Cooperation among unrelated individuals in social-dilemma-type situations is a key topic in social and biological sciences. It has been shown that, without suitable mechanisms, high levels of ...cooperation/contributions in repeated public goods games are not stable in the long run. Reputation, as a driver of indirect reciprocity, is often proposed as a mechanism that leads to cooperation. A simple and prominent reputation dynamic function through scoring: contributing behaviour increases one's score, non-contributing reduces it. Indeed, many experiments have established that scoring can sustain cooperation in two-player prisoner's dilemmas and donation games. However, these prior studies focused on pairwise interactions, with no experiment studying reputation mechanisms in more general group interactions. In this paper, we focus on groups and scores, proposing and testing several scoring rules that could apply to multi-player prisoners' dilemmas played in groups, which we test in a laboratory experiment. Results are unambiguously negative: we observe a steady decline of cooperation for every tested scoring mechanism. All scoring systems suffer from it in much the same way. We conclude that the positive results obtained by scoring in pairwise interactions do not apply to multi-player prisoner's dilemmas, and that alternative mechanisms are needed.
Research on polyamines (PAs) in plants laps a long way of about 50 years and many roles have been discovered for these aliphatic cations. PAs regulate cell division, differentiation, organogenesis, ...reproduction, dormancy-break and senescence, homeostatic adjustments in response to external stimuli and stresses. Nevertheless, the molecular mechanisms of their multiple activities are still matter of research. PAs are present in free and bound forms and interact with several important cell molecules; some of these interactions may occur by covalent linkages catalyzed by transglutaminase (TGase), giving rise to "cationization" or cross-links among specific proteins. Senescence and programmed cell death (PCD) can be delayed by PAs; in order to re-interpret some of these effects and to obtain new insights into their molecular mechanisms, their conjugation has been revised here. The TGase-mediated interactions between proteins and PAs are the main target of this review. After an introduction on the characteristics of this enzyme, on its catalysis and role in PCD in animals, the plant senescence and PCD models in which TGase has been studied, are presented: the corolla of naturally senescing or excised flowers, the leaves senescing, either excised or not, the pollen during self-incompatible pollination, the hypersensitive response and the tuber storage parenchyma during dormancy release. In all the models examined, TGase appears to be involved by a similar molecular mechanism as described during apoptosis in animal cells, even though several substrates are different. Its effect is probably related to the type of PCD, but mostly to the substrate to be modified in order to achieve the specific PCD program. As a cross-linker of PAs and proteins, TGase is an important factor involved in multiple, sometimes controversial, roles of PAs during senescence and PCD.
•The effects of different putrescine concentrations (0.05, 0.25, 0.5 and 2.5 mM) on pollen performance were analyzed.•Pollen germination and tube growth was induced by 0.05 and 0.25 mM while growth ...was inhibited by 0.5 and 2.5 mM putrescine.•Putrescine concentration above 0.25 mM caused callose accumulation and increased actin filament anisotropy at tube apex.•Putrescine concentration above 0.25 mM disrupted the detoxification mechanisms of reactive oxygen species.
One of the most substantial molecules for pollen germination and tube growth are polyamines. Putrescine is the most abundant polyamine and the molecule from which spermine and spermidine originate. In this study, the effects of different exogenous putrescine concentrations (0.05, 0.25, 0.5 and 2.5 mM) on pollen performance of hazelnut (Corylus avellana) were investigated. Germination ratio and tube length were induced by 0.05 and 0.25 mM putrescine treatment. Putrescine concentration above 0.25 mM inhibited the pollen germination, tube elongation and, caused morphological alterations such as apex swelling. While the 0.05 and 0.25 mM putrescine treatment did not cause significant change in callose accumulation and actin filament distribution at tube apex, concentrations above 0.25 mM caused dense callose accumulation and increased the actin filament anisotropy at tube apex. Moreover, putrescine treatment caused an increase of reactive oxygen species level at the apex, especially in swollen tube apex, at the concentration of 2.5 mM. Reactive oxygen species detoxification mechanisms, which can be examined by changes in the amount of hydrogen peroxide and enzyme activities, were not disrupted by 0.05 and 0.25 mM putrescine treatment, while they are affected by 0.5 and 2.5 mM putrescine treatment. Eventually, low doses (0.05 and 0.25 mM) of putrescine can be used as a performance enhancing agent for hazelnut pollen tube growth, while the higher concentrations (0.5 and 2.5 mM) cause adverse effects reducing fertilization success.
This review describes a 50-year-long research study on the characteristics of
L. tuber dormancy, its natural release and programmed cell death (PCD), as well as on the ability to change the PCD so as ...to return the tuber to a life program. The experimentation on the tuber over the years is due to its particular properties of being naturally deficient in polyamines (PAs) during dormancy and of immediately reacting to transplants by growing and synthesizing PAs. This review summarizes the research conducted in a unicum body. As in nature, the tuber tissue has to furnish its storage substances to grow vegetative buds, whereby its destiny is PCD. The review's main objective concerns data on PCD, the link with free and conjugated PAs and their capacity to switch the destiny of the tuber from a program of death to one of new life. PCD reversibility is an important biological challenge that is verified here but not reported in other experimental models. Important aspects of PA features are their capacity to change the cell functions from storage to meristematic ones and their involvement in amitosis and differentiation. Other roles reported here have also been confirmed in other plants. PAs exert multiple diverse roles, suggesting that they are not simply growth substances, as also further described in other plants.
