Enhanced shoot regeneration from Brassica campestris by silver nitrate

The morphogenetic response of Brassica campestris genotype R500 to inhibitors of ethylene biosynthesis and action was investigated. A medium containing 1.0 mg.l(-1) NAA, 2.0 mg.l(-1) BAP, and 30 or 60 μM AgNO3 significantly enhanced both the percentage shoot regeneration and the number of shoots per cotyledon expiant. Although callus proliferation occurred on hypocotyl segments, no shoots were formed in response to AgNO3 with expiants older than five days. Cotyledons older than six days formed shoots only with AgNO3. Cobalt chloride at 20 and 30 μM increased cotyledon shoot regeneration but was inferior to AgNO3. Hypocotyl segments were unresponsive. Salicylic acid at 25 and 50 μM prevented both shoot regeneration and callusing without any obvious toxic effects. Removal of expiants from AgNO3 after 12 days did not alter the percentage of shoot regeneration but increased the number of shoots per expiant. This response was dependent on the level of BAP. Percentage shoot regeneration and number of shoots per cotyledon explant were not affected by removal of CoCl2. These results indicate that the poor regenerative capacity of this genotype may be related to ethylene biosynthesis or metabolism.