Arginine Decarboxylase and Putrescine Oxidase in Ovaries of Pisum sativum L. (Changes during Ovary Senescence and Early Stages of Fruit Development)

Enzymatic activities involved in putrescine metabolism in ovaries of Pisum sativum L. during ovary senescence and fruit set were investigated. Accumulation of putrescine was observed during incubation of extracts from gibberellic acid-treated unpollinated ovaries (young developing fruits) but not in extracts from untreated ovaries (senescent ovaries). Extracts from pea ovaries showed arginine decarboxylase (ADC) activity, but ornithine decarboxylase and arginase activity were not detected. ADC activity decreased in presenescent ovaries and increased markedly after induction of fruit set with gibberellic acid. Increases in ADC activity were also observed with application of other plant growth substances (benzy-ladenine and 2,4-dichlorophenoxyacetic acid), after pollination, and in the slender (la crys) pea mutant. By contrast, putrescine oxidase activity increased in presenescent ovaries but did not increase during early fruit development. All of these results suggest that ADC and putrescine oxidase are involved in the control of putrescine metabolism. Ovary senescence is characterized by the absence of putrescine biosynthesis enzymes and increased levels of putrescine oxidase and fruit development by an increase in ADC and a constant level of putrescine oxidase.     

Purification and characterization of a thiol-protease induced during senescence of unpollinated ovaries of Pisum sativum

A senescence-specific protease has been purified from senescent unpollinated ovaries of Pisum sativum L. cv. Alaska by acidic extraction. (NH₄)₂SO₄ fractionation, ion exchange chromatography on CM-Sephadex, and affinity chromatography on ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco)-Sepharose. Characterization of the purified protease indicated that it is a thiol-endoprotease (EC 3. 4. 22 class) active over a wide pH range. Purified antibodies against this protease inhibit the degradation of Rubisco in autodigested extracts of senescent ovaries, suggesting that Rubisco might be a substrate for the protease in senescent pea ovaries. The relative levels of the protease were determined by an enzyme-linked immunosorbent assay (ELISA) along the processes of ovary senescence and gibberellic acid (GA)-induced fruit development, indicating its induction at the beginning of senescence and the suppression of its synthesis by GA treatment.     

Involvement of a neutral proteolytic activity in the senescence of unpollinated ovaries of Pisum sativum>

Carrasco, P. and Carbonell, J. 1988. Involvement of a neutral proteolytic activity in the senescence of unpollinated ovaries of Pisum sativum . - Physiol. Plant. 72: 610–616.
The study of proteolysis by autodigestion in extracts from developing (gibberellic acid-treated) or senescing (non-treated) unpollinated ovaries of Pisum sativum L. cv. Alaska indicated the presence of two main proteolytic activities sensitive to inhibitors of sulfhydryl proteases. One of them was active at acidic pH and was present both in developing and senescent ovaries. The other one, active at neutral pH, was only detected in non-treated ovaries and was identified by the hydrolysis of the large subunit of ribulose-l,5-bisphosphate (RuBP) carboxylase (EC 4.1.1.39). Senescence of non-treated ovaries was also associated with an increase in proteolytic activity measured with a Coomassie Blue reagent and by determination with ninhydrin of a-NH₂ groups released after autodigestion of the extracts. The presence of the neutral proteolytic activity only in senescing ovaries, but not in developing ones, suggests that it plays a key role in the senescence of pea ovaries and that its appearance is prevented by gibberellic acid.     

Biochemical and histochemical detection of endoproteolytic activities involved in ovary senescence or fruit development in Pisum sativum

The appearance of endoproteolytic activities related to the senescence of unpollinated pea ( Pisum sativum L. cv. Alaska) ovaries, or with fruit development induced by gibberellic acid (GA₃), was examined simultaneously by biochemical and histochemical techniques using gelatin as substrate. Biochemical detection was carried out by gelatin-containing sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. Histochemical detection was performed using a gelatin film technique. No differences in endopeptidase activity were found in extracts from non-treated or developing ovaries during the two first days post-anthesis. After day 3 non-treated ovaries showed a marked increase in activity as well as two new bands with proteolytic activity, associated with the beginning of the senescence. At the same time a new activity was also located at the endocarp. In developing ovaries activity was only observed around vascular cells of the mesocarp at the end of the period studied (4–5 days post-anthesis). Activity detected in the ovules was essentially the same in both GA₃-treated and non-treated ovaries.     

