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In observing chaparral species’ resistance to abiotic plant stresses, this investigation sought to study plant defense against UVA radiation in sun and shade leaves. We predicted that sun leaves would have higher absorbance of UV radiation considering their day-long exposure to sunlight.

UVA (350nm-400nm) absorbance in sun and shade leaves of Heteromeles arbutifolia and Malosma laurina were measured using an integrating sphere. Four leaves from each group were surveyed for reflectance and absorbance. Using the spectrophotometer, reflectance in the green wavelengths (500-600nm) was measured and divided by reflectance in the red (600-700nm) to give a quantitative estimation of the redness of the samples and thus the anthocyanin content. Samples were cross-sectioned and examined under the microscope to measure cuticle size and determine location of anthocyanin pigments.

There showed no correlation between either cuticle thickness or amount of red pigmentation and absorbance in the UVA spectrum (R2<.90), nor were the sun leaves of either species H.arbutifolia and M.laurina significantly better at absorbing UVA radiation than shade leaves (P>.05). Anthocyanins were present mainly in the leaves’ palisade layers in each species.

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