The Experts below are selected from a list of 2199 Experts worldwide ranked by ideXlab platform
Norman W. Pammenter - One of the best experts on this subject based on the ideXlab platform.
-
Towards understanding the incidence and evolutionary history of Seed recalcitrance: An analytical review
Perspectives in Plant Ecology Evolution and Systematics, 2019Co-Authors: Ashley Subbiah, Norman W. Pammenter, Syd Ramdhani, Angus H. H. Macdonald, SershenAbstract:Abstract This analytical review builds on previous descriptions of the Recalcitrant Seed trait’s taxonomic and phylogenetic coverage and provides new insights into the Recalcitrant Seed trait’s apomorphic or plesiomorphic character state, transition rates and residence time in relation to Earth’s geological history. A comprehensive global list of Recalcitrant-Seeded species (RSS) was compiled to assess taxonomic and phylogenetic coverage. Plesiomorphic character state (orthodox or Recalcitrant) was established via a comparison of the species stem ages of RSS and orthodox-Seeded species (OSS) within specific lineages. Using a previously published tree, frequency by which transitions between OSS and RSS occur and the average time spent in each state was calculated. The Recalcitrant Seed trait occurred in 721 species, 297 genera and 84 families, with 92% of RSS being tropical phanerophytes. The Recalcitrant Seed trait was apomorphic in numerous extant lineages, with the earliest representative species appearing in the late Cretaceous. The ratio of RSS to OSS divergence changes from favouring recalcitrance in the late Cretaceous, to the Eocene, when it favoured orthodoxy, reaching the highest difference in the Pleistocene and abating in the Holocene. Transition rates from the orthodox to the Recalcitrant state were lower than vice versa. The average time RSS spent in the Recalcitrant state is considerably shorter than that spent by OSS in the orthodox state. Recalcitrance is more likely a consequence of gradual adaptation and taxa appear to be more likely to transition from Recalcitrant to orthodox than the reverse. By occurring in relatively warm and wet environments, RSS need not invest in desiccation tolerance mechanisms, constituting a metabolic ‘saving’. However, some RSS persist in arid and temperate regions, and have arisen during and survived periods associated with major climatic changes. This, together with their representation in numerous ancient lineages, suggests that RSS are ‘evolutionary survivors’.
-
A comparison of partial dehydration and hydrated storage-induced changes in viability, reactive oxygen species production, and glutathione metabolism in two contrasting Recalcitrant-Seeded species
Acta Physiologiae Plantarum, 2017Co-Authors: Anushka Moothoo-padayachie, Norman W. Pammenter, Babu Varghese, Patrick GovenderAbstract:This study compared the responses of Avicennia marina and Trichilia dregeana Seeds, both of which are Recalcitrant, to partial dehydration and storage. Seeds of A. marina exhibited a faster rate of water and viability loss (± 50% viability loss in 4 days) during partial dehydration, compared with T. dregeana (± 50% viability loss in 14 days). In A. marina embryonic axes, reactive oxygen species (ROS) production peaked on 4 days of dehydration and was accompanied by an increase in the GSH:GSSG ratio; it appears that the glutathione system alone could not overcome dehydration-induced oxidative stress in this species. In A. marina, ROS and axis water content levels increased during hydrated storage and were accompanied by a decline in the GSH:GSSG ratio and rapid viability loss. In T. dregeana embryonic axes, ROS production (particularly hydrogen peroxide) initially increased and thereafter decreased during both partial dehydration and hydrated storage. Unlike in A. marina embryonic axes, this reduced ROS production was accompanied by a decline in the GSH:GSSG ratio. While T. dregeana Seeds may have incurred some oxidative stress during storage, a delay in and/or suppression of the ROS-based trigger for germination may account for their significantly longer storage longevity compared with A. marina. Mechanisms of desiccation-induced Seed viability loss may differ across Recalcitrant-Seeded species based on the rate and extent to which they lose water during partial drying and storage. While Recalcitrant Seed desiccation sensitivity and, by implication, storage longevity are modulated by redox metabolism, the specific ROS and antioxidants that contribute to this control may differ across species.
