Nitrate Nutrition and Temperature Effects on Wheat: Photosynthesis and Photorespiration of Leaves

Lawlor, D. W., Boyle, F. A., Young, A. T., Keys, A. J. and Kendall,A. C. 1987. Nitrate nutrition and temperature effects on wheat:photosynthesis and photorespiration of leaves.—J. exp.Bot. 38: 393–408. Photosynthetic and photorespiratory carbon dioxide exchangeby the third leaf of spring wheat (Triticum aestivum cv. Kolibri),was analysed for plants grown at 13/10 °C (day/night temperature)and 23/18 °C with two rates of nitrate fertilization (abasal rate, — N, and a 4-fold larger rate, +N) and, insome experiments, with two photon fluxes. Net photosynthesiswas greatest at the time of maximum lamina expansion, and forleaves grown with additional nitrate. Maximum rate of photosynthesis,carboxylation efficiency and photochemical efficiency at maturitywere slightly decreased by nitrate deficiency but photosystemactivity was similar under all conditions. As leaves aged, photosynthesisand photochemical efficiency decreased; carboxylation efficiencydecreased more than photochemical efficiency particularly withbasal nitrate. Low oxygen increased the carboxylation and photochemicalefficiencies, and increased the maximum rate of assimilationby a constant proportion in all treatments. Photorespiration,measured by CO₂ efflux to CO₂-free air, by ¹⁴CO₂ uptake, andfrom compensation concentration, was proportional to assimilationin all treatments. It was greater, and formed a larger proportionof net photosynthesis, when measured in warm than in cold conditionsbut was independent of growth conditions. Assimilation was relatedto RuBPc-o activity in the tissue. Relationships between photosynthesis,photorespiration and enzyme complement are discussed. Key words: Wheat, leaves, nitrate nutrition, temperature effect, photosynthesis, photorespiration     

不同磷营养水平对烟草叶片光合作用和光呼吸的影响(英文)

研究了不同磷营养水平(0,1/4,1/2,1,2 P)对烟草(Nicotiana rustica L.)叶片光合、光呼吸、乙醇酸合成和乙醇酸氧化酶活性的影响,结果如下; 光合强度在0～1P范围内随磷水平的提高而增高,但在2P水平中略为下降。光呼吸强度在1/4～2P范围内与光合强度有相同的变化趋势,但在磷水平为零时最高;光呼吸/光合比值亦在磷水平为零时最高,并随磷营养的增加而下降。 HPMS抑制乙醇酸氧化酶活性,乙醇酸的积累量随磷水平的变化与光呼吸有一致的趋势。 在加入FMN时,不同磷营养水平的烟草叶片中乙醇酸氧化酶的活性随磷水平的提高而下降;加入FMN对酶活性的促进作用亦随磷水平的提高而下降。 叶片无机磷、有机磷及总磷含量均随磷营养水平的提高而增加。 用不同浓度的磷酸盐溶液真空渗入在1P培养的烟草叶圆片,并在0.25,0.5,10mmol/LNaHCO_3溶液中测定光合和光呼吸,结果表明在0.25和 0.5mmol/L NaHCO_3中,光呼吸随磷浓度的增加而下降;在 10mmol/L中光呼吸完全受抑制。光合作用与磷浓度关系呈单峰曲线,随着NaHCO_3浓度的提高,其高峰位置向右移,即光合最适磷浓度增大。 根据试验结果及从化学计量学推算,认为磷营养有抑制光呼吸的作用,而光呼吸的运转则有补充叶绿体内进行光合作用所需的无机磷的功能。     

不同磷营养水平对烟草叶片光合作用和光呼吸的影响

随着磷营养水平的提高,烟草叶片的CO_2补偿点下降、光合速率上升。光呼吸在缺磷时最高。用光呼吸抑制剂处理烟草叶片后,光合的最适磷浓度提高。当CO_2浓度为560μl/L时,缺磷的烟草叶片在从21％O_2转入2％O_2时出现光合振荡,表明光呼吸与磷营养有密切关系。光呼吸在形成乙醇酸时所释放的磷,有回补叶绿体进行光合作用所需的磷的作用。     

