Structural Development of the Oat Plant - Chapter 3-1.1 Seedling structure - Light-Grown Seedlings

Sep 17, 2026

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Structural Development of the Oat Plant focuses on how the vegetative oat plant forms and changes, with emphasis on the oat species Avena sativa. It summarizes prior anatomical work and highlights more recent, less-noted findings relevant to oat breeders, agronomists, and plant physiologists. Section 3-1.1 details seedling organization, contrasting light-grown and dark-grown development, describing coleoptile, mesocotyl, scutellum, epiblast, coleorrhiza, and root system components, and explaining gravitropism regulation via auxin.

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Structural Development of the Oat Plant

3-1 STRUCTURE OF THE VEGETATIVE OAT PLANT

3-1.1 Seedling structure

3-1.1.1 Light-Grown Seedlings

3-1.1.2 Dark-Grown Seedlings

3-1.2 Vegetative Shoot and Root Systems

3-1.2.1 External Structure

“ 3 # Structural Development of the Oat Plant PETER B.KAUFMAN AND THOMAS G.BROCK University of Michigan Ann Arbor,Michigan The anatomical structure and morphology of the oat plant(Avena sativa L.)have been reviewed previously by Hector(1936),Bonnett(1961a,b)and Coff-man(1977).In addition,Bonnett published detailed accounts of oat panicledevelopment (1937,1961a,b).This work has been summarized by Esau inher book,Anatomy of Seed Plants,in 1977.It is not the purpose of thepresent authors to simply go over all this same material again in a repetitivefashion,but rather,to emphasize some of the more recent and previouslyoverlooked work on structural development of the oat plant,with emphasison the major cultivated species,A.sativa(see Stanton,1955;Coffman,1977for descriptions of this species).The material presented here should be ofuse to oat breeders,agronomists,and plant physiologists. 3-1 STRUCTURE OF THE VEGETATIVE OAT PLANT ## 3-1.1 Seedling structure 3-1.1.1 Light-Grown Seedlings The light-grown oat seedling initially consists of a cylindrical coleoptile(a sheathing leaf that protects the shoot apex and undeveloped leaves),thecoleoptilar node,where the coleoptile is attached,a mesocotyl or first inter-node,a scutellum (cotyledon),epiblast,coleorrhiza,and seminal(seedling)root system. At germination,the shoot portion of the seedling emerges from the api-cal end of the grain(caryopsis).The structure that emerges first is the coleop-tile.Anatomically,the coleoptile consists of inner and outer epidermises,ground parenchyma tissue between the two epidermises,and two vascularbundles.As the seedling develops in the light,the first true leaf emerges fromthe coleoptile through an apical pore.The first true leaf consists of a bladeportion only,with no sheath present,in contrast to later-formed leaves.Ex-ceptional detail of oat coleoptile structure is depicted in Avery(1930),Averyand Burkholder(1936),Bohmer(1958),Thimann and O'Brien(1965),andO'Brien and Thimann(1965,1967). Fig.3-1.Early development in light-grown oat seedlings.The first true leaf has emerged fromthe coleoptile of the seedling on the left.The coleoptile of the seedling on the right is display-ing the bending characteristic of gravitropism. From the initiation of emergence,the coleoptile manifests competencyfor negative gravitropism,or upward growth,regardless of initial orienta-tion with respect to gravity(Fig.3-1).Coleoptile elongation is largely regu-lated by the hormone,auxin (indole-3-acetic acid),which is produced by thecoleoptile tip,moves basipetally via an active transport system,and promotescell elongation in a growth zone located below the tip.Since gravitropismis,finally,asymmetric growth,oat coleoptile gravitropism is an auxin-regulated process.The physiology of auxin action in oat growth andgravitropism is discussed further in Thimann(1977),Kaufman and Song(1987),and Kaufman et al.(1987). In contrast to the coleoptile,the mesocotyl is very short in light-grownoat seedlings.It consists of an epidermis,cortical parenchyma,and severalvascular bundles composed of primary xylem and phloem.Two of these vas-cular bundles are connected to the scutellum,or cotyledon,located at thebase of the mesocotyl.The others connect with vascular bundles of the coleop-tile above and the root vascular cylinder(stele)of the radicle,or seed root,below.Further anatomical detail of the oat mesocotyl is presented by Boydand Avery(1936). As noted above,the oat seedling has three specialized appendages otherthan the coleoptile:the scutellum,the epiblast,and the coleorrhiza.The scutel-lum and epiblast are inserted 180°opposite each other at the base of themesocotyl.The coleorrhiza surrounds the radicle or primary seminal rootof the seedling.The scutellum is vascularized whereas the epiblast and thecoleorrhiza are not(Boyd &Avery,1936). STRUCTURAL DEVELOPMENT OF OAT The root system of the seedling is composed of several seminal (seed)roots that arise from the

FAQs

What main structures are present in a light-grown oat seedling at the start?

A light-grown oat seedling initially includes the coleoptile, coleoptilar node, mesocotyl, scutellum (cotyledon), epiblast, coleorrhiza, and a seminal root system.

How do light-grown and dark-grown oat seedlings differ in development?

Dark-grown seedlings develop a greatly elongated mesocotyl, with coleoptile and mesocotyl cells much more elongated than in light-grown seedlings, altering the growth pattern and bringing young leaves toward light.

What role does auxin play in coleoptile development and gravitropism?

Coleoptile elongation is regulated by auxin (indole-3-acetic acid) produced at the coleoptile tip, which promotes cell elongation in a growth zone and supports asymmetric, auxin-regulated gravitropic growth.

Sep 17, 2026

Uploaded by Blaney