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  • 1
    ISSN: 1423-0445
    Keywords: Key words. defense allocation — hydroxamic acids — leaf age — optimal defense theory — rye —Secale cereale— Poaceae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary. The among-leaves allocation of DIBOA, a hydroxamic acid associated with plant resistance, in the shoot of rye (Secale cereale) was evaluated over the vegetative development of the plant. The appropriateness of using the concentration of secondary metabolites, DIBOA in this case, as the parameter to evaluate defense allocation in plants is discussed. Both biological and statistical arguments are put forward to suggest that allocation of chemical defenses should refer to absolute content and not to concentration. Results showed that leaf age was significantly linked to leaf concentration of DIBOA, young leaves having higher concentrations. In contrast, leaf content of DIBOA, our proposed currency of allocation, was not significantly higher in younger leaves. Furthermore, a regression analysis showed that the DIBOA content of leaves was better explained by the leaf relative biomass (proportion of shoot biomass) than by leaf biomass itself. It is suggested that, rather than leaf age, leaf relative biomass is the major factor determining DIBOA allocation in rye shoots. It is proposed that studies addressing within-plant defense allocation should use chemical defense content as the currency, emphasizing the major factors driving this process and its underlying mechanisms. Likewise, it is proposed that studies aiming at characterizing optimal patterns of plant defense should use chemical defense concentration as the currency, and be accompanied by evaluations of the actual resistance against herbivores of the plant parts analyzed, together with the effect on plant fitness.
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  • 2
    ISSN: 1423-0445
    Keywords: Key words. defense - induced defense - herbivory - aphids - Rhopalosiphum padi - wild wheat - Triticum uniaristatum - Poaceae - hydroxamic acids - costs of defense
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary. We characterized the induction of hydroxamic acids (Hx) by aphid infestation in the wild wheat Triticum uniaristatum by addressing the following questions: i) Do different leaves have similar responses to aphid damage?, ii) Is the Hx induction localized or systemic?, iii) How long does the induction last?, and iv) Is the degree of damage related to the magnitude of induced Hx? Based on earlier results on this wheat/aphid system (lack of costs of Hx induction) we expected to find the plant exhibiting cost-saving patterns of response to herbivory. Aphid infestation in the primary leaf led to induced levels of Hx, but no differences in Hx levels were found after infestation of the secondary leaf. Induction of Hx was restricted to the infested leaf (primary leaf). Induced Hx levels exhibited by the primary leaf at the end of aphid infestation were not observed 2 days later. Finally, different aphid densities (between 10 and 40 aphids per leaf) did not produce significant differences in Hx levels in infested primary leaves. Characteristics of Hx induction by aphid infestation in T. uniaristatum partially support the expected cost-saving patterns in the allocation of induced defenses.
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  • 3
    ISSN: 1573-5060
    Keywords: aphids ; cereal breeding ; DIBOA ; Diuraphis noxia ; hydroxamic acids ; pest resistance ; Poaceae ; Schizaphis graminum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract Hydroxamic acids are secondary metabolites typical of Poaceae that play a role in cereal resistance against pests and pathogens. The content of the hydroxamic acid aglucones DIBOA (2,4-dihydroxy-1,4-benzoxazin-3-one) and DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one) was evaluated in wild Poaceae belonging to the tribes Triticeae (genera Hordeum and Elymus) and Aveneae (genera Deschampsia and Phalaris). The concentration of DIBOA in seedling extracts of the wild barleys Hordeum chilense, H. brevisubulatum subsp. violaceum and H. bulbosum was negatively correlated with parameters related to performance of the cereal aphids Schizaphis graminum and Diuraphis noxia. The relevance of the results obtained for breeding programs aimed at increasing cereal resistance against aphids is discussed.
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  • 4
    ISSN: 1573-1561
    Keywords: Defoliation ; regrowth ; induced responses ; chemical defense ; hydroxamic acids ; rye ; Secale cereale ; Poaceae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The effect of defoliation and consecutive defoliation (condefoliation) of rye seedlings on the allocation patterns of biomass and hydroxamic acids (Hx) was evaluated five days after treatment. Growth of condefoliated seedlings was lower than that of defoliated and nondefoliated ones. Concentration of Hx decreased in shoots of condefoliated seedlings compared to nondefoliated ones, while concentration of Hx in root exudates increased. Allocation of Hx to roots and root exudates increased at the expense of allocation to the shoots in condefoliated seedlings. The ratio of Hx-aglucone to Hx-glucoside was higher in shoots of defoliated and condefoliated seedlings. The decrease in quantity of defense in shoots was accompanied by an increase in its quality, given that aglucones are more toxic than glucosides. The increase in concentration of Hx—an allelopathic compound also involved in mineral uptake by roots—in root exudates of condefoliated seedlings was suggested to lead to an advantage in the acquisition of resources for the regeneration of lost biomass.
