Effect of cytokinin preparations on the pools of pigments and proteins of wheat cultivars differing in their tolerance to water stress

Contents of chlorophylls, carotenoids, soluble leaf proteins, and the key enzyme of carbon metabolism--ribulose bisphosphate carboxylase/oxygenase (RuBisCO; EC 4.1.1.39)--in young seedlings and adult leaves of the wheat Triticum aestivum L. cultivars Mironovskaya 808 and Lyutestsens 758, contrasting in their water stress tolerances, were compared under conditions of normal available water supply, water deficiency, and subsequent rehydration. It was discovered that compounds displaying a cytokinin activity (6-benzylaminopurine, thidiazuron, cartolin-2, and cartolin-4) reduced the decreases in contents of chlorophylls, carotenoids, soluble leaf proteins, and RuBisCO progressing with development of water stress. These compounds with cytokinin activity also accelerated restoration of the compounds studied to their initial concentrations during rehydration. The cartolin preparations caused a maximal protective effect. Water stress had a more pronounced negative effect on cultivar Lyutestsens 758. Dehydration resulted in a more extensive destruction of seedlings compared to leaves of adult plants.     

A protector effect of cytokinin preparations on the photosynthetic apparatus of wheat plants under water deficiency conditions

The protective effects of the cytokinin 6-benzylaminopurine and the compounds thidiazuron and kartolin, displaying a cytokinin activity, on the photosynthetic apparatus of young seedlings and leaves of adult plants of two wheat (Triticum aestivum L.) cultivars, Mironovskaya 808 (more drought tolerant) and Lutescens 758 (less tolerant to water stress), were compared on the background of an increasing water deficiency. At the stages of drought and subsequent rehydration, cartolin preparations were the most efficient protectors, enhancing a less pronounced decrease in the intensity of photosynthesis, carboxylating activity of the key enzyme of carbon metabolism--ribulose bisphosphate carboxylase/oxygenase (EC 4.1.1.39)-and the activity of NADP-glyceraldehyde phosphate dehydrogenase--the enzyme complex comprising phosphoglycerate kinase (EC 2.7.2.3) and glyceraldehyde phosphate dehydrogenase (EC 1.2.1.13). This effect also included an increase in the leaf specific density and plant productivity. The negative influence of water stress on the photosynthetic apparatus was more pronounced in a less tolerant cultivar Lutescens 758 and in the seedlings as compared with the adult plants.     

A protector effect of cytokinin preparations on the photosynthetic apparatus of wheat plants under water deficiency conditions

The protective effects of the cytokinin 6-benzylaminopurine and the compounds thidiazuron and kartolin, displaying a cytokinin activity, on the photosynthetic apparatus of young seedlings and leaves of adult plants of two wheat (Triticum aestivum L.) cultivars, Mironovskaya 808 (more drought tolerant) and Lutescens 758 (less tolerant to water stress), were compared on the background of an increasing water deficiency. At the stages of drought and subsequent rehydration, kartolin preparations were the most efficient protectors, enhancing a less pronounced decrease in the intensity of photosynthesis, carboxylating activity of the key enzyme of carbon metabolism—ribulose bisphosphate carboxylase/oxygenase (EC 4.1.1.39)—and the activity of NADP—glyceraldehyde phosphate dehydrogenase—the enzyme complex comprising phosphoglycerate kinase (EC 2.7.2.3.) and glyceraldehyde phosphate dehydrogenase (EC 1.2.1.13). This effect also included an increase in the leaf specific density and plant productivity. The negative influence of water stress on the photosynthetic apparatus was more pronounced in a less tolerant cultivar Lutescens 758 and in the seedlings as compared with the adult plants.     

Effects of Cytokinin Preparations on the Stability of the Photosynthetic Apparatus of Two Wheat Cultivars Experiencing Water Deficiency

Carboxylase activity of the key enzyme of carbon metabolism, ribulose-bisphosphate carboxylase/oxygenase (RuBisCO; EC 4.1.1.39), and phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31), as well as the intensity of carbon dioxide photosynthetic assimilation in young seedlings and adult leaves of the wheat Triticum aestivum L. cultivars Mironovskaya 808 (a more tolerant) and Lyutestsens758 (a less tolerant), were compared under conditions of progressive water deficiency. The water stress had more pronounced negative effects on all the studied characteristics of the photosynthetic apparatus of the cultivar Lyutestsens758. Its seedlings were more sensitive to water stress. Compounds with a cytokinin activity (6-benzylaminopurine, thidiazuron, kartolin 2, and kartolin 4) played a protective role, increasing the stability of the photosynthetic apparatus under conditions of water deficiency. Preparations of kartolins displayed the maximum protective effect.     

