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1.
In the 20th century, annual mean temperatures in the European Alps rose by almost 1 K and are predicted to rise further, increasing the impact of temperature on alpine plants. The role of light in the heat hardening of plants is still not fully understood. Here, the alpine dwarf shrub Vaccinium gaultherioides was exposed in situ to controlled short‐term heat spells (150 min with leaf temperatures 43–49°C) and long‐term heat waves (7 days, 30°C) under different irradiation intensities. Lethal leaf temperatures (LT 50) were calculated. Low solar irradiation [max. 250 photosynthetic photon flux density (PPFD)] during short‐term heat treatments mitigated the heat stress, shown by reduced leaf tissue damage and higher Fv/ Fm (potential quantum efficiency of photosystem 2) than in darkness. The increase in xanthophyll cycle activity and ascorbate concentration was more pronounced under low light, and free radical scavenging activity increased independent of light conditions. During long‐term heat wave exposure, heat tolerance increased from 3.7 to 6.5°C with decreasing mean solar irradiation intensity (585–115 PPFD). Long‐term exposure to heat under low light enhanced heat hardening and increased photosynthetic pigment, dehydroascorbate and violaxanthin concentration. In conclusion, V. gaultherioides is able to withstand temperatures of around 50°C, and its heat hardening can be enhanced by low light during both short‐ and long‐term heat treatment. Data showing the specific role of light during short‐ and long‐term heat exposure and the potential risk of lethal damage in alpine shrubs as a result of rising temperature are discussed. 相似文献
2.
Photosynthesis rate ( An) becomes unstable above a threshold temperature, and the recovery upon return to low temperature varies because of reasons not fully understood. We investigated responses of An, dark respiration and chlorophyll fluorescence to supraoptimal temperatures of varying duration and kinetics in Phaseolus vulgaris asking whether the instability of photosynthesis under severe heat stress is associated with cellular damage. Cellular damage was assessed by Evans blue penetration (enhanced membrane permeability) and by H 2O 2 generation [3,3′‐diaminobenzidine 4HCl (DAB)‐staining]. Critical temperature for dark fluorescence ( F0) rise ( TF) was at 46–48 °C, and a burst of respiration was observed near TF. However, An was strongly inhibited already before TF was reached. Membrane permeability increased with temperature according to a switch‐type response, with enhanced permeability observed above 48 °C. Experiments with varying heat pulse lengths and intensities underscored the threshold‐type loss of photosynthetic function, and indicated that the degree of photosynthetic deterioration and cellular damage depended on accumulated heat‐dose. Beyond the ‘point of no return’, propagation of cellular damage and reduction of photosynthesis continued upon transfer to lower temperatures and photosynthetic recovery was slow or absent. We conclude that instability of photosynthesis under severe heat stress is associated with time‐dependent propagation of cellular lesions. 相似文献
3.
Lichen thalli were exposed to 4 regimes differing in irradiance and duration of irradiation. Photosynthetic efficiency of
thalli was monitored by chlorophyll fluorescence parameters and xanthophyll cycle analysis. Maximal quantum yield of photosystem
2 (F V/F M) decreased gradually with time in long-term treatment. The effect of additional short-term high irradiance (HI) treatment
applied each 24 h was not significant. Nevertheless, short-term HI applied repeatedly on thalli kept in the dark led to a
significant decrease of F V/F M. Non-photochemical quenching recorded during the long-term treatment corresponded to the content of zeaxanthin (Z). In short-term
treatment, however, proportion of Z (and antheraxanthin) to total amount of xanthophyll cycle pigments recovered to the initial
values every 24 h after each repeated short-term HI event in thalli kept in dark. Thus duration of irradiation rather than
irradiance and frequency of HI events is important for a decrease in primary photosynthetic processes in wet thalli of Lasallia pustulata. Rapidly responding photoprotective mechanisms, such as conversion of xanthophyll cycle pigments, are involved mainly in
short-term irradiation events, even at HI. 相似文献
4.
