Limitations to photosynthesis of lettuce grown under tropical conditions: alleviation by root-zone cooling.

Aerial parts of lettuce plants were grown under natural tropical fluctuating ambient temperatures, but with their roots exposed to two different root-zone temperatures (RZTs): a constant 20 degrees C-RZT and a fluctuating ambient (A-) RZT from 23-40 degrees C. Plants grown at A-RZT showed lower photosynthetic CO2 assimilation (A), stomatal conductance (gs), midday leaf relative water content (RWC), and chlorophyll fluorescence ratio Fv/Fm than 20 degrees C-RZT plants on both sunny and cloudy days. Substantial midday depression of A and g(s) occurred on both sunny and cloudy days in both RZT treatments, although Fv/Fm did not vary diurnally on cloudy days. Reciprocal temperature transfer experiments investigated the occurrence and possible causes of stomatal and non-stomatal limitations of photosynthesis. For both temperature transfers, light-saturated stomatal conductance (gs sat) and photosynthetic CO2 assimilation (A(sat)) were highly correlated with each other and with midday RWC, suggesting that A was limited by water stress-mediated stomatal closure. However, prolonged growth at A-RZT reduced light- and CO2-saturated photosynthetic O2 evolution (Pmax), indicating non-stomatal limitation of photosynthesis. Tight temporal coupling of leaf nitrogen content and P(max) during both temperature transfers suggested that decreased nutrient status caused this non-stomatal limitation of photosynthesis.     

The response of the high altitude C(4) grass Muhlenbergia montana (Nutt.) A.S. Hitchc. to long- and short-term chilling.

The acclimation of C(4) photosynthesis to low temperature was studied in the montane grass Muhlenbergia montana in order to evaluate inherent limitations in the C(4) photosynthetic pathway following chilling. Plants were grown in growth cabinets at 26 degrees C days, but at night temperatures of either 16 degrees C (the control treatment), 4 degrees C for at least 28 nights (the cold-acclimated treatment), or 1 night (the cold-stress treatment). Below a measurement temperature of 25 degrees C, little difference in the thermal response of the net CO(2) assimilation rate (A) was observed between the control and cold-acclimated treatment. By contrast, above 30 degrees C, A in the cold-acclimated treatment was 10% greater than in the control treatment. The temperature responses of Rubisco activity and net CO(2) assimilation rate were similar below 22 degrees C, indicating high metabolic control of Rubisco over the rate of photosynthesis at cool temperatures. Analysis of the response of A to intercellular CO(2) level further supported a major limiting role for Rubisco below 20 degrees C. As temperature declined, the CO(2) saturated plateau of A exhibited large reductions, while the initial slope of the CO(2) response was little affected. This type of response is consistent with a Rubisco limitation, rather than limitations in PEP carboxylase capacity. Stomatal limitations at low temperature were not apparent because photosynthesis was CO(2) saturated below 23 degrees C at air levels of CO(2). In contrast to the response of photosynthesis to temperature and CO(2) in plants acclimated for 4 weeks to low night temperature, plants exposed to 4 degrees C for one night showed substantial reduction in photosynthetic capacity at temperatures above 20 degrees C. Because these reductions were at both high and low CO(2), enzymes associated with the C(4) carbon cycle were implicated as the major mechanisms for the chilling inhibition. These results demonstrate that C(4) plants from climates with low temperature during the growing season can fully acclimate to cold stress given sufficient time. This acclimation appears to involve reversal of injury to the C(4) cycle following initial exposure to low temperature. By contrast, carbon gain at low temperatures generally appears to be constrained by the carboxylation capacity of Rubisco, regardless of acclimation time. The inability to overcome the Rubisco limitation at low temperature may be an inherent limitation restricting C(4) photosynthetic performance in cooler climates.     

Leaf photosynthetic parameters of two maize (Zea mays) cultivars in response to various patterns of chilling temperatures and photon flux densities

Chilling‐induced photosynthetic impairment was examined in leaves of maize (Zea mays L.) seedlings of two cultivars, one adapted to western Europe and one adapted to Mexican highlands. Three experiments were performed in a controlled environment. The effects of chilling night temperatures, of chilling at high light intensity and of variable chilling day temperatures on photosynthetic parameters, were evaluated. Chilling in the dark period resulted in stomatal limitation of net photosynthesis. Chilling at moderate to high light intensities caused chilling‐dependent photoinhibition of CO₂ uptake. Photobleached maize leaves did not resume normal photosynthetic function. Maize cv. Batan 8686 from the highlands of Mexico was less susceptible to photosynthetic damage than maize cv. Bastion adapted for cultivation in W. Europe, when exposed to chilling night temperatures, or to mild chilling photoinhibitory conditions.     

