of carbon fixation may be an important factor contributing towards
niche partitioning. Mean integrated diurnal A (A
diurnal) in the gap, partial shade and understory were, respectively, 122.9, 52.7, 20.5 mmol m−2 day−1. Differences occurred in A
diurnal of dipterocarp species between light environments. When Macaranga was included, differences in A
diurnal were evident in the gap and partial shade, and in both cases were attributed to the pioneer. For the variable A
diurnal, there was of a shift in the rank position of Macaranga among light environments, but a shift did not occur among the dipterocarp species. Results from this study are consistent
with the idea that rates of carbon fixation per unit leaf area may contribute towards niche differentiation between the climax
and single pioneer species, but not within the group of climax species. Other physiological and/or carbon allocation factors
may be involved in any niche partitioning; dipterocarp species often have inherently different growth rates and susceptibility
to herbivory. As an alternative to niche partitioning, dipterocarp species may co-exist in natural light environments as a
result of habitat disequilibrium or purely stochastic processes.
Received: 2 April 1997 / Accepted: 13 July 1997 相似文献
14.
Genotypic variation in photosynthesis in cacao is correlated with stomatal conductance and leaf nitrogen 总被引:1,自引:0,他引:1
Variation in photosynthetic parameters was observed between eight contrasting cacao (Theobroma cacao) genotypes. Net photosynthetic rate (PN) ranged from 3.4 to 5.7 μmol(CO2) m−2 s−1 for the genotypes IMC 47 and SCA 6, respectively. Furthermore, genotypic differences were detected in quantum efficiency
ranging from 0.020 to 0.043 μmol(CO2) μmol−1(photon) for UF 676 and AMAZ 15/15, respectively. Differences in PN were correlated with both stomatal conductance (gs) and leaf nitrogen per unit area. Some variation in water use efficiency was observed between genotypes, both intrinsic (PN/gs) and instantaneous (PN/transpiration rate). Both measures of water use efficiency were a negative function of specific leaf area. Evidence was found
for a trade-off mechanism between cacao genotypes in photosynthesis and leaf structure. High photosynthetic rate, expressed
on a mass basis was associated with smaller leaves. Furthermore, thinner leaves were compensated for by a higher nitrogen
content per unit mass. 相似文献
15.
The ability of spring barley (Hordeum vulgare cv. Akcent) to adjust the composition and function of the photosynthetic apparatus to growth irradiances of 25–1200 μmol
m−2 s−1 was studied by gas exchange and chlorophyll a fluorescence measurements and high-performance liquid chromatography. The increased growth irradiance stimulated light- and
CO2-saturated rates of CO2 assimilation expressed on a leaf area basis up to 730 μmol m−2 s−1 (HL730), whereas at an irradiance of 1200 μmol m−2 s−1 (EHL1200) both rates decreased significantly. Further, the acclimation to EHL1200 was associated with an extremely high chlorophyll
a/b ratio (3.97), a more than doubled xanthophyll cycle pool (VAZ) and a six-fold higher de-epoxidation state of the xanthophyll
cycle pigments as compared to barley grown under 25 μmol m−2 s−1 (LL25). EHL1200 plants also exhibited a long-term inhibition of Photosystem II (PS II) photochemical efficiency (F
v/F
m). Photosynthetic capacity, chlorophyll a/b and VAZ revealed a linear trend of dependence on PS II excitation pressure in a certain range of growth irradiances (100–730
μmol m−2 s−1). The deviation from linearity of these relationships for EHL1200 barley is discussed. In addition, the role of increased
VAZ and/or accumulation of zeaxanthin and antheraxanthin in acclimation of barley to high irradiance is studied with respect
to regulation of non-radiative dissipation and/or photochemical efficiency within PS II.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
16.
The purpose of this study was to clarify effects of anthocyanins on photosynthesis and photoinhibition in green and red leaves
of Oxalis triangularis. Gas analysis indicated that green plants had the highest apparent quantum yield for CO2 assimilation [0.051 vs. 0.031 μmol(CO2) μmol−1(photon)] and the highest maximum photosynthesis [10.07 vs. 7.24 μmol(CO2) m−2 s−1], while fluorescence measurements indicated that red plants had the highest PSII quantum yield [0.200 vs. 0.143 μmol(e−) μmol−1(photon)] and ETRmax [66.27 vs. 44.34 μmol(e−) m−2 s−1]. Red plants had high contents of anthocyanins [20.11 mg g−1(DM)], while green plants had low and undetectable levels of anthocyanin. Red plants also had statistically significantly
(0.05>p>0.01) lower contents of xanthophyll cycle components [0.63 vs. 0.76 mg g−1(DM)] and higher activities of the reactive oxygen scavenging enzyme ascorbate peroxidase [41.2 vs. 10.0 nkat g−1(DM)]. Anthocyanins act as a sunscreen, protecting the chloroplasts from high light intensities. This shading effect causes
a lower photosynthetic CO2 assimilation in red plants compared to green plants, but a higher quantum efficiency of photosystem II (PSII). Anthocyanins
contribute to photoprotection, compensating for lower xanthophyll content in red plants, and red plants are less photoinhibited
than green plants, as illustrated by the Fv/Fm ratio. 相似文献
17.
