Comparison of spectral properties of phytochromes from different preparations.

The spectral parameters of phytochrome in vitro described in several recent studies have been determined in purer and less degraded phytochrome samples than those used by Butler, Hendricks and Siegelman more than 20 years ago. There are considerable differences between the old and the new data. It seems logical that the researchers interested in phytochrome-mediated photomorphogenesis should use the new data for ;native' phytochrome instead of the old ones, still in common use. A comparison of the spectral properties of phytochrome described in old and recent studies show that the differences among the ;new' data are as large or larger, depending on the particular parameter and wavelength region considered, than the differences between ;old' and ;new' data. Therefore, if one should decide to use the new data instead of the old ones, one must also decide which set of new data should be used. The latter is a difficult choice. No matter what the choice, it should be open to revision in the future, the limitations associated with the choice should be noted, and the use of any set of spectral parameters of phytochrome should be made with extreme caution.