A DIRECT LIGHT EFFECT ON MAINTAINING PHOTOSYNTHETIC ACTIVITY OF NITELLA CHLOROPLASTS

The chloroplasts of internodal cells of Nitella are fixed to a stationary layer of cytoplasm whereas the nuclei and most of the cytoplasm stream along the longitudinal axis. Isolated internodal cells were maintained for several days with half the cell kept in the dark, the other half kept under continuous light. Photosynthetic activity of the cells was checked by placing the cell evenly illuminated in a 14CO2 atmosphere. Chloroplasts of the previously dark half of the cell were found to fix only half as much CO2 as the chloroplasts which were continuously illuminated. These results are discussed in relation to the possible direct effect of light on biosynthetic reactions of mature chloroplasts.

Effects of Growth-Regulatory Chemicals on the Action Spectra for 14C Assimilation and Transport in Sugarcane Leaves

Pretreatment of sugarcane with the growth hormone gibberellic acid (GA3) and the growth depressant Polaris [N,N-bis (phosphonomethyl) glycine] significantly altered the action spectra for 14C assimilation and transport by leaf tissues. Leaf segments enclosed in a 14CO2 atmosphere were illuminated with discrete wavelengths of equal quantum flux from 400 to 710 nanometers (nm). Both compounds significantly lowered 14C assimilation in the blue, from 437 to 480 nm. Polaris accentuated a green depression at 550 nm while lowering assimilation peaks in the red at 600-640 nm and at 670 nm. Translocation of 14C, as percentages of the total nuclide assimilated, was vastly increased by both materials in the blue-violet (400 nm) and by GA3 in the blue (437-480 nm). Polaris increased transport from the blue-green to yellow (520-600 nm). A high sensitivity of control plants to far-red light (710 nm) was unaffected by either material. These results support the theory that chemical ripening may involve sugar synthesis and transport processes in addition to growth-regulatory effects in sink tissues.