Activity of NADP-dependent glyceraldehyde-phosphate dehydrogenase and phosphoenolpyruvate carboxylase in wheat leaves under water stress

The activities of NADP: glyceraldehyde-phosphate dehydrogenase (GAPDH), an enzyme complex comprising of phosphoglycerate kinase (EC 2.7.2.3) and glyceraldehyde-phosphate dehydrogenase (EC 1.2.1.13), and phosphoenolpyruvate carboxylase (PEPK; EC 4.1.1.31) in seedlings and leaves of wheat (Triticum aestivum L.) plants of the cultivars Mironovskaya 808 and Lutescens 758 have been compared under conditions of normal water supply, water deficiency, and subsequent rehydration. GAPDH activity, which determines the carbohydrate route of photosynthetic metabolism at the initial stages, is decreased by water stress to a greater extent than that of PEPK, on the activity of which non-carbohydrate metabolic pathways depend. Pretreatment of seedlings and mature plants with natural (6-benzylaminopurine) and synthetic (tidiazuron, kartolin-2, and kartolin-4) cytokinins attenuates the loss of enzyme activities during drought and facilitates their recovery within the period of rehydration; both effects are underlain by augmentation of reparation processes. The relative intensification of non-carbohydrate pathways of photosynthetic metabolism, observed under conditions of water deficiency, is accompanied by an increase in the osmotic pressure of cell sap. Possible mechanisms of this protector effect of cytokinin preparations are discussed.     

Activity of NADP-dependent glyceraldehyde-phosphate dehydrogenase and phosphoenolpyruvate carboxylase in wheat leaves under water stress

The activities of NADP: glyceraldehyde-phosphate dehydrogenase (GAPDH), an enzyme complex comprising of phosphoglycerate kinase (EC 2.7.2.3) and glyceraldehyde-phosphate dehydrogenase (EC 1.2.1.13), and phosphoenolpyruvate carboxylase (PEPK; EC 4.1.1.31) in seedlings and leaves of wheat (Triticum aestivum L.) plants of the cultivars Mironovskaya 808 and Lutescens 758 have been compared under conditions of normal water supply, water deficiency, and subsequent rehydration. GAPDH activity, which determines the carbohydrate route of photosynthetic metabolism at the initial stages, is decreased by water stress to a greater extent than that of PEPK, on the activity of which non-carbohydrate metabolic pathways depend. Pretreatment of seedlings and mature plants with natural (6-benzylaminopurine) and synthetic (tidiazuron, kartolin-2, and kartolin-4) cytokinins attenuates the loss of enzyme activities during drought and facilitates their recovery within the period of rehydration; both effects are underlain by augmentation of reparation processes. The relative intensification of non-carbohydrate pathways of photosynthetic metabolism, observed under conditions of water deficiency, is accompanied by an increase in the osmotic pressure of cell sap. Possible mechanisms of this protector effect of cytokinin preparations are discussed.     

Effects of cytokinin preparations on the stability of the photosynthetic apparatus of two wheat cultivars under water deficiency

Carboxylase activities of the key enzyme of carbon metabolism, ribulose-bisphosphate carboxylase/oxygenase (RuBisCO; EC 4.1.1.39), and phosphoenolpyruvate carboxylase (PEPC; EC 4.1.1.31), as well as intensities of carbon dioxide photosynthetic assimilation in young seedlings and adult leaves of the wheat Triticum aestivum L. cultivars Mironovskaya 808 (a more tolerant) and Lyutestsens 758 (a less tolerant), were compared under conditions of progressive water deficiency. The water stress had more pronounced negative effects on all the studied characteristics of photosynthetic apparatus of cultivar Lyutestsens 758 photosynthetic machinery of the cultivar Lyutestsens 758. Its seedlings were more sensitive to water stress. Compounds with a cytokinin activity (6-benzylaminopurine, thidiazuron, cartolin 2, and cartolin 4) played a protective role, increasing the stability of the photosynthetic machinery under conditions of water deficiency. Preparations of cartolins displayed the maximum protective effect.     

