Comparative study of an antioxidant defense mechanism in genotypes of eastern white pine which show differential foliar characteristics

Approximately 10-15% of field-grown eastern white pine (Pinus strobus L.) within a nursery plantation expressed foliar characteristics similar to that induced by oxidant pollution. Sensitive genotypes (based on foliar characteristics), had a 50% reduction in needle growth, severe needle tip burn, mottling, and early needle shed during a high O₃, drought-type growing season (1988) compared to a low O₃, non-drought growing season (1989). Tolerant genotypes showed little difference in needle growth or visible injury during the two growing season.

Seasonal needle ascorbate concentrations were similar during the two years however, needle glutathione (GSH) content has not. Total GSH content was two-to three-fold greater in both genotypes during the summer of 1989 compared to 1988. Cloned, tolerant trees also had 23% more total GSH when exposed to forced ambient air compared to charcoal-filtered air in open-top chambers. Cloned sensitive trees had similar GSH concentrations when exposed to different chamber treatments.

One-year-old needles always had lower ratios of ascorbate/ dehydroascorbate, ascorbate/α-tocopherol and GSH/GSSG than current year needles. One-year-old needles from the tolerant tree also maintained a higher glutathione reductase (GR) activity than the sensitive tree during the late summer.

Needles of eastern white pine had two isoforms of GR (GR_A and GR_B). GR_A and GR_B accounted for 17% and 83% of the GR recovered, respectively. GR_A and GR_B had different physical and kinetic properties. Antibody produced from GRR was reactive with both native and denatured GR_B, but was cross-reactive with only native GR_A.

Tolerant and sensitive clones exposed to control (< 0.025 ppm) or high (4.5 ppm∙hr total dose) O₃ for O to 72 hr, showed no increase in GR activity. Only in the high-O₃-treated trees did the amount of GR protein increase. Needles from the sensitive clone contained 14, 62, and 464 ng GR mgP⁻¹ and needles from the tolerant clone contained 21, 138, and 2800 ng GR mgP⁻¹ after 0, 24 and 72 hr O₃ exposure, respectively.

The results of this dissertation indicate that differential foliar characteristics in eastern white pine may be correlated with GSH turnover and its regulation by GR during periods of high oxidant stress.