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Jürg Stöcklin - One of the best experts on this subject based on the ideXlab platform.
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Demography of the giant Monocarpic herb Rheum nobile in the Himalayas and the effect of disturbances by grazing.
Annals of Botany, 2020Co-Authors: Bo Song, Peter Stoll, De-li Peng, Jürg StöcklinAbstract:BACKGROUND: Perennity of giant rosette species in combination with a single 'big bang' reproduction followed by death of the genetic individual is relatively rare among plants. Such long-lived Monocarpic plants are usually slow growing and can be found in deserts, bogs or in alpine regions of the tropics or sub-tropics. Due to their longevity, Monocarpic perennials risk losing everything before reproduction, which make them particularly susceptible to disturbances. Because of the inherent difficulties in assessing whether long-lived populations are growing or declining, usually neither their demography nor the consequences of increasing grazing pressure are known. METHODS: We used integral projection modelling (IPM) to measure the growth rate and passage time to flowering of Rheum nobile, a Monocarpic perennial, and one of the most striking alpine plants from the high Himalayas. Rosettes which were no longer found due to disturbances or grazing by yaks were either treated as missing or as dead in two series of analysis, thereby simulating demography with and without the impact of grazing cattle. Data were collected from plants at 4500 m a.s.l. in Shangri-la County, Yunnan Province, south-west China. In four consecutive years (2011-2014) and in two populations, 372 and 369 individuals were measured, respectively, and size-dependent growth, survival and fecundity parameters were estimated. In addition, germination percentage, seedling survival and establishment probability were assessed. KEY RESULTS: The probability of survival, flowering and fecundity were strongly size dependent. Time to reach flowering size was 33.5 years [95 % confidence interval (CI) 21.9-43.3, stochastic estimate from pooled transitions and populations]. The stochastic population growth rate (lambdas) of Rheum nobile was 1.013 (95 % CI 1.010-1.017). When disturbance by grazing cattle (yaks) was accounted for in the model, lambdas dropped to values
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demography of the giant Monocarpic herb rheum nobile in the himalayas and the effect of disturbances by grazing
Annals of Botany, 2019Co-Authors: Bo Song, Peter Stoll, De-li Peng, Jürg StöcklinAbstract:BACKGROUND: Perennity of giant rosette species in combination with a single 'big bang' reproduction followed by death of the genetic individual is relatively rare among plants. Such long-lived Monocarpic plants are usually slow growing and can be found in deserts, bogs or in alpine regions of the tropics or sub-tropics. Due to their longevity, Monocarpic perennials risk losing everything before reproduction, which make them particularly susceptible to disturbances. Because of the inherent difficulties in assessing whether long-lived populations are growing or declining, usually neither their demography nor the consequences of increasing grazing pressure are known. METHODS: We used integral projection modelling (IPM) to measure the growth rate and passage time to flowering of Rheum nobile, a Monocarpic perennial, and one of the most striking alpine plants from the high Himalayas. Rosettes which were no longer found due to disturbances or grazing by yaks were either treated as missing or as dead in two series of analysis, thereby simulating demography with and without the impact of grazing cattle. Data were collected from plants at 4500 m a.s.l. in Shangri-la County, Yunnan Province, south-west China. In four consecutive years (2011-2014) and in two populations, 372 and 369 individuals were measured, respectively, and size-dependent growth, survival and fecundity parameters were estimated. In addition, germination percentage, seedling survival and establishment probability were assessed. KEY RESULTS: The probability of survival, flowering and fecundity were strongly size dependent. Time to reach flowering size was 33.5 years [95 % confidence interval (CI) 21.9-43.3, stochastic estimate from pooled transitions and populations]. The stochastic population growth rate (lambdas) of Rheum nobile was 1.013 (95 % CI 1.010-1.017). When disturbance by grazing cattle (yaks) was accounted for in the model, lambdas dropped to values <1 (0.940, 95 % CI 0.938-0.943). CONCLUSION: We conclude that natural populations of this unique species are viable, but that conservation efforts should be made to minimize disturbances by grazing and to protect this slow-growing flagship plant from the high Himalayas.