Expression of thiol proteases decreases in tomato ovaries after fruit set induced by pollination or gibberellic acid

The modulation of the expression of thiol proteases during both senescence and development was investigated Proteolytic activity and some thiol proteases were analyzed in unpollinated tomato (Lycopersicon esculentum Mill. cv. Rutgers) ovaries during presenescence and during early fruit development induced by treatment with gibberellic acid (GA) or by natural pollination. Proteolytic activity in extracts was tested on azocasein and by observing degradation of the ribulose-1,5-bisphosphate carboxylase large subunit in western blots. There was no correlation between total activity and protein content. Thiol proteases were analyzed by western blot with antibodies raised against papain and a recombinant tomato C14 thiol protease. A 58-kDa polypeptide was recognized by both antibodies and two more polypeptides of 47 and 36 kDa were detected with the second one. All these polypeptide levels increased in untreated unpollinated ovaries at the presenescent stage. Natural pollination or GA treatment of unpollinated ovaries resulted in decreases of these polypeptides at an early developmental stage. The same pattern was observed for the levels of C14 mRNA. Our results suggest that the expression of C14 thiol protease occurs in unpollinated ovaries at the presenescent stage and that it can be suppressed by factors that induce fruit set and development.     

Changes in the synthesis of rubisco in rice leaves in relation to senescence and N influx

BACKGROUND AND AIMS: The amount of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) synthesized in a leaf is closely correlated with N influx into the leaf throughout its lifetime. Rubisco synthesis and N influx are most active in the young leaf during expansion, but are very limited in the senescent leaf. However, it is not established whether Rubisco synthesis can be observed if N influx is increased, even in a very senescent leaf. This study first investigated changes in the relationships between rbcS and rbcL mRNA contents and Rubisco synthesis per unit of leaf mass with leaf senescence. Next, leaves were removed during late senescence, to examine whether Rubisco synthesis is re-stimulated in very senescent leaves by an increase in N influx. METHODS: Different N concentrations (1 and 4 mm) were supplied to Oryza sativa plants at the early (full expansion), middle and late stages (respectively 8 and 16 d after full expansion) of senescence of the eighth leaf. To enhance N influx into the eighth leaf 16 d after full expansion, all leaf blades on the main stem, except for the eighth leaf, and all tillers were removed and plants received 4 mm N (removal treatment). KEY RESULTS: Rubisco synthesis, rbcS and rbcL mRNAs and the translational efficiencies of rbcS and rbcL mRNAs decreased with leaf senescence irrespective of N treatments. However, in the removal treatment at the late stage, they increased more strongly with an increase in N influx than in intact plants. CONCLUSIONS: Although Rubisco synthesis and rbcS and rbcL mRNAs decrease with leaf senescence, leaves at the late stage of senescence have the potential actively to synthesize Rubisco with an increase in N influx.     

Temporal and spatial expression of a thiolprotease gene during pea ovary senescence, and its regulation by gibberellin

Clones encoding a thiolprotease (tpp) have been isolated from a cDNA library of unpollinated, senescent pea ovaries and its pattern of expression during both ovary senescence and parthenocarpic development have been studied. The sequence of the tpp cDNA displays a high similarity with other plant and animal thiolproteases of the papain group. The homology is highest around the Cys-His of the active centre; a 109 amino acid sequence at the carboxy terminus was found to be homologous only to thiolproteases of plant origin; this part of the mRNA is also present in another pea mRNA that exhibits similar patterns of induction. tpp mRNA shows a temporal pattern of accumulation that precedes that observed for proteolytic activity. Such accumulation did not occur when ovaries were induced to grow parthenocarpically by gibberellic acid (GA) treatment; furthermore the initial low level of expression present in ovaries decreased after GA treatment, indicating that the gene is down-regulated by gibberellins. Spatially, tpp mRNA is localized mainly within the ovule and ovary vascular elements, and transiently within the endocarp of senescent ovaries. This pattern of expression precedes the development of the cytopathogenic effects observed as unpollinated ovaries undergo senescence.     

