CHARACTERIZATION OF SUBCOLEOPTILE INTERNODE ELONGATION IN GRASSES GROWN IN LOW-LIGHT

The subcoleoptile internode (SCI) of developing Panicoid grass seedlin gs often elongates excessively, and results in placement of the coleop tilar 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 co ntrolled by the interaction of Pc, and an aurin-producing system in th e coleoptile. Grass species which have an elevated CN in field situati ons 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 sho ot elongation and, for sorghum, to also determine if variability in re sponse existed among inbred lines, and if heterosis was observed for e ither shoot or SCI elongation. Seed were planted in commercial potting media and resulting plants measured for 7 d. For all species, SCI elo ngation appeared to cease by 4 d, although shoots continued to elongat e. Heterosis (above high parent) was observed for shoot length, but no t for SCI length, for all sorghum hybrids. Variability in SCI length a mong sorghum inbreds suggests that genetic variability exists for sens itivity to light, and subsequent CN placement. If this technique was u sed in a plant breeding scheme, desired seedlings could be chosen by 4 d post planting (when seedlings are more able to survive transplantin g). This system may be useful in a plant breeding approach to modify p hotomorphogenic responses of monocot seedlings.