-
different assessments of the effect of drying rates on Recalcitrant Seed material
American Journal of Biology and Life Sciences, 2015Co-Authors: Tobias M Ntuli, Patricia Berjak, Norman W. PammenterAbstract:The results of the germination and tetrazolium (TZ) tests of axes of Pisum sativum, Quercus robur and Trichilia dregeana were in agreement during both drying and wet storage. The TZ test overestimated viability of Avicennia marina, Trichilia emetica and Strychnos madagascariensis axes in comparison to the germination test during dehydration. Thus, the germination test is a method of choice during desiccation and the TZ test may be a better indicator of viability during hydrated storage than drying. The survival of axes of Q. robur during slow dehydration and moist storage was unexpectedly poor possibly as a result of an unfavourable temperature during treatments. Hence, rapid desiccation is recommended for determinations of minimum ‘critical water contents’. The relationship between electrolyte leakage and water content during drying and wet storage of axes of T. dregeana harvested in 2001 and S. madagascariensis showed a ‘classic pattern’ as dehydration and hydrated storage proceeded. Consequently, the conductivity test is a poor measure of the ‘critical water contents’ but may be an indicator of differences in vigour among harvests of the same species along with the germination and TZ tests during slow desiccation. Less leakage occurred during rapid than slow drying in all species. Desiccation-sensitive Seeds can be divided into three categories on the basis of the predominant mechanism of loss of viability during dehydration: minimally, moderately and highly desiccation-sensitive in which desiccation, metabolic and physical damage predominate, respectively. Irrespective of the mode of dying, the effect of rate drying of was always apparent.
-
from avicennia to zizania Seed recalcitrance in perspective
Annals of Botany, 2007Co-Authors: Patricia Berjak, Norman W. PammenterAbstract:† Background Considered only in terms of tolerance of, or sensitivity to, desiccation (which is an oversimplification), orthodox Seeds are those which tolerate dehydration and are storable in this condition, while highly Recalcitrant Seeds are damaged by loss of only a small proportion of water and are unstorable for practical purposes. Between these extremes, however, there may be a gradation of the responses to dehydration ‐ and also to other factors ‐ suggesting perhapsthat Seedbehaviourmightbebestconsideredasconstitutingacontinuumsubtendedbyextremeorthodoxyand the highest degree of recalcitrance. As the characteristics of Seeds of an increasing number of species are elucidated, non-orthodoxSeed behaviourisemerging asconsiderably more commonplace ‐ andits basisfarmore complex ‐ than previously suspected. † Scope Whatever the post-harvest responses of Seeds of individual species may be, they are the outcome of the properties of pre-shedding development, and a full understanding of the subtleties of various degrees of nonorthodox behaviour must await the identification of, and interaction among, all the factors conferring extreme orthodoxy. Appreciation of the phenomenon of recalcitrance is confounded by intra- and interseasonal variability across species, as well as within individual species. However, recent evidence suggests that provenance is a pivotal factor in determining the degree of Recalcitrant behaviour exhibited by Seeds of individual species. Non-orthodox ‐ and, in particular, Recalcitrant ‐ Seed behaviour is not merely a matter of desiccation sensitivity: the primary basis is that the Seeds are actively metabolic when they are shed, in contrast to orthodox types which are quiescent. This affects all aspects of the handling and storage of Recalcitrant Seeds. In the short to medium term, Recalcitrant Seeds should be stored in as hydrated a condition as when they are shed, and at the lowest temperature not diminishing vigour or viability. Such hydrated storage has attendant problems of fungal proliferation which, unless minimized, will inevitably and significantly affect Seed quality. The life span of Seeds in hydrated storage even under the best conditions is variable among species, but is curtailed (days to months), and various approaches attempting to extend non-orthodox Seed longevity are discussed. Conservation of the genetic resources by means other than Seed storage is then briefly considered, with detail on the potential for, and difficulties with, cryostorage highlighted. † Conclusions There appears to be little taxonomic relationship among species exhibiting the phenomenon of Seed recalcitrance, suggesting that it is a derived trait, with tolerance having been lost a number of times. Although Recalcitrant Seededness is best represented in the mesic tropics, particularly among rainforest climax species, it does occur in cooler, drier and markedly seasonal habitats. The selective advantages of the trait are considered.
