Frond senescence inLemna gibbaG3 was characterized, and its control by light, ABA and kinetin investigated. The plant exhibits a determinate growth pattern with a frond producing a set number of daughter fronds before undergoing senescence and death regardless of whether or not it flowers. When a frond was cut in half, the distal half (half frond) which lacks any meristem underwent rapid senescence as compared with intact fronds. In both intact and half fronds, the onset of senescence was accelerated by ABA and retarded by kinetin. Continuous white light accelerated senescence in both intact and half fronds over the dark controls. Under different photoperiodic light regime, the pace of daughter frond production is accelerated in proportion to the length of light period. In half fronds, however, very short photoperiodic light treatments (e.g. 1L: 23D or 3L: 21D) rather delayed senescence over the dark controls. Two separate light control systems operating in opposite directions inLemanasenescence appear to exist.
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