Research Observations: Standardized Terminology for Structures Resulting in Emergence and Crown Placement of 3 Perennial Grasses

Abstract

A significant problem we encountered in grass establishment research was confusion in the literature over seedling structures and terminology. From review of the historical literature and our observations of growth-chamber grown sideoats grama [&I&loua curtipen&~ (Michx.) Torr.], western wheatgrass [Agropyron smithii Rydb.; new cytogenetic = Pascopyron smithii Rydb. (LSve)], and smooth bromegrass (Bromus inermis Leyss.) seed-Ungs, we suggest standard structures and terminology for grass seedlings. The nodes of a grass seedling are defined as the scutellar node, coleoptilar node, and leaf nodes named in sequence from first to last. The internode between the scutellar and coleoptilar nodes is termed the mesocotyl. The internode that develops inside the coleoptile between the coleoptilar and first leaf nodes is defined as the first leaf internode. Subsequent internodes are named for the leaf node immediately above; e.g., second leaf internode. Using these structures and terminology we found the "mechanism" of emergence for these grass seedlings from a 25-mm seeding depth was elongation of the mesocotyl (when expressed) and elongation of the coleoptile. Sideoats grama had a long mesocotyl and short coleoptiie; western wheatgrass lacked or had a short mesocotyl and a long coleoptile; and smooth bromegrass had intermediate mesocotyl and coleoptile lengths. The "mechanism" of crown placement for seedlings that emerged and survived from a Q-mm seeding depth was non-elongation or elongation of the mesocotyl and leaf internodes. The crowns of sideoats grama seedlings were at the coleoptilar node, which was close to the soil surface. Western wheatgrass seedlings have their crowns near planting depth, usually at the coleoptilar node. Smooth bromegrass crowns were at variable depths because of variable elongation of the mesocotyl and leaf internodes.Terminology for morphological structures of developing grass seedlings remains confusing because of the historical controversy regarding the nature. of the parts of the grass embryo and associated terminology (Esau 1977). A standardized terminology for grass seedling structures would improve communications and understanding of grass seedling development, better describe the location of nodes and internodes for young grass seedlings, and clearly contrast similarities and differences between grass seedlings.This paper reviews the historical development of the terminology describing grass seedling morphology and suggests standardized structures and terminology for grass seedlings. This terminology is used to characterize the morphological development resulting in emergence and crown placement of growth-chamber grown sideoats grama, western wheatgrass, and smooth bromegrass seedlings.Authors are range scientist and research agronomist, USDA-AR.% Northern Great

The shoot and root growth of Brachypodium and its potential as a model for wheat and other cereal crops

“…6a-d) (see also Raju and Steeves 1998). Mesocotyls are reported in other grasses including maize and oats (Radford and Key 1993) and in smooth bromegrass (Ries and Hofmann 1991). Wheat did not have an elongated internode in this position in our experiments.…”

“…Brachypodium had one primary axile root from the seed, did not produce a scutellar node axile root and the development of axile roots from the node above the seed was slightly delayed compared with that of the wheat coleoptile node roots, or may have been associated with leaf one main stem node. Brachypodium may have genes regulating early root types that are more closely related to the warm climate cereals, rice, maize, sorghum (Sorghumm bicolour L.), pearl millet (Pennisatum glaucum L.) and the forage grasses such as smooth bromegrass (Bromus inermis Leyss), which all generally have one primary axile root (Hoshikawa 1969;Wenzel et al 1989;Ries and Hofmann 1991;Hochholdinger et al 2004;M. Watt, unpubl.…”

Viewpoint: Selection for Improved Drought Response in Cool-Season Grasses

“…Most cool-season grasses exhibited a festucoid-type of seedling, which had transitionary-node (seminal) root development, lacked or had little mesocotyl (subcoleoptile internode) elongation, and had no mesocotylar roots. Seedling root morphological development has been examined in various cool-season grasses (Newman and Moser 1988, Aguirre and Johnson 1991b, Ries and Hofmann 1991. Johnson and Aguirre (1991) found that the competitive nature of cheatgrass seedlings was primarily associated with seminal roots that had high branching density, long lateral growth, and external-external links.…”

Seed Size, Sediment, and Spatial Heterogeneity: Post-Flood Species Coexistence in Dryland Riparian Ecosystems

“…Deeply buried, small dicot seeds may not have sufficient maternal reserves to allow the cotyledons to reach the soil surface and begin to photosynthesize. Grass seeds, however, have hypogeal emergence, wherein the mesocotyl elongates above the cotyledon, pushing the coleoptile (which encloses and protects the shoot tip) directly toward the soil surface, and thereby enabling photosynthesis (Ries and Hofmann 1991;Andrews et al 1997). …”