Physiological regulations and the evaluation technologiesof the crop photosynthesis
Yu Tanaka (Graduate School of Agriculture, Kyoto University)
tanaka.yu.2s@kyoto-u.ac.jp
Single leaf photosynthesis is one of the most important traits affecting the crop dry matter productivity.
Until now, however, limited information is available for the enhancement of crop productivity throughincreased photosynthetic capacity. This is due to the complexed process of the environmental responsesof leaf photosynthesis and biomass production under the field conditions, with lower throughput of themeasurement of leaf photosynthesis. The present study aimed to elucidate the physiological mechanisms
underlying the genetic variations of leaf photosynthesis and their environmental responses in soybean
and rice, and to develop the technologies enabling the high-throughput measurement of the leaf
photosynthesis.
The significant genetic variation of the single leaf photosynthetic capacity was observed between thehigh yielding US varieties, popular Japanese varieties and landraces from Asia. The observed variation
was explained by both of the gas exchange activity through stomata and carboxylation activity in themesophyll cells. The high yielding varieties from US tended to show the greater stomatal density perunit leaf area1). The study showed that there is a room to improve the photosynthetic capacity of soybean
by combining the beneficial traits observed in the various genetic resources.
Typically, it takes several minutes per sample to measure the leaf photosynthesis using the conventional
open gas exchange systems. This is due to the stabilization time of the CO2 concentration in the leafchamber. The present study developed the new instrument based on the closed system, which directly
detects the instantaneous decrease of the CO2 concentration caused by the photosynthesis of single leaf
enclosed in the leaf chamber. The developed instrument, MIC-100, enables the 7 times greatermeasurement throughput of the leaf photosynthesis with the practical accuracy compared with theconventional ones2). MIC-100 will be a powerful tool to conduct the screening of the photosynthetic
capacity among large scaled plant populations.
The leaf photosynthetic rate does not respond immediately to the sudden increase of light intensity, but
gradually responds with significant delay. This study elucidated that the potential loss of the carbon gain
was up to 20% due to the existence of this delay in the photosynthetic response3). The significant natural
genetic variation of the speed of photosynthetic response to the fluctuating light intensity was observed
among rice and soybean varieties, and it was regulated independently from the photosynthetic capacity
under the steady state. The response of the leaf photosynthesis to the light fluctuation will be one of thekey traits to improve the biomass productivity of crop species.
1) Tanaka, Y., Fujii K., Shiraiwa, T.: Variability of Leaf Morphology and Stomatal Conductance inSoybean [Glycine max (L.) Merr.] Cultivars. Crop Sci. 50, 2525-2532 (2010)
2) Tanaka, Y., Taniyoshi, K., Imamura, A., Mukai, R., Sukemura, S., Sakoda, K., Adachi, S.: MIC-100,
a new system for high-throughput phenotyping of instantaneous leaf photosynthetic rate in the field.
Functional Plant Biology. 49, 496-504. (2022)
3) Tanaka, Y., Adachi, S., Yamori, W.: Natural genetic variation of the photosynthetic induction response
to fluctuating light environment. Curr. Opin. Plant Biol. 49, 52-59. (2019)