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Physiological Section

Johnson, Daniel M. [1], Vogelmann, Thomas C. [2], Smith, William K. [1].

Chlorophyll fluorescence in cotyledons and primary needles of a high-altitude conifer.

High-altitude plants are faced with extreme conditions even in summer when near freezing nighttime temperatures are frequently followed by intense sunlight the next morning. This combination has been associated with substantial low temperature photoinhibition of photosynthesis (LTP) that appears to contribute to inhibited growth and high mortality in conifer seedlings. By measuring chlorophyll fluorescence inside the leaf mesophyll, effects of LTP on internal light processing in both emergent (cotyledonous) and surviving older seedlings were evaluated. Chlorophyll fluorescence was measured by viewing cross-sections of needles and exposing either the adaxial, abaxial or cross-sectional surface to monochromatic light (red, green or blue; blue only in the case of cross-section surface exposure). Chlorophyll content and light absorption profiles were inferred from fluorescence patterns. In Abies fraseri , chlorophyll fluorescence profiles, chlorophyll content, and light absorption profiles across the mesophyll were different for cotyledons versus primary needles. Both cotyledons and primary needles had bimodal chlorophyll distributions, with one peak near the adaxial surface and one near the abaxial surface. However, in cotyledons both the adaxial and abaxial peaks occurred deeper into the leaf. Light absorptance from an adaxial light source decreased linearly with depth for all three wavelengths in cotyledons, whereas the decrease in absorptance with depth was sigmoidal in primary needles for all wavelengths. Also, light absorptance from abaxial illumination decreased linearly with depth for all three wavelengths in both needle types. Ongoing studies are currently analyzing the effects of low temperature and high light on light processing in cotyledons and primary needles. Based on previous studies, cotyledons are expected to be more susceptible to LTP. There may be differences in light absorption and LTP susceptibility that can be attributed to structural differences between cotyledons and primary needles.

1 - Wake Forest University, Department of Biology, P.O. Box 7325, Winston-Salem, North Carolina, 27109-7325, U.S.A.
2 - University of Vermont, Department of Botany, Marsh Life Sciences Building, Burlington, Vermont, 05405-0086

Abies fraseri
light processing.

Presentation Type: Paper
Session: 11-6
Location: White Pine (Cliff Lodge)
Date: Monday, August 2nd, 2004
Time: 11:30 AM
Abstract ID:441

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