Article

Evidence for Lack of Turnover of Ribulose 1,5-Diphosphate Carboxylase in Barley Leaves

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Abstract

Turnover of ribulose 1,5-diphosphate carboxylase in barley leaves (Hordeum vulgare L.) was followed over time in light and dark. The enzyme was degraded in prolonged darkness and was resynthesized after the plants were returned to light. Labeling with (14)C showed that simultaneous synthesis and degradation (turnover) did not occur in light. In contrast, the remaining soluble protein was turned over rapidly in light. Although ribulose 1,5-diP carboxylase can be both degraded and synthesized, these processes seem not to occur simultaneously, but can be induced independently by changing environmental conditions.

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... A number of authors have reported either that the enzymatic activity of RuBPCase per nag of the enzyme (or Fraction I protein) decreased or increased during senescence (Callow 1974;Hall and Brady 1977;Hall et al. 1978;Kawashima and Mitake 1969) or during senescence induced by darkness or leaf detachment (Brady et al., 1971;Peterson and Huffaker 1975;Peterson et al. 1973). There have been other reports of a parallel decline in enzymatic activity and RuBP-Case protein. ...
... This value ~ lO is somewhat lower than expected using the activating ~-O RuBPCase assay of Lorimer et al. (1977), but this ~ s may have resulted from storage of the enzyme at _~ 6 0~~ prior to assay (Henson and Bahr 1977), or ~ 4 the reduced nitrogen status of the plants at anthesis ~-a E 2 (Waters et al. 1980). Although the measured specific = activities were lower than those observed by Wittenbach (1979), they still compare favourably with those observed in flag leaves of wheat (Hall et al. 1978) and in the primary leaves of wheat (Wittenbach 1978) and barley (Peterson et al. 1973). ...
Article
The flag leaf of wheat was examined for changes in quantity and activity of ribulose-bisphosphate carboxylase (RuBPCase; EC 4.1.1.39), in the proteolytic degradation of RuBPCase and other native proteins, and in the ultrastructure of the leaf cells during grain development. Proteolytic degradation of RuBPCase at pH 4.8 increased until 8-10 d after anthesis, then declined, and increased again 16-18 d after anthesis. The second peak coincided with the onset of a preferential loss of immunologically recognizable RuBPCase. The specific activity and number of active sites per molecule of RuBPCase did not change during senescence. Examination of ultrastructure with the electron microscope showed little change in the appearance of the mitochondria as the flag leaf aged. Prominent cristae were still evident 35 d after anthesis. In contrast, the chloroplasts showed a progressive disruption of the thylakoid structure and an increasing number of osmiophilic glubules. The double membrane envelope surrounding the chloroplast appeared intact until at least 20 d after anthesis. The tonoplast also appeared intact up to 20 d. At later stages of senescence of the leaf the outer membrane of the chloroplast adjacent to the tonoplast appeared to break but the inner membrane of the envelope appeared intact until at least 35 d after anthesis.
... techniques with conflicting results. Peterson et al. (20) reported that, in the first leaf of 6-day-old barley seedlings kept in continuous light following '4COrlabeling, the amount of RuBPCase protein and the radiospecific activity of this protein remained constant, indicating that no degradation was occurring. In continuous darkness, there was a loss of RuBPCase protein and a low level of incorporation of "CO2 into the enzyme. ...
... turnover) of the protein. Peterson et al. (20) reported no turnover of RuBPCase in barley leaves in the light and concluded that, although the enzyme can be both degraded and synthesized, the processes are not concomitant, degradation taking place during periods of darkness. Preliminary experiments incidate that there is incorporation of tritiated water into RuBPCase protein (i.e. ...
Article
The rate of protein degradation in Zea mays leaves has been estimated by using tritiated water and [³H]acetic anhydride as the labeling agents. Both methods circumvent many of the problems usually associated with measuring protein degradation in plants. The half-life of ribulose-1,5-bisphosphate carboxylase protein in second leaves of 13-day-old seedlings under continuous light was found to be 7.8 ± 0.9 days by the tritiated water technique and 6.5 ± 0.8 days by the [³H]acetic anhydride method. The half-lives determined under a 14-hour-light, 10-hour-dark photoperiod are 6.2 ± 0.8 days with tritiated water and 5.4 ± 0.4 days with [³H]acetic anhydride. Whereas the values obtained by the two methods do not differ significantly, the use of either method for the determination of protein half-life can be recommended.
... In the absence of apparent root N uptake, we found a relative rate of N depletion (k) for leaf laminae of 0.0035 [°Cd] 21 , which is 3.5 times higher than values reported for the degradation of Rubisco for rice (Oryza sativa) leaf laminae . For barley leaves (Hordeum vulgare), Peterson et al. (1973) measured rates of Rubisco turnover in the range 0.06 to 0.38 d 21 . Considering an average daily temperature of 19.6°C, as observed in both of the experiments reported in this study, the value of k calculated here corresponds to 0.07 d 21 , which is in the lower part of the range reported by Peterson et al. (1973). ...
... For barley leaves (Hordeum vulgare), Peterson et al. (1973) measured rates of Rubisco turnover in the range 0.06 to 0.38 d 21 . Considering an average daily temperature of 19.6°C, as observed in both of the experiments reported in this study, the value of k calculated here corresponds to 0.07 d 21 , which is in the lower part of the range reported by Peterson et al. (1973). In good agreement with our results, Makino et al. (1984) reported a significant effect of N nutrition on Rubisco content for fully expanded rice leaves, but they did not find any differences in the rate constant of Rubisco degradation during leaf aging. ...
Article
Full-text available
Nitrogen is an important resource for plant growth and crop pathogens. The objective of this study is to propose a process-based modelling of N dynamics within a wheat plant after anthesis. To achieve that, a functional-structural approach was used. Experiments were performed to quantify the spatio-temporal nitrogen dynamics within a wheat culm after anthesis. Nitrogen mass per unit surface area of laminae and sheaths decreased with canopy depth, but was homogeneously distributed across lamina and sheath surfaces. In addition, nitrogen dynamics were synchronous for each phytomer and similar except for a scale factor. In the period of no root nitrogen uptake, those dynamics followed first order kinetics. Based on these results, a functional-structural model of nitrogen dynamics within the culm botanical structure has been developed. Model main assumptions are: (i) the lamina nitrogen content is determined by the turnover of the proteins of the photosynthetic apparatus; (ii) the different entities of the culm share a common pool of mobile nitrogen. The model has been validated for a contrasted range of experimental conditions with a unique set of six parameters. The nitrogen - light relationships are an emerging property of processes described at a local scale. This work paves the way for simulating the regulation of nitrogen dynamics in individual-based models of plant population.