Development of Photorespiration during Chloroplast Biogenesis in Wheat Leaves

Tobin, A. K., Sumar, N., Patel, M., Moore, A. L. and Stewart,G. R. 1988. Development of photorespiration during chloroplastbiogenesis in wheat leaves.—J. exp. Bot. 39: 833–843. The rate of light-dependent ammonia accumulation in L-methioninesulphoximine (MSO: glutamine synthetase inhibitor)-treated wheat(Triticum aestivum L. cv. Maris Huntsman) primary leaf sectionsincreased with mesophyll cell maturity. Ammonia production inthe more mature sections (beyond 2.0 cm from the basal meristem)was inhibited by elevated CO₂ concentrations and by incubationwith 10 mol m^–3 pyrid-2-yl hydroxymethane sulphonate (HPMS).In contrast, the low levels of ammonia which accumulated inthe immature sections (0 to 2.0 cm from the base) were unaffectedby such treatments. This indicates that the ammonia producedin mature wheat leaf sections is of photorespiratory originand that the capacity of this pathway increases with mesophyllcell and chloroplast development. Rates of CO₂-dependent oxygenevolution by leaf sections (under saturating CO₂) increasedin parallel with ammonia production. Levels of endogenous nitratewere relatively high and increased from 5.15 mol x 10^–13mesophyll cell^–1 in meristematic cells to 6.6 mol x 10^–12mesophyll cell^–1 in mature tissue. There was no significantchange in leaf nitrate level during 30 min light incubationof the wheat leaf sections, indicating that the majority ofthe nitrate was metabolically inactive and stored in the vacuole.Activities of key enzymes of photorespiration (glutamine synthetase,glycollate oxidase), nitrogen metabolism (nitrate reductase,glutamate dehydrogenase, glutamine synthetase) and mitochondrialrespiration (cytochrome oxidase), showed specific and distinctpatterns of development during leaf growth. Chloroplast glutaminesynthetase (GS₂) and peroxisomal glycollate oxidase developedin apparent synchrony with the major increase in activity occurringin regions beyond4.0 cm from the leaf base, i.e. where photorespirationwas developing. Cytosolic glutamine synthetase (GS₁) and nitratereductase (in vivo) activities were identical throughout leafgrowth, reaching maximum rates at 4.0 cm from the base and thenremaining constant. Activities of the mitochondrial enzymesglutamate dehydrogenase (GDH) and cytochrome oxidase were highin meristematic cells and increased in parallel, attaining amaximum towards the leaf tip. This indicated a respiratory,as opposed to a photorespiratory, role for GDH in wheat leafmetabolism. The evidence for controlled, co-ordinated synthesisof pathway enzymes at specific stages of organelle biogenesisis discussed. Key words: Photorespiration, organelle biogenesis     

Effect of Oxygen on Photosynthesis, Photorespiration and Respiration in Detached Leaves. II. Corn and other Monocotyledons

The effect of O₂ on the CO₂ exchange of detached leaves of corn (Zea mays), wheat (Triticum vulgare), oats (Avena sativa), barley (Hordeum vulgare), timothy (Phleum pratense) and cat-tail (Typha angustifolia) was measured with a Clark oxygen electrode and infrared carbon dioxide analysers in both open and closed systems.

Corn leaves did not produce CO₂ in the light at any O₂ concentration, as was shown by the zero CO₂ compensation point and the absence of a CO₂ burst in the first minute of darkness. The rate of photosynthesis was inhibited by O₂ and the inhibition was not completely reversible. On the other hand, the steady rate of respiration after a few minutes in the dark was not affected by O₂.

These results were interpreted as indicating the absence of any measurable respiration during photosynthesis. Twelve different varieties of corn studied all responded to O₂ in the same way.

The other 5 monocotyledons studied did produce CO₂ in the light. Moreover, the CO₂ compensation point increased linearly with O₂ indicating a stimulation of photorespiration.