小麦和大豆叶片的气孔不均匀关闭现象

用14CO2放射自显影的方法研究了田间小麦和大豆叶片在水分胁迫下的气孔关闭状况。正常浇水的小麦和大豆叶片呈现出对14CO2的均匀吸收。在小麦与大豆"片水势分别降至-1．75和-1．32MPa的土壤干旱条件下,两种作物叶片都发生气孔不均匀关闭。离休叶片在空气中快速脱水易引起气孔不均匀关闭。正常供水小麦叶片在晴天中午明显的光合午休时,无CO2的不均匀吸收。某些晴天中午,在大豆光合午休低谷时段观察到较明显的气孔不均匀关闭,用气体交换资料计算出的细胞间隙CO2浓度并不随气孔年度的降低而下降,反而略有回升。     

Study on the Photosynthetic Characteristics of Eucommia ulmoides Leaves

A field study on the photosynthetic characteristics in Eucommia ulmoides Oliv. was conducted using a LI-6200 Portable Photosynthesis Analysis System as a measuring device and the modified half-leaf method. It was revealed that the light-saturating photosynthetic rate measured in leaves was in a range of 6~10 μmol CO2 · m-2 · s-1, and the lowest apparent quantum requirement was about 17. The CO2 compensation concentration of photosynthesis was a little more than 100μmol · mol-1 indicating that E. ulmoides was a C3 type plant. Besides stomatal limitation, photoinhibition of photosynthesis was a possible cause of the midday depression in photosynthetic rate. Only about 14 percent of the photosynthetic product was transported from the leaves during photosynthesis.     

Photosynthesis of Coffea arabica after chilling

Net photosynthetic CO₂ exchange of 1-year-old plants of Coffea arabica L. was studied after the above-ground parts had been exposed once or repeatedly to night temperatures in the chilling range. Chill-reduced rates of CO₂ uptake (measured at 24°C and at natural CO, level) were observed after a 12 h night exposure to about 6°C. After exposure to 4°C, activity was reduced to less than half of that of the controls, and after exposure to 0.5°C the leaves suffered visible necrotic injury and were no longer able to take up Co₂ If the leaves were not lethally injured, net photosynthesis recovered completely within 2 to 6 days. About 25% of chill-induced reduction of CO₂ uptake was due to reduced stomatal aperture and 75% to impairment of carboxylation efficiency.
Chilling on successive nights at 4–6°C reduced CO, uptake progressively on each day following treatment. After 10 nights, activity was decreased to less than 10% of initial performance. Conditioning at temperatures slightly above the chilling level (e.g. 15/I2°C) for 2 weeks led to almost complete impairment of photosynthetic activity without additional chilling stress instead of improving chilling tolerance.     

Limitation of photosynthetic carbon metabolism by dark chilling in temperate and tropical soybean genotypes.

In the experiments reported in this paper, we characterised the physiological and biochemical factors involved in the chilling-induced inhibition of photosynthetic carbon metabolism in soybean [Glycine max (L.) Merr.] genotypes of temperate and tropical adaptation. Plants of Maple Arrow (temperate genotype) and Java 29 (tropical genotype) were exposed to a single night at 8 degrees C. Dark chilling resulted in the inhibition of diurnal CO2 assimilation rate and decreased stomatal conductance in both genotypes. Further analysis, however, revealed a difference in the response of the two genotypes. Stomatal limitation was largely responsible for the inhibition of CO2 assimilation in Maple Arrow, whereas mesophyll limitation dominated the inhibition in Java 29. The results indicate that inhibition of stromal fructose-1,6-bisphosphatase (sFBPase; EC 3.1.3.11) activity and impaired electron transport capacity were responsible for the decrease in ribulose-1,5-bisphosphate (RuBP) regeneration capacity in Java 29. Sucrose-phosphate synthase (SPS; EC 2.4.1.14) activity was progressively inhibited during the light period in this genotype and might impose an additional constraint on photosynthesis. Maple Arrow appears to possess, at least with respect to photosynthetic carbon metabolism, physiological and biochemical characteristics that contribute towards its superior dark chilling tolerance.     