Activity of Carbon Metabolism Enzymes in Wheat Plants Treated with Kartolin-4 and Exposed to Water Stress

Enzymatic activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) (EC 4.1.1.39), phospho(enol)pyruvate carboxylase (EC 4.1.1.31), NAD malate dehydrogenase (EC 1.1.1.37), and NADP glyceraldehyde phosphate dehydrogenase complex including phosphoglycerate kinase (EC 2.7.2.3) and glyceraldehyde phosphate dehydrogenase (EC 1.2.1.13) were comparatively assayed in wheat seedlings of the cultivar Lyutestsens 758 grown under normal conditions, water deficiency conditions, and subsequent rehydration. Water stress was found to decrease the activity of all enzymes tested, the effect being most pronounced in the case of Rubisco. The content of Rubisco in wheat plants exposed to water deficiency was reduced less significantly than the activity of the enzyme. Pretreatment of plant seeds with kartolin-4 (o-isopropyl-N-2-hydroxyethyl carbamate), a preparation with cytokinin activity, reduced the dehydration-induced inhibition of enzymatic activity. Upon a subsequent rehydration, kartolin-4 facilitated rapid recovery of the photosynthetic activity, the process being based on the kartolin-induced stimulation of reparation reactions. Under conditions of water stress, a partial decrease in the activity of carbon metabolism enzymes in vitrowas accompanied by complete inhibition of photosynthesis in vivo, perhaps, as a result of an abrupt increase in the stomatal resistance.     

The Activity and Content of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase in Wheat Plants as Affected by Water Stress and Kartolin-4

The carboxylating activity and content of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO, EC 4.1.1.39), and other soluble proteins in young seedlings and mature leaves of Lutescens-758, a drought-sensitive cultivar of soft spring wheat Triticum aestivum L., were studied under the conditions of drought and subsequent rehydration. Seedlings and mature plants preliminarily treated with the cytokinin-like compound kartolin-4 were compared to untreated plants. Drought-induced decrease in RuBPCO activity should be attributed not only to proteolytic decomposition of the enzyme protein itself but also to a partial inhibition of its catalytic activity. The decrease in RuBPCO activity was larger than that in RuBPCO content. Water stress induced a marked decrease in the soluble protein content. Kartolin-4 increased the resistance to drought.     

Activity of carbon metabolism enzymes in wheat plants treated with kartolin-4 and exposed to water stress]

Enzymatic activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) (EC 4.1.1.39), phospho(enol)pyruvate carboxylase (EC 4.1.1.31), NAD malate dehydrogenase (EC 1.1.1.37), and NADP glyceraldehydephosphate dehydrogenase complex including phosphoglycerate kinase (EC 2.7.2.3) and glyceraldehydephosphate dehydrogenase (EC 1.2.1.13) were comparatively assayed in wheat seedlings of the cultivar Lyutestsens 758 grown under normal conditions, water deficiency conditions, and subsequent rehydration. Water stress was found to decrease the activity of all enzymes tested, the effect being most pronounced in case of Rubisco. The content of Rubisco in wheat plants exposed to water deficiency was reduced less significantly than the activity of the enzyme. Preliminary treatment of plant seeds with kartolin-4 (o-isopropyl-N-2-hydroxyethyl carbamate), a preparation with cytokinin activity, reduced the dehydration-induced inhibition of enzymatic activity. Upon a subsequent rehydration, kartolin-4 facilitated rapid recovery of the photosynthetic activity, the process being based on the kartolin-induced stimulation of reparation reactions. Under conditions of water stress, a partial decrease in the activity of carbon metabolism enzymes in vitro was accompanied by complete inhibition of photosynthesis in vivo, perhaps, as a result of an abrupt increase in the stomatal resistance.     

Protective Role of Kartolin-4 in Wheat Plants Exposed to Soil Draught

Parameters of photosynthesis, heat-resistance, and osmotic pressure of cell exudate of leaves of the drought-sensitive cultivarLyutestsens 758 of wheat, Triticum aestivum, were studied under conditions of normal water supply, soil drought, and subsequent rehydration. The plants preliminarily treated with kartolin-4 were compared to untreated plants. Kartolin-4, a preparation with cytokinin-like activity, partially prevented the drought-induced inhibition of the photosynthetic assimilation of carbon dioxide and carboxylation activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39), the key enzyme of carbon metabolism in plants. Upon subsequent rehydration, kartolin-4 stimulated the reparation reactions and facilitated the rapid recovery of normal photosynthetic activity. Kartolin-4 also increased the plant resistance to overheating and water deficiency.     