The implications of the lack of photorespiration in studies of primary productivity are discussed.

     

Effect of CO(2), O(2), and Light on Photosynthesis and Photorespiration in Wheat

Unidirectional O₂ fluxes were measured with ¹⁸O₂ in a whole plant of wheat cultivated in a controlled environment. At 2 or 21% O₂, O₂ uptake was maximum at 60 microliters per liter CO₂. At lower CO₂ concentrations, it was strongly inhibited, as was photosynthetic O₂ evolution. At 2% O₂, there remained a substantial O₂ uptake, even at high CO₂ level; the O₂ evolution was inhibited at CO₂ concentrations under 330 microliters per liter. The O₂ uptake increased linearly with light intensity, starting from the level of dark respiration. No saturation was observed at high light intensities. No significant change in the gas-exchange patterns occurred during a long period of the plant life. An adaptation to low light intensities was observed after 3 hours illumination. These results are interpreted in relation to the functioning of the photosynthetic apparatus and point to a regulation by the electron acceptors and a specific action of CO₂. The behavior of the O₂ uptake and the study of the CO₂ compensation point seem to indicate the persistence of mitochondrial respiration during photosynthesis.     

The Effect of Temperature on Photosynthesis of Ryegrass and White Clover Leaves

The rate of photosynthesis of leaves of perennial ryegrass (Loliumperenne L.) and white clover (Trifollum pratense L.) grown atdifferent temperatures was measured at a range of temperatures.There was a small effect of the temperature at which a leafhad grown on its photosynthetic rate, but a large effect ofmeasurement temperature, especially in bright light, where photosyntheticrates at 15°C were about twice those at 5°C. It appearsthat temperature could affect sward photosynthesis in the field.Ryegrass and clover had similar photosynthetic rates which respondedsimilarly to temperature. Lolium perenne L., ryegrass, Trifolium pratense L., white clover, photosynthesis, temperature, irradiance     

Influence of Temperature on the Ratio of Ribulose Bisphosphate Carboxylase to Oxygenase Activities and on the Ratio of Photosynthesis to Photorespiration of Leaves

Lehnherr, B., Mächler, F. and Nösberger, J. 1985.Influence of temperature on the ratio of ribulose bisphosphatecarboxylase to oxygenase activities and on the ratio of photosynthesisto photorespiration of leaves.—J. exp. Bot. 36: 1117–1125. Rates of net and gross photosynthesis of intact white cloverleaves were measured by infrared gas analysis and by short termuptake of ¹⁴CO₂ respectively. Ribulose bisphosphate carboxylaseoxygenase (RuBPCO) was purified from young leaves and kineticproperties investigated in combined and separate assays. Theratio of carboxylase to oxygenase activities was compared withthe ratio of photosynthesis to photorespiration at various temperaturesand CO₂ concentrations. The ratio of photosynthesis to photorespiration at 30 Pa p(CO₂)was consistent with the ratio of carboxylase activity to oxygenaseactivity when each was measured above 20 °C. However, theratio of photosynthesis to photorespiration increased with decreasingtemperature, whereas the ratio of carboxylase to oxygenase activitywas independent of temperature. This resulted in a disagreementbetween the measurements on the purified enzyme and intact leafat low temperature. No disagreement between enzyme and leafat low temperature occurred, when the ratio of photosynthesisto photorespiration was determined at increased CO₂ concentrations. The results suggest an effect of low temperature and low CO₂concentration on the ratio of photosynthesis to photorespirationindependent of the enzyme. Key words: Ribulose bisphosphate carboxylase oxygenase, photorespiration, temperature     

Photosynthesis and Photorespiration in Typha latifolia

Photosynthetic rates of Typha latifolia, the broad-leaved cattail, are the equivalent of rates reported in tropical grasses and other plants which assimilate carbon by the phosphopyruvate carboxylase reaction, but photosynthesis in T. latifolia proceeds by a typical Calvin cycle. Glycolate oxidase, the photorespiratory enzyme, is present in high concentration in this species, but only minor quantities of the assimilated carbon pass through the photorespiratory pathway. However, continued operation of the pathway is apparently essential in the maintenance of assimilatory capacity. Glycolate oxidase function is not closely coupled to stomatal operation in T. latifolia.     