... immediately after the labelling period, are not able to tion contrast with those of Peterson et al. (1973) and Huffaker and Miller (1978), who reported that the enzyme incorporate isotope that is likely to be within their leaf cells. On the contrary, the plants chased after the labelling from barley does not degrade while it is being synthesized. ...
... This decay rate of 0n2 d − " corresponds to a half-life of 0n69\k l 3n5 d. Peterson, Kleinkopf and Huffaker (1973) measured turnover rates for rubisco in the range 0n06 to 0n38 d − ". The differential equation for the rate of change of the photosynthetic N pool is ...
Article
A simple model of photosynthesis in a mature C3leaf is described, based on a non-rectangular hyperbola: the model allows the high-light asymptote of that equation (Pmax) to respond dynamically to light and nitrogen. This causes the leaf light response equation to acclimate continuously to the current conditions of light and N nutrition, which can vary greatly within a crop canopy, and through a growing season, with important consequences for gross production. Predictions are presented for the dynamics of acclimation, acclimated and non-acclimated photosynthetic rates are compared, and the dependence of leaf properties on light and N availability is explored. There is good correspondence of predictions with experimental results at the leaf level. The model also provides a mechanism for a down regulation of photosynthesis in response to increased carbon dioxide concentrations, whose magnitude will depend on conditions, particularly of nitrogen nutrition.
... Therefore, leaf photosynthetic acclimation to light occurs together with leaf ageing, which is characterized by the protein degradation constant D r and the constant t d describing the decrease of protein synthesis rate in our model. The D r values of N V and N J fall within the range of in vivo quantifications reported by Peterson et al. (1973) and Li et al. (2017). The low value of t d (Table 1) explains the modest influence of ageing on leaf photosynthetic capacity observed under constant light conditions (Pettersen et al., 2010a). ...
Article
Full-text available
Plants acclimatize their photosynthetic functions in leaves constantly to the fluctuating light, thereby optimizing the use of photosynthetic nitrogen (Nph) at the canopy level. To investigate the complex interplay between external signals during the acclimation processes, a mechanistic model based on the concept of protein turnover (synthesis and degradation) was proposed and parameterized using cucumber grown under nine combinations of nitrogen and light in growth chambers. Integrating this dynamic model into a multi-layer canopy model provided accurate predictions of photosynthetic acclimation of greenhouse cucumber canopies grown under high (HN) and low (LN) nitrogen supply in combination with day-to-day fluctuations in light at two different levels. This allowed us to quantify the degree of optimality in canopy nitrogen use for maximizing canopy carbon assimilation, which was influenced by Nph distribution along canopy depth or Nph partitioning between functional pools. Our analyses suggest that Nph distribution is close to optimum and Nph reallocation is more important under LN. Nph partitioning is only optimal under the light level similar to the average light intensity during acclimation, meaning that day-to-day light fluctuations inevitably result in sub-optimal Nph partitioning. Our study provides insights into photoacclimation and can be applied for crop model improvement.
... A similar high rate of turnover of total cell protein in the dark has also been noted by Jones et al. (32). In differentiating barley seedlings, Peterson et al. (44) reported a slow degradation of the carboxylase in the dark with synthesis occurring in the light. On the other hand, Sitz et al. (45) found that the carboxylase of Chlorella is degraded fairly rapidly in the light in the presence of cycloheximide, with a half-life of approximately 4.4 h. ...
Article
The chloroplast enzyme ribulose-1,5-bisphosphate (Ru-1,5-P2) carboxylase (EC 4.1 1.39) is made up ot two nonidentical subunits, one synthesized in the chloroplast and the other outside. Both of these subunits of the assembled enzyme are synthesized in a stepwise manner during the synchronous cell cycle of the green alga Chlamydomonas reinhardtii. The activity of this enzyme increases in the light and this increase is due to de novo protein synthesis as shown by the measurement of the amount of protein and by the pulse incorporation of radioactive arginine in the 18S enzyme peak in linear sucrose density gradients. During the dark phase of the cell cycle, there is little change in the enzymatic activity as well as in the amount of this enzyme. Pulse-labeling studies using radioactive arginine indicated that there is a slow but detectable rate of synthesis of the carboxylase and of its subunits in the dark. Ru-1,5-P2 carboxylase, prelabeled with radioactive arginine throughout the entire light period, shows a similarly slow rate of degradation in the following dark period. This slow turnover of the enzyme in the dark accounts for the steady levels of carboxylase protein and of enzymatic activity during this period. A wide variety of inhibitors of protein synthesis by 70S and 80S ribosomes abolished the incorporation of [3H]arginine into total Ru-1,5-P2 carboxylase during short-term incubation. These results suggest a tight-coordinated control of the biosynthesis of the small and large subunits of the enzyme. This stringent control is further substantiated by the finding that both subunits are synthesized in sychrony with each other, that the ratio of radioactivity of the small to the large subunit remains constant throughout the entire light-dark cycle, and that the rates of synthesis and of degradation of both subunits are similar to that of the assembled enzyme.
... Besford et al. (1990) have shown for tomato leaves that Rubisco activity and protein content peak and then decline earlier during leaf expansion in high CO 2 than in ambient CO 2 . Although transcriptional regulation of Rubisco small and large subunits has been shown to be affected by [CO 2 ] in some instances (Winder et al., 1992), the level of regulation by translation and posttranslational turnover is complicated by the fact that photosynthetically competent Rubisco has a relatively slow turnover rate (Peterson et al., 1973). ...
Article
The accumulation of soluble carbohydrates resulting from growth under elevated CO2 may potentially signal the repression of gene activity for the small subunit of ribulose-1,5-bisphosphate carboxylase/oxygenase (rbcS). To test this hypothesis we grew rice (Oryza sativa L.) under ambient (350 μL L⁻¹) and high (700 μL L⁻¹) CO2in outdoor, sunlit, environment-controlled chambers and performed a cross-switching of growth CO2 concentration at the late-vegetative phase. Within 24 h, plants switched to high CO2 showed a 15% and 23% decrease in rbcSmRNA, whereas plants switched to ambient CO2 increased 27% and 11% in expanding and mature leaves, respectively. Ribulose-1,5-bisphosphate carboxylase/oxygenase total activity and protein content 8 d after the switch increased up to 27% and 20%, respectively, in plants switched to ambient CO2, but changed very little in plants switched to high CO2. Plants maintained at high CO2 showed greater carbohydrate pool sizes and lower rbcS transcript levels than plants kept at ambient CO2. However, after switching growth CO2 concentration, there was not a simple correlation between carbohydrate and rbcS transcript levels. We conclude that although carbohydrates may be important in the regulation of rbcS expression, changes in total pool size alone could not predict the rapid changes in expression that we observed.