Six months old in vitro-grown Anoectochilus formosanus plantlets were transferred to ex-vitro acclimation under low irradiance, LI [60 μmol(photon) m−2 s−1], intermediate irradiance, II [180 μmol(photon) m−2 s−1], and high irradiance, HI [300 μmol(photon) m−2 s−1] for 30 d. Imposition of II led to a significant increase of chlorophyll (Chl) b content, rates of net photosynthesis (P
N) and transpiration (E), stomatal conductance (g
s), electron transfer rate (ETR), quantum yield of electron transport from water through photosystem 2 (ΦPS2), and activity of ribulose-1,5-bisphosphate carboxylase/ oxygenase (RuBPCO, EC 4.1.1.39). This indicates that Anoectochilus was better acclimated at II compared to LI treatment. On the other hand, HI acclimation led to a significant reduction of
Chl a and b, P
N, E, g
s, photochemical quenching, dark-adapted quantum efficiency of open PS2 centres (Fv/Fm), probability of an absorbed photon reaching an open PS2 reaction centre (Fv′/Fm′), ETR, ΦPS2, and energy efficiency of CO2 fixation (ΦCO2/ΦPS2). This indicates that HI treatment considerably exceeded the photo-protective capacity and Anoectochilus suffered HI induced damage to the photosynthetic apparatus. Imposition of HI significantly increased the contents of antheraxanthin
and zeaxanthin (ZEA), non-photochemical quenching, and conversion of violaxanthin to ZEA. Thus Anoectochilus modifies its system to dissipate excess excitation energy and to protect the photosynthetic machinery. 相似文献
18.
Stomatal and non-stomatal limitations to photosynthesis in field-grown grapevine cultivars 总被引:1,自引:1,他引:0
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 (ΦPS2) in late May. Net photosynthetic rate (PN) 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 PN was 13.7 and 12.5 μmol m−2 s−1 in Campbell Early and Kyoho, respectively. The stomatal conductance (gs) and transpiration rate changed in parallel with PN, indicating that PN was greatly affected by gs. However, the decrease in PN after midday under saturating PPFD was also associated with the observed depression of ΦPS2 at high PPFD. The substantial increase in the leaf to air vapour pressure deficit after midday might also contribute to decline
of gs and PN. 相似文献
19.
The differences in pigment levels, photosynthetic activity and the chlorophyll fluorescence decrease ratio R
Fd (as indicator of photosynthetic rates) of green sun and shade leaves of three broadleaf trees (Platanus acerifolia Willd., Populus alba L., Tilia cordata Mill.) were compared. Sun leaves were characterized by higher levels of total chlorophylls a + b and total carotenoids x + c as well as higher values for the weight ratio chlorophyll (Chl) a/b (sun leaves 3.23–3.45; shade leaves: 2.74–2.81), and lower values for the ratio chlorophylls to carotenoids (a + b)/(x + c) (with 4.44–4.70 in sun leaves and 5.04–5.72 in shade leaves). Sun leaves exhibited higher photosynthetic rates P
N on a leaf area basis (mean of 9.1–10.1 μmol CO2 m−2 s−1) and Chl basis, which correlated well with the higher values of stomatal conductance G
s (range 105–180 mmol m−2 s−1), as compared to shade leaves (G
s range 25–77 mmol m−2 s−1; P
N: 3.2–3.7 μmol CO2 m−2 s−1). The higher photosynthetic rates could also be detected via imaging the Chl fluorescence decrease ratio R
Fd, which possessed higher values in sun leaves (2.8–3.0) as compared to shade leaves (1.4–1.8). In addition, via R
Fd images it was shown that the photosynthetic activity of the leaves of all trees exhibits a large heterogeneity across the
leaf area, and in general to a higher extent in sun leaves than in shade leaves. 相似文献
20.
In vitro regenerated shoots of Spathiphyllum from bioreactor were hydroponically cultured for 30 days. The response of plant growth and photosynthesis to different substrates,
photosynthetic photon flux (PPF), nutrient scheduling and electrical conductivity (EC) of hydroponic solution were studied.
The best plant growth response was observed in perlite based substrates with moderate PFF (70–100μmol m−2 s−1). Highest fresh weight, dry weight, shoot length, root length, root number and photosynthetic characteristics (chlorophyll,
carotenoids and Fv/Fm) was observed in continuous immersion system. Plant growth responses, photosynthetic rate, stomatal
conductance and transpiration rate were also found to be affected by EC levels. The optimum EC of a balanced nutrient solution
was recorded as 1.2 dS m−1. Photosynthetic activity was also characterized in terms of photochemical efficiency using measurements of chlorophyll fluorescence.
Fv/Fm (it is a measure of the intrinsic or maximum efficiency of PSII i.e. the quantum efficiency if all PSII centers were
open) also decreased significantly in plants grown under higher EC level; a decrease in this parameter indicates down regulation
of photosynthesis or photoinhibition. Antioxidant defense enzymes such as catalase (CAT), ascorbate peroxidase (APX), peroxidase
(POD), glutathione reductase (GR) and monodehydroascorbate reductase (MDHAR) significantly elevated in the leaves and roots
of plantlets at higher EC levels. This increase could reflect a defense response to the cellular damage provoked by higher
EC levels in the nutrient solution. 相似文献