Water relations of cotton plants under nitrogen deficiency

Nitrogen deficiency in cotton plants (Gossypium hirsutum L.) increased the threshold water potentials for both stomatal closure and leaf senescence (defined as loss of chlorophyll and protein) during drought. These studies attempted to answer two questions: (1) What is the basis for the N/water interaction on senescence? (2) Is there a direct relationship between stomatal closure and senescence? Young and old leaves from N-deficient and N-sufficient plants maintained their relative sensitivities to water stress when excised leaf discs were floated on solutions of polyethylene glycol in dim light. In this leaf disc system, both leaf aging and N deficiency increased the threshold water potential for senescence. Leaf aging and N deficiency also decreased the concentration of exogenous abscisic acid necessary to initiate senescence in discs. A role for cytokinins in controlling senescence could not be clearly shown. In young leaves of both N-deficient and N-sufficient plants, stomata closed at water potentials much higher than those causing senescence. During leaf aging, the water potentials causing senescence increased more than those causing stomatal closure. The two processes thus occurred at about the same potentials in the oldest leaves. These data argue against a general cause-and-effect relationship between stomatal closure and senescence. Rather, each process apparently responded independently to absicsic acid accumulated during drought.     

水稻叶片的衰老与超氧物歧化酶活性及脂质过氧化作用的关系

研究了从抽穗开花到籽粒成熟过程中,水稻植株顶部三片叶子的超氧物歧化酶(SOD),脂质过氧化产物丙二醛(MDA)含量及二磷酸核酮糖羧化酶活性的变化。实验结果表明:叶片的衰老伴随着 SOD 活性、RuBP 羧化酶活性及叶绿素含量的降低、丙二醛含量显著增高。分离了三个 SOD 的同工酶,证明为 Cu—Zn SOD。观察了 SOD 同工酶在叶片老化及酶液存放不同时间中的变化。讨论了叶片衰老过程中氧自由基对酶及质膜的损伤影响。     

Changes in Photosynthetic Capacity in Rice Leaves from Emergence through Senescence. Analysis from Ribulose-1,5-bisphosphate Carboxylase and Leaf Conductance

Changes in the rates of gas exchange and the amount of ribulose1,5-bisphosphate (RuBP) carboxylase protein were determinedin the 12th leaf blades of rice during the reproductive stages.RuBP carboxylase exhibited a large change similar to that inthe assimilation rate at 2% O₂ throughout the leaf's life, butits decrease during senescence was barely faster than the decreasein the assimilation rate. Consequently, the overall relationshipwas slightly curvilinear. By contrast, leaf conductance decreasedmore slowly than the assimilation rate which resulted in theintercellular CO₂ concentration increasing during senescence. In order to determine the maximum activity of RuBP carboxylaseat the intercellular CO₂ concentration, the kinetic parametersand their pH response were determined using purified, and completelyactivated, rice RuBP carboxylase. The maximum carboxylase activityat the intercellular CO₂ concentration was linearly correlatedwith the assimilation rate at 2% O₂ (r=0.989), and was veryclose to that needed to account for the assimilation rate. We conclude that changes in both the amount of RuBP carboxylaseprotein and leaf conductance reflect the change in photosynthesisduring the life span of the leaf. (Received November 26, 1983; Accepted February 20, 1984)     

Proteolysis of ribulose-1,5-bisphosphate carboxylase/oxygenase in leaves of Citrus explants throughout the annual cycle and its regulation by ethylene