Protective role of kartolin-4 in soil drought in wheat plants

Parameters of photosynthesis, heat-resistance, and osmotic pressure of cell exudate of leaves of the drought-sensitive cultivar Lyutestsens 758 of wheat, Triticum aestivum, were studied under conditions of normal water supply, soil drought, and subsequent rehydration. The plants preliminarily treated with kartolin-4 were compared to untreated plants. Kartolin-4, a preparation with cytokininlike activity, partially prevented the drought-induced inhibition of the photosynthetic assimilation of carbon dioxide and carboxylation activities of ribulose-1,5-bisphosphate carboxylase/oxygenase (EC 4.1.1.39), the key enzyme of carbon metabolism in plants. Upon a subsequent rehydration, kartolin-4 stimulated the reparation reactions and facilitated rapid recovery of normal photosynthetic activity. Kartolin-4 also increased plant resistance to overheating and water deficiency.     

Some effects of enhanced UV-B irradiation on the growth and composition of plants

Barley (Hordeum vulgare), corn (Zea mays), bean (Phaseolus vulgaris), and radish (Raphanus sativus) seedlings were continuously irradiated under a lighting device for 5–10 d at an increased ultraviolet (UV)-B fluence rate. In their growth parameters, composition, and leaf surface, these four species responded differently to the increased UV-B exposure. Bean seedlings suffered the most serious effects, radish and barley less, and corn was hardly influenced at all. In all plant species, the fresh weight, the leaf area, the amounts of chlorophylls, carotenoids and the galactolipids of the chloroplasts were reduced. The lipid content of the corn and bean seedlings also diminished. But all the irradiated plants showed a rise in their protein content compared to the control plants. The content of flavonoids increased in barley and radish seedlings by about 50%. The effects on growth parameters and composition were more extensive with increasing UV-B fluence rates, at least as shown in the case of barley seedlings. The fresh weights fell proportionally with the chlorophylls and carotenoids. In contrast, the flavonoid content of barley leaves rose parallel to the increasing UV-B fluence rates and reached 180% of the value in the control plants with the highest UV-B fluence rate. Scorching appeared regularly in the form of bronze leaf discoloration at the highest UV-B fluence rates. Scanning electron micrographs of the leaf surface of UV-B irradiated plants showed deformed epidermal structures.Abbreviations MGDG monogalactosyldiglyceride - DGDG digalactosyldiglyceride - SL sulfoquinovosyldiglyceride - PG phosphatidylglycerol - PC phosphatidylcholine - PE phosphatidylethanolamine - PI phosphatidylinositol - LA leaf are - FW fresh weight - DW dry weight - SEM scanning electron microscopy - C total carotenoids - Chl total chlorophyll     

Changes in Mulberry Leaf Metabolism in Response to Water Stress

A series of experiments were conducted to characterize the water stress-induced changes in the activities of RuBP carboxylase (RuBPCO) and sucrose phosphate synthase (SPS), photosystem 2 activity, and contents of chlorophylls, carotenoids, starch, sucrose, amino acids, free proline, proteins and nucleic acids in mulberry (Morus alba L. cv. K-2) leaves. Water stress progressively reduced the activities of RuBPCO and SPS in the leaf extracts, the chlorophyll content, and PS2 activity in isolated chloroplasts. Plants exposed to drought showed lower content of starch and sucrose but higher total sugar content than control plants. While the soluble protein content decreased under water stress, the amino acid content increased. Proline accumulation (2.5-fold) was noticed in stressed leaves. A reduction in the contents of DNA and RNA was observed. Reduced nitrogen content was associated with the reduction in nitrate reductase activity. SDS-PAGE protein profile showed few additional proteins (78 and 92 kDa) in the water stressed plants compared to control plants.     

Phosphorylation upon cold stress in rice (Oryza sativa L.) seedlings

The response of plants to cold stress is not well understood at the biochemical level, although it has been studied extensively at the ecological level. To investigate whether protein phosphorylation may play an important role in cold stress, we exposed rice seedlings to low temperatures, prepared protein extracts from the leaves and incubated these in the presence of [γ-³²P]ATP. The proteins were then separated by two-dimensional polyacrylamide gel electrophoresis. While several proteins were found to be phosphorylated upon cold stress one protein, pp35, which has an isoelectric point of 8.0, was more phosphorylated than the others. The pp35 protein was found to be phosphorylated when rice seedlings were incubated for 6 h at 5°C before the leaf protein extract was prepared and radioactive labeling was performed. The pp35 was, however, significantly more phosphorylated in cold-tolerant rice varieties. Antibodies were raised against purified pp35 in adult rabbits. Using this pp35 antibody, which can recognize the RuBisCO large-chain subunit (LSU), and from amino acid sequencing of pp35, we were able to identify and confirm the pp35 protein as the fragment of RuBisCO LSU (EC 4.1.1.39). Phosphorylation of the RuBisCO LSU may be important in cold tolerance. Received: 7 July 1998 / Accepted: 19 December 1998     