The entire pollen life span is driven by polyamine (PA) homeostasis, achieved through fine regulation of their biosynthesis, oxidation, conjugation, compartmentalization, uptake, and release. The ...critical role of PAs, from microsporogenesis to pollen-pistil interaction during fertilization, is suggested by high and dynamic transcript levels of PA biosynthetic genes, as well as by the activities of the corresponding enzymes. Moreover, exogenous supply of PAs strongly affects pollen maturation and pollen tube elongation. A reduction of endogenous free PAs impacts pollen viability both in the early stages of pollen development and during fertilization. A number of studies have demonstrated that PAs largely function by modulating transcription, by structuring pollen cell wall, by modulating protein (mainly cytoskeletal) assembly as well as by modulating the level of reactive oxygen species. Both free low-molecular weight aliphatic PAs, and PAs conjugated to proteins and hydroxyl-cinnamic acids take part in these complex processes. Here, we review both historical and recent evidence regarding molecular events underlying the role of PAs during pollen development. In the concluding remarks, the outstanding issues and directions for future research that will further clarify our understanding of PA involvement during pollen life are outlined.
Pollen Tube and Plant Reproduction Cai, Giampiero; Del Duca, Stefano
International journal of molecular sciences,
01/2019, Letnik:
20, Številka:
3
Journal Article
Recenzirano
Odprti dostop
The pollen tube was a fundamental step forward in the evolution of terrestrial plants; in fact, it allowed plants to liberate themselves from water demand during reproduction ....
Although pollen structure and morphology evolved toward the optimization of stability and fertilization efficiency, its performance is affected by harsh environmental conditions, e.g., heat, cold, ...drought, pollutants, and other stressors. These phenomena are expected to increase in the coming years in relation to predicted environmental scenarios, contributing to a rapid increase in the interest of the scientific community in understanding the molecular and physiological responses implemented by male gametophyte to accomplish reproduction. Here, after a brief introduction summarizing the main events underlying pollen physiology with a focus on polyamine involvement in its development and germination, we review the main effects that environmental stresses can cause on pollen. We report the most relevant evidence in the literature underlying morphological, cytoskeletal, metabolic and signaling alterations involved in stress perception and response, focusing on the final stage of pollen life, i.e., from when it hydrates, to pollen tube growth and sperm cell transport, with these being the most sensitive to environmental changes. Finally, we hypothesize the molecular mechanisms through which polyamines, well-known molecules involved in plant development, stress response and adaptation, can exert a protective action against environmental stresses in pollen by decoding the essential steps and the intersection between polyamines and pollen tube growth mechanisms.
Ongoing global climate change suggests that crops will be exposed to environmental stresses that may affect their productivity, leading to possible global food shortages. Among these stresses, ...drought is the most important contributor to yield loss in global agriculture. Drought stress negatively affects various physiological, genetic, biochemical, and morphological characteristics of plants. Drought also causes pollen sterility and affects flower development, resulting in reduced seed production and fruit quality. Tomato (
L.) is one of the most economically important crops in different parts of the world, including the Mediterranean region, and it is known that drought limits crop productivity, with economic consequences. Many different tomato cultivars are currently cultivated, and they differ in terms of genetic, biochemical, and physiological traits; as such, they represent a reservoir of potential candidates for coping with drought stress. This review aims to summarize the contribution of specific physio-molecular traits to drought tolerance and how they vary among tomato cultivars. At the genetic and proteomic level, genes encoding osmotins, dehydrins, aquaporins, and MAP kinases seem to improve the drought tolerance of tomato varieties. Genes encoding ROS-scavenging enzymes and chaperone proteins are also critical. In addition, proteins involved in sucrose and CO
metabolism may increase tolerance. At the physiological level, plants improve drought tolerance by adjusting photosynthesis, modulating ABA, and pigment levels, and altering sugar metabolism. As a result, we underline that drought tolerance depends on the interaction of several mechanisms operating at different levels. Therefore, the selection of drought-tolerant cultivars must consider all these characteristics. In addition, we underline that cultivars may exhibit distinct, albeit overlapping, multilevel responses that allow differentiation of individual cultivars. Consequently, this review highlights the importance of tomato biodiversity for an efficient response to drought and for preserving fruit quality levels.
TGases (transglutaminases) are a class of calcium-dependent enzymes that catalyse the interactions between acyl acceptor glutamyl residues and amine donors, potentially making cross-links between ...proteins. To assess the activity of apple (Malus domestica) pollen TGase on the functional properties of actin and tubulin, TGase was prepared from apple pollen by hydrophobic- interaction chromatography and assayed on actin and tubulin purified from the same cell type. The enzyme catalysed the incorporation of putrescine into the cytoskeleton monomers. When tested on actin filaments, pollen TGase induced the formation of high-molecular-mass aggregates of actin. Use of fluorescein-cadaverine showed that the labelled polyamine was incorporated into actin by pollen TGase, similar to with guinea pig liver TGase. The pollen TGase also reduced the enzyme activity and the binding of myosin to TGase-treated actin filaments. Polymerization of tubulin in the presence of pollen TGase also yielded the formation of high-molecular-mass aggregates. Furthermore, the pollen TGase also affected the binding of kinesin to microtubules and reduced the motility of microtubules along kinesin-coated slides. These results indicate that the pollen TGase can control different properties of the pollen tube cytoskeleton (including the ability of actin and tubulin to assemble and their interaction with motor proteins) and consequently regulate the development of pollen tubes.
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