-
The influence of rehydration technique on the response of Recalcitrant Seed embryos to desiccation
Seed Science Research, 2004Co-Authors: Rosa Peran, Norman W. Pammenter, Janine Naicker, Patricia BerjakAbstract:The concept of ‘imbibitional damage’ arose when it was observed that considerable leakage of cell contents could occur when dry Seed or pollen tissues are plunged directly into water. It is now common practice to imbibe dehydrated tissue slowly, to permit the re-establishment of functional membranes, prior to placing the tissue into liquid water. However, this argument may not hold if the tissue of interest is inherently desiccation-sensitive. Slow drying of desiccation-sensitive (Recalcitrant) Seeds or excised embryonic axes results in damage at high water contents, because it permits time for aqueous-based deleterious processes to occur. The same argument may apply if partially dried material is re-imbibed slowly, as this technique will also expose the tissue to intermediate water contents for protracted periods. This hypothesis was tested using embryos or axes from Seeds of three Recalcitrant species ( Artocarpus heterophyllus , Podocarpus henkelii and Ekebergia capensis ). Excised material was rapidly dried to water contents within the range over which viability is lost during drying, and re-imbibed either rapidly, by plunging directly into water, or slowly, by placing the material on damp filter paper or exposing it to a saturated atmosphere for several hours. Although details of the response differed among species and developmental stage, in all cases direct re-imbibition in water resulted in higher (or similar, but never lower) survival than either of the slow rehydration techniques.
Patricia Berjak - One of the best experts on this subject based on the ideXlab platform.
-
different assessments of the effect of drying rates on Recalcitrant Seed material
American Journal of Biology and Life Sciences, 2015Co-Authors: Tobias M Ntuli, Patricia Berjak, Norman W. PammenterAbstract:The results of the germination and tetrazolium (TZ) tests of axes of Pisum sativum, Quercus robur and Trichilia dregeana were in agreement during both drying and wet storage. The TZ test overestimated viability of Avicennia marina, Trichilia emetica and Strychnos madagascariensis axes in comparison to the germination test during dehydration. Thus, the germination test is a method of choice during desiccation and the TZ test may be a better indicator of viability during hydrated storage than drying. The survival of axes of Q. robur during slow dehydration and moist storage was unexpectedly poor possibly as a result of an unfavourable temperature during treatments. Hence, rapid desiccation is recommended for determinations of minimum ‘critical water contents’. The relationship between electrolyte leakage and water content during drying and wet storage of axes of T. dregeana harvested in 2001 and S. madagascariensis showed a ‘classic pattern’ as dehydration and hydrated storage proceeded. Consequently, the conductivity test is a poor measure of the ‘critical water contents’ but may be an indicator of differences in vigour among harvests of the same species along with the germination and TZ tests during slow desiccation. Less leakage occurred during rapid than slow drying in all species. Desiccation-sensitive Seeds can be divided into three categories on the basis of the predominant mechanism of loss of viability during dehydration: minimally, moderately and highly desiccation-sensitive in which desiccation, metabolic and physical damage predominate, respectively. Irrespective of the mode of dying, the effect of rate drying of was always apparent.