Effect of phytoplasma infection on metabolite content and antioxidant enzyme activity in lime (<Emphasis Type="Italic">Citrus aurantifolia</Emphasis>)

The objective of the present work was to study biochemical alterations in lime plants infected by the Candidatus Phytoplasma aurantifoliae. Changes in antioxidant activities, content of chlorophylls (Chl), carotenoids (Car), soluble proteins, sugars and auxin (IAA) in infected plant were investigated. The activities of polyphenol oxidase (PPO), peroxidase (POX) and superoxide dismutase (SOD) were observed to be greater in infected leaves than the healthy control. Also according to non-denaturing PAGE, in infected leaves all the antioxidative enzymes isoforms were stronger than that of the healthy control. These results suggest that antioxidant enzymes can be activated in response to infection by phytoplasma. The decrease in content of proteins, total soluble and reducing sugars in infected plants point out changes in host metabolism due to the phytoplasma infection. The reduction in chlorophylls and auxin content shows that the phytoplasma can interfere in photosynthesis and induces senescence in the leaf. In conclusion, this study provides new insights into the lime response to phytoplasma infection.     

Reconstitution of chlorophylls and photosynthetic CO2 assimilation upon rehydration of the desiccated poikilochlorophyllous plant Xerophyta scabrida (Pax) Th. Dur. et Schinz

Resynthesis of the photosynthetic apparatus and resumption of CO₂ assimilation upon rehydration is reported for the monocotyledonous and poikilochlorophyllous desiccation-tolerant (PDT) plant Xerophyta scabrida (Pax) Th. Dur. et Schinz (Velloziaceae). During desiccation there was a complete breakdown of chlorophylls whereas the total carotenoid content of air-dried leaves was reduced to about 22% of that of functional leaves. The prerequisites for the resynthesis of photosynthetic pigments and functional thylakoids were the reappearance of turgor and maximum leaf water content at 2 and 10 h after rehydration, respectively. The period of increased initial respiration after rewetting leaves (rehydration respiration) lasted up to 30 h and was thus 6 to 10 times longer than in homoiochlorophyllous desiccation-tolerant plants (HDTs) in which chlorophylls are retained during desiccation. Accumulation of chlorophylls a + b and total carotenoids (xanthophylls and carotene) started 10 h after rehydration. Normal levels of chlorophyll and carotenoids were obtained 72 h after rehydration. Values for the variable-fluorescence decrease ratio (Rfd690 values), an indicator of photochemical activity, showed that photochemical function started 10 h after rehydration, but normal values of 2.7 were reached only 72 h after rehydration. Net CO₂ assimilation started 24 h after rewetting and normal rates were reached after 72 h, at the same time as normal values of stomatal conductance were obtained. The increasing rates of net CO₂ assimilation were paralleled by decreasing values of the intercellular CO₂ concentration. All photosynthetic parameters investigated showed values normal for functional chloroplasts by 72 h after the onset of rehydration. Fully regreened leaves of the presumed C₃ plant X. scabrida exhibited a net CO₂ assimilation rate which was in the same range as that of other C₃ plants and higher than that of recovered HDT plants. The fundamental difference between air-dried PDT plants, such as X. scabrida, which have to resynthesize the photosynthetic pigment apparatus, and air-dried HDT plants, which only undergo a functional recovery, is discussed.Abbreviations c -carotene - c_i intercellular CO₂ concentration - Car x + c total carotenoid content x + c - Chl a + b total chlorophyll a + b content - g_s stomatal conductance - HDT homoiochlorophyllous desiccation tolerant - LWC leaf-water content - P_N net photosynthesis rate - PDT poikilochloro phyllous desiccation tolerant - R_d dark respiration - Rfd variable fluorescence decrease ratio (Rfd = fd/fs) - x xanthophylls The senior author thanks the Deutschem Akademischem Auslandsdienst (Bonn, Germany), Soros Foundation (Budapest, Hungary) and European Community (Brussels, Belgium) for providing fellowships for research periods at Karlsruhe. The research was also supported by the Hungarian Scientific Research Foundation (OTKA I/848, OTKA I/3.1545 and OTKA I/4.F.5359). We wish to thank Professor T. Pocs (Eger, Hungary — Morogoro, Tanzania) for collecting the plant material and to the linguist Mr. A. Jackson for correcting the English.     

