Chang Tian-Gen, Song Qing-Feng, Zhao Hong-Long, Chang Shuoqi, Xin Changpeng, Qu Mingnan, Zhu Xin-Guang
National Key Laboratory for Plant Molecular Genetics, Center of Excellence for Molecular Plant Sciences, Chinese Academy of Sciences, Shanghai, 200031 China.
University of Chinese Academy of Sciences, Beijing, 100049 China.
Plant Methods. 2020 Jul 6;16:92. doi: 10.1186/s13007-020-00633-1. eCollection 2020.
Photosynthesis of reproductive organs in C 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.
Here 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 , - hybrid and 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 5 days after heading under photon flux density (PFD) of 2000 μmol (photons) m s, which represent some 20-38% of that of the corresponding flag leaves; (3) rice panicle photosynthesis has higher apparent CO compensation point, light compensation point and apparent CO 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, value < 0.0001).
Rice 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.
谷类作物生殖器官的光合作用通常被认为对作物产量很重要。然而，与叶片光合作用相比，生殖器官的光合特性了解得要少得多，主要是由于方法上的限制。迄今为止，已经开发了许多间接方法来研究生殖器官的光合作用及其对籽粒产量的贡献，如器官遮光、施用除草剂以及对离体器官或组织进行光合测量，这些方法可能具有侵入性并导致偏差。因此，需要开发一种可靠的原位方法。
在此，我们报告了一种定制的穗光合作用室（P室）的开发，该室可连接到标准红外气体分析仪，以研究水稻穗的光合/呼吸速率。利用P室，我们测量了7个高产优良杂交稻和常规稻品种的穗光合特性。结果表明：（1）水稻穗在灌浆期具有光合活性，无论在整穗、面积或单个小穗基础上，穗光合和呼吸速率品种间都存在显著差异；（2）在7个供试品种中，抽穗后5天，在光子通量密度（PFD）为2000 μmol（光子）m² s⁻¹条件下，整穗总光合速率为17 - 54 nmol s⁻¹，约占相应剑叶的20 - 38%；（3）与典型叶片相比，水稻穗光合作用具有更高的表观CO₂补偿点、光补偿点和表观CO₂饱和点；（4）抽穗后5天单个小穗的总光合速率与收获时的结实率之间存在强烈且显著的正相关（皮尔逊相关系数r = 0.93，P值<0.0001）。
水稻穗总光合作用显著，具有很大的自然变异，在籽粒产量形成中发挥着未被充分认识的作用。P室可作为研究不规则非叶植物器官，如穗、茎、叶鞘、果实和枝条原位光合特性的工具，这是当前谷类作物育种领域较少探索的一个领域。
