Gibberellins and Inhibitors in Relation to Flowering of White Clovers (Trifolium repens L.)

Flower primordia appeared sooner and flowering intensity increasedas day length was extended beyond 8 h (short day) in two whiteclovers: cv. Tamar and cv. Tammisto, originating from Israeland Finland, respectively. Application of GA₃ under short dayscaused Tamar to flower more intensively as much as the doseof GA₃ was increased, but it did not affect the flowering ofTammisto. The level of gibberellin-like substances in stolon apices washigher under long (16 h) than under short days in both cultivars.The level of inhibitors extracted from leaves was not affectedby day length in Tamar. However, in Tammisto this level wasalmost twice as high under short than under long days. It issuggested that the presence of a relatively high level of inhibitorsin Tammisto when grown under short days interfered with theactivity of gibberellins in its effect on flowering. ABA wasamong the inhibitors: its application under long days had noeffect on flowering, but it increased the number of stolons.Possibly inhibitors other than ABA are involved in the preventionof flowering. Leaf expansion responded to day length and GA₃ and ABA applicationin a similar way as the response of flowering, i.e. towardsflowering the size of the leaves increased.