The development of desiccation tolerance by vegetative tissues was an important step in the plants’ conquest of land. To counteract
the oxidative stress generated under these conditions the xanthophyll cycle plays a key role. Recent reports have shown that
desiccation itself induces de-epoxidation of xanthophyll cycle pigments, even in darkness. The aim of the present work was
to study whether this trait is a common response of all desiccation-tolerant plants. The xanthophyll cycle activity and the
maximal photochemical efficiency of PS II ( F
v/ F
m) as well as β-carotene and α-tocopherol contents were compared during slow and rapid desiccation and subsequent rehydration
in six species pairs (with one desiccation-sensitive and one desiccation-tolerant species each) belonging to different taxa.
Xanthophyll cycle pigments were de-epoxidised in darkness concomitantly with a decrease in F
v/ F
m during slow dehydration in all the desiccation-tolerant species and in most of the desiccation-sensitive ones. De-epoxidation
was reverted in darkness by re-watering in parallel with the recovery of the initial F
v/ F
m. The stability of the β-carotene pool confirmed that its hydroxylation did not contribute to zeaxanthin formation. The α-tocopherol
content of most of the species did not change during dehydration. Because it is a common mechanism present in all the desiccation-tolerant
taxa and in some desiccation-sensitive species, and considering its role in antioxidant processes and in excess energy dissipation,
the induction of the de-epoxidation of xanthophyll cycle pigments upon dehydration in the dark could be understood as a desiccation
tolerance-related response maintained from the ancestral clades in the initial steps of land occupation by plants. 相似文献
5.
Fluorimetric, photoacoustic, polarographic and absorbance techniques were used to measure in situ various functional aspects of the photochemical apparatus of photosynthesis in intact pea leaves ( Pisum sativum L.) after short exposures to a high temperature of 40 ° C. The results indicated (i) that the in-vivo responses of the two photosystems to high-temperature pretreatments were markedly different and in some respects opposite, with photosystem (PS) II activity being inhibited (or down-regulated) and PSI function being stimulated; and (ii) that light strongly interacts with the response of the photosystems, acting as an efficient protector of the photochemical activity against its inactivation by heat. When imposed in the dark, heat provoked a drastic inhibition of photosynthetic oxygen evolution and photochemical energy storage, correlated with a marked loss of variable PSII-chlorophyll fluorescence emission. None of the above changes were observed in leaves which were illuminated during heating. This photoprotection was saturated at rather low light fluence rates (around 10 W · m –2). Heat stress in darkness appeared to increase the capacity for cyclic electron flow around PSI, as indicated by the enhanced photochemical energy storage in far-red light and the faster decay of P
700
+
(oxidized reaction center of PSI) monitored upon sudded interruption of the far-red light. The presence of light during heat stress reduced somewhat this PSI-driven cyclic electron transport. It was also observed that heat stress in darkness resulted in the progressive closure of the PSI reaction centers in leaves under steady illumination whereas PSII traps remained largely open, possibly reflecting the adjustment of the photochemical efficiency of undamaged PSI to the reduced rate of photochemistry in PSII.Abbreviations B 1 and B 2
fraction of closed PSI and PSII reaction centers, respectively
- ES
photoacoustically measured energy storage
- F o, F m and F s
initial, maximal and steady-state levels of chlorophyll fluorescence
- P 700
reaction center of PSI
- PS (I, II)
photosystem (I, II)
- V = (F s – F o)/(F m – F o)
relative variable chlorophyll fluorescence
We wish to thank Professor R. Lannoye (ULB, Brussels) for the use of this photoacoustic spectrometer and Mrs. M. Eyletters for her help. 相似文献
6.
Most plants growing in temperate desert zone exhibit brief temperature-induced inhibition of photosynthesis at midday in the
summer. Heat stress has been suggested to restrain the photosynthesis of desert plants like Alhagi sparsifolia S. It is therefore possible that high midday temperatures damage photosynthetic tissues, leading to the observed inhibition
of photosynthesis. In this study, we investigated the mechanisms underlying heat-induced inhibition of photosynthesis in A. sparsifolia, a dominant species found at the transition zone between oasis and sandy desert on the southern fringe of the Taklamakan
desert. The chlorophyll (Chl) a fluorescence induction kinetics and CO 2 response curves were used to analyze the thermodynamic characters of both photosystem II (PSII) and Rubisco after leaves
were exposed to heat stress. When the leaves were heated to temperatures below 43°C, the initial fluorescence of the dark-adapted
state (F o), and the maximum photochemical efficiency of PSII (F v/F m), the number of active reaction centers per cross section (RCs) and the leaf vitality index (PI) increased or declined moderately.