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  • 5
    ISSN: 1573-1561
    Keywords: Temperature ; photoperiod ; hydroxamic acids ; growth ; defense ; secondary metabolites ; wheat ; Gramineae
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The effects of temperature and photoperiod on accumulation of hydroxamic acids (Hx) in wheat (Triticum aestivum L.) seedlings were evaluated under laboratory conditions. Hx concentrations were significantly higher at higher temperatures. No such clear trend was found for the photoperiod effect. The significant effect of temperature and photoperiod on growth rate of seedlings and the significant positive correlation between growth rate prior to analysis and levels of Hx, suggested that environmental effects on Hx accumulation were at least partially mediated through their effect on plant growth rate. After uncoupling the effect of environmental conditions from the effect of plant growth rate by statistical means the effect of temperature on Hx was no longer significant. Therefore, temperature effect was fully mediated by plant growth rate. Implications of the patterns found are discussed in issues of plant-defense general theories.
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  • 6
    ISSN: 1573-1561
    Keywords: Defense ; herbivory ; aphids ; wheat ; Gramineae ; hydroxamic acids ; Defense theory ; Carbon/Nutrient theory
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract Hydroxamic acids (Hx) are natural products of Gramineae that are associated with cereal resistance to pests. We aimed at characterizing the induction of Hx accumulation in seedlings of wheat,Triticum aestivum, by short-term infestation of the cereal aphid,Rhopalosiphum padi. A load of 25 aphids increased significantly the Hx levels in the infested primary leaf in comparison with control levels. Lower loads did not increase Hx concentration. Aphid infestation lasting 16 hr did not elicit induction of Hx, even after a time-lag of 32 hr to allow the expression of any induced response. Forty-eight hours was the minimum duration of aphid infestation required to trigger Hx induction. The age of the infested tissue (the primary leaf) did not affect induction. Similar increases of Hx were found in unfolding, expanding, and totally expanded primary leaves. It was determined that the regime of nutrient supply (N-intensive nutritive solutions at low and high concentration) to wheat seedlings had no effect on the magnitude of the aphid-induced Hx (N-based secondary metabolites). Results obtained are discussed in the framework of general theories of plant defense allocation.
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  • 7
    ISSN: 1570-7458
    Keywords: Rhopalosiphum padi ; cereal aphids ; wheat ; induced responses ; feeding site
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
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  • 8
    ISSN: 1432-1939
    Keywords: Temperature ; Growth ; Hydroxamic acids ; Herbivory ; Induced defences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The effects of temperature and photoperiod on the ability of wheat (Triticum aestivum L.) seedlings to show induced responses (increased accumulation of hydroxamic acids, Hx) upon infestation by the bird cherry-oat aphid, Rhopalosiphum padi L. were evaluated under laboratory conditions. Induction of Hx was significantly higher at lower temperatures. No such clear trend was found for the photoperiod effect. The significant effect of environmental conditions on growth rate of seedlings and the significant negative correlation between growth rate prior to infestation and induction of Hx suggested that environmental effects on induced responses were at least partially mediated through their effect on plant growth rate. After statistically uncoupling the effect of environmental conditions from the effect of plant growth rate, the effect of temperature on induction of Hx was no longer significant. Therefore, the temperature effect was mediated by plant growth rate.
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  • 9
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    Wiley
    In:  Annals of the New York Academy of Sciences, 1206 (1). pp. 35-55.
    Publication Date: 2016-08-22
    Description: Global change drivers create new environmental scenarios and selective pressures, affecting plant species in various interacting ways. Plants respond with changes in phenology, physiology, and reproduction, with consequences for biotic interactions and community composition. We review information on phenotypic plasticity, a primary means by which plants cope with global change scenarios, recommending promising approaches for investigating the evolution of plasticity and describing constraints to its evolution. We discuss the important but largely ignored role of phenotypic plasticity in range shifts and review the extensive literature on invasive species as models of evolutionary change in novel environments. Plasticity can play a role both in the short-term response of plant populations to global change as well as in their long-term fate through the maintenance of genetic variation. In new environmental conditions, plasticity of certain functional traits may be beneficial (i.e., the plastic response is accompanied by a fitness advantage) and thus selected for. Plasticity can also be relevant in the establishment and persistence of plants in novel environments that are crucial for populations at the colonizing edge in range shifts induced by climate change. Experimental studies show taxonomically widespread plastic responses to global change drivers in many functional traits, though there is a lack of empirical support for many theoretical models on the evolution of phenotypic plasticity. Future studies should assess the adaptive value and evolutionary potential of plasticity under complex, realistic global change scenarios. Promising tools include resurrection protocols and artificial selection experiments.
    Type: Article , PeerReviewed
    Format: text
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  • 10
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