Photosynthesis and photoinhibition after night chilling in seedlings of two tropical tree species grown under three irradiances

We investigated the physiological effect of night chilling (CN) on potted seedlings of two tropical tree species, Calophyllum polyanthum and Linociera insignis, in Xishuangbanna, southwest China. Seedlings grown under 8, 25, and 50 % daylight for five months were moved to a 4–6 °C cold storage house for three consecutive nights, and returned to the original shaded sites during the day. CN resulted in strong suppression of photosynthesis and stomatal conductance for L. insignis, and reduced photorespiration rates, carboxylation efficiency, and maximum photochemical efficiency of photosystem 2 (PS2) at dawn and midday for both species. CN increased dawn and midday rates of non-photochemical quenching, and the contents of malondialdehyde and H₂O₂ for both species. CN also induced inactivation or destruction of PS2 reaction centres. The impacts of CN on tropical seedlings increased with the number of CN. Shading could significantly mitigate the adverse effects of CN for both species. After 3-d-recovery, gas exchange and fluorescence parameters for both species returned to pre-treatment levels in most cases. Thus CN induced mainly stomatal limitation of photosynthesis for L. insignis, and non-stomatal limitation for C. polyanthum. C. polyanthum was more susceptible to CN than L. insignis. Fog, which often occurs in Xishuangbanna, could be beneficial to chilling sensitive tropical seedlings in this area through alleviating photoinhibition or photodamage by reducing sunlight.     

Search for an endotherm in chloroplast lamellar membranes associated with chilling-inhibition of photosynthesis

The phase transition of chloroplast lamellar membrane lipids has been proposed to be the underlying cause of chilling-induced inhibition of photosynthesis in sensitive plants. Differential scanning calorimetry has been used to search for any endotherms arising from lipid state changes in chloroplast lamellar membranes of the chilling-sensitive plants cantaloupe , kidney bean, domestic tomato, and soybean. For comparison, calorimetric scans of chloroplast lamellar membranes from the chilling-insensitive plants spinach, pea, and wild tomato were made. A large reversible endotherm, extending from below 10 degrees to nearly 40 degrees C, was observed in chloroplast membranes from tomatoes of both chilling-sensitive (Lycopersicon esculentum Mill. cv. Floramerica ) and chilling-insensitive (L. hirsutum LA 1361) species. A much smaller endotherm, approximately 5 to 10% of the area of that seen in the two tomato species, and extending over a similar temperature range, was detected in chloroplasts from chilling-insensitive spinach and peas, and also was generally observed in chloroplasts from chilling-sensitive cantaloupe , kidney bean, and soybean. The enthalpy of these smaller endotherms indicates that, if the endotherm arose entirely from a lipid transition, then it corresponded to the melting of less than about 10% of the total membrane polar lipid. On the basis of these data it is concluded that there is no correlation between chilling sensitivity of photosynthesis and the presence or absence of a phase transition of bulk membrane lipids of the chloroplast lamellar membrane at temperatures above 5 degrees C.     

铁皮石斛叶片光合作用的碳代谢途径

 利用LI-6400光合测定系统测定了不同天气条件下铁皮石斛（Dendrobium officinale）叶片24h CO2吸收的动态以及CO2吸收对光强和温度的响应。晴天的白天和夜间铁皮石斛都能吸收CO2,中午CO2吸收速率为负值, CO2的交换方式具景天酸代谢途径(CAM)的特点。阴雨天,只有白天吸收CO2,夜间表现为暗呼吸,光合作用碳代谢的途径为C3途径。在多云的天气条件下,白天吸收CO2,并持续至日落后。夜间21∶00仍有CO2吸收,23∶00以后至次日凌晨处于暗呼吸状态。在500 μmol·m-2·s-1光照件下,20℃出现最大CO2吸收值。在夜间,25℃时CO2的吸收速率最高。有光和无光条件下,低温或高温引起CO2吸收速率下降均为非气孔因素所致。晴天上午,铁皮石斛叶片的表观量子产额为0.035,光合补偿点为2.9μmol·m-2·s-1,饱和光强为500μmol·m-2·s-1,强光下出现光抑制现象。叶片受到强光预先照射后,即使光照减弱光抑制效应仍保持一段时间,致使光合补偿点升高,表观量子产额下降,相同光强下的CO2吸收效率降低。结果表明：铁皮石斛为兼性CAM植物,随着环境条件的变化,其光合作用在景天酸代谢途径(CAM)与C3途径间变化。     

Dorsoventral variations in dark chilling effects on photosynthesis and stomatal function in Paspalum dilatatum leaves