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pollen dispersal and gene flow within and into a population of the alpine Monocarpic plant campanula thyrsoides
Annals of Botany, 2012Co-Authors: J. F. Scheepens, Eva S. Frei, Georg F. J. Armbruster, Jürg StöcklinAbstract:BACKGROUND AND AIMS: Gene flow by seed and pollen largely shapes the genetic structure within and among plant populations. Seed dispersal is often strongly spatially restricted, making gene flow primarily dependent on pollen dispersal within and into populations. To understand distance-dependent pollination success, pollen dispersal and gene flow were studied within and into a population of the alpine Monocarpic perennial Campanula thyrsoides. METHODS: A paternity analysis was performed on sampled seed families using microsatellites, genotyping 22 flowering adults and 331 germinated offspring to estimate gene flow, and pollen analogues were used to estimate pollen dispersal. The focal population was situated among 23 genetically differentiated populations on a subalpine mountain plateau (<10 km(2)) in central Switzerland. KEY RESULTS: Paternity analysis assigned 110 offspring (33·2 %) to a specific pollen donor (i.e. 'father') in the focal population. Mean pollination distance was 17·4 m for these offspring, and the pollen dispersal curve based on positive LOD scores of all 331 offspring was strongly decreasing with distance. The paternal contribution from 20-35 offspring (6·0-10·5 %) originated outside the population, probably from nearby populations on the plateau. Multiple potential fathers were assigned to each of 186 offspring (56·2 %). The pollination distance to 'mother' plants was negatively affected by the mothers' degree of spatial isolation in the population. Variability in male mating success was not related to the degree of isolation of father plants. CONCLUSIONS: Pollen dispersal patterns within the C. thyrsoides population are affected by spatial positioning of flowering individuals and pollen dispersal may therefore contribute to the course of evolution of populations of this species. Pollen dispersal into the population was high but apparently not strong enough to prevent the previously described substantial among-population differentiation on the plateau, which may be due to the Monocarpic perenniality of this species.
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Pollen dispersal and gene flow within and into a population of the alpine Monocarpic plant Campanula thyrsoides.
Annals of Botany, 2012Co-Authors: J. F. Scheepens, Eva S. Frei, Georg F. J. Armbruster, Jürg StöcklinAbstract:Background and Aims Gene flow by seed and pollen largely shapes the genetic structure within and among plant populations. Seed dispersal is often strongly spatially restricted, making gene flow primarily dependent on pollen dispersal within and into populations. To understand distance-dependent pollination success, pollen dispersal and gene flow were studied within and into a population of the alpine Monocarpic perennial Campanula thyrsoides.
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evolutionary demography of long lived Monocarpic perennials a time lagged integral projection model
Journal of Ecology, 2008Co-Authors: Patrick Kuss, Mark Rees, Stephen P Ellner, Hafdis Hanna Aegisdottir, Jürg StöcklinAbstract:1. The evolution of flowering strategies (when and at what size to flower) in Monocarpic perennials is determined by balancing current reproduction with expected future reproduction, and these are largely determined by size-specific patterns of growth and survival. However, because of the difficulty in following long-lived individuals throughout their lives, this theory has largely been tested using short-lived species (> 5 years). 2. Here, we tested this theory using the long-lived Monocarpic perennial Campanula thyrsoides which can live up to 16 years. We used a novel approach that combined permanent plot and herb chronology data from a 3-year field study to parameterize and validate integral projection models (IPMs). 3. Similar to other Monocarpic species, the rosette leaves of C. thyrsoides wither over winter and so size cannot be measured in the year of flowering. We therefore extended the existing IPM framework to incorporate an additional time delay that arises because flowering demography must be predicted from rosette size in the year before flowering. 4. We found that all main demographic functions (growth, survival probability, flowering probability and fecundity) were strongly size-dependent and there was a pronounced threshold size of flowering. There was good agreement between the predicted distribution of flowering ages obtained from the IPMs and that estimated in the field. Mostly, there was good agreement between the IPM predictions and the direct quantitative field measurements regarding the demographic parameters lambda, R-0 and T. We therefore conclude that the model captures the main demographic features of the field populations. 5. Elasticity analysis indicated that changes in the survival and growth function had the largest effect (c. 80%) on λ and this was considerably larger than in short-lived monocarps. We found only weak selection pressure operating on the observed flowering strategy which was close to the predicted evolutionary stable strategy. 6. Synthesis. The extended IPM accurately described the demography of a long-lived Monocarpic perennial using data collected over a relatively short period. We could show that the evolution of flowering strategies in short- and long-lived monocarps seem to follow the same general rules but with a longevity-related emphasis on survival over fecundity.