... Although cereal leaves retain the ability to synthesize Rubisco after expansion, synthesis and turnover remain very low (Peterson et al., 1973). After full expansion, there is a coordinated decline in synthesis of both subunits up to senescence (Gutteridge and Keys, 1985). ...
Article
Repression of photosynthetic genes by increased soluble carbo- hydrate concentrations may explain acclimation of photosynthesis to elevated CO, concentration. This hypothesis was examined in a field crop of spring wheat (Triticum aestivum L.) grown at both ambient (approximately 360 pmol mol-') and elevated (550 pmol mol-') atmospheric CO, concentrations using free-air CO, enrich- ment at Maricopa, Arizona. The correspondence of steady-state levels of mRNA transcripts (coding for the 83-kD photosystem I apoprotein, sedoheptulose-1,7-bisphosphatase, phosphoribuloki- nase, phosphoglycerokinase, and the large and small subunits of ribulose-l,5-bisphosphate carboxylase/oxygenase) with leaf carbo- hydrate concentrations (glucose-6-phosphate, glucose, fructose, su- crose, fructans, and starch) was examined at different stages of crop and leaf development and through the diurna1 cycle. Overall only a weak correspondence between increased soluble carbohydrate con- centrations and decreased levels for nuclear gene transcripts was found. The difference in soluble carbohydrate concentration be- tween leaves grown at elevated and current ambient CO, concen- trations diminished with crop development, whereas the difference in transcript levels increased. In the flag leaf, soluble carbohydrate concentrations declined markedly with the onset of grain filling; yet transcript levels also declined. The results suggest that, whereas the hypothesis may hold well in model laboratory systems, many other factors modified its significance in this field wheat crop.
... Therefore, vacuolar compartmentation does appear to be retained during senescence (Lin and Wittenbach, 1981). Earlier, Peterson et al. (1973) demonstrated that the turnover of RuBPCase in nonsenescing barley leaves occurred very slowly. Therefore, vacuolar localization of these proteases in nonsenescing tissue may represent a compartmentation prior to the onset of senescence and the breakdown of RuBPCase. ...
Chapter
Abstract The study of leaf senescence is one of the major fields of plant physiology and has become a popular topic these days. It has one great advantage over the process in whole plants—namely, it is under direct control. With the whole plant, one has to wait until the end of the life cycle, which is practically impossible for perennials; but with leaves, we can rapidly induce senescence in a number of ways, and there is as yet no reason to think that such induced senescence differs in any way from the natural process. However, leaves suffer from different issues and obstacles, being bearers of photosynthetic apparatuses, and yet this is acceptable because it shows the promise of leading to a general concept of the nature of the senescence process in organs and tissues. Many studies have been carried out about the phenomenon of leaf senescence, which revealed that leaf development reaches its peak in terms of its physiological function, and then it declines and ultimately dies off. This process involves a considerable number of changes, but in an orderly manner. It is never a chaotic breakdown. It is a gradual process that involves a series of morphological, physiochemical, and biochemical changes, including accumulation of a number of metabolic disorders that occurs throughout the life of a plant. But all these changes accompanying leaf senescence are different facets of its development and serve a wide variety of adaptive functions. Decline in chlorophyll and protein content is key to this process. Alterations in proteolytic activity are also associated with leaf senescence, with most studies confirming an increase in its activity. Not much is known about the factors that trigger increase in proteolytic activity with the onset of leaf senescence. But senescence and proteolysis are now regarded as two processes with one destiny. As we review proteolytic processes during leaf senescence in this chapter, we will go through the general changes in the metabolic activities during leaf senescence and the importance of senescence in nutrient allocation and reallocation. We also intend to survey the degenerative and structural changes that occur in leaves during senescence. Then we will turn to leaf hydrolytic enzymes that degrade proteins, their estimation, their location, specificity, and gene expression and discuss their possible significance. Keywords ProteolysisProtein degradationProgrammed cell death (PCD)Nutrient recyclingPigment changes
... Determination of protein as nitrogen in digests (Derman et al., 1978) or through dye binding to washed protein on paper disks ( Van den Broek et al, 1973) can avoid many problems. Given the centrality of chlorophyll in photosynthesis and the fact that ribulose bisphosphate carboxylase is the major leaf protein (Lyttleton and Ts'o, 1958;Peterson et al, 1973;Telek and Graham, 1983), chlorophyll and total soluble protein are not fundamentally different measures. Both reflect changes in chloroplasts that may or may not be central to senescence (Chapter 15). ...
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Chloroplasts isolated from leaves of 14 d old Pisum sativum plants show endo- and exopeptidase activity. The substrates 131J-casein, L-alanine- and L-leucine-4-(phenylazo)-phenylamide were degraded. The optimum pH of proteinase activity was 5. Idoacetamide inhibited the enzyme activity partially, whereas diisopropylfluorophosphate had no effect. Treatment with Triton X-100 increased the proteinase activity of the chloroplasts. Isolated membranes showed proteinase activity at the same level as the whole chloroplasts but no aminopeptidase activity. The proteolytic activity of the membranes increased with the age of the plants. Chloroplasts from the oldest leaves of 4 week old plants showed considerably higher activities of proteinase and aminopeptidase than chloroplasts from leaves of 14d old plants. The origin of proteolytic enzymes and their role within the chloroplasts are discussed
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Evidence is presented that the organelles of Lemna minor do not degrade as functional units. The proteins of Lemna show wide differences in their rates of degradation and ribulose bisphosphate carboxylase (EC 4.1.1.39) has a particularly slow rate of degradation. Contrary to some earlier evidence, we found no correlation between the rate of soluble-protein degradation and either charge or size of proteins. We could find no correlation between protein degradation and subunit size in any of the organelles of Lemna.
Article
It has been confirmed that shading leaves from day 5 onwards lowers the rate of CO2 fixation when they are placed in saturating irradiances. The reduction due to shade treatment is about 46 per cent and a similar reduction in maximum chlorophyll content of the leaf follows shading. Maximum amounts of total soluble protein and of Fraction I protein are less in shaded leaves than in control leaves and prolonged treatment leads to a decline in leaf protein content. The relative amounts of different protein are also affected by treatment; in control leaves Fraction I protein accounts for about 45 per cent of the total but in shaded leaves the value is about 30 per cent. Increases and decreases in leaf protein amount, with concomitant changes in the ratio of Fraction I to total protein can be brought about by removing shades and re-applying them. Such changes can be induced even in fully expanded leaves in which net protein synthesis is not usually found. Maximal amounts of leaf protein are found in irradiances of 60 W m⁻² or more, with lower values at lower light intensities. Where the first leaf is held in a stream of CO2-free air a lower level of protein is found. This, and the ratio of Fraction I to total protein, are similar to values for shaded leaves, and suggest the involvement of photosynthetic carbon fixation in determining leaf protein amount. A 1:1 linear correlation between amount of Fraction I protein and RuDP carboxylase activity is shown but the rate of CO2 incorporation by leaf extracts is 2–3 times greater than that of the intact leaf. The significance of this and the effect of irradiance on leaf protein amount are discussed.