Effect of Temperature, CO(2) Concentration, and Light Intensity on Oxygen Inhibition of Photosynthesis in Wheat Leaves

The effect of 21% O₂ and 3% O₂ on the CO₂ exchange of detached wheat leaves was measured in a closed system with an infrared carbon dioxide analyzer. Temperature was varied between 2° and 43°, CO₂ concentration between 0.000% and 0.050% and light intensity between 40 ft-c and 1000 ft-c. In most conditions, the apparent rate of photosynthesis was inhibited in 21% O₂ compared to 3% O₂. The degree of inhibition increased with increasing temperature and decreasing CO₂ concentration. Light intensity did not alter the effect of O₂ except at light intensities or CO₂ concentrations near the compensation point. At high CO₂ concentrations and low temperature, O₂ inhibition of apparent photosynthesis was absent. At 3% O₂, wheat resembled tropical grasses in possessing a high rate of photosynthesis, a temperature optimum for photosynthesis above 30°, and a CO₂ compensation point of less than 0.0005% CO₂. The effect of O₂ on apparent photosynthesis could be ascribed to a combination of stimulation of CO₂ production during photosynthesis, and inhibition of photosynthesis itself.     

小麦叶片光合作用与其渗透调节能力的关系

在缓慢干旱条件下,小麦叶片渗透调节能力在一定范围内随胁迫程度的加剧而增加,而在快速干旱下,渗透调节能力丧失。小麦叶片通过渗透调节使光合速率和气孔导度对水分胁迫的敏感性降低,叶片维持较高的电子传递能力、RuBP羧化酶活性和叶绿体光合能量转换系统活性,并推迟了小麦叶片光合速率受气孔因素限制向叶肉细胞光合活性限制转变的时间。     

Effect of Low Temperature on the Protein Metabolism of Wheat Leaves

The effect of low temperature on the protein metabolism of wheat primary leaves was examined. In seedlings transferred from 25 to 5 °C, total soluble protein accumulation, in vivo protein synthesis and breakdown, in vitro protein breakdown, and SDS-PAGE profiles of proteinases in gelatine-containing gels were analysed. Leaf protein content increased within a 7-d period (70 % over the initial value) in plants exposed to 5 °C. The fast protein accumulation observed on days 0 – 2 was mainly attributed to a decreased breakdown. In further days, parallelly to a slowdown in the rate of protein accumulation, the leaf proteolytic activity increased. The incubation temperature also had an influence on the proteolytic activity: Q ₁₀ values for the 15 – 5 °C range were 80 – 200 % higher than those observed for the 25 – 15 °C range. On the other hand, the in vivo protein synthesis capacity, at either 25 or 55 °C, was not significantly modified in cold-treated plants. In addition to the enhanced activities of two serine-proteinases (previously found in control plants by SDS-PAGE analysis), cold-treated plants displayed a new proteinase, which had not been detected so far.     

Effect of Temperature on Photosynthetic Activities of Senescing Detached Wheat Leaves