Maria B Garcia - One of the best experts on this subject based on the ideXlab platform.
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adaptation of the long lived Monocarpic perennial saxifraga longifolia to high altitude
Plant Physiology, 2016Co-Authors: Sergi Munnebosch, Alba Cotado, Melanie Morales, Eva Fletasoriano, Jesus Villellas, Maria B GarciaAbstract:Global change is exerting a major effect on plant communities, altering their potential capacity for adaptation. Here, we aimed at unveiling mechanisms of adaptation to high altitude in an endemic long-lived Monocarpic, Saxifraga longifolia, by combining demographic and physiological approaches. Plants from three altitudes (570, 1100, and 2100 m above sea level [a.s.l.]) were investigated in terms of leaf water and pigment contents, and activation of stress defense mechanisms. The influence of plant size on physiological performance and mortality was also investigated. Levels of photoprotective molecules (α-tocopherol, carotenoids, and anthocyanins) increased in response to high altitude (1100 relative to 570 m a.s.l.), which was paralleled by reduced soil and leaf water contents and increased ABA levels. The more demanding effect of high altitude on photoprotection was, however, partly abolished at very high altitudes (2100 m a.s.l.) due to improved soil water contents, with the exception of α-tocopherol accumulation. α-Tocopherol levels increased progressively at increasing altitudes, which paralleled with reductions in lipid peroxidation, thus suggesting plants from the highest altitude effectively withstood high light stress. Furthermore, mortality of juveniles was highest at the intermediate population, suggesting that drought stress was the main environmental driver of mortality of juveniles in this rocky plant species. Population structure and vital rates in the high population evidenced lower recruitment and mortality in juveniles, activation of clonal growth, and absence of plant size-dependent mortality. We conclude that, despite S. longifolia has evolved complex mechanisms of adaptation to altitude at the cellular, whole-plant and population levels, drought events may drive increased mortality in the framework of global change.
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sex allocation in a long lived Monocarpic plant
Plant Biology, 2003Co-Authors: Maria B GarciaAbstract:: Hermaphroditic plants with perfect flowers often show within-inflorescence flower differentiation, lower female success (and therefore female investment) as the inflorescence develops, and size-dependent sex allocation to male and female functions. Here, I present the results of a descriptive and experimental study in the long-lived Monocarpic Saxifraga longifolia, a sequentially blooming plant showing a large variation in the size of the inflorescence. Natural patterns of relative investment in male and female reproductive components were explored, and flowers were removed from different positions, in order to test two models on sex allocation which predict that female investment increases with resource availability. Results of this study agree with this prediction at the flower level (within inflorescences), but not at the plant level. Pre- and post-mating female allocation declined from early to late-position flowers, while the pollen: ovule increased. Removal of flowers indicated that architectural effects do not prevent full compensation for overall seed production, although the participation of terminal flowers in female reproduction was low in most cases. There seem to be some ontogenic differences in specialization among early- and late-produced flowers, so that the progressive maleness over time is reinforced after fertilization by a sink-source effect, possibly combined with selective abortion. Overall seed production was significantly correlated with plant size; nevertheless, female success was not maximum for the largest plants, but for intermediate sized plants.
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Sex Allocation in a Long‐Lived Monocarpic Plant
Plant Biology, 2003Co-Authors: Maria B GarciaAbstract:: Hermaphroditic plants with perfect flowers often show within-inflorescence flower differentiation, lower female success (and therefore female investment) as the inflorescence develops, and size-dependent sex allocation to male and female functions. Here, I present the results of a descriptive and experimental study in the long-lived Monocarpic Saxifraga longifolia, a sequentially blooming plant showing a large variation in the size of the inflorescence. Natural patterns of relative investment in male and female reproductive components were explored, and flowers were removed from different positions, in order to test two models on sex allocation which predict that female investment increases with resource availability. Results of this study agree with this prediction at the flower level (within inflorescences), but not at the plant level. Pre- and post-mating female allocation declined from early to late-position flowers, while the pollen: ovule increased. Removal of flowers indicated that architectural effects do not prevent full compensation for overall seed production, although the participation of terminal flowers in female reproduction was low in most cases. There seem to be some ontogenic differences in specialization among early- and late-produced flowers, so that the progressive maleness over time is reinforced after fertilization by a sink-source effect, possibly combined with selective abortion. Overall seed production was significantly correlated with plant size; nevertheless, female success was not maximum for the largest plants, but for intermediate sized plants.
