Cross-reactivity of monoclonal antibodies against rye and pea phytochrome with phytochromes extracted from eight different plant species

Cross-reactivity of 6 monoclonal anti-rye phytochrome antibodies (mAR1–6) and 6 monoclonal anti-pea phytochrome antibodies (mAP1–6) with ‘large’ phytchromes extracted from etiolated tissues of duckweed, rice, rye, oat, radish, soybean, mung bean and pea was examined by radioimmunoassay using sheep red blood cells coupled to rye or pea phytochrome as target cells. Oat phytochrome reacted with only mAR5 and mAR6. Radish phytochrome reacted with mAP6, and soybean phytochrome reacted with mAP5 and mAP6. Mung bean phytochrome reacted with mAP4, mAP5 and mAP6. No cross-reactions were observed with any other possible combinations except those of mARs with antigen rye phytochrome and of mAPs with pea phytochrome. These results are discussed in terms of the sites on phytochrome molecules which are recognized by these monoclonal antibodies.