Abstract
Plants in the field experience dynamic changes of sunlight rather than steady-state irradiation. Therefore, increasing the photosynthetic rate of an individual leaf under fluctuating light is essential for improving crop productivity. The high-yielding indica rice (Oryza sativa L.) cultivar Takanari is considered a potential donor of photosynthesis genes because of its higher steady-state photosynthesis at both atmospheric and elevated CO2 concentrations than those of several Japanese commercial cultivars, including Koshihikari. Photosynthetic induction after a sudden increase in light intensity is faster in Takanari than in Koshihikari, but whether the daily carbon gain of Takanari outperforms that of Koshihikari under fluctuating light in the field is unclear. Here we report that Takanari has higher non-steady-state photosynthesis, especially under low nitrogen (N) supply, than Koshihikari. In a pot experiment, Takanari had greater leaf carbon gain during the initial 10 min after a sudden increase in irradiation and higher daily CO2 assimilation under simulated natural fluctuating light, at both atmospheric (400 ppm) and elevated (800 ppm) CO2 concentrations. The electron transport rate during a day under field conditions with low N supply was also higher in Takanari than in Koshihikari. Although the advantages of Takanari were diminished under high N supply, photosynthetic N use efficiency was consistently higher in Takanari than in Koshihikari, under both low and high N supply. This study demonstrates that Takanari is a promising donor parent to use in breeding programs aimed at increasing CO2 assimilation in a wide range of environments, including future higher CO2 concentrations.
Highlights
Most of the research programs conducted to improve photosynthetic performance of leaves through genetic engineering and conventional breeding have examined CO2 assimilation rate (A) at steadystate conditions in stable light environments (Yamori et al, 2016; Sage et al, 2017; Simkin et al, 2019)
We have reported that Takanari has a greater photosynthetic induction response to a sudden increase in irradiance than Koshihikari, which could be explained by a combination of a faster response of electron transport rate, larger accumulation of metabolites in the Calvin cycle, and rapid elevation of gs (Adachi et al, 2019a)
We examined the dynamics of electron transport rate using a pulse-amplitudemodulation (PAM) chlorophyll fluorometer in the field
Summary
Most of the research programs conducted to improve photosynthetic performance of leaves through genetic engineering and conventional breeding have examined CO2 assimilation rate (A) at steadystate conditions in stable light environments (Yamori et al, 2016; Sage et al, 2017; Simkin et al, 2019). When the crop canopy is exposed to a sunfleck, leaf A gradually increases to reach a new steady-state level, which takes several seconds to minutes (Pearcy, 1990; Yamori, 2016; Tanaka et al, 2019). This process, which is termed photosynthetic induction, may reduce photosynthetic light use efficiency, and the photosystems may be damaged by excess sunlight (Yamori, 2016). Improving non-steady-state photosynthesis under fluctuating light is an essential challenge to increase crop productivity
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