Microanatomia del seme di mays

Ottobre 31, 2021 in Senza categoria

Raccolta di immagini del seme di mais con diversi ingrandimenti

Descrizione presa da https://www.flickr.com/photos/146824358@N03/33762056788/in/album-72157679942049418/

The Bran is the outermost layer of the seed. It consists of a seed coat that is fused with the pericarp, which is made of several different layers. These layers are the epidermis, the mesocarp, a section of cross cells and a section of tube cells. These extra layers and the seed coat make up the Bran.

Past the Bran lies the outermost layer of the endosperm, a single layer of darkly staining cuboidal cells known as the Aleurone layer (foto3). The cells of the Aleurone layer are rich in protein and lipid inclusion bodies. The Aleurone layer functions in the synthesis of the enzyme α-amylase which is secreted during germination, and moves into the endosperm in order to begin breaking down starch into maltose and glucose.

The endosperm is the bulk of the seed. It serves mostly to store starch as a fuel reserve for the seed during germination, and has been known to store proteins. The Endosperm is split between two types of cells, horny endosperm and floury endosperm. Horny endosperm is more abundant near the pericarp and cotyledon, and stains pink. Floury endosperm sits roughly in the middle, and stains blue. Floury endosperm cells are generally larger, and the starch granules are more likely to be spherical and less compact, compared to the horny endosperm, which is has polygonal and compact granules and smaller cells. Horny endosperm also generally has more granules than floury.

The Cotyledon is the outermost layer of the embryonic section. An alternative name for the Cotyledon is the scutellum. The Cotyledon is generally the “first leaf” of the plant, in that it ejects from the kernel and grows to the surface. It’s border with the endosperm is clearly marked by a distinct layer of palisade like epidermis. These elongated epithelial cells secrete hormones into the endosperm that activate the enzymatic digestion of starches. These starches are absorbed by the Cotyledon and transferred to the developing embryo. A well-defined vascular strand can be seen forming within the parenchyma cells of the cotyledon.

The Embryo, or germ consists of the coleoptile, plumule, radical, hypocotyl, and coleorhiza. The coleoptile begins with the northernmost tip of the embryo, and can be distinguished by its cuticle and palisade epidermis. It has typical leaf properties, likely because it functions as a protective sheath surrounding the shoot. Underneath the coleoptile is the plumule, or embryonic shoot, which is a section of rapidly dividing cells. The plumule bears the true “first leaves” of the plant. Below the plumule is the hypocotyl, which is a connecting structure between the plumule and radicle. It functions by helping to “push” the cotyledon out of the ground during development, and will eventually become part of the stem. The radicle is the curved structure beneath the hypocotyl, and will eventually turn into the primary roots of the plant. Just beneath the radicle are an inner dark staining root cap and outer pink staining coleorhiza that protect the root tip during germination.