Light-induced nuclear translocation of endogenous pea phytochrome A visualized by immunocytochemical procedures

Although the physiological functions of phytochrome A (PhyA) are now known, the distribution of endogenous PhyA has not been examined. We have visuali zed endogenous PhyA apoprotein (PHYA) by immunolabeling cryosections of pea tissue, using PHYA-deficient mutants as negative controls. By this method, we examined the distribution of PHYA in different tissues and changes in i ts intracellular distribution in response to light. In apical hook cells of etiolated seedlings, PHYA immunolabeling was distributed diffusely in the cytosol. Exposure to continuous far-red (cFR) light caused a redistribution of the immunolabeling to the nucleus, first detectable after 1.5 hr and gr eatest at 4.5 hr. During this time, the amounts of spectrally active phytoc hrome and PHYA did not decline substantially. Exposure to continuous red (c R) light or to a brief pulse of red light also resulted in redistribution o f immunolabeling to the nucleus, but this occurred much more rapidly and wi th a different pattern of intranuclear distribution than it did in response to cFR light. Exposures to cR light resulted in loss of immunolabeling, wh ich was associated with PHYA degradation. These results indicate that the l ight-induced intracellular location of PHYA is wavelength dependent and imp ly that this is important for PhyA activity.