Analysis of the capacity of extracts from normal human young and senescent fibroblasts to support DNA synthesis in vitro

Cytoplasmic extracts from early-passage (young), late-passage (senescent) normal human fibroblast (HF) cultures and immortalized human cell lines (HeLa, HT-1080, and MANCA) were analyzed for their ability to support semiconservative DNA synthesis in an in vitro SV40-ori DNA replication system. Unsupplemented extracts from the three permanent cell lines were demonstrated to be active in this system; whereas young HF extracts were observed to be minimally active, and no activity could be detected in the senescent HF extracts. The activity of these extracts was compared after supplementation with three recombinant human replication factors: (1) the catalytic subunit of DNA polymerase alpha (DNA pol-alpha-cat), (2) the three subunits of replication protein A (RPA), and (3) DNA topoisomerase I (Topo I). The addition of all three recombinant proteins is required for optimum activity in the young and senescent HF extracts; the order of the level of activity is: transformed > young HF > senescent HF. Young HF extracts supplemented with RPA alone are able to support significant replicative activity but not senescent extracts which require both RPA and DNA pol-alpha-cat for any detectable activity. The necessary requirement for these factors is confirmed by the failure of unsupplemented young and senescent extracts to activate MANCA extracts that have been immunodepleted of DNA pol-alpha-cat or RPA. Immunocytochemical studies revealed that RPA, DNA pol-alpha, PCNA, and topo I levels are higher in the immortal cell types used in these studies. In the HF cells, levels of DNA pol-alpha-cat and PCNA are higher (per mg protein) in the low-passage than in the senescent cells. By contrast, RPA levels, as determined by immunocytochemical or Western blot studies, were observed to be similar in both young and senescent cell nuclei. Taken together, these results indicate that the low to undetectable activity of young HF extracts in this system is due mainly to reduced intracellular levels of RPA, while the senescent HF extracts are relatively deficient in DNA polymerase alpha and probably some other essential replication factors, as well as RPA. Moreover, the retention of RPA in the senescent HF nuclei contributes to the low level of this factor in the cytoplasmic extracts from these cells.     

Proteolytic activities and ribulose 1,5 bisphosphate carboxlyase degradation in leaves of soybean (Glycine max L. Merril) with different nitrogen status

Changes in soluble proteins and Rubisco (E.C.4.1.1.39) contents were examined in leaves of nitrogen-deprived and nitrogen-sufficient soybeans. Rubisco content was very responsive to nitrogen stress, and this protein appeared to be the largest source of mobilizable nitrogen in the senescent leaf. Loss of soluble proteins and Rubisco was associated with a decrease in the activities of several proteolytic enzymes measured using artificial substrates: carboxypeptidase, aminopeptidase and haemoglobinase.The in vitro activity of enzyme(s) which can degrade Rubisco was investigated using endogenous Rubisco and in vitro radiolabelled Rubisco as substrates. Highest endopeptidic cleavage of endogenous Rubisco occured at pH 4; the enzyme responsible for this breakdown appeared to be a sulfhydryl-dependent proteinase. In contrast, [¹⁴C] Rubisco was attacked preferentially at pH 9, by a peptide hydrolase sensitive to EDTA. No increase in Rubisco-degrading activities was detected in nitrogen-deficient soybean leaves compared to control plant leaves.Abbreviations EDTA Ethylenediaminetetraacetate - LS Large Subunit of Rubisco - NEM N-ethylmaleimide - pCMB Parachloromercuribenzoate - PMSF Phenylmethylsulfonyl-fluoride - Rubisco Ribulose 1,5 Bisphosphate Carboxylase/Oxygenase     

'Senescence-associated vacuoles' are involved in the degradation of chloroplast proteins in tobacco leaves

