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

Plants of Lamium amplexicaule, grown under short-day field conditionsin Northern California produce predominantly closed flowers.Under long-day field conditions, plants may produce up to 50per cent open flowers, the same total number of flowers beingproduced under each daylength regime. A 20 ml drop of GA₃ or GA₇ (100µM) was applied to themain shoot apex of plants growing under short-day conditions,and all subsequently produced flowers opened. CCC, an inhibitorof gibberellin synthesis, was applied (0.06 per cent) to thesoil of seedlings grown under long-day conditions. The CCC-treatedplants were dwarfed and bore only closed flowers. With GA₇ appliedexogenously to the CCC-treated shoots, inhibition was released,resulting in elongated internodes and open flower production.The timing of flower production and internodal extension inLamium amplexicaule are positively correlated. When floral primordiawere removed from main shoots, the average internode lengthsdecreased. The number of nodes produced in treated plants wasincreased as a result of flower removal. Exogenous GA₇ (10 µM)applied to the nodes from which flowers were removed resultedin internodal extension but had no effect on node number. Twoprocesses that may contribute to the control of the productionof open and closed flowers in Lamium amplexicaule are: (1) anincreasing anther sac size from lower to upper node flowersthat may exert control locally, via GN production, on corollaexpansion, and (2) a photoperiodic control. Lamium amplexicaule L, henbit, cleistogamy, chasmogamy, gibberellins, gibberellic acid (GA₃), (2 chloroethyl) trimethylammonium chloride (cycocel)