An in situ approach to characterizing photosynthetic gas exchange of rice panicle

Tian-Gen Chang,Xin-Guang Zhu,Hong-Long Zhao,Shuoqi Chang,Changpeng Xin,Mingnan Qu,Qing-Feng Song

doi:10.1186/s13007-020-00633-1

Abstract

BackgroundPhotosynthesis of reproductive organs in C3 cereals is generally regarded as important to crop yield. Whereas, photosynthetic characteristics of reproductive organs are much less understood as compared to leaf photosynthesis, mainly due to methodological limitations. To date, many indirect methods have been developed to study photosynthesis of reproductive organs and its contribution to grain yield, such as organ shading, application of herbicides and photosynthetic measurement of excised organs or tissues, which might be intrusive and cause biases. Thus, a robust and in situ approach needs to be developed.ResultsHere we report the development of a custom-built panicle photosynthesis chamber (P-chamber), which can be connected to standard infrared gas analyzers to study photosynthetic/respiratory rate of a rice panicle. With the P-chamber, we measured panicle photosynthetic characteristics of seven high-yielding elite japonica, japonica-indica hybrid and indica rice cultivars. Results show that, (1) rice panicle is photosynthetically active during grain filling, and there are substantial inter-cultivar variations in panicle photosynthetic and respiratory rates, no matter on a whole panicle basis, on an area basis or on a single spikelet basis; (2) among the seven testing cultivars, whole-panicle gross photosynthetic rates are 17–54 nmol s−1 5 days after heading under photon flux density (PFD) of 2000 μmol (photons) m−2 s−1, which represent some 20–38% of that of the corresponding flag leaves; (3) rice panicle photosynthesis has higher apparent CO2 compensation point, light compensation point and apparent CO2 saturation point, as compared to that of a typical leaf; (4) there is a strong and significant positive correlation between gross photosynthetic rate 5 days after heading on a single spikelet basis and grain setting rate at harvest (Pearson correlation coefficient r = 0.93, p value < 0.0001).ConclusionsRice panicle gross photosynthesis is significant, has great natural variation, and plays an underappreciated role in grain yield formation. The P-Chamber can be used as a tool to study in situ photosynthetic characteristics of irregular non-foliar plant organs, such as ears, culms, leaf sheaths, fruits and branches, which is a relatively less explored area in current cereal breeding community.

Highlights

Photosynthesis of reproductive organs in C3 cereals is generally regarded as important to crop yield
Reproductive organs have several potential advantages over leaves in terms of photosynthate production and transportation: (1) they generally locate at the upper canopy, where light levels are higher than those at the lower canopy; (2) they are physically closer to the developing grains than the leaves, which shorten the path of assimilates transport to developing grains [9]; (3) they have large surface area, e.g. the ear surface areas were 1.1-5.5 folds greater than that of the corresponding flag leaves in wheat and barley [6]; 4) reproductive organs tend to senesce later than leaves, especially under adverse conditions such as drought [10, 11]
Performance of the panicle photosynthesis P‐chamber The P-chamber is connected to a gas analyzer Li-6400 (Li-Cor Inc., Lincoln, Nebraska, USA) to measure gas exchange rate of a rice panicle (Fig. 1a, b)

Summary

Introduction

Photosynthesis of reproductive organs in C3 cereals is generally regarded as important to crop yield. Reproductive organs have several potential advantages over leaves in terms of photosynthate production and transportation: (1) they generally locate at the upper canopy, where light levels are higher than those at the lower canopy; (2) they are physically closer to the developing grains than the leaves, which shorten the path of assimilates transport to developing grains [9]; (3) they have large surface area, e.g. the ear surface areas were 1.1-5.5 folds greater than that of the corresponding flag leaves in wheat and barley [6]; 4) reproductive organs tend to senesce later than leaves, especially under adverse conditions such as drought [10, 11] Due to these reasons, photosynthesis of reproductive organs gained more and more attraction in recent years (see reviews in [12,13,14,15])

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Conclusion