Sanson, Gordon , Heraud, Philip .
Plant silica: structure and the implications for support and defence.
Suggested roles of silica in plants include stress, support and herbivore deterrence. This paper extends recent findings of one aspect, the conventional view that silica provides protection from herbivory, particularly by mammals. Silica forms phytoliths in cell walls or more rarely in the cell lumen. Phytoliths have been reported as being harder than mammalian tooth enamel and a significant contributor to tooth wear. An unresolved issue is the presumption that herbivores can detect abrasives in plants providing an agent leading to selection for phytolith accumulation. Recently it has been shown that phytoliths in five grass species are not harder than tooth enamel and are unlikely to be a major source of tooth wear. Pennisetum plants were grown in silica-free conditions and in normal conditions. Leaves from both treatments were tested in 3-point bending tests and silica-free leaves were less stiff than silicious leaves. However, the silica-free leaves were thicker, suggesting some kind of compensation. The composition of phytoliths extracted from Paspalum and the silicious Pennisetum leaves were examined with scanning transmission x-ray microscopy (STXM) and produced a signature and density characteristic of the nanospheres of aerogel. There was no evidence of crystalline silica. These findings suggest that silica in the phytoliths of at least these species is in a form that is unable to produce wear in mammalian enamel. This is consistent with the measured hardness of individual phytoliths with respect to enamel, but not with respect to insect mandible hardness. There may be some interaction between the cellulose scaffold of plant silica and hardness which is yet to be explained.
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1 - Monash University, School of Biological Sciences, Victoria, 3800, Australia
2 - Monash University, Centre for Biospectroscopy, School of Chemistry, Melbourne, Victoria, 3800, Australia
Presentation Type: Oral Paper:Papers for Sections
Location: 551B/Convention Center
Date: Monday, August 2nd, 2010
Time: 4:30 PM