Antioxidative defence and photoprotection in pine needles under field conditions. A multivariate approach to evaluate patterns of physiological responses at natural sites

Measurements of antioxidants and chloroplast pigments have been widely used as markers of stress and vitality of conifers in the held. However, due to the high variability of these data and the multiple environmental influenc es tress are exposed to, a quantification of physiological stress responses has only scarcely been possible. Physiological stress responses cannot be monitored by single stress markers, but are governed by many different inte ractions. The objective of this study was to evaluate patterns of biochemic al stress markers in an objective and repeatable manner. For this purpose, a data set of 12 stress-physiological variables (chloroplast pigments, epox idation slate of the xanthophyll cycle, alpha-tocopherol, ascorbate and deh ydroascorbate, GSH and GSSG) measured on field-grown Pinus canariensis need les (n = 90) was subjected to explorative statistical techniques. Four prin cipal components (PC), which explained 80% of the variance of the original data, were extracted by principal component analysis. According to stress-p hysiological principles, complex responses were assigned to these PCs. Prin cipal component 1 was positively affected by concentrations of alpha-tocoph erol and total ascorbate, and negatively by the proportion of epoxides in t he xanthophyll cycle and by alpha-carotene contents. Principal component 2 was composed of chlorophyll, lutein, neoxanthin, and beta-carotene contents , PC 3 contained information about GSH concentrations and the proportions o f GSSG and dehydoascorbate; and PC 4 mainly comprised the pool size of the xanthophyll cycle. These components could be ascribed physiological princip les such as antioxidative response in chloroplasts (PC 1), pigment content (PC 2), or antioxidant regeneration (PC 3). Via cluster analysis a classifi cation of samples was made based on the patterns of their PC scores. The re sulting clusters represented typical physiological response patterns: Clust er 1 was related to initial stages of oxidative damage, cluster 2 to antiox idative responses, whereas cluster 3 represented healthy trees. The spatial distribution of members of these clusters among field plots revealed that different response patterns could be observed at the same plot, a fact that might be ascribed to small scale differences and/or individually differing resistances, and something that is frequently overlooked in the field.