Renu Khannachopra - One of the best experts on this subject based on the ideXlab platform.
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wheat cultivars differing in heat tolerance show a differential response to oxidative stress during Monocarpic senescence under high temperature stress
Protoplasma, 2015Co-Authors: Renu Khannachopra, Shakti ChauhanAbstract:Wheat crop may experience heat stress during post-anthesis phase associated with oxidative stress, enhanced senescence, and reduced productivity. Stay green is a desirable character for the selection for heat tolerance in wheat. In the present study, antioxidant metabolism was studied under post-anthesis heat stress in field during Monocarpic senescence by comparing two wheat genotypes, namely Hindi62 (heat tolerant and delayed senescent) and PBW343 (heat susceptible and early senescent). Hindi62 exhibited lesser oxidative stress, membrane damage, and coordinated antioxidant defense as compared to PBW343 under heat stress during post-anthesis stage. Higher activity of SOD, CAT, APX, GR, and MDHAR under heat stress contributed towards delayed senescence in Hindi62 compared to PBW343. GSH/GSSG ratio was also maintained at higher level in Hindi62 under heat stress compared to PBW343 during senescence. Hence, the present study clearly shows that upregulated level of the total antioxidant capacity during grain development contributed towards delayed senescence and heat tolerance in Hindi62 compared to the heat-susceptible PBW343.
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the developing reproductive sink induces oxidative stress to mediate nitrogen mobilization during Monocarpic senescence in wheat
Biochemical and Biophysical Research Communications, 2004Co-Authors: B Srivalli, Renu KhannachopraAbstract:Abstract Removal of reproductive ‘sink,’ i.e., spikelets from wheat, after anthesis delays the rate of flag leaf senescence. Oxidative stress and the oxidative damage to proteins were studied in relation to nitrogen mobilization in wheat plants showing normal and delayed senescence. Wheat plants lacking a reproductive sink showed decreased oxidative stress, lower lipid peroxidation and maintained higher protein, oxidatively damaged proteins, and nitrogen levels as compared to plants with reproductive sink during Monocarpic senescence. Oxidative damage to the proteins when not followed by high proteolytic activities led to a slower nitrogen mobilization in wheat plants lacking a reproductive sink. Thus, the influence of the reproductive sink was due to its ability to drive forward the nitrogen mobilization process through high ROS levels which mediated both damage to the proteins and influenced proteolytic activities.
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induction of new isoforms of superoxide dismutase and catalase enzymes in the flag leaf of wheat during Monocarpic senescence
Biochemical and Biophysical Research Communications, 2001Co-Authors: B Srivalli, Renu KhannachopraAbstract:Leaf senescence is a programmed cell death phenomenon and involves oxidative stress. Superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT EC 1.11.1.6) activities were studied in the flag leaf of Triticum aestivum cv. Kundan at different stages of grain development. Both SOD and CAT activities showed a decline during Monocarpic senescence. Three SOD isozymes were observed in the cytosol, of which one isozyme was observed in the chloroplasts as well. Mitochondria showed the presence of three low abundant SOD isoforms. Inhibitor studies revealed the cytosolic and chloroplastic isoforms to be Cu/Zn SODs. In mitochondria however, two isozymes were MnSOD and one of them appeared to be FeSOD. These isoforms present in the mitochondria increased in activity as senescence progressed. Three isoforms of CAT were observed in peroxisomes which responded differentially during Monocarpic senescence. The changes in the kind and pattern of the antioxidant enzymes supported the ordered sequence of events during leaf senescence. This is the first report showing an increase in mitochondrial FeSOD activity during leaf senescence.