Leaf senescence and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBP carboxylase, EC 4.1.1.39) degradation in orange [ Citrus sinensis (L.) Osbeck cv. Washington Navel] explants have been investigated. Explants consisted of a segment of stem (ca 15 cm) and 5 mature leaves. In vitro RuBP carboxylase degradation was determined by culturing the explants in water for different periods of time (3 days usually) and quantifying the two RuBP carboxylase subunits in the extracts following sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). In vitro RuBP carboxylase degradation was estimated by autodigestion of leaf extracts and SDS-PAGE. The extent of in vivo RuBP carboxylase degradation in explants cultured under 16 h light/8 h dark photoperiod varied throughout the year and showed a cyclic behaviour correlated with the growth cycle of Citrus. The highest proteolytic activity both in vivo and in vitro was found in explants made from April to August coinciding with the maximum vegetative growth period of the tree.
Leaf senescence and abscission could be retarded significantly at any time of the year by maintaining the explants continuously in the dark. Treatment of the explants in the dark with a continuous flow of ethylene enhanced both leaf abscission and rate of RuBP carboxylase degradation, proportionally to ethylene concentration (0.1-0.6 ppm). Ethylene-induced senescence of Citrus leaf explants in the dark appears to be a convenient model system to study the regulation of the proteolytic degradation of RuBP carboxylase.     

Degradation of ribulose-1,5-bisphosphate carboxylase and chlorophyll in senescing barley leaf segments triggered by jasmonic acid methylester, and counteraction by cytokinin

Barley ( Hordeum vulgare L. cv. Salome) primary leaf segments responded to the application of a putative plant growth regulator, ± jasmonic acid methylester (JA-Me). with accelerated senescence, as indicated by the loss of chlorophyll and the rapid decrease in activity and immunoreactive protein content of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBP carboxylase, EC 4.1.1.39). The senescence-promoting action of JA-Me differed in light and in darkness; e.g. the initial rates of chlorophyll and RuBP carboxylase breakdown were markedly higher in light than in darkness in the presence of 4.10⁻⁵ M JA-Me. Cytokinin (benzyladenine, 4.10⁻⁵ M ) stopped the loss of chlorophyll and RuBP carboxylase during senescence; however, the rapid drop induced by JA-Me in the early phase of leaf segment senescence could not be prevented by concomitant or previous addition of BA. On the other hand, BA added 24 h after JA-Me application resulted in a recovery of chlorophyll and RuBP carboxylase at the later stages, indicating a possible rapid inactivation of JA-Me in the tissues. The activities of a number of other chloroplastic and cytosolic enzymes were not significantly altered in JA-Me-treated leaf segments compared with controls floated on water. Time-dependent chlorophyll decrease in isolated chloroplasts did not change upon JA-Me addition to the isolated organelles. It is suggested that JA-Me acts on chloroplast senescence by promoting cytoplasic events which eventually bring about the degradation of chloroplast constituents.     

Rapid N transport to pods and seeds in N-deficient soybean plants

Non-nodulated soybean (Glycine max (L.) Merr.) plants were cultivated hydroponically under N-sufficient (5 mM NaNO(3)) or N-deficient (0.5 mM NaNO(3)) conditions. (13)N- or (15)N- labelled nitrate was fed to the cut end of the stems, and the accumulation of nitrate-derived N in the pods, nodes and stems was compared. Real-time images of (13)N distribution in stems, petioles and pods were obtained using a Positron Emitting Tracer Imaging System for a period of 40 min. The results indicated that the radioactivity in the pods of N-deficient plants was about 10 times higher than that of N-sufficient plants, although radioactivity in the stems and nodes of N-deficient versus N-sufficient plants was not different. A similar result was obtained by supplying (15)NO(3) to cut soybean shoots for 1 h. The fact that the N translocation into the pods from NO(3) fed to the stem base was much faster in N-deficient plants may be due to the strong sink activity of the pods in N-deficient plants. Alternatively, the redistribution of N from the leaves to the pods via the phloem may be accelerated in N-deficient plants. The temporal accumulation of (13)NO(3) in nodes was suggested in both N-sufficient and N-deficient plants. In one (13)NO(3) pulse-chase experiment, radioactivity in the stem declined rapidly after transferring the shoot from the (13)NO(3) solution to non-labelled NO(3); in contrast, the radioactivity in the node declined minimally during the same time period.     

