Investigations of growth-promoting factors in conditioned soybean root cells and in the liquid medium in which they grow: ammonium, glutamine, and amino acids

Abstract

Cells cultured in sterile, liquid media from a number of Phaseolus spp., soybean cotyledons, shoots, and roots and from rice explants grew, in terms of dry-weight increase, much better in the presence of NH4+ and NO3− as sources of nitrogen than with NO3− alone. Other cultures tested, including other legumes, either did not respond positively to added NH4+ or, as in the case of Haplopappus gracilis cells, grew better in its absence.Earlier it had been shown that soybean (Glycine max. L. cv. Mandarin) root cells grew better in the presence of NH4+ than in its absence and that 'conditioning' substances were produced by cells and excreted into the medium between about the 15th and 35th h of incubation. These observations and those above with other cell cultures led to the initiation of an investigation of why some cells respond to NH4+ while others do not.This investigation has so far taken the form of an analysis of nitrogenous compounds in soybean root cells and in the NH4+-containing medium in which they were grown during 120 h of incubation and especially after 24 h of incubation, the time of maximum production of growth-enhancing ability in both cells and medium.Growth enhancement can be accounted for, apparently, by the occurrence of residual NH4+ in conditioned medium and by the presumed occurrence of NH4+ in cells. However, glutamine and its derivatives are implicated in the conditioning process.