The sporophytic type of self-incompatibility exhibited by Ipomoea cairica Sweet (Convolvulaceae) was partially overcome in vitro by treating the pollen and/or stigma with 10 -'to 10 -'M methionine, a precursor of ethylene . The implications of these observations are discussed in relation to other experiments involving use of the ethylene antagonist AgNO 3 , individually and in combination with methionine and an optimum level of indole-3-acetic acid (10 -'M). The results suggest a role for ethylene (which could also be IAA-induced) in regulating pollen germination and further tube growth in sporophytic self-incompatible systems . A hypothesis on the action of hormones in pollen germination and tube growth in a sporophytic self-incompatible (SSI) system is presented .

Self-incompatibility is exhibited by callose deposition in the stigmatic papillae and total inhibition of pollen germination in sporophytic self-incompatible (SSI) systems of Ipomoea cairica (Convolvulaceae), Brassica campestris and Raphanus sativus (Brassicaceae) . This has been partially overcome, in vitro by treating pollen and/or stigma with gibberellic acid (GAO ) . Experiments employing tryptophan and chlorocholine chloride either alone or in combination with GA 3 (10 -'M) further elucidate the role of gibberellin in overcoming the barrier to self-compatibility . These results support cur earlier contention [7, 24] that growth regulators play a significant role in pollen-pistil recognition in SSI systems .