Document: MAR-3-29-8

Spatial patterns in freeze-induced photoinhibition of field-grown Eucalyptus pauciflora.

BALL, M.C.*, A.M.GILMORE, A.B.NICOTRA and M.HOFMANN

Australian National University ¹

Abstract:
Photosynthesis is sensitive to low temperatures, with freezing conditions naturally inducing chronic photoinhibition (i.e., light-dependent decrease in efficiency of photosystem II) in over-wintering leaves of eucalypts and other evergreen species. Analysis of in vivo fluorescence characteristics in field grown leaves of snow gum (Eucalyptus pauciflora) showed that chronic cold-induced photoinhibition is due to a previously unknown chlorophyll-carotenoid-protein complex that facilitates extremely rapid non-radiative dissipation of absorbed light energy without a requirement for a transthylakoid pH gradient. This photoprotective complex may be critical to survival of evergreens during winter when leaves are least able to cope with excess irradiance. A unique spectral emission band signifies the reversible formation of this novel photoprotective complex. High resolution hyperspectral imaging was used to measure spatial variation in light reflected from leaf surfaces. These data were used to map spatial variation in reflectance associated with the novel photoprotective complex (r² = 0.92). Apparent concentrations of the complex were lowest near leaf centers and increased toward leaf tips and edges, consistent with the spatial pattern in leaf temperatures and freeze-induced changes in chlorophyll content and a/b ratios. These data provide explicit spatial linkage between environmental stress and physiological responses to it.

Keywords: Photosynthesis, freezing temperatures, photoinhibition, Eucalyptus, novel photoprotective pigment, hyperspectral imaging.

This abstract is being presented at: 2:00 PM in session:
Oral Session #10: Light Relations in Plants.