CHARACTERIZATION OF SUBCOLEOPTILE INTERNODE ELONGATION IN GRASSES GROWN IN LOW LIGHT

Authors: Tischler, Charles; Voigt, Paul; MONK, R - CARGILL HYBRID SEEDS TX

Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: For a warm-season grass seedling to survive and grow, adventitious roots, which arise at the crown of the plant, must form and grow into the soil. This does not occur until the seedling is about 14 days old. During the process of germination, elongation of a structure called the subcoleoptile internode (SCI) elevates the crown of the plant to near the soil surface, at which time SCI elongation should stop. This happens when the shoot tip senses light. However, in some grasses too much elongation occurs, and the crown is above the soil surface. Because it is difficult for adventitious roots to grow through air down to the soil, few seedlings with an elevated crown survive. We grew seedlings of several grasses and sorghum breeding lines and hybrids in constant dim light to study elongation of the SCI. In all the species, SCI elongation was complete by four days after planting, and the mean length of the SCI was different for each species. Also, we observed much variability for SCI length within each grass species. In sorghum, three sets of hybrids and their respective parents were studied. Results indicated that SCI growth rate or sensitivity to light do not exhibit hybrid vigor, but are under precise genetic control. The fact that total elongation of the SCI at day four differed between the different hybrids indicates that genetic variation may exist for sensitivity of this response to light. Selection and plant breeding for lower placement of the crown should be successful. Realization of this goal would greatly improve seedling establishment in a number of warm- season grasses, by making it much easier for the plant to develop adventitious roots.

Technical Abstract: The subcoleoptile internode (SCI) of developing Panicoid grass seedlings often elongates excessively, placing the coleoptilar node (CN) at or above the soil surface. Most seedlings with a CN located on or above the soil surface perish. Location of the CN is controlled by the interaction of Pfr and an auxin-producing system in the coleoptile. Grass species which have an elevated CN in the field also have elevated nodes when grown under continuous dim light. To refine a plant culture system which could be used in a plant breeding program to reduce CN elevation, four forage grasses and three sorghum (Sorghum bicolor [L.] Moench) hybrids and their parents were grown in this system. Objectives were to determine the kinetics of SCI and shoot elongation and, for sorghum, to determine if variability in response existed among inbred lines, and if heterosis was observed for either shoot or SCI elongation. For all species, SCI elongation appeared to cease by 4 days, although shoots continued to elongate. Heterosis (above high parent) was observed for shoot length, but not for SCI length, for all sorghum hybrids. Variability in SCI length among sorghum inbreds suggests that genetic variability exists for sensitivity to light, and subsequent CN placement. Were this technique used in a plant breeding scheme, desired seedlings could be chosen by 4 days post planting (when seedlings are more able to survive transplanting). This system may be useful in a plant breeding approach to modify photomorphogenic responses of monocot seedlings.