Water Stress Increases Alkaloid Concentrations in Threadleaf Groundsel (<i>Senecio longilobus</i>)

Briske, David D.; Camp, Bennie J.

doi:10.1017/s0043174500026278

Cited by 47 publications

(18 citation statements)

References 13 publications

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“…The effects of latex and foliar cardenolides under drought may be due both to induced physiological processes as well as the reduced biomass of drought-stressed plants; the latter being relevant to the fact that we measure cardenolides as a concentration on a dry mass basis, and that larger plants typically exude more latex. Across other systems, plant defense compounds often increase in response to drought, but water content often declines (Briske andCamp 1982, English-Loeb et al 1997). Accordingly, our results with milkweed may reflect the general pattern of increased secondary metabolite concentrations under drought, but the reduced latex may simply depend on water availability.…”

Section: Resultsmentioning

confidence: 99%

Tests of the coupled expression of latex and cardenolide plant defense in common milkweed (Asclepias syriaca)

2014

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Abstract. The coexpression of plant resistance traits suggests the hypothesis that they may have complementary functions in defense against herbivory. To address the extent to which defensive traits are necessarily coupled in plants grown under various conditions, we focused on latex and cardenolides, two potent defenses of milkweeds. We measured defenses across ontogenetic stages, different biotic and abiotic environments, and across genetic families of the common milkweed Asclepias syriaca. We first addressed the extent to which foliar cardenolides are derived from latex because latex actively flows through canals in leaves. We rinsed latex out of shredded leaves, which had no impact on foliar cardenolides, suggesting cardenolides are allocated to leaves independently of latex. Accordingly, there is potential for independent expression of the two traits. We next followed a cohort of plants from germination over three years; expression of both latex exudation and cardenolides increased annually, with the exception of a second year dip in cardenolides. Damage by monarch caterpillars induced '50% increases of both latex and cardenolides, with the former occurring rapidly within a day and the latter taking five days of herbivory; these responses were preceded by an earlier peak of the signaling hormones jasmonic acid and abscisic acid. Endogenous jasmonic acid showed an instantaneous positive correlation with latex exudation and foliar cardenolides. Under drought stress, latex and cardenolide expression were reversed, with water stress suppressing latex exudation, but nearly doubling cardenolide concentrations. These drought effects were not driven by phytohormones in the expected manner, as jasmonic acid was unaffected, salicylic acid was strongly suppressed, and abscisic acid tripled in response to drought. Finally, a meta-analysis of four previously published field studies representing 85 genetic families of A. syriaca revealed no evidence for a genetic correlation between latex exudation and foliar cardenolide concentrations. The same lack of a correlation was observed across 22 populations of A. syriaca when grown in a common environment. Thus, the two most important defensive traits of milkweeds, although often coexpressed, can become uncoupled during some ontogenetic stages, under some biotic and abiotic conditions, and there is no evidence that they evolve together.

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Section: Resultsmentioning

confidence: 99%

Tests of the coupled expression of latex and cardenolide plant defense in common milkweed (Asclepias syriaca)

2014

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“…a/. , 1977 and alkaloids in particular (Marten & Frelich 1977;Majak et al 1979;Briske & Camp 1982), the PA content of H. europaeum declined independently of rainfall and plant growth through the growing season (Table 2; Fig. 4).…”

Section: Discussionmentioning

confidence: 95%

Seasonal dynamics in the pyrrolizidine alkaloids of Heliotropium europaeum

O'Dowd

Edgar

1989

Australian Journal of Ecology

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lasiocarpine and curopine differ markedly in their toxic properties, large shifts in their relative coneentrations may have important eonsequenees for ihese and other herbivores. Environmentally induced quality shifts in these secondary compounds may be as important as, or even override, changes in total quantity in causing PA toxieity to grazing animals. AbstractAn analysis ofthe pyrrolizidine alkaloids (PA) of the introduced annual weed, Heliotropium europaeum (Boraginaeeae), at two sites in south-eastern Australia showed that percentage PA in above-ground parts of the weed differed significantly between sites and declined markedly through the season, from initial levels of >2.2% in the seedling stage to <0.5% prior to senescence. N-oxide forms of PA predominated at both sites, averaging >95% of total alkaloid. Major PA constituentseuropine, heliotrine, and lasiocarpine-varied significantly between sites and sampling dates but no marked seasonal trend was detected. Lasiocarpine and europine content varied reciprocally in the free base and 'N-oxideforms, indicating that these compounds may be readily interconvertible. Correlation of rainfall and average number of leaves per plant with lasiocarpine and europine levels suggested that rainfall, either directly by altering the metabolism of existing leaves or indirectly through plant growth, initiated large short-term shifts in PA composition of H. europaeum without corresponding changes in total PA concentration.At both sites, sheep consumedH. europaeum. reducing both plant density and biomass. Biomass differences between exclosure and access plots of H. europaeum were correlated with grazing intensity. Since heliotrine,

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“…So far, it is not clear what type and combination of environmental factors alters PA concentration in different Senecio species. In some studies nutrient availability and water stress were shown to affect alkaloid concentration, while in others no such interactions were found (Briske & Camp, 1982;Toppel et al, 1988;Vrieling and van Wijk, 1994;Brown & Molyneux, 1996).…”

Section: Discussionmentioning

confidence: 99%

Pyrrolizidine alkaloid content in Senecio : ontogeny and developmental constraints

2003

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The ontogeny of pyrrolizidine alkaloid (PA) synthesis and constraints on defence level during the seedling stage were examined in the annual Senecio vulgaris and the monocarpic perennial Senecio jacobaea. In both species, PAs were actively synthesized from the onset of seedling growth so that juvenile stages did not go through an undefended stage. Roots are known to be the exclusive sites where PAs are produced. Root biomass was the single most important biomass parameter explaining variation in total PAs per seedling. All correlation coefficients between relative growth rate and PA concentration were negative, but none was significant. However, a significant negative correlation was found between shoot to root ratio and PA concentration in S. jacobaea seedlings, suggesting a dilution effect of the PAs. Earlier studies have shown that the shoot to root ratio is positively correlated with relative growth rate of established S. jacobaea plants. It is therefore suggested that young S. jacobaea plants with a high shoot to root ratio and hence a high growth capacity necessarily have lower PA defence levels than plants with a low shoot to root ratio.

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Water Stress Increases Alkaloid Concentrations in Threadleaf Groundsel (Senecio longilobus)

Cited by 47 publications

References 13 publications

Tests of the coupled expression of latex and cardenolide plant defense in common milkweed (Asclepias syriaca)

Tests of the coupled expression of latex and cardenolide plant defense in common milkweed (Asclepias syriaca)

Seasonal dynamics in the pyrrolizidine alkaloids of Heliotropium europaeum

Pyrrolizidine alkaloid content in Senecio : ontogeny and developmental constraints

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