SYNERGISTIC EFFECTS OF PROLINE AND INORGANIC MICRONUTRIENTS AND EFFECTS OF INDIVIDUAL MICRONUTRIENTS ON SOYBEAN (GLYCINE-MAX) SHOOT REGENERATION IN-VITRO

We reported earlier that adding 2 g.L(-1) L-proline and raising fourfo ld the level of inorganic micronutrients in a modified Murashige and S koog (MS) medium enhances shoot regeneration from primary-leaf-node ex plants of 7-d-old soybean (Glycine max [L.] Merr.) seedlings. These fi ndings are here extended to regeneration from explants consisting of a cotyledon cut from a 7-d-old soybean seedling. For both kinds of expl ant, a synergistic, approximately threefold stimulation of shoot regen eration by these two supplements in combination is documented. Proline increased number but decreased length of regenerated shoots, whereas raising micronutrient level generally increased both shoot number and length and, thus, partly overcame the effect of proline on length. Exa mining the effects of singly including, omitting, raising the levels o f, and lowering the levels of the seven different micronutrient elemen ts of the original MS medium provides evidence that the supply of coba lt is near-optimal at the original MS concentration but the other six elements are in less than optimal supply. Altering the zinc supply had the strongest effects overall.