The effects of dark chilling on the leaf-side-specific regulation of photosynthesis were characterized in the C(4) grass Paspalum dilatatum. CO(2)- and light-response curves for photosynthesis and associated parameters were measured on whole leaves and on each leaf side independently under adaxial and abaxial illumination before and after plants were exposed to dark chilling for one or two consecutive nights. The stomata closed on the adaxial sides of the leaves under abaxial illumination and no CO(2) uptake could be detected on this surface. However, high rates of whole leaf photosynthesis were still observed because CO(2) assimilation rates were increased on the abaxial sides of the leaves under abaxial illumination. Under adaxial illumination both leaf surfaces contributed to the inhibition of whole leaf photosynthesis observed after one night of chilling. After two nights of chilling photosynthesis remained inhibited on the abaxial side of the leaf but the adaxial side had recovered, an effect related to increased maximal ribulose-1,5-bisphosphate carboxylation rates (V(cmax)) and enhanced maximal electron transport rates (J(max)). Under abaxial illumination, whole leaf photosynthesis was decreased only after the second night of chilling. The chilling-dependent inhibition of photosynthesis was located largely on the abaxial side of the leaf and was related to decreased V(cmax) and J(max), but not to the maximal phosphoenolpyruvate carboxylase carboxylation rate (V(pmax)). Each side of the leaf therefore exhibits a unique sensitivity to stress and recovery. Side-specific responses to stress are related to differences in the control of enzyme and photosynthetic electron transport activities.     

甘薯(Ipomoea batatas)叶光合作用“午睡”现象初探

在探讨叶片光合产物水平与光合机构运转关系时,我们曾观测到田间甘薯叶片干重增长速率日变化进程中有明显的中午降低即“午睡”现象(图1)。为了揭示这一现象的形成机理,在人工气候室作了以下一些研究。     

Photoinhibition of photosynthesis in leaves of grapevine (<Emphasis Type="Italic">Vitis vinifera</Emphasis> L. cv. Riesling). Effect of chilling nights

Photoinhibition of photosynthesis was investigated in control (C) and chilling night (CN) leaves of grapevine under natural photoperiod at different sampling time in a day. The degree of photoinhibition was determined by means of the ratio of variable to maximum chlorophyll fluorescence (F_v/F_m) and photosynthetic electron transport measurements. When the potential efficiency of photosystem (PS) 2, F_v/F_m was measured at midday, it markedly declined with significant increase of F₀ in CN leaves. In isolated thylakoids, the rate of whole chain and PS2 activity were markedly decreased in CN leaves than control leaves at midday. A smaller inhibition of PS1 activity was also observed in both leaf types. Later, the leaves reached maximum PS2 efficiencies similar to those observed in the morning during sampling at evening. The artificial exogenous electron donors diphenyl carbazide, NH₂OH, and Mn²⁺ failed to restore the PS2 activity in both leaf types at midday. Thus CN enhanced inactivation on the acceptor side of PS2 in grapevine leaves. Quantification of the PS2 reaction centre protein D1 following midday exposure of leaves showed pronounced differences between C and CN leaves. The marked loss of PS2 activity in CN leaves noticed in midday samples was mainly due to the marked loss of D1 protein of the PS2 reaction centre.     

Dark chilling effects on soybean genotypes during vegetative development: parallel studies of CO2 assimilation,chlorophyll a fluorescence kinetics O-J-I-P and nitrogen fixation

The effects of dark chilling on CO2 assimilation, chlorophyll a fluorescence kinetics and nitrogen fixation were compared in two Glycine max (L.) Merr. genotypes. The aim was to elucidate the mechanisms by which photosynthesis was inhibited as well as identification of selection criteria for dark chilling tolerance. Seedlings were dark chilled (8 degrees C) for 9 consecutive nights but kept at normal day temperatures (28 degrees C). CO2 gas exchange analysis indicated that photosynthesis in Maple Arrow was inhibited largely as a result of stomatal limitation, while in Fiskeby V, it indicated inhibition of the mesophyll reactions. Increased intercellular CO2 concentration and decreased carboxylation efficiency suggested loss of Rubisco activity in Fiskeby V, although no effect on the KM (CO2) of Rubisco was observed. Quantification and deconvolution of the Chl a fluorescence transients into several phenomenological and biophysical parameters (JIP-test) revealed large genotypic differences in the response of PSII to dark chilling. These parameters differentially changed in the two genotypes during the progression of the chilling treatment. Among them, the performance index, reflecting several responses of the photochemical apparatus, provided the best preliminary overall assessment of the genotypes. In contrast, the quantum yield of primary photochemistry varphiPo (FV/FM) was quite insensitive. The recovery of most of the JIP-test parameters in Maple Arrow after 6 and 9 nights of dark chilling was a major genotypic difference. Genotypic differences were also observed with regard to the ureide response and N2 fixation appeared to be more sensitive to dark chilling than CO2 assimilation. The JIP-test provided information consistent with results derived from CO2 assimilation and N2 fixation studies suggesting that it can substitute the much more time-consuming methods for the detection of chilling stress and can well satisfy the requirements of a rapid and accurate screening method.     