Photosynthetic activity and water relations of sprouts ofPasania edulis

In order to investigate the factors causing fast growth of sprouts ofPasania edulis, photosynthetic activity and water relation characteristics of lower (mature) leaves and upper (expanding) leaves of the sprouts were compared with those of seedlings and adult trees ofP. edulis. Apparent quantum yield was generally low. Maximum photosynthetic rate was highest in the lower leaves of sprouts. Stomatal frequency was higher in sprout leaves than in seedling leaves. Osmotic potential at the water saturation point and water potential at the turgor loss point, in leaves, were higher in sprouts than in seedlings and adult trees. Symplasmic water content per unit leaf area was higher in sprouts than in seedlings. These water relation parameters in leaves indicated that sprout leaves are superior in maintaining cell turgor against water loss, but are not tolerant to water stress. In field measurements, sprout leaves showed higher stomatal conductance and transpiration rates. These results indicated that sprout leaves fully realized their high potential productivity even under field conditions. The leaf specific conductance, from the soil to the leaf, was higher in sprouts than in seedlings. Large and deep root systems of the original stumps of the sprouts may be attributed to the high leaf specific conductance.     

Growth and biochemical alterations in coffee due to selenite toxicity

Two experiments were conducted to investigate selenite toxicity in coffee (Coffea arabica cv. Catuaí). In the first aqueous selenite solution (10 µM Na₂SeO₃) was used to infiltrate leaves of an adult coffee plant. The infiltrated leaves and fruits adjacent to them showed enhanced contents of caffeine and soluble sugars. Amino acid contents were not affected, whereas pigments (chlorophylls, carotenoids and xanthophylls) exhibited a significant decrease. In the second experiment, coffee seedlings were irrigated with aqueous selenite solutions (10,100 and 1000 µM Na₂SeO₃) and the first and third pairs of leaves were analyzed. Control plants did not receive selenium. The plants were not different in height, but at the highest selenium concentration showed lower dry matter accumulation in roots and leaves, lower leaf area and thicker leaves. Increases in caffeine and soluble sugars were observed in the first pair of leaves at the highest selenium concentration, although selenium content itself increased steadily with increasing solution concentration. Phenols increased in both leaf pairs and pigments decreased in the third pair. Nitrate reductase activity, measured in the second leaf pair, was much lower at all selenium levels. The profile of free amino acid was altered in leaves of plants treated with selenium.     

Partitioning of Nitrogen among Ribulose-1,5-bisphosphate Carboxylase/Oxygenase, Phosphoenolpyruvate Carboxylase, and Pyruvate Orthophosphate Dikinase as Related to Biomass Productivity in Maize Seedlings

Maize (Zea mays L. cv Golden Cross Bantam T51) seedlings were grown under full sunlight or 50% sunlight in a temperature-controlled glasshouse at the temperatures of near optimum (30/25°C) and suboptimum (17/13°C) with seven levels of nitrate-N (0.4 to 12 millimolars). The contents of phosphoenolpyruvate carboxylase (PEPC), pyruvate orthophosphate dikinase (PPD), and ribulose-1,5-P₂ carboxylase/oxygenase (RuBisCO) were immunochemically determined for each treatment with rabbit antibodies raised against the respective maize leaf proteins (anti-PEPC and anti-PPD) or spinach leaf protein (anti-RuBisCO). The content of each enzymic protein increased with increasing N and raised under reduced temperature. The positive effect of light intensity on their contents was evident only at near optimal temperature. The relative increase in PEPC and PPD content with increasing N was significantly greater than that of RuBisCO irrespective of growth conditions. These enzymic proteins comprised about 8, 6, and 35% of total soluble protein, respectively, at near optimal growth condition. In contrast to significant increase in the proportion of soluble protein allocated to PEPC and PPD seen under certain conditions, the proportion allocated to RuBisCO decreased reciprocally with an increased biomass yield by N supply.

These results indicated that the levels of PEPC and PPD parallel to maize biomass more tightly than that of RuBisCO at least under near optimal growth condition.