A nuclear gene controlling seminal root growth response to hydroponic cultivation in barley

Abstract A root mutant of barley ( Hordeum vulgare ) was identified in hydroponics using the “sandwich method”. The roots of this mutant, which was first isolated as a grain mutant, did not show the growth pattern with windings and turnings usually observed on wild type barley roots before they submerged. Unlike wild type roots, mutant roots were much longer and grew straight down into the water without displaying any pronounced bending. Genetic analysis of crosses between the mutant and its parent line indicated that these root characteristics were controlled by a single nuclear gene which showed semi-dominant expression and segregated independently from the grain characteristics. Ethylene diffused from wild type roots was higher than that from mutant roots. Control seedlings treated with silver ions, which are antagonists of ethylene perception, copied the mutant phenotype. These observations pointed out the potential involvement of ethylene in the growth pattern displayed by wild type roots before submergence. It is proposed that the growth behavior of wild type roots may be related with a negative hydrotropic response. The barley root mutant here described is a promising experimental material for studies of root genetics and function, especially those regarding root environment sensing and hormonal regulation of root growth and development.