Photosynthesis and Ribulose 1,5-Bisphosphate Carboxylase in Rice Leaves: Changes in Photosynthesis and Enzymes Involved in Carbon Assimilation from Leaf Development through Senescence

Changes in photosynthesis and the ribulose 1,5-bisphosphate (RuBP) carboxylase level were examined in the 12th leaf blades of rice (Oryza sativa L.) grown under different N levels. Photosynthesis was determined using an open infrared gas analysis system. The level of RuBP carboxylase was measured by rocket immunoelectrophoresis. These changes were followed with respect to changes in the activities of RuBP carboxylase, ribulose 5-phosphate kinase, NADP-glyceraldehyde 3-phosphate dehydrogenase, and 3-phosphoglyceric acid kinase.

RuBP carboxylase activity was highly correlated with the net rate of photosynthesis (r = 0.968). Although high correlations between the activities of other enzymes and photosynthesis were also found, the activity per leaf of RuBP carboxylase was much lower than those of other enzymes throughout the leaf life. The specific activity of RuBP carboxylase on a milligram of the enzyme protein basis remained fairly constant (1.16 ± 0.07 micromoles of CO₂ per minute per milligram at 25°C) throughout the experimental period.

Kinetic parameters related to CO₂ fixation were examined using the purified carboxylase. The K_m(CO₂) and V_max values were 12 micromolar and 1.45 micromoles of CO₂ per minute per milligram, respectively (pH 8.2 and 25°C). The in vitro specific activity calculated at the atomospheric CO₂ level from the parameters was comparable to the in situ true photosynthetic rate per milligram of the carboxylase throughout the leaf life.

The results indicated that the level of RuBP carboxylase protein can be a limiting factor in photosynthesis throughout the life span of the leaf.

     

Variation of RuBP carboxylase activity among anther-derived plants of Solanum phureja

The effect of genotype and ploidy on RuBP carboxylase (EC 4.1.1.39) activity, chlorophyll content, leaf area, chloroplast ultrastructure and not photosynthesis among monoploid. diploid and tetraploid anther-derived plants of Solanum phureja Juz, and Buk. was studied. Within the monoploid group, RuBP carboxylase activity and concentration displayed a significant genotypic effect. For the diploids, variation among genotypes was significant for total protein content and maximum specific activity of RuBP carboxylase, and among the tetraploids for net photosynthesis and specific leaf weight. Ploidy effect was evident regarding net photosynthesis, leaf area and chlorophyll content. The different ploidy groups among the anther-derived plants surpassed the anther donor plant for all characteristics except maximum activity of RuBP carboxylase and net photosynthesis. For the latter only the tetra-ploid group was superior to the anther source plant. However, a monoploid genotype with an increase of 9% in maximum activity of RuBP carboxylase over the anther-donor plant was identified. Segregation of trails rind differential gene expression together with possible mutations during androgenesis are discussed as sources of variation.     

Superoxide Dismutase Activity and Lipid Peroxidation in Relation to Senescence of Rica Leaves

Superoxide dismutase (SOD), lipid peroxidation, ribulose 1, 5-bisphosphate earboxylasc and chlorophyll content in the leaves of rice were investigated during bloomJug to ripening stages. The results indicated that leaf senescence was associated with the decreascs of SOD and RuBP earboxylase activities and chlorophyll content. A marked increase of malondialdehyde(MDA)contcnt, a produet of lipid pcroxidation was observed during leaf senescence, However, the relative high activities of SOD and RuBP earboxylase and chlorophyll content, lower MDA content in hybrid rice senescenee leaves, compared with their three lines, suggest the presence of physiological hybrid vigor. The analysis of polyacrylamide gel eleetrophoresis showed that three SOD isozymes in leaf extract, which were Cu-Zn SOD. Changes of SOD isozymes were observed during leaf agling and at different time of storage of its extract. The destroying effect of oxygen free radical on enzymes and membrane in the course of leaf senescence was discussed.     