Massive degradation of photosynthetic proteins is the hallmark of leaf senescence; however the mechanism involved in chloroplast protein breakdown is not completely understood. As small 'senescence-associated vacuoles' (SAVs) with intense proteolytic activity accumulate in senescing leaves of soybean and Arabidopsis, the main goal of this work was to determine whether SAVs are involved in the degradation of chloroplastic components. SAVs with protease activity were readily detected through confocal microscopy of naturally senescing leaves of tobacco (Nicotiana tabacum L.). In detached leaves incubated in darkness, acceleration of the chloroplast degradation rate by ethylene treatment correlated with a twofold increase in the number of SAVs per cell, compared to untreated leaves. In a tobacco line expressing GFP targeted to plastids, GFP was re-located to SAVs in senescing leaves. SAVs were isolated by sucrose density gradient centrifugation. Isolated SAVs contained chloroplast-targeted GFP and the chloroplast stromal proteins Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) and glutamine synthetase, but lacked the thylakoid proteins D1 and light-harvesting complex II of the photosystem II reaction center and photosystem II antenna, respectively. In SAVs incubated at 30 degrees C, there was a steady decrease in Rubisco levels, which was completely abolished by addition of protease inhibitors. These results indicate that SAVs are involved in degradation of the soluble photosynthetic proteins of the chloroplast stroma during senescence of leaves.     

Isolation of a Protein Containing Covalently Linked Large and Small Subunits of Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase from Botryococcus braunii

Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) and a 66-kD protein were co-purified from solubilized microsomal preparations of the green alga Botryococcus braunii by Green A agarose, sucrose density gradient, MonoQ, and gel filtration. The 66-kD protein remained intact after 6 M urea treatment and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. It could be detected in the soluble fraction of the cell-free extract but appeared to be more abundant in the microsomal preparations. It cross-reacted with antibodies raised against Rubisco holoenzyme, large and small subunits, indicating that the 66-kD protein contains both the large and the small subunits of Rubisco. The N-terminal amino acid sequence of this protein and that of a proteolytic fragment showed high homology with the mature Rubisco small subunits, and the sequence of another proteolytic fragment showed high homology with that of the Rubisco large subunit. It is concluded that the 66-kD protein is produced by cross-linking of large and small sub-units of Rubisco in the cell.     

Modification of Rubisco and Altered Proteolytic Activity in O3-Stressed Hybrid Poplar (Populus maximowizii x trichocarpa)

Exposing hybrid poplar (Populus maximowizii x trichocarpa) plants to ozone (O3) resulted in an acceleration of the visual symptoms of senescence and a decrease in the activity and quantity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco). Whole plants, crude leaf extracts, and isolated intact chloroplasts of hybrid poplar clone 245 were used to test the hypothesis that O3-induced structural modifications of Rubisco affect the activity of this key photosynthetic enzyme. Proteolytic activity, per se, could not account for losses in Rubisco; acidic and alkaline protease activities declined or were unaffected in foliage of O3-treated poplar saplings. In vitro treatment of leaf extracts with O3 decreased total Rubisco activity and binding of the enzyme's transition-state analog, 2-carboxyarabinitol bisphosphate. Additionally, O3 increased the loss of Rubisco large subunit (LSU) when extracts were incubated at 37[deg]C. Treatment of isolated intact chloroplasts with O3 accelerated both the loss of the 55-kD Rubisco LSU and the accumulation of Rubisco LSU aggregates, as visualized by immunoblotting. The time-dependent modification in Rubisco structure was the primary response of the isolated organelles to O3 treatment, with little proteolytic degradation of the LSU detected.     