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vacuole cysteine proteases and ribulose 1 5 bisphosphate carboxylase oxygenase degradation during Monocarpic senescence in cowpea leaves
Photosynthetica, 2001Co-Authors: B Srivalli, Sudhakar Bharti, Renu KhannachopraAbstract:Characterisation of proteases degrading ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO, EC: 4.1.1.39) was studied in the cowpea leaf during Monocarpic senescence 3 and 9 d after flowering (DAF), representing early and mid pod fill. The stage at 3 DAF coincided with decrease in the metabolic parameters characterising senescence, i.e., contents of total soluble proteins, RuBPCO, and leaf nitrogen. At 9 DAF, there was a decline in total soluble proteins and an appearance of a 48 kDa cysteine protease. Characterisation of the proteases was done using specific inhibitors. Subcellular localisation at 3 DAF was studied by following the degradation of RuBPCO large subunit (LSU) in the vacuole lysates using immunoblot analyses. Cysteine proteases played a predominant role in the degradation of RuBPCO LSU at the crude extract level. At 9 DAF, expression of cysteine protease isoforms was monitored using polyclonal antibodies against papain and two polypeptides of molecular masses 48 and 35 kDa were observed in the vacuole lysates. We confirmed thus the predominance of cysteine proteases in the vacuoles during different stages of pod development in cowpea leaf.
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effect of altering pod intensity on Monocarpic senescence in cowpea
1998Co-Authors: B Srivalli, Renu KhannachopraAbstract:Monocarpic senescence is a genetically programmed decline in physiological functions which are induced during fruit development following a single reproductive phase. Leaf senescence, is subject to regulation by many environmental and internal factors, where the internal factors include reproductive development (Gan and Amasino, 1997)1. In legumes, each reproductive node behaves as an independent unit, where the leaf at a particular reproductive node supports the fruits developing in its axil (Grover et al., 1985)2. In the present investigation, it has been examined whether (I) the regulation of sink strength on Monocarpic senescence is due to altered protease activity, using the in vivo substrate, Rubisco and a non-plant substrate, casein and (ii) the neutral protease activity has a role in nitrogen mobilisation or not. The results suggest that the reproductive sink regulates Monocarpic senescence, the removal of which delays it, also making the source leaf as a temporary carbohydrate reserve. These observations are related to the previously observed (Khanna-Chopra and Reddy, 1988)3 changes in leaf area, chlorophyll content and total soluble proteins.
Tanguy Jaffre - One of the best experts on this subject based on the ideXlab platform.
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mass flowering and parental death in the regeneration of cerberiopsis candelabra apocynaceae a long lived Monocarpic tree in new caledonia1
American Journal of Botany, 2008Co-Authors: Jennifer Read, Martin Burd, Gordon Drummond Sanson, Tanguy JaffreAbstract:Monocarpy is rare among forest trees, and the selective conditions allowing this life history to evolve are poorly known. Here we examined the regeneration dynamics of a New Caledonian Monocarpic tree species, Cerberiopsis candelabra, to better understand how postreproductive mortality and mass flowering might contribute to the success of this strategy. We investigated population size structures and seedling establishment patterns in 18 stands following the 2003 flowering event. We found little evidence of recent recruitment. Instead, population size structures suggested a history of one or more substantial recruitment events followed by recruitment failure, despite multiple flowering events in most populations. The canopy gap created by death of an individual parent appeared generally insufficient to allow seedling establishment, but mass flowering and consequent death of many adults appeared to enhance seedling recruitment by opening more of the canopy. Site means of seedling density below dead parents correlated strongly with light availability and with the proportional density of flowering trees. Therefore, we suggest that mass flowering and gregariousness may have been necessary preconditions for the evolution of monocarpy in this species. However, the degree to which regeneration relies on synchronous flowering and gregariousness vs. infrequent catastrophic disturbances remains uncertain.
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age size plasticity for reproduction in Monocarpic plants
Ecology, 2006Co-Authors: Martin Burd, Jennifer Read, Gordon Drummond Sanson, Tanguy JaffreAbstract:Empirical and theoretical investigations of monocarpy have usually addressed the question of minimum or threshold sizes for reproduction. However, the range of flowering sizes observed in many Monocarpic species is extraordinarily large (well beyond what can be called a "threshold"), and the sizes of flowering and nonflowering plants may overlap greatly. We attempt to explain these reproductive patterns in terms of optimal reaction norms predicted by simple deterministic life history models. We assume that individuals differ in their growth trajectories due to the heterogeneous quality of microsites and ask how the optimal age and size at flowering varies with environmental variation in growth and for different assumptions about fecundity and mortality. Under two very different growth functions (one with no age- or size-related decline in growth rate and another with such a decline as size approaches an asymptote), the optimal reaction norms imply considerable plasticity for size at reproduction, particularly when poor growth is associated with higher mortality or lower asymptotic size. Deterministic models such as these may be more applicable to long-lived than to short-lived monocarps, because fitness potential should be less affected by stochastic variability in yearly growing condition in the former than in the latter. We consider the case of a tropical Monocarpic and masting tree species, Cerberiopsis candelabra (Apocynaceae), and show that our model results can account for wide ranges of reproductive size and overlap in size of flowering and nonflowering plants, in accord with observation. We suggest that empirical attention to norms of reaction across growth environments will be a more profitable approach than investigation of size thresholds per se.