Changes in various components of photosynthetic activity duringthe dark induced senescence of detached wheat leaves, maintainedat 25°C (control) and 35°C (mildly elevated temperaturetreatment), were examined. Senescence-associated decline measuredup to 96 h, in photosynthetic activity was appreciably hastenedat 35°C, than at 25°C as evident by the relative higherlosses of chlorophyll, photosystem (PS) II and PS I catalyzedphotochemical activities and ribulose-1,5-bisphosphate (RuBP)carboxylase activity. In addition, a comparatively higher risein light scattering profile of isolated chloroplasts was notedat 35°C than at 25°C. Senescence-induced degradationof chlorophyll was faster at 35°C than at 25°C; on theother hand, the degradation of carotenoids was faster at 25°Cthan at 35°C. Furthermore, the ratio of carotenoids to chlorophyllincreased with senescence up to 96 hours, higher ratio beingobtained at 35°C than at 25°C. Both PS II and PS I activitiesshowed a transient rise in the beginning phase of dark incubation,whereas loss in chlorophyll was continuous throughout the periodof senescence. The initial rise observed in photochemical activitieswas attributable to the uncoupling of electron transport fromphotophosphorylation. Elevated temperature treatment resultedin greater inactivation of RuBP carboxylase than control. Itappears that during senescence the loss in chlorophyll and RuBPcarboxylase activity are triggered simultaneously. (Received June 7, 1985; Accepted October 30, 1985)     

Effects of Temperature on Photosynthesis by Maize and Wheat

Maize and wheat plants were grown in controlled environmentswith day temperatures of 13, 18, 23, or 28 ?C. Leaves from maizegrown at 23 ?C photosynthesized faster than leaves from maizegrown at 13 or 18 ?C and, except when measured at 28 ?C, fasterthan leaves from maize grown at 28 ?C;leaves of maize grownat13 ?C were yellow and photosynthesized at insignificant rates.Leaves from wheat grown at 18 ? or 13 ?C had faster rates ofphotosynthesis than leaves from wheat grown at 23 or 28 ?C.The best rates for maize were faster than the best rates forwheat when the measurements were made at 23 or 28 ?C but at13 or 18 ?C the best rates for maize were not significantlybetter than the best rates for wheat. Leaves of maize that developedin the environment with 23 ?C as the day temperature did notrapidly lose their green colour when transferred to the environmentwith the day temperature of 13 ?C and the rate of photosynthesisof these leaves did not decline rapidly. However, new leavesexpanding in the cooler conditions were yellow and not effectivein photosynthesis. At 13 or 18 ?C maize, a C4 plant, which photorespiresslowly, did not photosynthesize more effectively than wheat,which photorespires rapidly. The maize did not produce its mosteffective leaves at 13 or 18 ?C and its optimum temperaturefor photosynthesis was 23?C or higher. It may therefore be consideredill-adapted to the temperate climate.     

A Mathematical Model of Photorespiration and Photosynthesis

A comprehensive mathematical model of C₃ leaf carbon metabolism,involving the Calvin cycle and the glycolate and glycerate pathwaysof photorespiration, is formulated in terms of a system of non-lineardifferential equations. A steady state, which is found to beeffectively stable, is derived. The model behaves realisticallywhen tested under varying external carbon dioxide and oxygenconcentrations: photosynthesis is inhibited by higher oxygenlevels, while photorespiration is inhibited by higher carbondioxide levels. Calvin cycle, differential equations, glycolate pathway, mathematical model, photorespiration, photosynthesis     

Photosynthesis of Ears and Flag Leaves of Wheat and Barley

Immediately after anthesis ears of spring wheat absorbed lessthan 0.5 mg CO₂, per hour in daylight and later evolved CO₂,in the light and in the dark. The rate of apparent photosynthesisof the combined flag-leaf lamina and sheath and peduncle (collectivelycalled flag leaf) of two spring wheat varieties, Atle and JufyI, was 3–4 mg per hour; the rates of the flag leaf andthe ear of two spring barleys, Plumage Archer and Proctor, wereeach about 1 mg per hour. The gas exchange of ears and flag leaves between ear emergenceand maturity accounted for most of the final grain dry weight.The CO₂, fixed by the wheat ear was equivalent to between 17and 30 per cent of the grain weight, but more than this waslost by respiration, so assimilation in the flag leaf was equivalentto 110–20 per cent of the final grain weight. In barley,photosynthesis in the flag leaf and the net CO₂ uptake by theear each provided about half of the carbohydrate in the grain. Barley ears photosynthesized more than wheat ears because oftheir greater surface, and flag leaves of wheat photosynthesizedmore than those of barley because they had more surface anda slightly greater rate of photosynthesis per dm².     

