Role of boron in the far-red delay of nyctinastic closure of albizzia pinnules.

Boron has been found to be necessary for the delaying action of 710 nanometer irradiation on the nyctinastic closing of Albizzia julibrissin pinnules. It is effective only over a narrow micromolar range. In contrast, the delaying action of 470 nanometer irradiation on closure is inhibited by boron. The effect of boron on leaflet closing occurs rapidly. Boron is suggested to be involved in a phytochrome action that precedes and is required for a delaying effect on pinnule closing subsequently induced by an unknown far-red absorbing pigment.