The testa of higher plant seeds protects the embryo against
adverse environmental conditions. Its role is assumed mainly by
controlling germination through dormancy imposition and by limiting
the detrimental activity of physical and biological agents during
seed storage. To analyze the function of the testa in the model
plant Arabidopsis, we compared mutants affected in testa pigmentation
and/or structure for dormancy, germination, and storability.
The seeds of most mutants exhibited reduced dormancy. Moreover,
unlike wild-type testas, mutant testas were permeable to tetrazolium
salts. These altered dormancy and tetrazolium uptake properties
were related to defects in the pigmentation of the endothelium
and its neighboring crushed parenchymatic layers, as determined by
vanillin staining and microscopic observations. Structural aberrations
such as missing layers or a modified epidermal layer in specific
mutants also affected dormancy levels and permeability to tetrazolium.
Both structural and pigmentation mutants deteriorated faster
than the wild types during natural aging at room temperature, with
structural mutants being the most strongly affected.