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DEVELOPMENT OF THE PHYTOMELANIN LAYER IN FRUITS OF AGERATUM CONYZOIDES (COMPOSITAE)
Author(s) -
Pandey Arun K.,
Wilcox Lee W.,
Sack Fred D.,
Stuessy Tod F.
Publication year - 1989
Publication title -
american journal of botany
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.218
H-Index - 151
eISSN - 1537-2197
pISSN - 0002-9122
DOI - 10.1002/j.1537-2197.1989.tb11368.x
Subject(s) - biology , endoplasmic reticulum , ageratum conyzoides , epidermis (zoology) , anatomy , layer (electronics) , parenchyma , botany , microbiology and biotechnology , chemistry , organic chemistry , weed
The development of the phytomelanin layer in the achenes of Ageratum conyzoides (Compositae, Eupatorieae) was studied using light and electron microscopy. At the level of the embryo sac, the young ovary wall contains an outer zone, consisting of an epidermis and two hypodermal layers, and an inner zone, consisting of developing fiber cells and 3–5 layers of parenchyma. A schizogenous space forms between the developing fibers and the inner hypodermis at about the time that the embryo sac is fully organized. At this stage, the developing fibers contain papilla which are outgrowths that connect the fibers to the inner hypodermal cells. After fertilization, phytomelanin accumulates on the cell walls lining this space. Subsequently, by the time the fruit matures, the phytomelanin fills the space completely and forms a solid, black layer. The surface of the inner hypodermis that faces the space forms a mold; the characteristic peglike projections of the mature phytomelanin layer develop by filling the invaginations between the hypodermal cells. During phytomelanin accumulation, abundant smooth endoplasmic reticulum is present in the hypodermis, especially in the outer layer. It is hypothesized that the precursors of the phytomelanin are synthesized in this endoplasmic reticulum and that these precursors migrate into the space where the phytomelanin is polymerized.