THE KINETICS OF TYPE-1 PHYTOCHROME IN GREEN, LIGHT-GROWN WHEAT (TRITICUM-AESTIVUM L)

The kinetics of type 1 phytochrome were investigated in green, light-g rown wheat. Phytochrome was measured by a quantitative sandwich enzyme -linked immunosorbent assay using monoclonal antibodies. The assay was capable of detecting down to 150 pg of phytochrome. In red light, rap id first-order destruction of the far-red-light-absorbing form of phyt ochrome (Pfr) with a half-life of 15 min was observed. Following white light terminated by red, phytochrome synthesis was delayed in darknes s by about 15 h compared to plants given a terminal far-red treatment. Synthesis of the red-light-absorbing form of phytochrome (Pr) was zer o-order in these experiments. Phytochrome synthesis in far-red light w as approximately equal to synthesis in darkness in wheat although net destruction occurred in light-grown Avena sativa tissues in continuous far-red light, as has been reported for other monocotyledons. In whea t, destruction of Pfr apparently did not occur below a certain thresho ld level of Pfr or Pfr/total phytochrome. These results are consistent with an involvement of type 1 phytochrome in the photoperiodic contro l of flowering in wheat and other long-day plants.