Breaking strengths of pollen grain walls

LAP3, a novel plant protein required for pollen development, is essential for proper exine formation

“…As a testament to the elasticity and strength of the exine, even when the diameters of pollen grains were much larger than the clearance for the piston, most pollen survived the treatment intact, showing only slight cracks in the exine wall, or in some cases, pollen grains within pollen grains. Bolick and Vogal more quantitatively measured pollen wall strength using a calibrated vise to assay the 50% breaking point pressure for pollen from eleven different species, with most species tested having an average wall strength between 2 and 90 MN/m 2 (Bolick and Vogel 1992). Finally, some aberrantly constructed pollen walls have shown chemical sensitivity to acetolysis treatment (Scott 1994;Aarts et al 1997;Ariizumi et al 2003).…”

How to shape a cylinder: pollen tube as a model system for the generation of complex cellular geometry

“…This elastic property is crucial for pollen function, as it allows for the harmomegathic changes that accommodate volume changes associated with dehydration and rehydration of the pollen grain (Wodehouse 1935;Payne 1972;HeslopHarrison 1975HeslopHarrison , 1979bMuller 1979;Bolick 1981;Payne 1981;Pacini 1990;Scotland et al 1990). On the other hand, the resistance to compressive forces normal to the surface may be of particular use as a protective means during pollen dehydration, when the shrinking protoplast pulls inwards (Payne 1972;Muller 1979;Bolick and Vogel 1992). One of the mechanical functions of the exine, especially in highly desiccated grains might, therefore, be the prevention of complete and potentially irreversible collapse of the pollen grain wall.…”

Pollen from Arabidopsis thaliana and other Brassicaceae are functionally omniaperturate

“…Our AFM measurements of A. thaliana pollen exine are of local material stiffness and are not to be confused with measurements of the breaking strengths of complex structures (Wainwright et al, 1976; Gordon, 1978; Bolick and Vogel, 1992). In addition, we applied a localized force perpendicular to and from the exterior of a curved surface; the cell wall's responses to the AFM probe are therefore unlike its responses to turgor‐induced stresses running parallel with the cell wall and forces applied from the grain's interior.…”

“…Microindenter measurements of cell wall stiffness in extended pollen tubes, though difficult to compare with our AFM measurements, do reveal that tube wall stiffness is heterogeneous within 20 µm of the tube apex (Geitmann and Parre, 2004; Bolduc et al, 2006). When entire pollen grains are subjected to mechanical stress (instead of local AFM nanoindentation), the majority of the tested pollen grains have 50% breaking strengths between 2 and 55 MPa (see the full list of Bolick and Vogel, 1992; no Brassicaceae family members were studied). Such strength measurements can also be adjusted, based on pollen grain radii and wall thickness, to measurements of stress at 50% breaking (Bolick and Vogel, 1992).…”

“…The outer exine of living pollen is durable and strong, but also dynamic, flexible, and elastic (Bolick and Vogel, 1992; Rowley and Skvarla, 2000). Pollen wall materials and architectures permit large volume changes during grain desiccation and hydration, termed harmomegathy (Wodehouse, 1935; Payne, 1972; Heslop‐Harrison, 1976, 1979a, c; Blackmore and Barnes, 1986; Scotland et al, 1990), and allow grains to be resilient to shock (Rowley and Skvarla, 2000).…”