Interactive Effects of Lateral Shading and Jasmonic Acid on Morphology, Phenology, Seed Production, and Defense Traits in Arabidopsis thaliana

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Plastic responses of plants to one factor may alter their response to others, placing limits on the benefits of phenotypic plasticity. To examine interactions between two phenotypically plastic responses, I studied the effects of lateral shading and jasmonic acid treatment of Arabidopsis thaliana rosettes on morphology, phenology, seed production, and chemical defense traits. Lateral shading was imposed by growing A. thaliana rosettes in pots equipped with opaque forest‐green plastic collars that disproportionately reduced lateral light availability relative to vertical light availability and altered light quality. Lateral shading greatly delayed flowering but increased leaf number, main stem height, and total seed production. Leaves of shaded plants were longer and had a lower blade‐to‐petiole length ratio than leaves of unshaded plants. Leaves of jasmonic acid–treated plants had a higher blade‐to‐petiole length ratio than leaves of untreated plants in both light environments but were shorter than leaves of untreated plants in shaded conditions only. Peroxidase activity in uninduced plants was similar in both light environments and was induced by jasmonic acid only in shaded plants. Trypsin inhibitor levels were lower overall in unshaded plants than in shaded plants, but their levels were inducible by jasmonic acid in both light environments. In turn, jasmonic acid treatment had an effect on seed production only in the shaded treatment, in which peroxidase activity and trypsin inhibitor reached high levels. Increases in seed production in shaded plants are probably the result of increased leaf production resulting from delayed flowering. Lateral shading and associated plant responses largely increased expression of the jasmonic acid–inducible defenses measured in this study. However, alterations in leaf length resulting from altered petiole and blade elongation are identified as a potentially important shade avoidance trait of A. thaliana that can be modified by jasmonic acid treatment.

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