Relationship of steroidal structure to ethylene production by etiolated mung bean segments

Several brassinosteroid (BR) analogues, cholesterol and aldosterone were evaluated for their effectiveness alone and in combination with indole‐3‐acetic acid (IAA) in stimulating ethylene production by etiolated mung bean (Vigna radiata L. Rwilcz cv. Berken) hypocotyl segments. Changing the conformation of the two hydroxyl groups on C‐22 and C‐23 positions from α to β did not greatly reduce the efficiency of these compounds to stimulate ethylene production alone or in combination with IAA. There was little difference in activity observed when the conformation of the methyl group in the C‐24 position was changed from α to β. However, when hydroxyls were deleted from the side chain in the C‐22 and C‐23 positions, the compound was rendered inactive alone or in combination with IAA. The compound was also inactivated by removing the 7‐oxa function on the B‐ring and by substituting an ethyl group for the methyl group in the C‐24 position. Both aldosterone and cholesterol were ineffective in promoting ethylene production. This study shows that very stringent structural features are required for a steroid to have BR‐like activity and to act synergistically with auxin in the promotion of ethylene synthesis.