Abstract Detail

Physiological Section

Smith, Christopher P. [1], Huth, John K. [2], Lackney, Stephen M. [1], Carrell, Skyler C. [1], Cote, Gary G. [1].

Calcium Oxalate Crystals in Petioles of Deciduous Trees.

Microscopic intracellular crystals of calcium oxalate are produced throughout the plant kingdom. While it has often been proposed that these crystals defend against herbivory, other roles have been suggested, including that they sequester calcium from cell walls during controlled breakdown of plant tissues. One case of such controlled breakdown involving cell wall changes is the abscission of spent leaves and floral parts, in which a layer of cells with weakened cell walls is formed. Calcium oxalate crystals have been extensively studied in leaf blades of a large diversity of plants, but there have been few reports of crystals in petioles. We collected abscised autumn leaves and young spring leaves from 16 species of deciduous trees, and prepared cleared specimens of both leaves and petioles for examination by brightfield and polarization microscopy. Species differed in the presence and shape of petiolar crystals. Five species, Gingko biloba, Acer saccharum, Carpinus caroliniana, Crataegus mollis, and Tilia americana var. heterophylla showed marked increases in crystal content of the petioles between spring and autumn, and were chosen for further study. Summer and early autumn petioles of these species showed intermediate levels of crystals. Within the leaf blades of these species there was no consistent pattern of crystal abundance. We collected leaves and petioles of these species at intervals from leaf unfurling in spring until leaf fall in autumn, and quantitated levels of total and soluble oxalate by chemical assay. The difference was taken to represent insoluble (presumably calcium) oxalate. In the petioles calcium oxalate was low in spring leaves and showed a dramatic increase over the summer, remaining high in the autumn. The timing of the increase, however, varied with species. In most species the levels increased gradually over the summer, but in Tilia americana var. heterophylla the levels increased dramatically in the few weeks before leaf fall. Levels of calcium oxalate in the blades are still being assayed. These results are consistent with the crystals playing a role in abscission of the leaves, especially in Tilia americana var. heterophylla.

1 - Radford University, Department of Biology, Radford, VA, 24142, USA
2 - Virginia Polytechnic Institute and State University , Department of Fish and Wildlife Conservation, Blacksburg, VA, 24061, USA

Keywords:
calcium oxalate crystals
deciduous trees
cell walls
Gingko biloba
Acer saccharum
Carpinus caroliniana
Crataegus mollis
Tilia americana.

Presentation Type: Poster:Posters for Sections
Session: P
Location: Hall D/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 5:30 PM
Number: PPS001
Abstract ID:257
Candidate for Awards:None