Isolation of photocontrolled gibberellin 3beta-hydroxylase in lettuce seeds.

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Gibberellin was mediated in the photoinduction of lettuce seeds germination. Feeding experiments of ^3H-GAs suggested that the final step of active GA synthesis, namely, 3beta-hydroxylation of GA_<20> to GA_1 was activated by light. The purpose of this research was isolate the 3 hydroxylase from lettuce seeds and to determine the change of activity directly.Enzyme activity of the lettuce seeds homogenate was too low to isolate it caused by the existence of plenty amount of phenolic compounds. Besides, the supply of lettuce seeds was shorted. Therefore, we must change the plant materials from lettuce to Phaseolus virgules.One dwarf variety of P. vergules named "Green dash" was selected from several variety on the viewpoint of photoinhibition of hypocotyl growth. Inhibition rate of hypocotyl growth by white light was age independent between 5 to 10 days after sowing. Effect of light was nearly saturated at 0.4Wm^<-2>. Inhibition rate was linear to the logarithm of irradiation period when it was shorter than 12 hr. Application of GA_3 recover the photoinhibited hypocotyl growth to the dark level. However, growth in the dark was little effected by GA_3. On the other hand, application of GA synthesis inhibitor highly suppress only the growth in the dark. These results suggested that the effect of light was visualize in the length of hypocotyl mediated by gibberellin. Growth inhibition obligated by the application of GA synthesis inhibitor was recovered by the application of GA_3. In this time, about 10 times higher concentration of GA_3 was required for the light grown seedling than dark grown one for full recovery. These results suggested that light induced the reduction of GA level in the hypocotyl and reduced the sensitivity of hypocotyl to GAs.