Evergreens favored by higher responsiveness to increased CO₂

Physical CO(2) diffusion from sub-stomatal cavities to the chloroplasts where photosynthesis takes place is an important limitation of photosynthesis largely neglected in research related to global climate change. This limitation is particularly important in leaves with robust structures such as evergreen sclerophylls. In these leaves, photosynthesis is less sensitive to changes in stomatal openness, which is considered to be the primary limitation of photosynthesis. In this review we state that, because of large limitations in internal diffusion in C(3) plants, photosynthesis and the intrinsic efficiency of the use of plant water responds more strongly to elevated levels of CO(2) in leaves with more robust structures. This provides an additional explanation for the current apparent expansion of evergreen sclerophylls in many Earth ecosystems, and adds a new perspective to research of the biological effects of increasing atmospheric CO(2).     

Diurnal changes in the chilling sensitivity of seedlings

Seedlings of tomato (Lycopersicon esculentum, Mill.) varied diurnally in their sensitivity to chilling temperatures. If chilled near the end of the dark period when they were most sensitive, the time taken to kill half of the seedlings was approximately 3 days, whereas in samples taken 4 hours after the onset of dark, a period of 6 days of chilling was required. Sensitivity dropped rapidly after the onset of the light period. This rhythm was exogenously controlled by the diurnal changes in light, rather than in the temperature. The susceptibility of predawn seedlings could be reduced by exposure to light, by water stress, or by abscisic acid applied to the leaves. However, the subsequent changes in sensitivity to chilling did not correlate with stomatal aperture. Six other chilling-sensitive species showed similar diurnal changes in their chilling sensitivity.     

Response of tomato plants to chilling stress in association with nutrient or phosphorus starvation

The experiments were conducted on two tomato cultivars: Garbo and Robin. Mineral starvation due to plant growth in 20-fold diluted nutrient solution (DNS) combined with chilling reduced the rate of photosynthesis (P _N) and stomatal conductance (g) to a greater extent than in plants grown in full nutrient solution (FNS). In phosphate-starved tomato plants the P _N rate and stomatal conductance decreased more after chilling than in plants grown on FNS. In low-P plants even 2 days after chilling the recovery of CO₂ assimilation rate and stomatal conductance was low. A resupply of phosphorus to low-P plants (low P + P) did not improve the rate of photosynthesis in non-chilled plants (NCh) but prevented P_N inhibition in chilled (Ch) plants. The greatest effect of P resupply was expressed as a better recovery of photosynthesis and stomatal conductance, especially in non-chilled low P + P plants. The F _v/F _m (ratio of variable to maximal chlorophyll fluorescence) decreased more during P starvation than as an effect of chilling. Supplying phosphorus to low-P plants caused the slight increase in the F _v/F _mratio. In conclusion, after a short-term chilling in darkness a much more drastic inhibition of photosynthesis was observed in nutrient-starved or P-insufficient tomato plants than in plants from FNS. This inhibition was caused by the decrease in both photochemical efficiency of photosystems and the reduction of stomatal conductance. The presented results support the hypothesis that tomato plants with limited supply of mineral nutrients or phosphorus are more susceptible to chilling.     

Impairment of photosynthesis by chilling-temperatures in tomato

Chilling of attached tomato leaves (cv. Rutgers) in the dark for 16 hours at 1 C decreased both photosynthesis and transpiration. To separate the effects of chilling on stomatal CO₂ conductance from more direct effects of chilling on the chloroplasts' activities, measurements of photosynthesis and transpiration were made at atmospheric and saturating CO₂ levels. At atmospheric CO₂, the inhibition of photosynthesis was approximately 60%, of which about 35% was attributable to the impairment of chloroplast function and about 25% was attributable to decreased stomatal conductance. However, the affinity of the photosynthetic apparatus for CO₂ was not changed by chilling, since the dependence of the relative rate of photosynthesis on the intercellular CO₂ concentration was unaltered. The apparent quantum requirement for CO₂ reduction also was identical in chilled and unchilled plants. This observation contradicts the widely held notion that the chilling-induced inhibition of photosynthesis is caused by an impairment of the water oxidation mechanism. The impairment of chloroplast activity was not a consequence of an unfavorable water status within the leaf, since chilling caused only a small drop (1 bar) in water potential. A small loss of chlorophyll resulted as a secondary effect of chilling, but this loss of chlorophyll was eliminated as a cause of the inhibition of photosynthesis.