-
from avicennia to zizania Seed recalcitrance in perspective
Annals of Botany, 2007Co-Authors: Patricia Berjak, Norman W. PammenterAbstract:† Background Considered only in terms of tolerance of, or sensitivity to, desiccation (which is an oversimplification), orthodox Seeds are those which tolerate dehydration and are storable in this condition, while highly Recalcitrant Seeds are damaged by loss of only a small proportion of water and are unstorable for practical purposes. Between these extremes, however, there may be a gradation of the responses to dehydration ‐ and also to other factors ‐ suggesting perhapsthat Seedbehaviourmightbebestconsideredasconstitutingacontinuumsubtendedbyextremeorthodoxyand the highest degree of recalcitrance. As the characteristics of Seeds of an increasing number of species are elucidated, non-orthodoxSeed behaviourisemerging asconsiderably more commonplace ‐ andits basisfarmore complex ‐ than previously suspected. † Scope Whatever the post-harvest responses of Seeds of individual species may be, they are the outcome of the properties of pre-shedding development, and a full understanding of the subtleties of various degrees of nonorthodox behaviour must await the identification of, and interaction among, all the factors conferring extreme orthodoxy. Appreciation of the phenomenon of recalcitrance is confounded by intra- and interseasonal variability across species, as well as within individual species. However, recent evidence suggests that provenance is a pivotal factor in determining the degree of Recalcitrant behaviour exhibited by Seeds of individual species. Non-orthodox ‐ and, in particular, Recalcitrant ‐ Seed behaviour is not merely a matter of desiccation sensitivity: the primary basis is that the Seeds are actively metabolic when they are shed, in contrast to orthodox types which are quiescent. This affects all aspects of the handling and storage of Recalcitrant Seeds. In the short to medium term, Recalcitrant Seeds should be stored in as hydrated a condition as when they are shed, and at the lowest temperature not diminishing vigour or viability. Such hydrated storage has attendant problems of fungal proliferation which, unless minimized, will inevitably and significantly affect Seed quality. The life span of Seeds in hydrated storage even under the best conditions is variable among species, but is curtailed (days to months), and various approaches attempting to extend non-orthodox Seed longevity are discussed. Conservation of the genetic resources by means other than Seed storage is then briefly considered, with detail on the potential for, and difficulties with, cryostorage highlighted. † Conclusions There appears to be little taxonomic relationship among species exhibiting the phenomenon of Seed recalcitrance, suggesting that it is a derived trait, with tolerance having been lost a number of times. Although Recalcitrant Seededness is best represented in the mesic tropics, particularly among rainforest climax species, it does occur in cooler, drier and markedly seasonal habitats. The selective advantages of the trait are considered.
-
The influence of rehydration technique on the response of Recalcitrant Seed embryos to desiccation
Seed Science Research, 2004Co-Authors: Rosa Peran, Norman W. Pammenter, Janine Naicker, Patricia BerjakAbstract:The concept of ‘imbibitional damage’ arose when it was observed that considerable leakage of cell contents could occur when dry Seed or pollen tissues are plunged directly into water. It is now common practice to imbibe dehydrated tissue slowly, to permit the re-establishment of functional membranes, prior to placing the tissue into liquid water. However, this argument may not hold if the tissue of interest is inherently desiccation-sensitive. Slow drying of desiccation-sensitive (Recalcitrant) Seeds or excised embryonic axes results in damage at high water contents, because it permits time for aqueous-based deleterious processes to occur. The same argument may apply if partially dried material is re-imbibed slowly, as this technique will also expose the tissue to intermediate water contents for protracted periods. This hypothesis was tested using embryos or axes from Seeds of three Recalcitrant species ( Artocarpus heterophyllus , Podocarpus henkelii and Ekebergia capensis ). Excised material was rapidly dried to water contents within the range over which viability is lost during drying, and re-imbibed either rapidly, by plunging directly into water, or slowly, by placing the material on damp filter paper or exposing it to a saturated atmosphere for several hours. Although details of the response differed among species and developmental stage, in all cases direct re-imbibition in water resulted in higher (or similar, but never lower) survival than either of the slow rehydration techniques.
