Molecular orientation: Spectral dependence of dichroism of chloroplasts in vivo

• 1.

  1. The spectral dependence of dichroism of chloroplasts in vivo was measured in order to determine if chloroplast bifluorescence is due to an oriented absorbing pigment system.

• 2.

  2. Dichroic ratios of 2.5–4.0 were obtained in the spectral region of 705 mμ where dichroism is maximum.

• 3.

  3. The direction or sense of the dichroism in chloroplasts indicates that the absorbing oscillator lies in or near the plane of the chloroplast lamellae. This is an accord with out previous observations of bifluorescence.

• 4.

  4. No dichroism of chloroplasts in vivo could be detected in the ultraviolet spectral region from 250 to 400 mμ nor in the visual region from 400 mμ to 570 mμ.

• 5.

  5. A consideration of the pigment orientation in terms of energy transfer and in terms of macromolecular complexes is offered in a discussion involving the comparison of chromophore orientation in analogous paracrystalline systems both in vivo and in vitro.