These responses were reversed, however, upon cooling. Moreover, the energy allocation in PSII remained stable. The gradual
appearance of a K point in the fluorescence curve at 48°C indicated that higher temperatures strongly impaired PSII and caused
irreversible damage. As the leaf temperature increased, the activity of Rubisco first increased to a maximum at 34°C and then
decreased as the temperature rose higher. Under high-temperature stress, cell began to accumulate oxidative species, including
ammoniacal nitrogen, hydrogen peroxide (H 2O 2), and superoxide (O 2
·−), suggesting that disruption of photosynthesis may result from oxidative damage to photosynthetic proteins and thylakoid
membranes. Under heat stress, the biosynthesis of nonenzyme radical scavenging carotenoids (Cars) increased. We suggest that
although elevated temperature affects the heat-sensitive components comprising of PSII and Rubisco, under moderately high
temperature the decrease in photosynthesis is mostly due to inactivation of dark reactions. 相似文献
7.
The heat tolerance of 8 temperate- and 1 subtropical-origin C 3 species as well as 17 tropical-origin ones, including C 3, C 4, and CAM species, was estimated using both F 0-T curve and the ratio of chlorophyll fluorescence parameters, prior to and after high temperature treatment. When leaves
were heated at the rate of ca. 1 °C min −1 in darkness, the critical temperature (T c) varied extensively among species. The T c's of all 8 temperate-origin species ranged between 40–46 °C in winter (mean temperature 16–19 °C), and between 32–48 °C in
summer (mean temperature ca. 30 °C). Those for 1 subtropical- and 12 tropical-origin C 3 species ranged between 25–44 °C and 35–48 °C, and for 1 CAM and 4 C 4 species were 41–47 and 45–46 °C, respectively. Acclimating three C 3 herbaceous plants at high temperature (33/28 °C, day/night) for 10 d in winter caused their T c's rising to nearly the values measured in summer. When leaves were exposed to 45 °C for 20 min and then kept at room temperature
in darkness for 1 h, a significant correlation between RF v/m (the ratio of F v/F m before and after 45 °C treatment) and T c was observed for all tested temperate-origin C 3 species as well as tropical-origin CAM and C 4 species. However, F 0 and F v/F m of the tropical-origin C 3 species were less sensitive to 45 °C treatment, regardless of a large variation of T c; thus no significant correlation was found between their RF v/m and T c. Thus T c might not be a suitable index of heat tolerance for plants with wide range of environmental adaptation. Nevertheless, T c's of tropical origin C 3 species, varying and showing high plasticity to seasonal changes and temperature treatment, appeared suitable for the estimation
of the degree of temperature acclimation in the same species. 相似文献
8.
The thermo-sensitivity of two new pea ( Pisum sativum L.) cultivars—Afila (mutant in the gene transforming leaves into mustaches) and Ranen (mutant for early ripening)—as compared
to the control cultivar Pleven-4 to either low (4 °C, T 4) or high temperature (38 °C, T 38) was investigated by means of chlorophyll (Chl) fluorescence kinetics. The low temperature treatment decreased the photosynthetic
activity, measured via a decline of the Chl fluorescence decrease ratios R Fd690 and R Fd735, and this was mainly due to a decline of the Chl fluorescence decrease parameter F d and maximum Chl fluorescence F m. In the new cv. Ranen the R Fd ratios at first decreased and increased again after 24-h exposure to 4 °C, indicating its good acclimation ability to low
temperature. The cold-induced changes in the photosynthetic performance of all cultivars were reversed after transferring
plants back to 23 °C for 48 h. In the Chl and carotenoid (Car) contents no or little changes occurred during the T 4 treatment, except for a slight but clear increase of the ratio Chl a/b and a decrease in the ratio Chl/Car. In contrast to this, the T 38 treatment for 72 h decreased the R Fd ratios more strongly than the T 4 exposure did. In fact, an irreversible injury of the photosynthetic apparatus was caused in the control pea cv. Pleven-4
