Two new plant growth regulators were isolated from a culture filtrate of Cladosporium cladosporioides. One of them is a root growth inhibitor of lettuce seedlings, cladospolide A, (E)-4, 5-dihydroxy-2-dodecen-11-olide and the other is a root growth promoter of lettuce seedlings, cladospolide B, (Z)-4, 5-dihydroxy-2-dodecen-11-olide. It is interesting that these isomers have different biological activities.