Article
Yamashita, T. 1987. Modulated degradation of ribulose ftisphosphate carboxylase in leaves on top-pruned shoots of the mulberry tree (Morus alba L.).—J. exp. Bot. 38: 1957–1964. The effects of pruning shoot tops on the synthesis and degradation of ribulose 1,5–Wsphosphate carboxylase (RuBPCase) in leaves on remaining shoots were investigated in mulberry trees. Leucine labelled with 14C was fed to leaf discs from field-grown mulberry trees and 14C incorporation into RuBPCase was examined. Proportion of 14C in RuBPCase to leucine–14C absorbed by leaf discs was remarkably lowered by top-pruning, though occasionally a slight increase was observed soon after pruning. Yet RuBPCase content in leaves on top-pruned shoots became progressively higher than that in leaves on intact shoots. Changes in 14C in Ru1BPCase in leaves of mulberry saplings previously fed 14CO2 were followed. Following 14CO2 feeding, the attainment of the maximal level of 14C in RuBPCase was retarded by top-pruning. The highest level of 14C in RuBPCase was maintained in leaves on top-pruned shoots but decreased in leaves on intact shoots. Specific radioactivity in RuBPCase continued to increase in leaves on top-pruned shoots even after attaining a maximum level in the control leaves. These facts suggest that the increase in RuBPCase by top-pruning results from a cessation of its degradation for the remobilization of nitrogen for newly developing leaves on shoot tops.
Article
Phytochrome controls the appearance of many enzymes in the mustard (Sinapis alba L.) cotyledons. The problem has been whether the effect of phytochrome on the appearance of enzymes in this organ is due to a common initial action of Pfr, e.g. due to the liberation of a “second messenger”. We have compared the modulation by light (phytochrome) of the appearance of phenylalanine ammonia lyase (PAL)+ and ribulosebisphosphate carboxylase (Carboxylase)+. PAL becomes detectable in the mustard cotyledons at 27 h after sowing while Carboxylase starts to appear only at 42 h after sowing (starting points, 25° C). The starting points cannot be shifted by light. As a major result, in the case of PAL the inductive effect of continuous red light (given from the time of sowing) remains fully reversible by 756 nm-light up to the starting point (27 h after sowing) while with Carboxylase full reversibility in continuous red light is lost at approximately 15 h after sowing. While the induction of Carboxylase is already saturated at a very low level of Pfr (e.g. continuous 756 nm-light saturates the response) and does not depend on irradiance (e.g. continuous 675 mW m-2 red light and 67.5 mW m-2 red light lead to the same time course), PAL induction is a graded response over a wide range of Pfr doses and depends strongly on the fluence rate (high irradiance response, HIR). It is concluded that PAL induction and Carboxylase induction are not only separated in time but differ in every regard except that both responses are mediated by phytochrome. The present data support the previous conclusion that the specification of the temporal and spatial pattern of development is independent of phytochrome even though the realization of the pattern of development can only occur in the presence of phytochrome (Pfr). It seems that there is no feedback from pattern realization to pattern specification.
Article
Protein turnover was examined, using tritiated water, in various 2-cm regions of 7-11-d-old, first leaves of barley (Hordeum vulgare). Differences were found between the regions in their protein turnover and their responses to stress. The rate constant for degradation for total protein was the same throughout the leaf and the average half-life (t1/2) of protein=approx. 220 h. Only in the older regions did a 24-h pulse of(3)H2O preferentially label protein with a t1/2 (90 h) considerably shorter than the t1/2 for total protein. 'Soluble' protein was degraded faster than 'insoluble' protein and contained an appreciable short-lived protein component observable by short-pulse labelling. The rate of protein synthesis was greatest in the cells of the youngest region and declined as each region aged. The mean rate of protein synthesis over the 4-d period was 4 and 7 nmol h(-1) of amino-N with respect to the regions 1-3 and 7-9 cm from the leaf tip. Seedlings, stressed by adding polyethylene glycol (2.0 MPa) to the roots, showed a marked loss of protein from the older leaf regions with only small losses in the younger regions. Amino acids accumulated in the younger region continuously whereas in the older region little accumulation occurred until day 3 of stress when proline levels increased. Protein synthesis was decreased by between 30% and 50% in all leaf regions. In the region 1-3 cm from the leaf tip, the rate of protein degradation of total protein was enhanced and equalled the rate of degradation of 24-h-pulse-labelled protein which was not itself significantly affected by stress (t1/2=approx. 90 h). In the region 3-5 cm, the degradation of both 4-d and 24-h-labelled protein was enhanced by stress to rates similar to those found in the region 1-3 cm. This was largely through increases in the degradation of the 'insoluble' protein, but the degradation of 'soluble' protein was also raised. Protein degradation in the region 7-9 cm was not affected by stress.
Article
Towards the end of the 19th century, plant physiologists considered the possibility that proteins undergo continuous breakdown and resynthesis. Despite the objections of Pfeffer, the idea of protein turnover was revived in the 1920’s and a great deal of work on the nitrogen balance of detached leaves was interpreted in terms of the temporal separation of degradation and synthesis. Mothes (1933) however, proposed that in leaves there was simultaneous synthesis and degradation of protein involving separate systems for synthesis and degradation. Paech (1935), on the other hand, argued that control of the nitrogen balance was exercized through mass action. Gregory and Sen (1931) noted that in leaves of potassium-starved barley there was an accumulation of amino acids, which, according to the mass action proposals of Paech, should have led to enhanced protein synthesis. However, the reverse happened and the continued accumulation of amino nitrogen suggested to them that the routes of protein synthesis and degradation were separable and that the rates of these processes might vary independently. They proposed a “PROTEIN CYCLE” according to which proteins undergo a cycle of synthesis and degradation (i.e., protein turnover), but also included the proposition that protein degradation is linked to the production of CO2. The extent to which protein turnover contributes to respiration is discussed in Section 3, but it is not central to the concept of turnover itself. The first direct evidence for protein turnover in plants was provided independently by Hevesey et al. (1940) and Vickery et al. (1940), who reported the assimilation of [15N]H3 into leaf protein, despite a net loss of protein from leaves.