by a 48-h T 38 exposure and for the new cv. Afila after a 72-h T 38 exposure. In contrast, the cv. Ranen was less and little sensitive to the T 38 exposure. In the heat-sensitive cvs. Pleven-4 and Afila, the decrease in R Fd values at T 38 was associated with a strong decline of the Chl a+b and total Car contents. The Chl a+b decline could also be followed via an increase of the Chl fluorescence ratio F 690/F 735. Parallel to this, a strong decline of Chl a/b from ca. 3.0 (range 2.85–3.15) to ca. 1.9 (range 1.85–1.95) occurred indicating a preferential decline of the Chl a-pigment proteins but not of the Chl a/b-pigment protein LHC2. In the relatively heat-tolerant cv. Ranen, however, the ratio Chl a/b declined only partially. After the T 4 treatment the stress adaptation index Ap was higher in cv. Ranen than in controls and reached in heat-treated Ranen plants
almost the starting value indicating a cold and heat stress hardening of the treated plants. The Chl fluorescence parameters
and pigment contents were influenced by T 38 and T 4 treatments in various ways indicating that the mechanisms of low and high temperature injury of the photosynthetic apparatus
are different. The new cv. Ranen exhibited a cross tolerance showing a fairly good acclimation ability to both T 4 and T 38, hence it is a very suitable plant for outdoor growth and for clarification of the acclimation mechanisms to unfavourable
temperatures. 相似文献
9.
Cross stress of heat and high irradiance (HI) resulted in the accumulation of active oxygen species and photo-oxidative damage
to photosynthetic apparatus of wheat leaves during grain development. Pre-treatment with calcium ion protected the photosynthetic
system from oxidative damage by reducing O -.
2 production, inhibiting lipid peroxidation, and retarding electrolyte leakage from cell. Therefore, high F v/F m [maximal photochemical efficiency of photosystem 2 (PS2) while all PS2 reaction centres are open], F m/F 0 (another expression for the maximal photochemical efficiency of PS2), Φ PS2 (actual quantum yield of PS2 under actinic irradiation), q P (photochemical quenching coefficient), and P
N (net photosynthetic rate) were maintained, and lower q NP (non-photochemical quenching coefficient) of the leaves was kept under heat and HI stress. EGTA (a chelant of calcium ion)
and LaCl 3 (a blocker of Ca 2+ channel in cytoplasmic membrane) had the opposite effect. Thus Ca ion may help protect the photosynthetic system of wheat
leaves from oxidative damage induced by the cross stress of heat and HI. 相似文献
10.
Heat stress is a major production constraint of sunflower worldwide. Therefore, various populations (parental, F 1, F 2, F 3, and plant progenies) of sunflower were screened for leaf gas-exchange traits with the objectives to formulate selection criteria of heat resistance and development of heat-resistant lines. Initial screening and F 2 seeds exposed to heat stress (45°C) resulted in the development of an adapted F 2 population that showed leaf gas-exchange and morphological traits better than the unadapted population. Correlation coefficients of traits were partitioned into direct and indirect effects via a path analysis technique to determine the cause of their relationship with a basic parameter such as a reproductive head mass (HM). Path analysis showed a positive direct effect of leaf temperature (T leaf) (0.32) on HM and also an indirect effect (0.77) of the transpiration rate ( E) on HM. Moreover, T leaf showed high heritability estimates. T leaf was used to select superior plants within the F 2 population. This selection brought about an improvement in the net photosynthetic rate ( P N) and E as it was indicated from progeny performance and realized heritability. Progenies selected on the basis of T leaf also showed an increase in achene yield and heat resistance over unselected F 3 progenies and a commercial hybrid. 相似文献
11.
