THE DEVELOPMENT OF SOLID SPECTRAL FILTERS FOR THE REGULATION OF PLANT-GROWTH

Phthalocyanine derivatives have been prepared and incorporated into po lymer films for use as spectral filters for the modification of plant growth. The unusual absorption characteristics of phthalocyanines, not ably the narrow absorption band in the visible region of the electroma gnetic spectrum, allows the selective filtering of wavelengths necessa ry for excitation of either of the two isomeric phytochrome species, T he resulting change in the photostationary state for the phytochrome i s shown to have a marked effect on the growth characteristics of both chrysanthemums and antirrhinums, Chrysanthemums (short-day plants) gro wn under a far-red-absorbing film showed a reduction in height (approx imate to 14%) and internodal length compared to those grown under a re d-absorbing film or a control with no absorption in the visible part o f the spectrum; both leaf number and time to flowering were not affect ed by the presence of the spectral filter. For antirrhinums Gong-day p lants) both a reduction in height and a substantial increase in leaf a rea (70%) of the plants grown under the far-red-absorbing film were ob served, although flowering was delayed. The potential of these filters as replacements for chemical plant growth regulators is discussed.