Chapter
Ribulose-1, 5-bisphosphate carboxylase (RuBPCase) is the protein responsible for fixation of CO2 in photosynthetic organisms. In many higher plants RuBPCase also appears to serve as a storage protein that is hydrolyzed during leaf senescence (Huffaker et al., 1978). This provides a source of reduced N that can be transported to newly developing leaves or fruits (Dalling et al., 1976). RuBPCase is a large protein (MW ∿ 550 kD) consisting of 8 large subunits (50–57 kD) and 8 small subunits (13–15 kD). The large subunit is coded on chloroplast DNA and is synthesized within the chloroplast (Blair et al., 1973; Chan et al., 1972; Criddle et al., 1970; Kung, 1976). The small subunit is coded on nuclear DNA (Kung, 1976), synthesized as a precursor protein in the cytoplasm (Criddle et al., 1970; Highfield et al., 1978), and then processed at or in the chloroplast. The native protein is assembled in the chloroplast and the active enzyme is localized in the stroma. The synthesis of RuBPCase occurs predominantly during the greening of etiolated leaf tissue (Kleinkopf et al., 1970; Smith et al., 1974) or leaf expansion (Friedrich and Huffaker, 1980). The cellular concentration of RuBPCase (which can constitute 50–70% of the total soluble leaf protein) then remains nearly constant for several days; little or no apparent turnover takes place (Huffaker, 1979; Peterson et al., 1973). During senescence, protein is rapidly degraded, and RuBPCase is the predominant protein lost during the initial stages (Friedrich and Huffaker, 1980; Peterson and Huffaker, 1975). A1- though there is much data concerned with the synthesis of RuBPCase, information about the control of its degradation and turnover is lacking. Exo—and endoproteinases in green and senescing leaf tissue have been described (Dalling et al., 1976; Huffaker and Miller, 1978; Martin and Thimann, 1972; Peterson and Huffaker, 1975; Sopanen and Lauriere, 1976; Thomas, 1978; Wittenbach, 1978) but very little is known about their role in senescence or in normal cellular protein turnover.
Chapter
Although the physiological significance of metabolic regulation has long been recognized, only recently has its complexity become evident through detailed examination of various metabolic pathways and their interrelationships. The diversity and complexity of cells of living organisms require metabolic regulation at several physical and chemical levels all of which may be relevant to a study of perturbed metabolism within host-parasite interactions (Larner, 1971). The most fundamental requirement of metabolic regulation is the insured maintenance of a steady state between the energy-generating catabolic processes and the myriad of energy-requiring synthetic reactions proceeding concurrently in the cell. It can be said that the result of any unrelieved disruption of the metabolic steady state, regardless of the cause, results in the “diseased state.” Indeed, the magnitude of the diseased state simply reflects the level and intensity of the perturbation in metabolic regulation and metabolism in general. The study of intermediary metabolism and its control therefore assumes central importance for understanding either normal or disease physiology.
Article
CO2-gas exchange behaviour and direct chlorophyll fluorescence kinetics were investigated to obtain a better insight into the stress-induced changes that occur in soybean (Glycine max L. Merr.) during cold stress. CO2 assimilation during photosynthesis was measured by infrared gas analysis, while the function of photosystem II (PSII) was assessed by fast-phase chlorophyll fluorescence at different periods of exposure to low night temperature (8°C). The rate of CO2 assimilation decreased by 87% after a single night of cold stress in the cultivar Fiskeby V. Analysis of A:C(i)* response curves and the polyphasic fast chlorophyll fluorescence rise, using the JIP test, showed that the observed inhibition of photosynthesis was due to mesophyll limitation. Cold stress markedly decreased the carboxylation efficiency of Fiskeby V and also resulted in severe impairment of PSII function, mainly through reaction centre deactivation and reduced electron transport capacity. We predict that CO2-gas exchange analysis and the JIP test will prove invaluable in future studies of the basis of cold injury and tolerance in soybean.
Article
Rice seedlings were pulse-labelled with15N by feeding15N-labelled KNO2 through culture solution and15N translocation in the plant was chased.N incorporated into older leaves was retranslocated to the youngest leaf. Nitrogen of newly developing leaves consisted of the newly absorbed and retranslocated nitrogen.Retranslocation of nitrogen seemed to occur from the older leaves than the second leaf below developing leaf although those older leaves had no significant change in total nitrogen content.hole protein in developed leaves had the half-life of 4-6 days, and the protein seemed to be consisted of proteins of different turnover rates.
Chapter
A satisfying numerical description of the growth of barley plants has not yet been given. Each part of the plant is initiated, undergoes a surge of growth, ceases growing, senesces and dies. Its demands upon, and contribution to the whole plant vary continuously with age, weather, soil conditions, and the alternation of day and night. Probably no two plants are ever truly identical. Over limited periods growth has been described by various formulae, but at best these seem to have descriptive value. Difficulties arise from (i) the plasticity of the plant, i.e. the dramatically altered forms achieved under different growing conditions (Table 6.1), and (ii) the difficulties of making adequate quantitative studies, especially on roots in the soil. To circumvent this last, and to provide uniform growing conditions, water culture is often used for experimental purposes. An acre (0.405ha) of Plumage—Archer barley contained 14.7 miles (23.7 km) of coulter row, with 6.75 in (17.2cm) between rows and contained 1.5–2 x 106 plants (Table 6.2) [102]. Of the seeds sown about 87% grew. While the average value was 22.6 grains/ft (30.5cm) coulter row, the range was from 3 to 35 plants/ft (30.5cm) row. The more widely spaced plants tillered more, but did not fully compensate for the effects of excessive spacing (however see Chapter 7). As the plant density increased, so the number of ears/plant declined.
Chapter
Dark starvation of intact plants and detached leaves is a well-known means of inducing senescence (1,11), which is characterized by loss of total protein and with some exceptions by the degradation of chlorophyll. The initial loss of soluble protein was shown to be due to the loss of RuBPCase (8,15) whereby a high selectivity of protease towards RuBPCase has been found (2,3). However, little is known about changes in RuBPCase synthesis during induced senescence (10), in contrast to the fact that its regulation during early phase of greening has been well investigated (5,7,12).