The influence of seasonally fluctuating photoperiods on the photosynthetic apparatus of Palmaria decipiens (Reinsch) Ricker was studied in a year‐round culture experiment. The optimal quantum yield (F v/F m) and the maximal relative electron transport rate (ETR max), measured by in vivo chl fluorescence and pigment content, were determined monthly. During darkness, an initial increase in pigment content was observed. After 3 months in darkness, ETR max and F v/F m started to decrease considerably. After 4 months in darkness, degradation of the light‐harvesting antennae, the phycobilisomes, began, and 1 month later the light harvesting complex I and/or the reaction centers of PSII and/or PSI degraded. Pigment content and photosynthetic performance were at their minimum at the end of the 6‐month dark period. Within 24 h after re‐illumination, P. decipiens started to accumulate chl a and to photosynthesize. The phycobiliprotein accumulation began after a time lag of about 7 days. Palmaria decipiens reached ETR max values comparable with the values before darkness 7 days after re‐illumination and maximal values after 30 days of re‐illumination. Over the summer, P. decipiens reduced its photosynthetic performance and pigment content, probably to avoid photodamage caused by excess light energy. The data show that P. decipiens is able to adapt to the short period of favorable light conditions and to the darkness experienced in the field. 相似文献
12.
The effects of enhanced UV-B (290-320 nm) radiation on two native Mediterranean pines ( Pinus pinea L., Pinus halepensis Mill.) were recorded during a one-year field study. Plants received ambient or ambient plus supplemental UV-B radiation (simulating a 15% stratospheric ozone depletion over Patras. Greece, 38.3°N. 29.1°E) and only natural precipitation, i.e. they were simultaneously exposed to other natural stresses. particularly water stress during summer. Supplemental UV-B irradiation started in early February, 1993 and up to late June, no effects were observed on growth and photochemical efficiency of photosystem II, as measured by chlorophy II fluorescence induction. Water stress during the summer was manifested in the control plants as a decline in the ratio of variable to maximum fluorescence (F v/F m), the apparent photon yield for oxygen evolution (φ l) and the photosynthetic capacity at 5% CO 2 (P m). In addition, a partial needle loss was evident. Under supplemental UV-B radiation, however, the decreases in F v/F m, φ i, and P m. as well as needle losses were significantly less. Soon after the first heavy autumn rains. photosynthetic parameters in both control and UV-B treated plants recovered to similar values. but the transient summer superiority of UV-B irradiated plants resulted in a significant increase in their dry weight measured at plant harvest. during late January. 1994. Plant height. UV-B absorbing compounds, photosynthetic pigments and relative water content measured at late spring. late summer and at plant harvest, were not significantly affected by supplemental UV-B radiation. The results indicate that enhanced UV-B radiation may be beneficial for Mediterranean pines through a partial alleviation of the adverse effects of summer drought. 相似文献
13.
Three prevalent aliphatic polyamines (PAs) include putrescine, spermidine, and spermine; they are low-molecular-mass polycations involved in many physiological processes in plants, especially, under stressful conditions. In this experiment, three bean (Phaseolus vulgaris L.) genotypes were subjected to well-watered conditions and two moderate and severe water-stressed conditions with and without spermidine foliar application. Water stress reduced leaf relative water content (RWC), chlorophyll contents, stomatal conductance (gs), intercellular CO2 concentration (Ci), transpiration rate, maximal quantum yield of PSII (Fv/Fm), net photosynthetic rate (PN), and finally grain yield of bean plants. However, spermidine application elevated RWC, gs, Ci, Fv/Fm, and PN, which caused an increase in the grain yield and harvest index of bean plants under water stress. Overall, exogenous spermidine could be utilized to alleviate water stress through protection of photosynthetic pigments, increase of proline and carotenoid contents, and reduction of malondialdehyde content. 相似文献
15.
This contribution is a practical guide to the measurement of the different chlorophyll (Chl) fluorescence parameters and gives
examples of their development under high-irradiance stress. From the Chl fluorescence induction kinetics upon irradiation
of dark-adapted leaves, measured with the PAM fluorometer, various Chl fluorescence parameters, ratios, and quenching coefficients
can be determined, which provide information on the functionality of the photosystem 2 (PS2) and the photosynthetic apparatus.
