Disappearance of rhythmicity in growth response to dark- and light-breaks inLemna gibbaG3 due to iron deficiency

摘要

Inhibition of flower initiation in light culture of a long-day duckweed,Lemna gibbaG3 by an inserted period of brief darkness changes its magnitude with the application time of the dark-break.‘Responsevs. time of the dark-break’curve consists of superimposed thermo-insensitive oscillatory and thermo-sensitive hourglass components. Oscillation is diurnal and damps in a few days. The situation is very similar to what has previously been revealed concerning the non-photosynthetic light-requirement of the same strain of duckweed for frond multiplication. Increasing photophily for flower production is likely accompanied by decreasing photophily for frond production, andvice versa. The presence of iron chelators such aso-phenanthroline andα,α′-dipyridyl or reduced iron concentration in culture medium abolishes the oscillatory change, without modifying the hourglass change, in either vegetative or reproductive photophily. Ferrous, but not ferric, ions likely mediate between the basic clock and the photophily. Critical daylength for flower induction is not affected by exogenous ch