Structure of the Covering Layers of the Wild Oat (Avena fatua) Caryopsis

Abstract

The anatomy of the husk (lemma and palea) and caryopsis coat (pericarp, seed coat or testa, and nucellar epidermis) of a typical mature wild oat (Avena fatua L.) caryopsis was investigated using both scanning electron microscopy and light microscopy. Both the lemma and palea consist of very thick-walled, lignified cells. In section, the lemma appears almost twice as thick as the palea. The pericarp is comprised of only one or two layers of relatively thin-walled cells and is closely appressed to the underlying seed coat over most of the grain. Both the outer seed-coat cuticle and the inner cuticle are present over almost the entire caryopsis and are continuous with the pigment strand that occurs deep in the crease region of the grain. The only discontinuities in the seed coat are at the basal end of the grain near the embryo. In the dorsal region of the caryopsis, the outer cuticle is approximately 3.5 μm in thickness, whereas the inner cuticle is less than 1 μm in thickness. Where the two pass over the embryo they are much thinner, with the inner cuticle becoming almost indistinguishable in places. The remains of the nucellar epidermis are tightly amalgamated to the seed coat and outer tangential walls of the underlying aleurone cells, which are clearly distinguishable by their large size and characteristic appearance.

The Biology of Canadian Weeds. 27.Avena fatuaL. (updated)

“…Extreme measurements are in parentheses. Plant, annual, often much tufted, green or light green; roots fibrous, extensive; juvenile growth, prostrate to erect, seedling leaves twisted counterclockwise; culms smooth, terete, erect, (60Á) 80Á150 ((160) cm high, with dark-coloured nodes; leaves linear-lanceolate; leaf blades flat, 20Á30 ((60) cm long, 4Á10 ( (18) mm wide, twisted counter-clockwise; leaf sheaths open, with white, transparent, slightly hairy edges; leaf blade bases smooth to very hairy; ligule 2Á5 mm long, acute at anthesis, grayish-white, papery, irregularly lacerate at the top; panicle equilateral, 10Á40 cm long, open, loose; spikelets large, occurring singly at the end of branches, drooping, each with two glumes containing three florets; glumes longer than the florets, almost equal, 1.8Á2.5 cm long, with 9Á11 nerves, membranous with convex dorsal side; lemma hairy or glabrous, with several veins, light yellow, grey, brown or black; callus at the base of the first floret usually covered with a dense growth of hairs; proximal and middle florets usually perfect, consisting of a lemma, a bikeeled palea, two lodicules, three stamens and a pistil; distal floret usually imperfect, often abnormal with rudimentary floral parts; stamens with short filaments and long basifixed anthers; pistil with two plumose stigmas, remaining outwardly curved at maturity; florets separate from each other by disarticulation of their respective rachilla segments; each floret with a long, twisted and geniculate awn 3Á4 cm long; seeds elliptical, 1 cm long, consisting of two flowering scales [lemma and palea, described in detail in Morrison and Dushnicky (1982)] enclosing the caryopsis, with a slanting, circular depressed scar (also called a sucker mouth) at the base, often surrounded by a circle of brown hairs. Cotyledons of the embryo dimorphic in structure and function, the scutellum interpreted as the first cotyledon, and the first photosynthesizing leaf as the second cotyledon.…”

Coleorhiza‐enforced seed dormancy: a novel mechanism to control germination in grasses

“…The diaspores (seed‐containing dispersal units) of cereals (barley, wheat, oat), grass weeds (e.g. common wild oat) and other grasses (Poaceae) differ considerably from eudicot seeds (Morrison & Dushnicky, 1982; Sreenivasulu & Wobus, 2013; Rodriguez et al ., 2015). They are or contain caryopses, simple dry fruits in which the pericarp (fruit coat) and seed coat are fused, and which are in many cases additionally covered by husks (Fig.…”

“…Morphophysiology of Avena fatua germination. (a) Diagrammatic representation of an A. fatua caryopsis cut longitudinally (left) and enlarged embryo (right); hyaline layer (HL), aleurone layer (AL); modified from Morrison & Dushnicky (1982), reproduced with permission. (b) Photographs of caryopses at different stages of the germination process, showing the coleorhiza (CRZ) emergence, CRZ rupture by the radicle (RAD) and RAD emergence, and shoot (SHT) emergence.…”

High nutrient availability reduces the diversity and stability of the equine caecal microbiota

“…Horse forage is commonly supplemented with whole oats to increase the energy intake. Whole oats consists of a core of easily fermentable starch that can partly be defined as resistant starch ( 9 – 11 ), since the starch-rich endosperm is encapsulated in a hull delaying the access of digestive enzymes to the starch ( 12 ). Thus, if not entirely chewed, a part of the starch given in the oat diet will escape small intestinal digestion, being a source for rapid hindgut fermentation.…”