These are the parameters F v, F m, F 0, F m′, F v′, NF, and ΔF, the Chl fluorescence ratios F v/F m, F v/F 0, ΔF/F m′, as well as the photochemical (q P) and non-photochemical quenching coefficients (q N, q CN, and NPQ). q N consists of three components (q N = q E + q T + q I), the contribution of which can be determined via Chl fluorescence relaxation kinetics measured in the dark period after the induction kinetics. The above Chl fluorescence
parameters and ratios, many of which are measured in the dark-adapted state of leaves, primarily provide information on the
functionality of PS2. In fully developed green and dark-green leaves these Chl fluorescence parameters, measured at the upper
adaxial leaf side, only reflect the Chl fluorescence of a small portion of the leaf chloroplasts of the green palisade parenchyma
cells at the upper outer leaf half. Thus, PAM fluorometer measurements have to be performed at both leaf sides to obtain information
on all chloroplasts of the whole leaf. Combined high irradiance (HI) and heat stress, applied at the upper leaf side, strongly
reduced the quantum yield of the photochemical energy conversion at the upper leaf half to nearly zero, whereas the Chl fluorescence
signals measured at the lower leaf side were not or only little affected. During this HL-stress treatment, q N, q CN, and NPQ increased in both leaf sides, but to a much higher extent at the lower compared to the upper leaf side. q N was the best indicator for non-photochemical quenching even during a stronger HL-stress, whereas q CN and NPQ decreased with progressive stress even though non-photochemical quenching still continued. It is strongly recommended
to determine, in addition to the classical fluorescence parameters, via the PAM fluorometer also the Chl fluorescence decrease ratio R Fd (F d/F s), which, when measured at saturation irradiance is directly correlated to the net CO 2 assimilation rate ( P
N) of leaves. This R Fd-ratio can be determined from the Chl fluorescence induction kinetics measured with the PAM fluorometer using continuous saturating
light (cSL) during 4–5 min. As the R Fd-values are fast measurable indicators correlating with the photosynthetic activity of whole leaves, they should always be
determined via the PAM fluorometer parallel to the other Chl fluorescence coefficients and ratios. 相似文献
16.
The effect of crop disease on photosynthetic characteristics is important for disease control. Two varieties, Shenzhou 98 and Neiwuyou 8015 with resistance and susceptibility to bacterial leaf blight (BLB), respectively, were selected, and the responses of the net photosynthetic rate ( PN) to active photon flux density (PPFD) and intercellular carbon dioxide concentration ( Ci), as well as chlorophyll fluorescence, pigments and stomatal resistance (SR), were measured. The results showed that BLB infection greatly decreased the maximum photosynthetic rate ( Pmax), light saturation point (LSP), carboxylation efficiency (CE), maximal fluorescence (F m) and actual photochemical efficiency of PSII ( Φ PSII) but increased the light compensation point (LCP) and dark respiratory rate ( RD), which suggested that the performance of rice photosynthesis was decreased by BLB infection. The BLB infection had a lower effect on resistant rice Shenzhou 98 than on susceptible rice Neiwuyou 8015. The reduction of pigment and increased SR caused by BLB infection may have resulted in the decline in the photosynthetic rate. Significant effects of the BLB infection were observed on chlorophyll fluorescence F m and Φ PSII in resistant and susceptible rice. These parameters may be useful for noninvasive monitoring of plant disease considering the negative effect caused by other stresses. 相似文献
17.
The effects of light on the accumulation of bacteriochlorophylland carotenoids were investigated in an aerobic photosyntheticbacterium, Roseobacter denitrificans during anaerobic respiration.Accumulation of pigments occurred in darkness but not in whitelight, with the growth rate being similar under both dark andlight conditions. Once pigments had accumulated during growthin darkness, subsequent irradiation with white light did notresult in degradation of the accumulated pigments, an indicationthat the pigments were stabilized in the membranes. The presentresults, therefore, exclude the possibility of inhibition ofthe accumulation of the photosynthetic pigments by the photochemicaldegradation of the pigments in the presence of molecular oxygenand light (blue light). The action spectrum for the inhibitionof the accumulation of the pigments showed that light at 470nm was the most effective and light at wavelengths longer than500 nm had little inhibitory effect. Together with previousresults [Shimada et al. (1992) Plant Cell Physiol. 33: 471],the present data suggest that a signal-transduction system associatedwith an unidentified blue pigment(s) is involved in the inhibitionof the accumulation of the photosynthetic pigments in R. denitrificans. (Received May 6, 1992; Accepted September 21, 1992) 相似文献
18.
