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Optimal defense in pine trees: constitutive and induced allocation of resin and
polyphenolics in Pinus radiata
Moreira X.1, Hernández A.1, Sampedro L.1 and Zas R.2
1
Centro de Investigación e Información Ambiental de Lourizán. Apdo. 127. E-36080
Pontevedra, Spain.
2
Misión Biológica de Galicia (CSIC). Apdo. 28. E-36080 Pontevedra, Spain.
Optimal defense theory is based on the assumption that the within-plant allocation of
defensive secondary metabolites is driven by the relative contribution to the overall
fitness of particular plant tissues and their value in terms of costs. In this study, we
examined the constitutive and induced strategy of optimal allocation of the two major
conifer defenses, resin and polyphenolics, to two tissues with contrasting fitness value,
stem and needles. We hypothesized that the upper meristematic tissues supporting
primary growth should be the better defended, but definitive adult basal needles could
be more defended than primary needles. We grew 72 Pinus radiata Don. seedlings
during two years under greenhouse, half of them were treated with methyl jasmonate
(80 mM MeJa in Tween 0.1%) to induce chemical defenses, leaving the other half as
controls (treated only with Tween 0.1%)for studying constitutive defences. We analyzed
the quantitative defensive chemistry in needles and stem, along three parts of the plants
(basal, medium and upper apical part).
We found that phenolics are major defensive compounds in needles, while resin
based defences appeared relevant both in stem and needles. We observed a marked
gradient of allocation within the plant, with different patterns between basal, medium
and apical tissues of the pines. Resin content in the stem tissues was greater along an
upward gradient. However, in leave tissues, both resin and phenolics content became
greater along a downwards gradient. Stem phenolics were scarce relative to leaves and
did not show significant changes within the plant.
Interestingly, induced responses of pine trees to MeJa were based on increased
concentrations of total phenolics in leaves and resin compounds in the stem, but not
significant changes were observed for phenolics in phloem either resin in needles.
Induced rising concentrations of those compounds were not accompanied bychanges in
their allocation patterns (not significant MeJa x part interaction).
Our results indicate a marked pattern of allocation of defenses along the plant and
among tissues relevant for plant fitness, which constitute the first report for pine trees.
Our observations escalate the Optimal Defense Theory to long lived plants, which look
for optimality in their secondary chemistry allocation since the crucial very first
developmental stages of their ontogeny.