Biochemical and physiological responses of Gracilaria tenuistipitata uuder two different nitrogen treatments

The influence of nitrogen on ribulose-1.5-bisphosphate carboxylase/oxygenase (Rubisco. EC 4.1.1.39) content is poorly understood in macroalgae. N-deficient Gracilaria tenuistipitata Zhang et Xia var. liui was cultivated in the laboratory under constant light intensity and temperature. Biochemical and physiological variables were monitored after a high (1 m M ) or low (o. 1 m M ) nitrate pulse. Rubisco content in crude extracts was estimated by SDS-PAGE with the Coomassie Blue Staining procedure. Nitrate was consumed immediately in the low-N treatment, but there was always an external nitrate source in the high-N treatment. Total soluble proteins and phycobiliproteins decreased as internal nitrogen diminished in the low-N treatment, but kept fairly constant in N-sufficient conditions. However, Rubisco content increased until the 7th day and then started to decrease in both cases. Fresh weight increment showed a better correlation with Rubisco than with pigment content.     

水稻叶片生育过程中RubisCO活性与光合、光呼吸的关系

水稻生育过程中,ＲｕＢＰ羧化酶活性与光合速率、ＲｕＢＰ加氧酶活性与光呼吸速率、ＲｕＢＰ羧化酶活性与加氢酶活性以及光合速率与光呼吸速率之间是相关的。籼型品种与粳型品种间酶活性的高低及光合、光呼吸速率的高低基本一致,籼型三系杂交稻（Ｆ１）无明显的光合优势。酶的羧化活性的高低只在一定范围内与光合速率的高低平行。在正常生育条件下,酶蛋白的数量不是水稻光合速率的限制因子。     

Photosynthesis and nitrogen relationships in leaves of C3 plants

Summary The photosynthetic capacity of leaves is related to the nitrogen content primarily bacause the proteins of the Calvin cycle and thylakoids represent the majority of leaf nitrogen. To a first approximation, thylakoid nitrogen is proportional to the chlorophyll content (50 mol thylakoid N mol^-1 Chl). Within species there are strong linear relationships between nitrogen and both RuBP carboxylase and chlorophyll. With increasing nitrogen per unit leaf area, the proportion of total leaf nitrogen in the thylakoids remains the same while the proportion in soluble protein increases. In many species, growth under lower irradiance greatly increases the partitioning of nitrogen into chlorophyll and the thylakoids, while the electron transport capacity per unit of chlorophyll declines. If growth irradiance influences the relationship between photosynthetic capacity and nitrogen content, predicting nitrogen distribution between leaves in a canopy becomes more complicated. When both photosynthetic capacity and leaf nitrogen content are expressed on the basis of leaf area, considerable variation in the photosynthetic capacity for a given leaf nitrogen content is found between species. The variation reflects different strategies of nitrogen partitioning, the electron transport capacity per unit of chlorophyll and the specific activity of RuBP carboxylase. Survival in certain environments clearly does not require maximising photosynthetic capacity for a given leaf nitrogen content. Species that flourish in the shade partition relatively more nitrogen into the thylakoids, although this is associated with lower photosynthetic capacity per unit of nitrogen.     

Comparison Between Growth Chamber and Field-Grown Zea mays Plants for Photosynthetic Carboxylase Activities and .Other Physiological Characteristics with Respect to Leaf Position

Baldy, P. 1986. Comparison between growth chamber and field-grownZea mays plants for photosynthetic carboxylase activities andother physiological characteristics with respect to leaf position.—J.exp. Bot. 37: 309–314. The lengths and fresh weights of leaves, and the amounts ofchlorophyll and protein per leaf, were higher in maize grownin a controlled environment than for field-grown maize harvestedat a similar stage of growth with the seventh leaf just emerging.However, the fresh weight and chlorophyll per unit leaf areawere not different and more protein was present per Unit leafarea in maize cultivated in the field, particularly in the 4thleaf. Except in the seventh leaf the youngest present, the PEP carboxylaseactivity was 2-fold higher in field-grown maize than in plantsfrom the controlled environment. The RuBP carboxylase activitywas not significantly affected by growth conditions. The maximumactivities of the carboxylases were found in the 5th leaf formaize grown in the controlled environment and the 4th leaf forfield maize; in these two leaves the ratios of the PEP: RuBPcarboxylasc activities were 3·0 and 4·4 respectively. The results are used to justify the choice of the fully expanded4th leaf of l9-d-old plants grown in a controlled environmentfor studies of the enzymes involved in the photosynthetic carbonmetabolism of this C₄ plant. Key words: Growth conditions, PEP carboxylase/RuBP carboxylase activity ratio, Zea mays leaf position     