We examined the in situ CO 2 gas-exchange of fruits of a tropical tree, Durio zibethinus Murray, growing in an experimental field station of the Universiti Pertanian Malaysia. Day and night dark respiration rates were exponentially related to air temperature. The temperature dependent dark respiration rate showed a clockwise loop as time progressed from morning to night, and the rate was higher in the daytime than at night. The gross photosynthetic rate was estimated by summing the rates of daytime dark respiration and net photosynthesis. Photosynthetic CO 2 refixation, which is defined as the ratio of gross photosynthetic rate to dark respiration rate in the daytime, ranged between 15 and 45%. The photosynthetic CO 2 refixation increased rapidly as the temperature increased in the lower range of air temperature T
c ( T
c <28.5 °C), while it decreased gradually as the temperature increased in the higher range ( T
c 28.5 °C). Light dependence of photosynthetic CO 2 refixation was approximated by a hyperbolic formula, where light saturation was achieved at 100 mol m –2 s –1 and the asymptotic CO 2 refixation was determined to be 37.4%. The estimated gross photosynthesis and dark respiration per day were 1.15 and 4.90 g CO 2 fruit –1, respectively. Thus the CO 2 refixation reduced the respiration loss per day by 23%. The effect of fruit size on night respiration rate satisfied a power function, where the exponent was larger than unity. 相似文献
19.
As global temperature rise, the threat of heat stress to rapeseed production is becoming more obvious. Exploring the response characteristics of two important biological pathways, oil accumulation and photosynthesis, to heat stress during B. napus seed filling is helpful in the genetic improvement of heat-tolerant rapeseed. The effects of heat stress on seed oil accumulation and chlorophyll fluorescence characteristics of 29 B. napus germplasms with different oil content and environmental sensitivity, including 6 rapeseed varieties which exhibited environment-sensitive/insensitive and with high, medium or low oil content, were tested by whole plant heat stress or the in vitro silique culture system. Both assay exhibited similar trend on oil content of the rapeseed germplasms. The heat effect on the chlorophyll fluorescence kinetic parameters Fv/Fm, ETR and Y(II) were also consistent. Heat stress significantly decreased oil content, although there was abundant genetic variation on heat tolerance among the genotypes. Correlation analysis showed that the decrease rate of Fv/Fm of silique heat-stressed B. napus developing seed was positive correlative to the decrease rate of mature seed oil content of the whole plant heat-stressed rapeseed ( R = 0.9214, P-value < 0.01). Overall, the results indicated that heat stress inhibited oil accumulation and photosynthesis in B. napus developing seed. The decrease rate of chlorophyll fluorescence parameter Fv/Fm of heat-stressed developing seed could be used as the index of heat tolerant rapeseed identification. Further, two heat insensitive rapeseed varieties with high oil content were identified. 相似文献
20.
The chlorophyll fluorescence parameter F v/F m reflects the maximum quantum efficiency of photosystem II (PSII) photochemistry and has been widely used for early stress detection in plants. Previously, we have used a three‐tiered approach of phenotyping by F v/F m to identify naturally existing genetic variation for tolerance to severe heat stress (3 days at 40°C in controlled conditions) in wheat ( Triticum aestivum L.). Here we investigated the performance of the previously selected cultivars (high and low group based on F v/F m value) in terms of growth and photosynthetic traits under moderate heat stress (1 week at 36/30°C day/night temperature in greenhouse) closer to natural heat waves in North‐Western Europe. Dry matter accumulation after 7 days of heat stress was positively correlated to F v/F m. The high F v/F m group maintained significantly higher total chlorophyll and net photosynthetic rate (P N) than the low group, accompanied by higher stomatal conductance (g s), transpiration rate (E) and evaporative cooling of the leaf (ΔT). The difference in P N between the groups was not caused by differences in PSII capacity or g s as the variation in F v/F m and intracellular CO 2 (C i) was non‐significant under the given heat stress. This study validated that our three‐tiered approach of phenotyping by F v/F m performed under increasing severity of heat was successful in identifying wheat cultivars differing in photosynthesis under moderate and agronomically more relevant heat stress. The identified cultivars may serve as a valuable resource for further studies to understand the physiological mechanisms underlying the genetic variability in heat sensitivity of photosynthesis. 相似文献
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