Development of male and female embryonic structures in the genus Stachys (Lamiaceae).

摘要

The development of male embryonic structures in the species S. aspera, S. sylvatica, S. palustris and S. trinervis occurs in the same way, but with some differences in the details. The anther is tetrasporangiate. Characteristic of all species is thepresence of sterile protuberances, placentoids, in a partition between microsporangia. The formation of the microsporangial wall occurs cenrtifugally according to the dicotyledonous type. The fully formed wall consists of an epidermis, endothecium, onemiddle layer and tapetum. The tapetum is heteromorphic and cellular (secretory), with orbicules. The number of nuclei per tapetal cell is 1 or 2, in S. trinervis sometimes 2-4. A middle layer is ephemeral. The endothecium and epidermis persist in matureanthers. Fibrous thickenings are formed in the cells of the endothecium and 3-4 connective layers. The epidermis is covered by a cuticle, with cells differing in configuration and form: in S. aspera they are papillioid and extended, in S. palustris slightly extended, and flat in the other 2 species. Only in S. trinervis are multicellular trichomes (glands) formed; they are observed during the whole period of anther development but are destroyed at anther maturity. Sporogenous tissue in S. trinervis is located in one line, in other species it is 2-serial, arch-like. The formation of microspore tetrads occurs according to the simultaneous type, and they are tetrahedral, in callose walls. Mature pollen grains are 2-celled. Anthers open introrsely by longitudinal splits with the help of insect pollinators. Before anther opening, the placentoids and part of the partition between microsporangia are destroyed. S. trinervis is a xerophytic subshrub growing in semi-desert conditions on saline and rich gypsaceos soils in Badkhys (Turkmenistan). It is distinguished from the other species investigated by the presence of a multicellular archesporium in its unitegmic tenuinucellate ovule. Up to 8 cells of the archesporium develop directly into megasporocytes whichsimultaneously undergo meiotic divisions. Numerous megaspore tetrads and some 2-nucleate embryo sacs are formed, of which only one reaches maturity. A complex of cells (derivatives of the archesporium) is present for a long time in the ovule, until embryo and endosperm development. The walls of these cells are significantly thickened, their cytoplasm and nucleus gradually degenerate. In the other Stachys species which are perennial herbs of forest communities, the ovule is anatropous, unitegmic and tenuinucellate, the archesporium is unicellular, similar to the majority of the Lamiaceae. The megaspore tetrad is linear. The development of the embryo sac conforms to the Polygonum-type. The presence of 2-celled archesporia in the family is very rare. Inthis group of species, which belong to different sections of the genus Stachys, the features, distinguishing them at the species level include the structure of the epidermis, the number of layers and cells of the sporogenous tissue, and the degree of thedevelopment of placentoids. In addition, S. trinervis differs from the others in the formation of multicellular glands on the epidermis and by its nucellus and archesporium. Thus, the multicellular archesporium of S. trinervis is a unique feature not only in Stachys, but also in the Lamiaceae. Such ancestral features indicate that S. trinervis is the most primitive species within the genus.