PARTIAL CHARACTERIZATION and LIGHT-INDUCED REGULATION OF GTP-BINDING PROTEINS IN Lemna paucicostata

Binding of GTP-binding proteins with [³⁵S]GTP7S in the extract containing membrane components of Lemna paucicostata 441 was inhibited by red or far red light by 20 to 25%, but blue light showed no or little effect. The plant used for the preparation of the extract was subjected to single darkness for 8 h, as both red and far red light inhibit flowering. The extract treated with 1% Lubrol was fractionated by gel filtration. Four species of GTP-binding proteins, GL1, GL2, GL3 and GL4 were detected with Km values 3, 7, 80 and 4 n M , respectively. GL1, GL2 and GL3 were ADP-ribosylated by pertussis toxin. The extract activated by [³⁵S]GTP-γS in darkness, under red light or under far red light was treated with 1% Lubrol and subsequent gel filtration of the extracts made it possible to detect GTP-binding protein with a small molecular weight only in an extract labeled in darkness. The reduction in the molecular weight of GTP-binding protein from the larger molecule associated with the binding of [³⁵S]GTPγS was confirmed by rechromatography of the larger molecule activated by [³⁵S]GTPγS in darkness. The binding of GL2 and/or GL3 with [³⁵S]GTPγS was suggested to be inhibited by red or far red light.     

RHYTHMIC OSCILLATION OF CYCLIC 3',5'AMP AND -GMP CONCENTRATION AND STIMULATION OF FLOWERING BY CYCLIC 3',5'-GMP IN Lemna paucicostata 381

Abstract— Rhythmic oscillation of the concentration of cyclic 3',5'-AMP and -GMP in a short day plant, Lemna paucicostata 381 in continuous darkness was detected after 2 cycles of 12 h dark and 12 h light entrainment. Cyclic 3',5'-AMP and -GMP, extracted from whole plant showed parallel oscillations in their concentrations for initial 36 h in continuous darkness and the oscillation in the concentration of cyclic 3',5'-AMP was roughly circadian. Their concentrations decreased during the initial 12 h (subjective night) and increased during 12 to 28 h. Exogenous addition of 2 μ.M of cyclic 3',5'-GMP or the dibutyryl derivative of it stimulated floral induction by 20 to 30%, when the plants were grown under 12 h light and 12 h dark regime. Cyclic 3',5'-AMP or the dibutyryl derivative of it showed little effect on flowering.