Histopathology of Seed-Borne Infections - Applied Research Center ...

Structure of Seeds 73(Zea and Sorghum), a tuft of hairs in Triticum. Caryopsis covered with lemma andpalea have base of awn on the terminal end and in Oryza lips of lemma and paleathey become hard and pointed and are called apiculus.Internal: Caryopsis coat thin to coriaceous or crustaceous, loose and membranous(Eleusine and Eragrostis); embryo lateral and endosperm abundant.Pericarp protective and usually consists of (1) epicarp, (2) mesocarp, (3) crosscells, and (4) tube cells. Epicarp, single layer, cells elongated along long axis, wallsthick and pitted, covered by a thick cuticle; mesophyll, number of layers vary, cellsof outer layers usually thick-walled, thickening gradually, decreasing from outsideto inside; cross cells, inner hypodermis, cells elongated at right angles to those ofepicarp or transversely, walls thick and pitted; tube cells, inner epidermis of pericarp,cells elongated along the long axis of the grain or at right angles to cross cells,intercellular spaces large, walls relatively thin and pitted. Pericarp zones one to fourclearly recognized in Triticum, Zea, Sorghum, Pennisetum, and Secale; zones recognizedin Oryza but mesocarp greatly reduced; undifferentiated in Hordeum coveredby multi-layered persistent adherent lemma and palea; and membranous, thin-walledin Eleusine and Eragrostis. In Oryza, hull or husk, formed by lemma and palea,epidermis of almost squarish cells, deeply sinuate walls, pointed hairs and stomatapresent; hypodernis of two or three layers of thick-walled elongated fibers; mesophyllspongy parenchyma; inner epidermis cells thin-walled, isodiametric, stomatapresent; vascular bundles present in inner zone of husk.Seed Coat: Usually adherent to pericarp, formed by inner epidermis of innerintegument, cells without or with tanniferous contents (Sorghum, Pennisetum, Oryza,and Echinochloa), crushed and only cuticle distinct (Zea, Triticum, Euchlaena, andSecale); seed coat well developed, formed by two layers of inner integument, outerthick-walled and horny, inner thin-walled with pigmented contents (Eleusine andEragrostis); rarely pigmented contents present in outer layer also.Placento-Chalazal Region: The placental tissue of the carpel and the adjoiningtissue of the campylotropous ovule merge without the intervention of the funiculus,the region is called placento-chalazal region. It is multi-layered differentiated intothree or more zones, cells below embryo-endosperm thin-walled, compressed; followedby a zone of compressed, nearly structureless cells with brown contents,closing zone; cells of the remaining layers thin or thick-walled, peripheral layerswith suberised walls.Nucellus: Usually as a thin cuticular membrane; when present, one- or twolayered,cells thin-walled.Embryo: Peripheral, basal, lateral, monocotyledonous — scutellate with typicalfeatures of grass embryo — coleorhiza, coleoptile, and epiblast present or absent;radicle with primordia of lateral roots, epicotyl with primordia of foliage leaves incultivated species.Endosperm: Abundant, starchy, floury or floury and horny; cells of epidermisor outer two to three layers with abundant aleurone grains and poor or with no starchgrains form the aleurone layer(s).