Development and Substructures of Pollen Grains Wall

El‐Ghazaly, Gamal

doi:10.1007/978-3-642-59969-9_14

Cited by 4 publications

(1 citation statement)

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“…Both were reduced in stiffer media, but moderate amounts of lyticase nevertheless had a significant stimulating effect. However, optimal enzyme concentrations and relative stimulation in stiff media had a tendency to differ from those observed in liquid medium, as summarized in Table II. protoplast (Roggen and Stanley, 1969;El-Ghazaly, 1999;Li et al, 1999;Johnson and McCormick, 2001;Ressayre et al, 2002). The presence of callose in the pollen grain and, in particular, at its aperture therefore provides an excellent experimental system to test whether or not callose is able to resist tension forces in living plant cells.…”

Section: Discussion Cell Wall Resistance To Tension Stress At the Polmentioning

confidence: 99%

More Than a Leak Sealant. The Mechanical Properties of Callose in Pollen Tubes

2005

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While callose is a well-known permeability barrier and leak sealant in plant cells, it is largely unknown whether this cell wall polymer can also serve as a load-bearing structure. Since callose occurs in exceptionally large amounts in pollen, we assessed its role for resisting tension and compression stress in this cell. The effect of callose digestion in Solanum chacoense and Lilium orientalis pollen grains demonstrated that, depending on the species, this cell wall polymer represents a major stress-bearing structure at the aperture area of germinating grains. In the pollen tube, it is involved in cell wall resistance to circumferential tension stress, and despite its absence at the growing apex, callose is indirectly involved in the establishment of tension stress resistance in this area. To investigate whether or not callose is able to provide mechanical resistance against compression stress, we subjected pollen tubes to local deformation by microindentation. The data revealed that lowering the amount of callose resulted in reduced cellular stiffness and increased viscoelasticity, thus indicating clearly that callose is able to resist compression stress. Whether this function is relevant for pollen tube mechanics, however, is unclear, as stiffened growth medium caused a decrease in callose deposition. Together, our data provide clear evidence for the capacity of cell wall callose to resist tension and compression stress, thus demonstrating that this amorphous cell wall substance can have a mechanical role in growing plant cells.b-1,3-Glucan (callose) is one of the most dynamic components of the plant cell wall. It is known to be synthesized and deposited at the outer surface of the plasma membrane by callose synthases that are localized in the membrane (Carpita and Gibeaut, 1993). The synthesis of this amorphous polymer is an important part of plant cell responses to pathogen attacks as well as physical and chemical stresses (Currier, 1957;Esau and Cronshaw, 1967;Coffey, 1976;Delmer and Amor, 1995). While injured plant cells use the polymer as a leak sealant, in certain plant cell types callose is produced during normal development (Esau, 1948;Currier, 1957;Heslop-Harrison, 1964;Scott et al., 1967;Morrison and O'Brien, 1976;Waterkeyn, 1981;Stone and Clarke, 1992). From the location of these callose deposits, it has been concluded that the polymer acts as a permeability barrier, as in pollen mother cell walls (Heslop-Harrison, 1964) and muskmelon endosperm envelopes (Yim and Bradford, 1998); as a matrix for deposition of other cell wall materials, as in developing cell plates and sieve-plate pores; and as a sealing or plugging material at the plasma membrane of pit fields, plasmodesmata, and sieve-plate pores (Eschrich, 1975). Despite the widespread occurrence of callose, its functions other than as a leak-sealing cement or permeability barrier are not well understood (Stone and Clarke, 1992). One of the few suggestions of callose playing a role in cell wall mechanics was made based on circumstantial evidence...

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