Floral induction in a photoperiodically neutral duckweed, Lemna paucicostata strain LP₆: role of chelating agents and iron

Abstract

Lemna paucicostata, strain LP₆, does not ordinarily flower under any photoperiodic schedule, when grown in the modified Bonner-Devirian medium supplemented with 10^-4 M EDTA and 1% sucrose (this is a medium which is otherwise satisfactory for short day induction of flowering of other strains of this duckweed). However, when the ferric citrate concentration in the culture medium containing EDTA was raised 10-fold over that in the normal medium, a low but significant flowering could be initiated in this duckweed, irrespective of the length of the photoperiod. A similar flowering response was obtained when ferric citrate was replaced by ferrous sulphate or ferric chloride, thereby indicating that the inductive effect of higher level of ferric citrate on flowering in strain LP₆ is due to its iron component. Some flowering in this strain could be induced even in medium containing normal level of iron, provided the level of EDTA, itself, was raised to 5×10^-4 (5% flowering) or to 10^-3 M (12% flowering), but replacement of EDTA by EDDHA led to truly remarkable effects. With EDDHA, flowering could be induced at very high levels (90%) under all photoperiodic regimes tried. Floral initiation could be obtained even with 10^-6 M EDDHA, though the optimal level ranged from 5×10^-6 to 10^-5 M.