Article
Determining the degradation characteristics of proteins is difficult due to the lack of appropriate methodologies, particularly in the case of leaf proteins. Previous studies suggest that ribulose bisphosphate carboxylase (RuBP carboxylase; EC 4.1.1.39) proteolysis may be fundamentally different in C3 and C4 plants. To test this hypothesis, the relative degradation rates of the total soluble protein, RuBP carboxylase and glycolate oxidase (EC 1.1.3.1) in the second leaves of intact C3 (Triticum aestivum L.) and C4 (Zea mays L. and Sorghum bicolor L.) plants was measured. The methodology utilized involved an efficient procedure to label the leaf proteins, the use of a double-labelling method to measure protein degradation and a singlestep purification of the labelled proteins under study. RuBP carboxylase is subjected to continuous degradation in all plants investigated. Its rate of degradation is higher for Z. mays, intermediate for T. aestivum and lower for S. bicolor. When the rate of RuBP carboxylase degradation was compared with that of the total soluble protein a differential pattern was obtained for the plant species examined: whereas maize presents a faster rate of RuBP carboxylase degradation than of the total soluble protein, wheat and sorghum show similar rates. However, the rate of RuBP carboxylase proteolysis in the three plant species studied is much lower than the rate of glycolate oxidase degradation. The results obtained indicate that, under the conditions of study, the degradation characteristics of plant RuBP carboxylase, as those of glycolate oxidase, are species specific, in a way suggesting that they do not depend on the type of photosynthetic metabolism of the species considered (C3 or C4).
Article
Workers are beginning to study the in vivo enzymatic activity of several leaf proteins. The relationship between in vivo activity and enzyme concentration suggests that in vivo regulation may often be more important than the concentra­ tion of the protein catalyst. In addition to allosteric effectors, the sources of energy that drive certain enzymatic reactions are important regulators. The activity of some cytoplasmic enzymes may be driven by glycolysis and by systems that shuttle ATP and reducing power from the chloroplast or mitochondria to the cytoplasm. For example, several biochemical pathways are integrated in the regulation of nitrate reductase (NR) activity. Since photosynthetic CO2 fixation supports both the synthesis and activity of nitrate reductase, the turnover of RuBPCase can strongly affect nitrate reductase (NR). The leaf storage proteins are extremely important in the maturation, repro­ duction, and final seed yields of plants. Nitrogen is a main factor that limits photosynthetic capacity and seed yield as the plant matures. Final seed yields often depend on the proteolysis of stored leaf N and its translocation to the seed (DALLING et al. 1975, HAGEMAN and LAMBERT 1981). Proteolysis of storage protein can be induced by environmental factors such as limitations in N supply, water, light, and temperature.
Article
The possible role of phytohormones in light-dependent plastogenesis is reviewed particularly in respect to the influence of cytokinins in this plant-specific differentiation process. The following aspects of cytokinin action in chloroplast formation are considered in detail: Ultrastructure and replication of chloroplasts, chlorophyll accumulation, plastid enzyme synthesis and activity, nucleic acid and protein biosynthesis. Some remarks are made about the importance of the physiological state of the responding tissue. Possible modes of action on the cellular and molecular levels are discussed in relation to plastogenesis.
Chapter
There are two terms “ageing” and “senescence” which are widely used in reference to changes which impair the structure or functioning of living organisms. Medawar (1) defined ageing as referring to all those changes which occur in time, without reference to death as a consequence, indeed its use need not be confined to living organisms. This is a convenient definition in that it allows of a clear distinction of senescence as describing those changes which lead sooner or later to the death of an organism or some part of it. As Medewar puts it “It is a curious thing that there is no word in the English language that stands for the mere increase in years; that is for ageing silenced of its overtones of increasing deterioration and decay. At present we are obliged to say that Dorian Gray did not exactly ‘age’ though to admit that he certainly grew older. We obviously need a word for mere ageing, and I propose to use ‘ageing’ itself for just that purpose. ‘Ageing’ hereafter stands for mere ageing, and has no other innuendo. I shall use the word ‘senescence’ to mean ageing accompanied by that decline of bodily faculties and sensibilities and energies which ageing colloquially entails. Dorian Gray aged, but only his portrait disclosed the changes of senescence. I hope that makes it clear.”
Chapter
Patterns of gas exchange and protein synthesis were measured in developing leaves of clonal Populus x euramericana plants. Net photosynthesis and apparent photorespiration (Warburg effect) were zero in very young leaves, but then increased to maximum levels in recently mature leaves. Both processes declined in old leaves, but the decline in photosynthesis was more rapid. Mitochrondrial (dark) respiration decreased with leaf age and was less in the light than in the dark, except in very old leaves, where it increased sharply in the light. Diffusion resistance and CO2 compensation concentration declined to minimum levels in recently mature leaves; however, resistances increased markedly in older leaves, whereas CO2 compensation remained at a minimum. Soluble protein concentrations and incorporation of 14C-photosynthate into protein declined throughout leaf development. Protein turnover was slight in expanding leaves, but was substantial after leaves matured. Expanding leaves synthesized predominantly Fraction I protein, but formation of this protein was slight once leaves matured. The significance of these findings in relation to the developmental pattern of net photosynthesis in poplar leaves is discussed.
Chapter
This chapter discusses the recent findings of chloroplast degradation and provides an overview of organelle senescence. Senescence is the last phase of development of a whole organism, organ, cell, or organelle. It is a degenerative process that leads to the death of a living system. Different tissues and cells of the leaves have their own pattern and timing of senescence. The initiation of senescence in mesophyll cells may not necessarily be synchronized with the process in vascular or epidermal tissues. Even different organelles of a single leaf cell––namely, chloroplasts, mitochondria, endoplasmic reticulum, ribosomes, and the nucleus do not show synchrony in the induction and progress of senescence. The chapter discusses a general pattern of temporal changes in the fine structure of different cellular organelles, including chloroplasts. Chloroplasts are the first organelles to show symptoms of disorganization when all other organelles are normal, followed by a change in the structure of the endoplasmic reticulum and loss of ribosomes. The loss of intrinsic electron transport components should follow the senescence-induced damage to the water-splitting system.
Chapter
This chapter reviews characteristic features of nitrogen metabolism, especially protein metabolism in the processes of leaf senescence. The nitrogen content of a leaf reaches the maximum level at around the completion of leaf expansion. In the course of leaf senescence, nitrogen (protein) content in the leaf gradually decreases with a concomitant loss of the photosynthetic activity. The decline in protein synthesis in senescing leaves can be attributed to multiple factors such as slowing down of the transcription rate, limited template availability (loss of chloroplast DNA), changes of transcript stability, decreased capacity for translation, and availability of substrates and energies. Effects of these factors on protein synthesis may differ among individual proteins, stages of leaf senescence, and plant species. The extent of the contribution of each step to regulating the protein level changes in the course of senescence and differ among protein species and plant species. Such a multiplicity of mechanisms regulating protein synthesis and degradation make the leaf able to senesce in a highly ordered and adapted manner.