Effects of season-dependent irradiance levels and nitrogen-deficiency on photosynthesis and photoinhibition in field-grown rice (Oryza sativa)

Photoinhibition and acclimation of photosynthesis in rice plants grown under N-sufficient (NS) and N-deficient (ND) field conditions were investigated during the tropical wet (WS) and dry (DS) seasons in the Philippines. Diurnal patterns of CO₂ assimilation were examined. There was a transient peak in CO₂ assimilation in the leaves of the NS plants in the early morning during the DS and the WS, which was not seen in the ND plants in either season. ND leaves had lower Ribulose bisphosphate carboxylase/oxygenase (Rubisco) contents and lower chlorophyll contents. A lowered quantum yield of photosystem II (φPSII) was observed in the ND plants at an intermediate irradiance though no differences between N treatments were seen at high irradiance. Analysis of carotenoids indicated a small increase in the de-epoxidation state of the xanthophyll cycle (DES) at mid-day in the ND leaves compared to NS. Photoinhibition was greater in ND leaves when incident mid-day irradiance was increased by altering the leaf angle. Although Rubisco contents were lower in ND plants, photosynthesis in situ did not decline proportionally. For NS plants, Chlorophyll content, but not Rubisco content, was season-dependent and results are discussed in terms of the interaction between irradiance use and N content of rice leaves.     

Restoration of Photosynthesis in Pot-Bound Tobacco Plants

Premature senescence is observed in pot-bound tobacco plants(Nicotiana tabacum L. cv. xanthii) and this is shown to be accompaniedby gross accumulation of leaf starch and a marked decline inphotosynthesis, ribulose- 1, 5-bisphosphate (RuBP) carboxylaseactivity, and soluble protein content. Starch content, uptakeof CO₂ by leaf discs, and the activity of RuBP carboxylase inwhole leaf extracts were measured daily following transfer ofrestricted plants to larger pots. Starch declined rapidly, whilstphotosynthetic activity was fully restored within a period ofseveral days, and frequently exceeded the maximum rates measuredin non-restricted plants. This overcompensation, which couldbe related to availability of carbohydrates accumulated as starch,is discussed in relation to the well-established horticulturalpractice of ‘potting on’.     

Leaf Phosphate Status, Photosynthesis and Carbon Partitioning in Sugar Beet: II. Diurnal Changes in Sugar Phosphates, Adenylates, and Nicotinamide Nucleotides

Sugar Beets (Beta vulgaris L. cv F58-554H1) were cultured hydroponically in growth chambers. Leaf orthophosphate (Pi) levels were varied nutritionally. The effect of decreased leaf phosphate (low-P) status was determined on the diurnal changes in the pool sizes of leaf ribulose 1,5-bisphosphate (RuBP), 3-phosphoglycerate (PGA), triose phosphate, fructose 1,6-bisphosphate, fructose-6-phosphate, glucose-6-phosphate, adenylates, nicotinamide nucleotides, and Pi. Except for triose phosphate, low-P treatment caused a marked reduction in the levels of leaf sugar phosphates (on a leaf area basis) throughout the diurnal cycle. Low-P treatment decreased the average leaf RuBP levels by 60 to 69% of control values during the light period. Low-P increased NADPH levels and NADPH/NADP⁺ ratio but decreased ATP; the ATP/ADP ratio was unaffected. Low P treatment caused a marked reduction in RuBP regeneration (RuBP levels were half the RuBP carboxylase binding site concentration) but did not depress PGA reduction to triose phosphate. These results indicate that photosynthesis in low-P leaves was limited by RuBP regeneration and that RuBP formation in low-P leaves was not limited by the supply of ATP and NADPH. We suggest that RuBP regeneration was limited by the supply of fixed carbon, an increased proportion of which was diverted to starch synthesis.     

