Photosynthesis Physiology

1. Genetic Improvement of Leaf Photosynthetic Capacity Note: Part of this research is supported by the Fukushima Institute for Research, Education and Innovation (F-REI) commissioned project "Development of Technology to Enhance CO2 Fixation Function of Rice for Achieving Negative Emission Agriculture from Fukushima."

Suddenly, how many "varieties" of rice and soybeans can you name? And how many rice and soybean varieties do you think exist in the world? 100? 500? In fact, it is said that there are 20,000 to 30,000 varieties and lines of each of these crops worldwide. However, most of these are not used for commercial cultivation. It is highly likely that among these unutilized genetic resources, there are materials with excellent photosynthetic capacity waiting to be discovered. Finding useful materials and elucidating their mechanisms is expected to lead to improved productivity of current varieties.

However, measuring photosynthetic capacity requires considerable time and effort, making it impractical to select for photosynthetic capacity across large collections of varieties. Therefore, we first developed a technology to efficiently measure photosynthetic capacity across numerous rice varieties. The result was the MIC-100, a high-speed photosynthesis measurement device. The successful development of this device has improved the efficiency of photosynthetic capacity measurement several-fold compared to conventional methods, enabling large-scale selection tests for photosynthetic capacity that were previously impossible. Currently, we are cultivating hundreds of rice varieties in paddy fields and selecting for photosynthetic capacity using the MIC-100. We hope to find varieties with extraordinarily high photosynthetic capacity that have not been discovered before.

2. Elucidation and Improvement of Photosynthetic Response Under Fluctuating Light Environments Crops growing in the field are exposed to various changes in their surrounding environment. For example, from spring sowing to autumn harvest, rice and soybeans grow over several months while being influenced daily by many factors such as temperature, light (solar radiation), moisture (rain), various stresses from pests and diseases, and soil fertility. Among these, solar radiation is an extremely important factor directly linked to photosynthetic activity in leaves.

Solar radiation changes dramatically over the course of a day. It follows a pattern of strengthening from morning to noon and weakening toward night. Basically, the stronger the light, the higher the photosynthetic activity. However, in addition to these gradual changes, solar radiation can change dramatically within minutes or even seconds when blocked by clouds. Previously, the detailed photosynthetic responses occurring in leaves exposed to such dramatic changes were not well understood.

We have demonstrated that there are significant varietal differences (genetic variations) in the speed at which photosynthesis activates when transitioning from a dark (cloudy) state to a bright (sunny) state, particularly in rice and soybeans. In other words, we have found that there are individual characteristics just like in humans, such as "rice varieties that wake up well" and "soybean varieties that wake up poorly." We consider this a surprising discovery.

If you could work at top speed right from waking up every morning, you would probably accomplish many tasks (unfortunately, I am not that type of person). Similarly, don't you think that if we selected and cultivated rice and soybeans that could photosynthesize at top speed as soon as solar radiation strengthens, they would perform more photosynthesis efficiently and grow more effectively?

Based on this idea, we are conducting research aimed at elucidating the physiological and genetic mechanisms that determine "how well crops wake up," and through this, creating crops that grow more efficiently in outdoor environments.