Physiological Controls on the Production of Cleistogamous and Chasmogamous Flowers in Lamium amplexicaule L

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Abstract
Plants of Lamium amplexicaule , grown under short-day field conditions in Northern California produce predominantly closed flowers. Under long-day field conditions, plants may produce up to 50 per cent open flowers, the same total number of flowers being produced under each daylength regime. A 20 ml drop of GA 3 or GA 7 (100μM) was applied to the main shoot apex of plants growing under short-day conditions, and all subsequently produced flowers opened. CCC, an inhibitor of gibberellin synthesis, was applied (0.06 per cent) to the soil of seedlings grown under long-day conditions. The CCC-treated plants were dwarfed and bore only closed flowers. With GA 7 applied exogenously to the CCC-treated shoots, inhibition was released, resulting in elongated internodes and open flower production. The timing of flower production and internodal extension in Lamium amplexicaule are positively correlated. When floral primordia were removed from main shoots, the average internode lengths decreased. The number of nodes produced in treated plants was increased as a result of flower removal. Exogenous GA 7 (10 μM) applied to the nodes from which flowers were removed resulted in internodal extension but had no effect on node number. Two processes that may contribute to the control of the production of open and closed flowers in Lamium amplexicaule are: (1) an increasing anther sac size from lower to upper node flowers that may exert control locally, via GN production, on corolla expansion, and (2) a photoperiodic control.