Activity and quantity of ribulose bisphosphate carboxylase-and phosphoenolpyruvate carboxylase-protein in two Crassulacean acid metabolism plants in relation to leaf age,nitrogen nutrition,and point in time during a day/night cycle

Activity of ribulose 1,5-bisphosphate (RuBP) carboxylase in leaf extracts of the constitutive Crassulacean acid metabolism (CAM) plant Kalanchoe pinnata (Lam.) Pers. decreased with increasing leaf age, whereas the activity of phosphoenolpyruvate (PEP) carboxylase increased. Changes in enzyme activities were associated with changes in the amount of enzyme proteins as determined by immunochemical analysis, sucrose density gradient centrifugation, and SDS gel electrophoresis of leaf extracts. Young developing leaves of plants which received high amounts of NO ₃ ^- during growth contained about 30% of the total soluble protein in the form of RuBP carboxylase; this value declined to about 17% in mature leaves. The level of PEP carboxylase in young leaves of plants at high NO ₃ ^- was an estimated 1% of the total soluble protein and increased to approximately 10% in mature leaves, which showed maximum capacity for dark CO₂ fixation. The growth of plants at low levels of NO ₃ ^- decreased the content of soluble protein per unit leaf area as well as the extractable activity and the percentage contribution of both RUBP carboxylase and PEP carboxylase to total soluble leaf protein. There was no definite change in the ratio of RuBP carboxylase to PEP carboxylase activity with a varying supply of NO ₃ ^- during growth. It has been suggested (e.g., Planta 144, 143–151, 1978) that a rhythmic pattern of synthesis and degradation of PEP carboxylase protein is involved in the regulation of -carboxylation during a day/night cycle in CAM. No such changes in the quantity of PEP carboxylase protein were observed in the leaves of Kalanchoe pinnata (Lam.) Pers. or in the leaves of the inducible CAM plant Mesembryanthemum crystallinum L.Abbreviations CAM Crassulacean acid metabolism - RuBP ribulose 1,5-bisphosphate - PEP phosphoenolpyruvate - G-6-P glucose-6-phosphate     

Response of Rice Leaves to Low Temperature I. Changes in Basic Biochemical Parameters

When the seedlings of two rice cultivars, IR8 (low-temperaturesensitive) and Somewake (low-temperature tolerant), were exposedto a low temperature of 15?C, the normal increase in the chlorophyllcontent of the developing 4th leaf blade completely ceased whileincreases in protein content continued at a low rate in bothcultivars. Analysis of soluble and insoluble proteins in the4th leaf blade of IR8 by SDS-polyacrylamide gel electrophoresisrevealed that synthesis of RuBP carboxylase and of several thylakoidproteins responsible for photosynthetic electron transport andphotophosphorylation was greatly inhibited at the low temperature.It was also found that increases in the activities of some enzymesof the Calvin cycle, such as RuBP carboxylase, fructose bisphosphataseand NADP-glyceraldehyde-3-P dehydrogenase, as well as of catalase,were specifically inhibited during growth at the low temperature.These results suggest that the synthesis of intracellular components,in particular of key proteins required for photosynthesis, isspecifically susceptible to low-temperature stress during developmentof rice leaves. (Received June 21, 1989; Accepted January 11, 1990)     

Weather,nitrogen-supply and growth rate of field vegetables

A new procedure was developed for interpreting data from multi-harvest N-fertilizer experiments on 5 different vegetable crops. Per cent N in the plant dry matter of each N-deficient crop was, throughout growth, almost proportional to relative growth rate (standardized to the average weather). After correcting for the effects of plant mass, growth rate of each N-sufficient crop varied considerably during the growth period and approximately in proportion to the growth rate when N-fertilizer was withheld. Some of the variation was associated with small changes in soil water which also greatly influenced C-partition between foliage and storage roots of at least one crop. Some of the variation was related to temperature and radiation. The significance of these findings to modeling the effects of N-nutrition and environment on growth is discussed.