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does tree size influence timing of flowering in cerberiopsis candelabra apocynaceae a long lived Monocarpic rain forest tree
Journal of Tropical Ecology, 2006Co-Authors: Jennifer Read, Gordon Drummond Sanson, Tanguy Jaffre, Martin BurdAbstract:Cerberiopsis candelabra is a long-lived Monocarpic rain-forest tree endemic to New Caledonia that shows mass flowering across a substantial proportion of a population, and across a substantial number of populations. We investigated the relationship between tree size and flowering (and subsequent dying) across 18 populations from the flowering event of 2003 in order to understand the role of possible size thresholds for flowering in the life history and regeneration ecology of this Monocarpic species. There was a strong positive correlation between trunk diameter and the incidence of flowering when population data were combined. However, the relationship between size and flowering was complex in that flowering occurred across a wide range of tree sizes, with almost complete overlap in size between flowering (5-79 cm dbh) and non-flowering trees (5-64 cm dbh), and with large trees in both the flowering and non- flowering state in the same population. In about half the populations studied there was no significant difference in mean trunk diameter of flowering and non-flowering trees. Nonetheless, we suggest that tree size may play a fundamental role in the life history and regeneration ecology of this species. The seedlings appear to be relatively shade-intolerant and dependent on large canopy gaps for recruitment. A significant effect of mass flowering and subsequent death of multiple large trees is the potential to form large canopy gaps and enhance seedling survival, as the gap is temporally linked with seed germination. However, it is unclear why there is such a large size range of flowering trees, i.e. whether this is just a consequence of the proximate cue, or whether the optimal size for flowering does indeed vary among individuals.
B Srivalli - One of the best experts on this subject based on the ideXlab platform.
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the developing reproductive sink induces oxidative stress to mediate nitrogen mobilization during Monocarpic senescence in wheat
Biochemical and Biophysical Research Communications, 2004Co-Authors: B Srivalli, Renu KhannachopraAbstract:Abstract Removal of reproductive ‘sink,’ i.e., spikelets from wheat, after anthesis delays the rate of flag leaf senescence. Oxidative stress and the oxidative damage to proteins were studied in relation to nitrogen mobilization in wheat plants showing normal and delayed senescence. Wheat plants lacking a reproductive sink showed decreased oxidative stress, lower lipid peroxidation and maintained higher protein, oxidatively damaged proteins, and nitrogen levels as compared to plants with reproductive sink during Monocarpic senescence. Oxidative damage to the proteins when not followed by high proteolytic activities led to a slower nitrogen mobilization in wheat plants lacking a reproductive sink. Thus, the influence of the reproductive sink was due to its ability to drive forward the nitrogen mobilization process through high ROS levels which mediated both damage to the proteins and influenced proteolytic activities.
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induction of new isoforms of superoxide dismutase and catalase enzymes in the flag leaf of wheat during Monocarpic senescence
Biochemical and Biophysical Research Communications, 2001Co-Authors: B Srivalli, Renu KhannachopraAbstract:Leaf senescence is a programmed cell death phenomenon and involves oxidative stress. Superoxide dismutase (SOD, EC 1.15.1.1) and catalase (CAT EC 1.11.1.6) activities were studied in the flag leaf of Triticum aestivum cv. Kundan at different stages of grain development. Both SOD and CAT activities showed a decline during Monocarpic senescence. Three SOD isozymes were observed in the cytosol, of which one isozyme was observed in the chloroplasts as well. Mitochondria showed the presence of three low abundant SOD isoforms. Inhibitor studies revealed the cytosolic and chloroplastic isoforms to be Cu/Zn SODs. In mitochondria however, two isozymes were MnSOD and one of them appeared to be FeSOD. These isoforms present in the mitochondria increased in activity as senescence progressed. Three isoforms of CAT were observed in peroxisomes which responded differentially during Monocarpic senescence. The changes in the kind and pattern of the antioxidant enzymes supported the ordered sequence of events during leaf senescence. This is the first report showing an increase in mitochondrial FeSOD activity during leaf senescence.