Changes in the Level of Peptidase Activities in Pea Ovaries during Senescence and Fruit Set Induced by Gibberellic Acid

The activities and changes in the levels of exopeptidase and endopeptidase activities were characterized in unpollinated ovaries of Pisum sativum L. cv Alaska during senescence and early fruit development induced by gibberellic acid (GA₃). Two aminopeptidases and one iminopeptidase were electrophoretically separated. These peptidases were sensitive to inhibitors of sulfhydryl proteases. Carboxypeptidase activity was inhibited by phenylmethyl sulfonyl fluoride. An azocasein-degrading endopeptidase, sensitive to thiol protease inhibitors, was also found. An increase in the specific activity of aminopeptidase during both fruit development and ovary senescence was observed. In contrast, the specific activity of carboxypeptidase and endopeptidase increased only during senescence of the ovary. Changes in exopeptidase activity in senescing ovaries could be mainly the consequence of a greater stability to proteolysis while the rise in endopeptidase activity appeared to be due to new or increased synthesis of the enzyme. These results suggest that endopeptidase, and not amino or carboxypeptidase, plays a key role in the senescence of pea ovaries and that the changes in unpollinated ovaries leading to ovary senescence or fruit development can be controlled by gibberellins.     

Fruit removal in soybean induces the formation of an insoluble form of ribulose-1,5-bisphosphate carboxylase/oxygenase in leaf extracts*

In some soybean (Glycine max (L.) Merr.) cultivars, fruit removal does not delay the apparent loss of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) activity and abundance or the decline in photosynthesis. Analysis of leaf extracts from defruited plants indicated a time-dependent increase in both Rubisco activity and abundance in a 30000 · g pellet fraction in cultivars which had been reported to lose all Rubisco protein from the supernatant fraction. Attempts to solubilize the pelleted Rubisco by increasing the buffer volume/tissue ratio or by adding alkylphenoxypolyethoxyethanol (Triton X-100), ethylenediaminetetraacetic acid (EDTA), or NaCl were unsuccessful. However, treatment of the pellets with denaturants such as 8 M urea or 5% (w/v) sodium dodecyl sulfate (SDS) did release Rubisco from the pellet. Redistribution of protein to the pellet fraction appeared to be specific for Rubisco since the amount of ribulose-5-phosphate kinase (EC 2.7.1.19) found in the pellet fraction of leaf extracts of control and defruited plants was small and constant over time. The loss of soluble Rubisco, and the concomitant increase in insoluble Rubisco, in response to fruit removal varied with genotype and was reproducible in both field and greenhouse environments. In addition, the effect was influenced by node position and light; lower and-or shaded leaves exhibited less Rubisco in the pellet fraction than leaves from the top of the plant that was fully exposed to sunlight. When isolated by sucrose-density-gradient centrifugation, the insoluble Rubisco was found to co-purify with a 30-kDa (kilodalton) polypeptide. These results indicate that alteration of the source/sink ratio by removing fruits results in the formation of an insoluble form of Rubisco in leaf extracts of soybean. Whether or not Rubisco exists as an insoluble complex with the 30-kDa polypeptide in intact leaves of defruited plants remains to be determined.Abbreviations kDa kilodalton - PGA kinase 3-phosphoglyceric acid kinase (EC 2.7.2.3) - Rubisco ribulose-1,5-bisphosphate car-boxylase/oxygenase (EC 4.1.1.39) - Ru5P kinase ribulose-5-phosphate kinase (EC 2.7.1.19) - SDS-PAGE sodium dodecyl sulfatepolyacrylamide gel electrophoresis     

The absence of Rubisco activase activity in total wheat leaf extracts is recovered in the purified protein

When desalted extracts of soluble protein from dark-adaptedwheat leaves were assayed for ribulose-1, 5-bisphosphate carboxylase/oxygenase(Rubisco) activase activity in the presence of 1 mM ATP andan ATP-regenerating system, very little ATP-dependent activationof RuBP-inactivated Rubisco was found. In extracts from light-adaptedleaves a very similar pattern of Rubisco activation was observedexcept that the overall level of Rubisco activity was much lowerthan in the extracts from dark-adapted leaves. These featureswere apparent both at low (120µg per ml) and high (640µg per ml) protein concentrations. We were unable to demonstrateRubisco activase activity in crude leaf extracts. Consequently,in order to establish that Rubisco activase was present in wheatleaf extracts the wheat leaf protein was purified to homogeneity.The identity of the protein was confirmed with antibodies tothe spinach enzyme, ATPase activity and activase-mediated releaseof the inhibitor, carboxyara-binitol-1-phosphate (CA1P) fromthe tertiary Rubisco complex. The pure wheat Rubisco activaserelieved the CA1P-induced inhibition of Rubisco activity. Rubiscoactivase had no significant effect on the affinity of wheatRubisco for the substrate, ribulose-1, 5-bisphosphate (RuBP). Key words: Rubisco activase, Rubisco, regulation     

