Histological study of seed coat development in Arabidopsis thaliana

A detailed analysis of Allabidopsis seed coat development using light and transmission electron microscopy revealed major morphologieal changes associated with the transition of the integuments into the mature seed coat. By the use of a metachromatic staining procedure, cyiological events such as the production of phenolic compounds and acidic polysaccharides were followed. Immediately after fertilization, the cells of the inner epidermis of the inner integument beeame vacuolated and subsequently accumulated pigment within them. This pigment started to disappear from the cytoplasm at the torpedo stage of the embryo, as it beeame green. During the torpedo stage, mucilage began to accumulate in the cells of the external epidermis of the outer integument. Furthermore, starch grains accumulated against the central part of the inner periclinal wall of these cells, resuiting in the formation of small pyramidal domes that persisted until seed maturity. At the maturation stage, when the embryo became dormant and colourless, a new pigment accumulation was observed in an amorphous layer derived from remnants of crushed integument layers. This second pigment layer was responsible for the brown seed colour. These resuits show that seed coat formation may proceed in a coordinated way with the developmental phases of embryogenesis.