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A transient in chlorophyll fluorescence after cessation of actinic light illumination, which has been ascribed to electron donation from stromal reductants to plastoquinone (PQ) by the NAD(P)H-dehydrogenase (NDH) complex, was investigated in Arabidopsis thaliana. The transient was absent in air in a mutant lacking the NDH complex (ndhM). However, in ndhM, the transient was detected in CO(2)-free air containing 2% O(2). To investigate the reason, ndhM was crossed with a pgr5 mutant impaired in ferredoxin (Fd)-dependent electron donation from NADPH to PQ, which is known to be redundant for NDH-dependent PQ reduction in the cyclic electron flow around photosystem I (PSI). In ndhM pgr5, the transient was absent even in CO(2)-free air with 2% O(2), demonstrating that the post-illumination transient can also be induced by the Fd- (or PGR5)-dependent PQ reduction. On the other hand, the transient increase in chlorophyll fluorescence was found to be enhanced in normal air in a mutant impaired in plastid fructose-1,6-bisphosphate aldolase (FBA) activity. The mutant, termed fba3-1, offers unique opportunities to examine the relative contribution of the two paths, i.e., the NDH- and Fd- (or PGR5)-dependent paths, on the PSI cyclic electron flow. Crossing fba3-1 with either ndhM or pgr5 and assessing the transient suggested that the main route for the PSI cyclic electron flow shifts from the NDH-dependent path to the Fd-dependent path in response to sink limitation of linear electron flow.

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Because global climate change has made agricultural supply unstable, plant factories are expected to be a safe and stable means of food production. As the light source of a plant factory or controlled greenhouse, the light emitting diode (LED) is expected to solve cost problems and promote plant growth efficiently. In this study, we examined the light condition created by using monochromatic red and blue LEDs, to provide both simultaneous and alternating irradiation to leaf lettuce. The result was that simultaneous red and blue irradiation promoted plant growth more effectively than monochromatic and fluorescent light irradiation. Moreover, alternating red and blue light accelerated plant growth significantly even when the total light intensity per day was the same as with simultaneous irradiation. The fresh weight in altering irradiation was almost two times higher than with fluorescent light and about 1.6 times higher than with simultaneous irradiation. The growth-promoting effect of alternating irradiation of red and blue light was observed in different cultivars. From the results of experiments, we offer a novel plant growth method named "Shigyo Method", the core concept of which is the alternating irradiation of red and blue light.