-
Evolutionary and ecological aspects of Recalcitrant Seed biology
Seed Science Research, 2000Co-Authors: Norman W. Pammenter, Patricia BerjakAbstract:There is a substantial literature on the basic physiology and response to desiccation of Recalcitrant Seeds, but little is known about their ecology and even less of their evolutionary status. It is difficult to assess the response of early land plants to dehydration, but it is likely that desiccation tolerance in vegetative tissue arose concomitantly with the invasion of the land. Similarly, from the fossil record it is not possible to assess the desiccation response of early Seeds, and furthermore, it is difficult to see phylogenetic relationships among species producing Recalcitrant Seeds. A consideration of the available evidence, however, suggests that the first Seeds were desiccation-sensitive, but tolerance evolved early and probably a number of times, independently. The desiccation sensitivity and short life span (generally shorter than the interval between flowering) of Recalcitrant Seeds have implications in terms of regeneration ecology. A long-term soil Seed bank as such does not exist; rather the Seeds germinate and form a Seedling bank. However, there is a wide range in post-shedding physiology among Recalcitrant Seed species, and although species producing Recalcitrant Seeds are common in the humid tropics, they do occur in habitats with more marked seasonal variation. Here regeneration strategies may be more specialized.
-
Some thoughts on the evolution and ecology of Recalcitrant Seeds.
Plant Species Biology, 2000Co-Authors: Norman W. Pammenter, Patricia BerjakAbstract:There are substantial scientific reports on the basic physiology and desiccation sensitivity of Recalcitrant Seeds, but ecological and evolutionary aspects of their biology have received scant attention. Recalcitrant Seeds are shed hydrated, are desiccation sensitive and have a short lifespan. In vegetative tissue, desiccation sensitivity is probably the ancestral state, but tolerance is thought to have evolved early and a number of times independently. It is difficult to see evolutionary relationships among species producing Recalcitrant Seeds. However, it is suggested that early evolved Seeds were desiccation sensitive and that desiccation tolerance is a derived characteristic. Desiccation sensitivity and short lifespan of Recalcitrant Seeds places constraints on the range of environmental conditions in which reproductive success can occur. Species producing Recalcitrant Seeds are common in humid tropical forests, where the Seeds of climax species germinate and form a Seedling bank, rather than contributing to the soil Seed bank. However, there is a wide range in post-shedding physiology among Recalcitrant Seed species, and Recalcitrant Seeds do occur in habitats with seasonal climates. Here, regeneration strategies may be more specialized.
Ewa Marzena Kalemba - One of the best experts on this subject based on the ideXlab platform.
-
the occurrence of peroxiredoxins and changes in redox state in acer platanoides and acer pseudoplatanus during Seed development
Journal of Plant Growth Regulation, 2019Co-Authors: Ewelina Ratajczak, Karljosef Dietz, Ewa Marzena KalembaAbstract:Norway maple (Acer platanoides L.) and sycamore (A. pseudoplatanus L.) are genetically closely related species that produce desiccation-tolerant (orthodox) and desiccation-sensitive (Recalcitrant) Seeds, respectively. Norway maple and sycamore Seeds were analyzed during their development from the 14th to 24th weeks after flowering (WAF) and 11th to 21st WAF, respectively, to explore redox-related biochemical properties related to their contrasting physiology. Selected similar stages of Seed development were characterized during the course of gradual decreasing water content in both Seed types. The levels of protein and non-protein thiols peaked at the 18th WAF in Norway maple embryonic axes, whereas these levels constantly increased in maturing sycamore Seeds. The glutathione half-cell reduction potential revealed that the cell environment adopted a more oxidized state in sycamore Seeds. Peroxiredoxins (Prxs), including cytosolic/nuclear 1-Cys-Prx, cytosolic PrxIIC, mitochondrial PrxIIE, and plastidic PrxIIF, 2-Cys-Prx, and PrxQ, were detected in both species, but Norway maple embryonic axes contained higher levels of PrxIIC and PrxIIE, two Prxs with the highest peroxide detoxification potential in Arabidopsis. Redox proteomics revealed that 2-Cys-Prx was present in reduced form in both species, whereas 1-Cys-Prx was reduced uniquely in Norway maple Seeds. Several enzymes, including glucose and ribitol dehydrogenase as well as fructose-bisphosphate aldolase, were oxidation-sensitive at all developmental stages in sycamore embryonic axes. Redox signaling as manifested by reactive oxygen species signals, and the oxidation of protein thiols to disulfides are discussed with respect to their significance in determining orthodox or Recalcitrant Seed characteristics.
