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Literature review
these channels permit the rapid exchange of water and solutes between the external
environment and the seed.
Even though these major morphological changes have a large influence on the
function of the cell, they do not significantly alter the general shape or dimensions of
the cells (EGERTON-WARBURTON, 1998). EGERTON-WARBURTON (1998)
speculated that the mechanism by which such morphological changes benefit the
plant may be a synergy between the observed increased cuticular permeability and a
simultaneous leaching of endogenous inhibitors of germination during imbibition.
They also further described the mechanism of formation of permeate channels.
Because the permeate channels occurs in the cuticle, the formation of channels has
to be the result of a preceding reaction between certain constituents of smoke and
the semi-crystalline structure of waxes (EGERTON-WARBURTON, 1998). This is a
rather promising argument as the pyrolysis of cellulose alone produces a collection of
compounds, such as aromatic hydrocarbons, ketones and a number of organic acids,
which all have the potential to dissolve or modify waxes.
Smoke also contains a number of compounds that may act as surfactants (e.g.
alcohols) (EGERTON-WARBURTON, 1998). These surfactants modify cuticular
layers by plasticizing the molecular structure of waxes (EGERTON-WARBURTON,
1998). The sorption of such surfactants to the cuticle also creates hydrophilic
channels. This increases the area of channels within the cuticle that leads to
accelerated transcuticular penetration of solutes in several species.
Using liquid chromatography, BLANK and YOUNG (1998) discerned over 30 organic
anions in aqueous extracts of soil heated between 250 to 450°C. BLANK and
YOUNG (1998) speculated that these unknown compounds or combinations of
compounds could be cueing agents.
FLEMATTI et al. (2004) identified the UV absorbance maximum and molecular
weight of a germination-enhancing compound in smoke. They also assigned a
molecular formula of C8H6O3 to the compound. They also identified the compound as
the butenolide, 3-methyl-2H-furo[2,3-c]pyran-2-one and were able to synthesize it.
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