Article
The activity of a range of endo- and exopeptidase enzymes have been measured in the glumes, flag leaf and stem during the period of grain development in wheat. The enzymes show a sequential pattern of appearance with activity peaks occurring at a number of intervals from anthesis until just prior to the cessation of grain growth. Of the enzymes studied only the haemoglobin- and casein-degrading activity and alanylglycine-dipeptidase activity increased during the period of rapid protein loss, while aminopeptidase, carboxypeptidase and leucyltyrosine dipeptidase reached maximum activity prior to this period.
Article
1.1. Enzymatic studies with Fraction-I protein prepared by differential ultracentrifugation suggested that Fraction-I protein may contain the three-enzyme sequence: phosphoriboisomerase (d-ribose-5-phosphate ketol-isomerase, EC 5.3.1.6), phosphoribulokinase (ATP: d-ribulose-5-phosphate 1-phospho-transferase, EC 2.7.1.19) and carboxydismutase (ribulose-1,5-diphosphate carboxylase).2.2. A protein fraction containing the “ribose-5-phosphate sequence” and Fraction-I protein was obtained from tobacco leaves by using gel filtration and diethylamino-ethyl-cellulose chromatography. The advantages of this method over that of differential centrifugation are indicated.3.3. A rabbit antibody specific to tobacco Fraction-I protein was developed.4.4. The quantitative precipitin relation between Fraction-I protein and the specific antibody was established.5.5. Fraction-I protein from the cellulose-chromatographic peak which contained the “ribose-5-phosphate sequence” enzymes was isolated by using the quantitative precipitin relationship.6.6. Fraction-I protein precipitated by the specific antibody contains carboxydismutase but not phosphoriboisomerase or phosphoribulokinase.
Article
Attached primary and secondary wheat leaves were supplied continuously with C14O2 during daily periods of photosynthesis for 3 days. Samples were analyzed for amounts and total activities of respired carbon, soluble sugars and amino acids, protein amino acids, and protein nitrogen. By labelling all possible protein precursors to the same extent it was possible to eliminate doubts about the specific activity of carbon entering protein. Hence turnover rates could be accurately established. Because tobacco leaves last for a long time, it was possible to label their proteins, wait until soluble compounds were at a low specific activity, and then measure turnover of proteins as radioactivity in them decreased.Protein amino acid turnover rates of 0.4–0.5% per hour were obtained in rapidly growing secondary wheat leaves and 0.2–0.3% per hour in non-growing primary wheat leaves. Turnover rates of 0.15–0.2% per hour were found in expanding tobacco leaves, but little or no turnover was found in fully expanded tobacco leaves.It is suggested that protein turnover is a facet of the biochemical differentiation that accompanies development, enlargement, or change in function of an organ without concomitant net protein synthesis.
Article
MORPHOGENETIC changes induced by red light (660 nm) and mediated by the pigment-protein phytochrome are well documented1,2. Less is known, however, about phytochrome-mediated effects of red light at the cellular level. We show here that red light induces the development of etiolated apices of pea stems and that one consequence of this development is the net synthesis of a plastid-localized protein, namely fraction I protein, and an increase in its associated enzyme activity, ribulose-1,5-bisphosphate (RuDP) carboxylase3. Two other enzymes of the Calvin cycle show similar increases in activity. The magnitude of these increases and their reversibility by irradiation with far-red light (730 nm) implicates phytochrome rather than protochlorophyllide as the primary photoregulator of the synthesis of these enzymes.
Article
Separation of the soluble proteins from leaves of Perilla by means of gel filtration on a Sephadex Groo column yielded two protein bands with molecular weights of approximately 400,000 and 23,000, which appear to correspond to the well-known Fraction I and Fraction II proteins respectively. The amount of Fraction I protein in the leaves decreased progressively from the time that the leaves became fully expanded whilst the amount of Fraction II protein decreased only in the later stages of senescence. Aleasurements of the activity of several enzymes in successive 4 ml fractions from the column showed that each occupied a different peak position within the two main protein fractions. Fach of the enzymes assayed showed a different pattern of change in the course of senescence of the leaves. These changes in protein content and enzyme activity are discussed in relation to earlier observations on the physiological functioning of senescing leaves of Perilla.
1.1.|The rate of release of high molecular weight water-soluble components from isolated chloroplasts has been studied.2.2.|Chloroplasts have been broken by osmosis and successively washed with hypotonic buffer solutions, or ruptured in a needle-valve disintegrator to free lamellae particles of soluble constituents. The resulting solubilized material has been examined by ultracentrifugation, and by polyacrylamide gel electrophoresis in homogeneous buffer system.3.3.|Fraction I protein was more readily liberated from the chloroplasts than the Fraction II components. A component of s20, w = 12 S was observed in some of the extracts, but the bulk of this was only liberated after complete disruption of the lamellae, and it is thought to be situated within the lamellae ‘loculi’ and ‘fret-channels’.4.4.|A procedure for the purification of Fraction I protein using DEAE-cellulose chromatography and gel filtration is described.5.5.|An investigation of the nature of our preparation of Fraction I protein is reported; the protein has a partial specific volume of 0.744 ml/g, and an s°20, w = 18.30 S. A minimum molecular weight of 24427 has been calculated from the amino acid analysis, and the molecular weight of the macromolecule has been determined by ultracentrifugation (on two preparations) as 585 000 and 561 000. The protein was observed to dissociate into subunits of 2.6–4.8 S, in alkali (pH 11.5), acetic acid (70%), urea (8 M) and sodium dodecyl benzene sulphate (detergent-protein, 1:2, w/w).6.6.|The isolated Fraction I protein contains 84% protein; the other material present is thought to be accounted for by carbohydrate and material giving rise to ash. The predominant monosaccharides in the hydrolysates of the protein have been identified as glucose and xylose.7.7.|Fraction I protein has been shown to be identical with the enzyme, ribulose-1,5-diphosphate carboxylase (EC 4.1.1.39). Correspondence between the physical properties of Fraction I protein and those of protochlorophyll-protein complex of etiolated tissues indicates another possible identity.
Article
The enzyme ribulose diphosphate carboxylase (RudPCase) has been shown to be present in high concentrations in chloroplasts (Lyttleton and Tso, 1958) however, the measured turnover of the isolated enzyme is so low that the exact role of this enzyme in CO2 fixation has been questioned (Trown, 1965; Gibbs et al., 1967). In addition the levels of CO2 required for efficient functioning of purified RudPCase are so high relative to the concentration of CO2 in the atmosphere that calculations by various workers have concluded that the enzyme could not support the known CO2 fixation rate in intact tissue. As a result, extensive investigations have been carried out to determine means of preserving or restoring activity to the isolated enzyme. This communication describes the isolation of a small factor both from tomato leaves and from isolated chloroplasts which increases the enzyme activity of ribulose diphosphate carboxylase both in crude extracts and in the isolated enzyme preparations. The factor has a chromophoric group with absorption maxiumum at 325 mμ. Moreover, the activation of RudPCase is light dependent with a maximum in the action spectrum also a 325 mμ.
