Pigments and photoprotection in needles of Pinus ponderosa trees with and without symptoms of ozone injury

The best documented ozone-induced damages on forest trees are found on Pinu s ponderosa Dougl. ex P. & C. Laws. in the San Bernardino Mountains in Sout hern California. The foliar injury to this species is characterized by spec ific visual symptoms ('chlorotic mottling'). In October 1997, ponderosa pine needles were collected at a severely impact ed plot in the San Bernardino Mountains where individuals showing severe Vi sual injury symptoms (symptomatic) and asymptomatic trees grow together. Th e symptomatic trees exhibit defoliation and thinned crowns caused by the pr emature loss of symptomatic needles (with typical 'chlorotic mottling') in late summer. At sampling time, the current year's flush and one-year old ne edles used for biochemical analysis did not show any or had only minimal sy mptoms of chlorotic motile. In these needles, pigment concentrations in dar k and light adapted needles were equal for the both symptomatic and asympto matic trees, except for chlorophyll a decline in the previous year's needle s of symtpomatic trees in the light. However, the de-epoxidation state of the xanthophyll cycle in sun adapted n eedles of the symptomatic trees (35% de-epoxidised groups) was significantl y higher than in needles of asymptomatic trees (20%). In the dark adapted s tage, about 10% of de-epoxides were retained in all samples. These results indicate an increased need for photoprotection of the symptom atic trees in the light and an early stage of (reversible) chlorophyll degr adation in the light. Since these alterations are detectable before visual symptoms appear on the needles, they might be useful for early indication o f risk associated with phytotoxic ozone stress to pines.