OPTIMIZING THE CALCIUM CONTENT OF A COPOLYMER ACRYLAMIDE-GEL MATRIX FOR DARK-GROWN SEEDLINGS

A copolymer acrylamide acrylate gel was investigated as the sole root matrix for dark-grown seedlings of soybean (Glycine max Merr. 'Century 84'). Increasing Ca2+ in the hydrating solution of the hydrogel from 1 to 10 mM decreased its water-holding capacity from 97 to 46 mL.g(-1) , yet water potential of the medium remained high, sufficient for norm al plant growth at all Ca2+ concentrations tested. Elongation rate of dark-grown soybean seedlings over a 54-hour period was 0.9, 1.5, and 1 .8 mm.h(-1) with 1.0, 2.5, or 5.0 mM Ca2+, respectively, but did not i ncrease with further increases in Ca2+ concentration. Further study re vealed that Na+ was released from the hydrogel medium and was taken up by the seedlings as Ca2+ increased in the medium. In dry hypocotyl ti ssue, sodium content correlated negatively with calcium content. Despi te the presence of Na+ in the hydrogel, seedling growth was normal whe n adequate Ca2+ was added in the hydrating solution. Acrylamide hydrog els hold good potential as a sole growth matrix for short-term experim ents with dark-grown seedlings without irrigation.