Degradation of Ribulose-1, 5-Bisphosphate Carboxylase/Oxygenase in Wheat Leaves During Dark-induced Senescence

The degradation of Ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco, EC 4.1.1.39) in wheat (Triticum aestivum L. cv. Yangmai 158) leaves during dark-induced senescence was studied. An in vivo degradation product of Rubisco large subunit (LSU) with molecular weight of 50 kD was detected by SDS-PAGE and immunoblotting with antibody against tobacco Rubisco. This fragment could also be detected in natural senescence. The result also suggested that the Rubisco holoenzyme had not dissociated when LSU hydrolyzed from 53 kD to 50 kD. And LSU could be fragmented to 50 kD at 30-35 ℃ and at pH 7.5 in crude enzyme extracts of wheat leaves dark-induced for 48 h, which suggested that maybe LSU was degraded to 50 kD by an unknown protease in chloroplast.     

Ribulose-1,5-bisphosphate carboxylase and fruit set or degeneration of unpollinated ovaries of Pisum sativum L.

The polypeptide patterns obtained by sodium dodecylsulphate-polyacrylamide gel electrophoresis of undigested and autodigested extracts from pea (Pisum sativum L.) ovaries at the early stages of development or degeneration have been studied. Development of unpollinated ovaries was stimulated by application of different plant growth regulators (gibberellic acid, 2,4-dichlorophenoxyacetic acid, and N⁶-benzyladenine) or by plant topping. Polypeptide bands of similar mobility to ribulose-1,5-bisphosphate carboxylase (RuBPCase) subunits (16 and 55 kDa) could be detected in all types of autodigested extracts from stimulated ovaries. However these bands were absent in electrophoretic patterns of autodigested extracts from unstimulated ovaries after 3 d post anthesis and in patterns of autodigested mixtures of these extracts with either those from stimulated ovaries or those from unstimulated ovaries before day 3. These observations indicate that a proteolytic activity which promotes the hydrolysis of RuBPCase appears in unstimulated ovaries about 3 d after anthesis. This event coincides with the loss of the capacity of unpollinated ovaries to develop in response to gibberellic acid and with the degeneration of the ovary wall.Abbreviations BA N⁶-benzyladenine - 2,4-D 2,4-dichlorophenoxyacetic acid - GA₃ gibberellic acid - RuBPCase ribulose-1,5-bisphosphate carboxylase - SDS-PAGE sodium dodecylsulphate-polyacrylamide gel electrophoresis     

Changes in the turnover of Rubisco and levels of mRNAs of rbcL and rbcS in rice leaves from emergence to senescence

Changes in the amount of ribulose 1,5‐bisphosphate carboxylase/oxygenase (Rubisco; EC 4·1·1·39) synthesized and degraded and the levels of rbcL and rbcS mRNAs were examined in the eighth leaf blades of rice from emergence to senescence. Synthesis of Rubisco was very active during leaf expansion, became quite low at the time of full expansion and then declined further during senescence. The changes in the levels of rbcL and rbcS mRNAs co‐ordinated approximately with those in the amount of Rubisco synthesized. Thus, it is suggested that the amount of Rubisco synthesized is determined primarily by the levels of rbcL and rbcS mRNAs during the life span of the leaves. Degradation of Rubisco started just before the time of full expansion and became far more active than its synthesis during senescence. Since the synthesis of Rubisco during senescence scarcely contributed to its amount, it can be concluded that the degradation of Rubisco is the major determinant for the amount of Rubisco in senescent leaves. The decline in the level of rbcL mRNA occurred much earlier in the developmental stage and proceeded at a much faster rate than that of rbcL DNA, indicating that the level of rbcL DNA is not a major determinant for the level of rbcL mRNA in senescent leaves of rice.