GREEN LIGHT DRIVES CO2 FIXATION DEEP WITHIN LEAVES

Maximal (CO2)-C-14-fixation in spinach occurs in the middle of the pal isade mesophyll [Nishio et al. (1993) Plant Cell 5: 953], however, nin ety percent of the blue and red light is attenuated in the upper twent y percent of a spinach leaf [Cui et al. (1991) Plant Cell Environ. 14: 493]. In this report, we showed that green light drives (CO2)-C-14-fi xation deep within spinach leaves compared to red and blue light. Blue light caused fixation mainly in the palisade mesophyll of the leaf, w hereas red light drove fixation slightly deeper into the leaf than did blue light. (CO2)-C-14-fixation measured under green light resulted i n less fixation in the upper epidermal layer (guard cells) and upper m ost palisade mesophyll compared to red and blue light, but led to more fixation deeper in the leaf than that caused by either red or blue li ght. Saturating white, red, or green light resulted in similar maximal (CO2)-C-14-fixation rates, whereas under the highest irradiance of bl ue light given, carbon fixation was not saturated, but it asymptotical ly approached the maximal (CO2)-C-14-fixation rates attained under the other types of light. The importance of green light in photosynthesis is discussed.