Effect of Oxygen on the Rate of Photorespiration in Detached Tobacco Leaves

The rate of carbon dioxide exchange in both light and darkness by detached tobacco leaves placed at various oxygen concentrations was measured by an Infra-Red CO₂ Analyzer and a Clark oxygen electrode. It was observed that during illumination oxygen had two different effects. One was to stimulate carbon dioxide evolution and the other to inhibit carbon dioxide absorption. Concentration of carbon dioxide at compensation point was found to be a linear function of oxygen concentration and this has been explained as due mainly to an increased evolution of carbon dioxide. Such an evolution during illumination has been called photorespiration. Increased concentrations of oxygen also had a stimulating effect on the magnitude of the initial post-illumination burst of carbon dioxide in darkness, but no effect on the subsequent steady rates. These data have been explained as due to the suspension of regular respiration in darkness and its replacement by a different process, tentatively called photorespiration. A second effect of oxygen was to reduce the efficiency (called “carboxylation efficiency”) with which a leaf was able to remove carbon dioxide from the atmosphere.     

温度对绿豆离体叶片光合作用的影响

绿豆离体叶片分别经25、30、35、40、45、50、55℃处理60 min后,发现净光合速率和光系统Ⅱ的最大量子效率(Fv/Fm)当温度分别高于35和40℃时明显下降;细胞间隙CO2浓度的变化趋势与净光合速率的基本相反.因此认为,Fv/Fm比净光合速率(Pn)更能耐受高温;气孔因素不是各种温度处理中净光合速率升高或降低的主要原因.     

The Effect of Rapid Temperature Increase on the Growth Rate of Wheat Leaves

The growth rate of the first leaf of eight-day-old wheat plants was measured using a DLT-2 highly sensitive linear displacement transducer. Leaf extensibility was evaluated from the growth rate under the increase in the pulling force by 2 g. An increase in the air temperature resulted in the doubling of the transpiration rate and immediate slowing of the leaf growth followed by the leaf shrinkage. However, growth was later resumed almost completely. Heat treatment did not induce any changes in the leaf extensibility, indicating that cell-wall mechanical properties were not changed. Growth retardation was supposed to result from a decrease in the water content in the leaf tissues because the balance between water influx from roots and its loss through transpiration was shifted toward the water loss. An initial drop in the relative water content (RWC) indicates such a misbalance. Subsequent growth resumption coincided with a decreased water deficiency. Since the rate of transpiration was not reduced, RWC and growth rate restoring evidently occurred due to the activated water uptake by roots, which can be explained by the increased hydraulic permeability detected in our experiments.     

Effect of L-Methionine Sulphoximine on the Products of Photosynthesis in Wheat (Triticum aestivum) Leaves

Methionine sulphoximine, an inhibitor of glutamine synthetase,caused ammonia accumulation in detached wheat leaves. The ratewas increased by increased oxygen in the atmosphere and by simultaneouslysupplying glycine or giving extra nitrate; it was decreasedby isonicotinyl hydrazide. Ammonia production was light-dependentand continued at a constant rate in air for at least 2 h. Photosynthesiswas progressively inhibited after the first hour; this inhibitionwas not because of increased stomatal resistance. Leaves suppliedwith 30 mol m^–3 ammonium chloride, without methioninesulphoximine, accumulated more ammonia than leaves treated withthe inhibitor but showed less inhibition of photosynthesis.The inhibitor decreased synthesis of [¹⁴C] amino acids from¹⁴CO₂ in the light but increased the synthesis of [¹⁴C] malateand, relatively, the incorporation of ¹⁴C into sugar phosphates.In the absence of inhibitor, nitrate increased and ammoniumion decreased synthesis of malate. Methionine sulphoximine,by causing a shortage of amino acids, probably inhibited photosynthesisin part by decreasing the recycling of carbon from the photorespiratorycycle back to the Calvin cycle. Key words: Photosynthetic ¹⁴CO₂ assimilation, Methionine sulphoximine, Detached wheat leaves