© 2001 Heron Publishing—Victoria, Canada
Multivariate patterns of biochemical responses of Pinus ponderosa trees at field plots in the San Bernardino Mountains, southern California
Michael Tausz (1), Andrzej Bytnerowicz (2), Michael J. Arbaugh (2), Astrid Wonisch (1) and Dieter Grill (1)
1. Institut für Pflanzenphysiologie, Universität Graz, Schubertstraβe 51, A-8010 Graz, Austria / 2. USDA, Forest Service, Pacific Southwest Research Station, 4955 Canyon Crest Drive, Riverside, CA 92507-6090, USA / Received November 29, 1999
Summary
Most environmental stress conditions promote the production of potentially toxic active oxygen species in plant cells. Plants
respond with changes in their antioxidant and photoprotective systems. Antioxidants and pigments have been widely used to
measure these responses. Because trees are exposed to multiple man-made and natural stresses, their responses are not reflected
by changes in single stress markers, but by complex biochemical changes. To evaluate such response patterns, explorative multivariate
statistics have been used. In the present study, 12 biochemical variables (chloroplast pigments, state of the xanthophyll
cycle, α-tocopherol, ascorbate and dehydroascorbate, glutathione and oxidized glutathione) were measured in previous-year
needles of field-grown Pinus ponderosa Dougl. ex Laws. The trees were sampled in two consecutive years in the San Bernardino Mountains in southern California, where a pollution
gradient is overlaid by gradients in natural stresses (drought, altitude). To explore irradiance effects, needle samples were
taken directly in the field (sun exposed) and from detached, dark-adapted branches. A principal component analysis on this
data set (n = 80) resulted in four components (Components 1–4) that explained 67% of the variance in the original data. Component 1 was
positively loaded by concentrations of α-tocopherol, total ascorbate and xanthophyll cycle pools, as well as by the proportion
of de-epoxides in the xanthophyll cycle. It was negatively loaded by the proportion of dehydroascorbate in the ascorbate pool.
Component 2 was negatively loaded by chlorophyll concentrations, and positively loaded by the ratios of lutein and b-carotene
to chlorophyll and by the de-epoxidation state of the xanthophyll cycle. Component 3 was negatively loaded by GSH concentrations
and positively loaded by the proportions of GSSG and tocopherol concentrations. Component 4 was positively loaded by neoxanthin
and negatively loaded by β-carotene. The four components could be assigned to the concerted action of the biochemical protection
system: high scores on Component 1 represent highly activated antioxidative defense, changes in pigment composition are represented
in Components 2 and 4, and the glutathione system, which is important for antioxidant regeneration, is represented in Component
2. Although Component 1 scores were generally higher (indicating activation of antioxidant defense) in light-adapted needles
relative to dark-adapted needles, they were also site dependent with increased scores at sites with less pollution, but higher
natural stress impacts. High scores of Components 2 and 3 at the highest elevation site, which was only moderately polluted,
indicated an increase in photoprotection by pigments and activation of the glutathione system. Significant differences between
light- and dark-adapted needles in Components 2 and 3 were only found at the site with the highest pollution. Use of accumulated
variables (components) instead of single biochemical variables enabled recognition of response patterns at particular sites
and a better comparison with results of other studies is expected. Typical response patterns could be assigned to particular
environmental stress combinations, providing a means of assessing potential biological risks within individual forest stands.
Keywords:
α-tocopherol, antioxidative defense patterns, ascorbate, field sites, glutathione, multivariate analysis, oxidative stress,
pigments, xanthophyll cycle.