Article
1. 1. Enzymatic studies with Fraction-I protein prepared by differential ultracentrifugation suggested that Fraction-I protein may contain the three-enzyme sequence: phosphoriboisomerase (d-ribose-5-phosphate ketol-isomerase, EC 5.3.1.6), phosphoribulokinase (ATP: d-ribulose-5-phosphate 1-phospho-transferase, EC 2.7.1.19) and carboxydismutase (ribulose-1,5-diphosphate carboxylase). 2. 2. A protein fraction containing the "ribose-5-phosphate sequence" and Fraction-I protein was obtained from tobacco leaves by using gel filtration and diethylamino-ethyl-cellulose chromatography. The advantages of this method over that of differential centrifugation are indicated. 3. 3. A rabbit antibody specific to tobacco Fraction-I protein was developed. 4. 4. The quantitative precipitin relation between Fraction-I protein and the specific antibody was established. 5. 5. Fraction-I protein from the cellulose-chromatographic peak which contained the "ribose-5-phosphate sequence" enzymes was isolated by using the quantitative precipitin relationship. 6. 6. Fraction-I protein precipitated by the specific antibody contains carboxydismutase but not phosphoriboisomerase or phosphoribulokinase.
Article
Since 1922 when Wu proposed the use of the Folin phenol reagent for the measurement of proteins (l), a number of modified analytical pro- cedures ut.ilizing this reagent have been reported for the determination of proteins in serum (2-G), in antigen-antibody precipitates (7-9), and in insulin (10). Although the reagent would seem to be recommended by its great sen- sitivity and the simplicity of procedure possible with its use, it has not found great favor for general biochemical purposes. In the belief that this reagent, nevertheless, has considerable merit for certain application, but that its peculiarities and limitations need to be understood for its fullest exploitation, it has been studied with regard t.o effects of variations in pH, time of reaction, and concentration of react- ants, permissible levels of reagents commonly used in handling proteins, and interfering subst.ances. Procedures are described for measuring pro- tein in solution or after precipitation wit,h acids or other agents, and for the determination of as little as 0.2 y of protein.
Article
The effects of various light intensities on in vivo increases in activities of phosphoriboisomerase, phosphoribulokinase and ribulose-1, 5-diP carboxylase and on synthesis of chlorophyll were studied in greening leaves of Hordeum vulgare L.Each enzyme was already present in dark-grown plants, but further increases in activities required both a light treatment of the intact plant and a favorable temperature. The amount of enzymatic activity and chlorophyll developed was governed by light intensity.Measured activities of phosphoriboisomerase and ribulose 1,5-diP carboxylase were highly correlated with synthesis of chlorophyll at all intensities studied. Measured activity of phosphoribulokinase was correlated with synthesis of chlorophyll only at saturating or near saturating light intensities. At decreasing light intensities the response curves of this enzyme differed from those of chlorophyll and of phosphoriboisomerase and ribulose-1, 5-diP carboxylase. A lag period of phosphoribulokinase increased with decreasing light intensity. After the lag period a rapid rate of increase occurred which did not level off during 48 hours of illumination. Thus, a different control mechanism may be operative in inducing increased activity of this enzyme.
Article
to photosynthesize during prolonged irradiation. At the same time, profound morphological and chemical changes occur in the leaf plastids (10). Among these are qualitative and quantitative changes in protein content. Percent protein contained in the plastid fraction of Cichorium (6) and protein content per plastid of Phaseolus (27) increases on prolonged irradiation of etiolated leaves. Increases also occur in TPN glyceraldehyde-3-P dehydrogenase (3, 11), PPNR4, transhydrogenase (20), ribulose-1,5-di P carboxylase (12), and alkaline fructose-1,6-diphosphatase (33). In contrast, synthesis of cytoplasmic DPN glyceraldehyde-3-P dehydrogenase is not dependent on light
Article
An antibody specific for ribulose 1,5-diphosphate carboxylase was used to isolate the enzyme from greening barley (Hordeum vulgare L.) leaves. The increase in enzymatic activity during greening was due to de novo synthesis of the enzyme. Increases in enzymatic activity were accompanied by corresponding increases in enzyme protein and by incorporation of radioactive leucine, all of which were inhibited by low concentrations of cycloheximide. (14)C-Labeled amino acids were incorporated into the enzyme by covalent peptide bonding.
Article
Activities of phosphoriboisomerase, phosphoribulokinase, and ribulose 1,5-diphosphate carboxylase, protein content, and chlorophyll accumulation in dark-grown barley seedlings were measured before and after illumination. Enzymatic activities, levels of soluble protein, and accumulation (upon illumination) of chlorophyll in leaves declined from tips toward the base. In response to increasing time of illumination, chlorophyll accumulation and activities of phosphoribulokinase and ribulose 1,5-diphosphate carboxylase (enzymes located in chloroplasts) increased most in tip portions whereas activity of phosphoriboisomerase and levels of soluble protein (constituents not confined to chloroplasts) increased similarly in all sections of the leaf. Maximum activity of phosphoribulokinase and maximum accumulation of chlorophyll shifted toward median portions of the leaf blade with increased age of seedling before illumination. Maximum activity of ribulose 1,5-diphosphate carboxylase and maximum level of soluble protein occurred in all leaf sections when the seedlings were 7 days of age before illumination.
Protein synthesis in dark green bean leaves
  • D And Racrsen
RACrSEN, D. AND M. FOOTE. 1965. Protein synthesis in dark green bean leaves. Can. J. Bot. 43: 817-824.
Ribulose diphosphate carboxylase. I. A factor involved in light activation of the enzyme Influence of age and il-of several Calvin cycle enzymes in greening 1965 Protein synthesis in dark green bean fraction I protein and the protein Plant Physiol
  • G F Wildner
WILDNER, G. F. AND R. S. GRIDDLE. 1969. Ribulose diphosphate carboxylase. I. A factor involved in light activation of the enzyme. Biochem. Biophys. Res. Comm. 37: 952-960. 1970. Influence of age and il-of several Calvin cycle enzymes in greening 1965. Protein synthesis in dark green bean fraction I protein and the protein Plant Physiol. Vol. 51, 1973