Articles
CONTINUOUS LIGHT EFFECTS ON PHOTOSYNTHESIS AND CARBON METABOLISM IN TOMATO
Fresh weights per leaf area, pigment composition (chlorophylls a and b and carotenoids), carbon fixation (carbon exchange rates and Rubisco activities) and whole-chain photosynthetic electron transport capacity were examined in the fourth leaf of young plants grown in controlled environment chambers under continuous light or 12 hours light/12 hours dark for various periods of time.
Measurements were made over a time course of symptom development and a range of injury severity.
Despite the development of visible mottled chlorosis soon after exposure to continuous light, pigment levels were not measurably lower than those of controls grown under a 12-hour photoperiod until injury was quite severe, indicating that pigment levels in green areas of the leaf compensated for pigment losses in chlorotic areas.
A slight, but possibly not significant, increase in the chlorophyll a/b ratio and a visible thickening and hardening of the leaves hinted at possible physiological changes similar to those found in high light leaves.
The addition of far-red light as a supplement to the white light greatly reduces these injury symptoms.
Additionally, carbohydrate levels (hexose, sucrose, and starch) are different in the far-red+white exposed plants, from the levels in the white-only exposed plants.
Possible causative mechanisms for these effects are discussed.