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vacuole cysteine proteases and ribulose 1 5 bisphosphate carboxylase oxygenase degradation during Monocarpic senescence in cowpea leaves
Photosynthetica, 2001Co-Authors: B Srivalli, Sudhakar Bharti, Renu KhannachopraAbstract:Characterisation of proteases degrading ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO, EC: 4.1.1.39) was studied in the cowpea leaf during Monocarpic senescence 3 and 9 d after flowering (DAF), representing early and mid pod fill. The stage at 3 DAF coincided with decrease in the metabolic parameters characterising senescence, i.e., contents of total soluble proteins, RuBPCO, and leaf nitrogen. At 9 DAF, there was a decline in total soluble proteins and an appearance of a 48 kDa cysteine protease. Characterisation of the proteases was done using specific inhibitors. Subcellular localisation at 3 DAF was studied by following the degradation of RuBPCO large subunit (LSU) in the vacuole lysates using immunoblot analyses. Cysteine proteases played a predominant role in the degradation of RuBPCO LSU at the crude extract level. At 9 DAF, expression of cysteine protease isoforms was monitored using polyclonal antibodies against papain and two polypeptides of molecular masses 48 and 35 kDa were observed in the vacuole lysates. We confirmed thus the predominance of cysteine proteases in the vacuoles during different stages of pod development in cowpea leaf.
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Vacuole Cysteine Proteases and Ribulose-1,5-Bisphosphate Carboxylase/Oxygenase Degradation during Monocarpic Senescence in Cowpea Leaves
Photosynthetica, 2001Co-Authors: B Srivalli, Sudhakar Bharti, Renu Khanna-chopraAbstract:Characterisation of proteases degrading ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO, EC: 4.1.1.39) was studied in the cowpea leaf during Monocarpic senescence 3 and 9 d after flowering (DAF), representing early and mid pod fill. The stage at 3 DAF coincided with decrease in the metabolic parameters characterising senescence, i.e., contents of total soluble proteins, RuBPCO, and leaf nitrogen. At 9 DAF, there was a decline in total soluble proteins and an appearance of a 48 kDa cysteine protease. Characterisation of the proteases was done using specific inhibitors. Subcellular localisation at 3 DAF was studied by following the degradation of RuBPCO large subunit (LSU) in the vacuole lysates using immunoblot analyses. Cysteine proteases played a predominant role in the degradation of RuBPCO LSU at the crude extract level. At 9 DAF, expression of cysteine protease isoforms was monitored using polyclonal antibodies against papain and two polypeptides of molecular masses 48 and 35 kDa were observed in the vacuole lysates. We confirmed thus the predominance of cysteine proteases in the vacuoles during different stages of pod development in cowpea leaf.
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effect of altering pod intensity on Monocarpic senescence in cowpea
1998Co-Authors: B Srivalli, Renu KhannachopraAbstract:Monocarpic senescence is a genetically programmed decline in physiological functions which are induced during fruit development following a single reproductive phase. Leaf senescence, is subject to regulation by many environmental and internal factors, where the internal factors include reproductive development (Gan and Amasino, 1997)1. In legumes, each reproductive node behaves as an independent unit, where the leaf at a particular reproductive node supports the fruits developing in its axil (Grover et al., 1985)2. In the present investigation, it has been examined whether (I) the regulation of sink strength on Monocarpic senescence is due to altered protease activity, using the in vivo substrate, Rubisco and a non-plant substrate, casein and (ii) the neutral protease activity has a role in nitrogen mobilisation or not. The results suggest that the reproductive sink regulates Monocarpic senescence, the removal of which delays it, also making the source leaf as a temporary carbohydrate reserve. These observations are related to the previously observed (Khanna-Chopra and Reddy, 1988)3 changes in leaf area, chlorophyll content and total soluble proteins.