Ewelina Ratajczak - One of the best experts on this subject based on the ideXlab platform.
-
the occurrence of peroxiredoxins and changes in redox state in acer platanoides and acer pseudoplatanus during Seed development
Journal of Plant Growth Regulation, 2019Co-Authors: Ewelina Ratajczak, Karljosef Dietz, Ewa Marzena KalembaAbstract:Norway maple (Acer platanoides L.) and sycamore (A. pseudoplatanus L.) are genetically closely related species that produce desiccation-tolerant (orthodox) and desiccation-sensitive (Recalcitrant) Seeds, respectively. Norway maple and sycamore Seeds were analyzed during their development from the 14th to 24th weeks after flowering (WAF) and 11th to 21st WAF, respectively, to explore redox-related biochemical properties related to their contrasting physiology. Selected similar stages of Seed development were characterized during the course of gradual decreasing water content in both Seed types. The levels of protein and non-protein thiols peaked at the 18th WAF in Norway maple embryonic axes, whereas these levels constantly increased in maturing sycamore Seeds. The glutathione half-cell reduction potential revealed that the cell environment adopted a more oxidized state in sycamore Seeds. Peroxiredoxins (Prxs), including cytosolic/nuclear 1-Cys-Prx, cytosolic PrxIIC, mitochondrial PrxIIE, and plastidic PrxIIF, 2-Cys-Prx, and PrxQ, were detected in both species, but Norway maple embryonic axes contained higher levels of PrxIIC and PrxIIE, two Prxs with the highest peroxide detoxification potential in Arabidopsis. Redox proteomics revealed that 2-Cys-Prx was present in reduced form in both species, whereas 1-Cys-Prx was reduced uniquely in Norway maple Seeds. Several enzymes, including glucose and ribitol dehydrogenase as well as fructose-bisphosphate aldolase, were oxidation-sensitive at all developmental stages in sycamore embryonic axes. Redox signaling as manifested by reactive oxygen species signals, and the oxidation of protein thiols to disulfides are discussed with respect to their significance in determining orthodox or Recalcitrant Seed characteristics.
Qi Chen - One of the best experts on this subject based on the ideXlab platform.
-
proteomic profiling and redox status alteration of Recalcitrant tea camellia sinensis Seed in response to desiccation
Planta, 2011Co-Authors: Qi Chen, Liming Yang, Parvaiz Ahmad, Xiaochun WanAbstract:Tea Seed is believed to be Recalcitrant based on its sensitivity to chilling or drying stress. Reactive oxygen species (ROS) and alterations in cytosolic redox status have been implicated in intolerance to desiccation by Recalcitrant Seed, but there is little information available regarding how ROS are regulated in Seeds susceptible to drying stress. We investigated changes in protein expression and activity in tea embryo in response to desiccation using physiological and proteomic methods. Results showed that desiccation treatment dramatically induced the accumulation of H2O2 in tea embryos, accompanied by increased activities of antioxidant enzymes like ascorbate peroxidase (APX) and superoxide dismutase (SOD). Proteomic analyses also demonstrated that 23 proteins associated with defense response, metabolism and redox status were up-regulated following desiccation. Increase in antioxidants, ascorbic acid (AsA) and catalase (CAT) (H2O2 scavengers) partially assuaged desiccation damage to tea Seed, resulting in improved germination rates. Higher accumulation of H2O2 aggravated desiccation damage to Seeds leading to lower germination activity. We propose that desiccation causes an over-accumulation of ROS that are not efficiently scavenged by increased levels of antioxidant enzymes. High levels of ROS alter the redox status and are detrimental to Seed viability. Reducing ROS to appropriate concentrations is an efficient way to reduce desiccation damage and improve germination rates of Recalcitrant Seeds.
