Michigan State University-Department of Energy Plant Research Laboratory, East Lansing, MI 48824, USA.
Department of Biochemistry and Molecular Biology, Michigan State University, East Lansing, MI 48824, USA.
J Exp Bot. 2023 May 19;74(10):3163-3173. doi: 10.1093/jxb/erad084.
Oscillations in CO2 assimilation rate and associated fluorescence parameters have been observed alongside the triose phosphate utilization (TPU) limitation of photosynthesis for nearly 50 years. However, the mechanics of these oscillations are poorly understood. Here we utilize the recently developed dynamic assimilation techniques (DATs) for measuring the rate of CO2 assimilation to increase our understanding of what physiological condition is required to cause oscillations. We found that TPU-limiting conditions alone were insufficient, and that plants must enter TPU limitation quickly to cause oscillations. We found that ramps of CO2 caused oscillations proportional in strength to the speed of the ramp, and that ramps induce oscillations with worse outcomes than oscillations induced by step change of CO2 concentration. An initial overshoot is caused by a temporary excess of available phosphate. During the overshoot, the plant outperforms steady-state TPU and ribulose 1,5-bisphosphate regeneration limitations of photosynthesis, but cannot exceed the rubisco limitation. We performed additional optical measurements which support the role of PSI reduction and oscillations in availability of NADP+ and ATP in supporting oscillations.
近 50 年来，人们一直在观察二氧化碳同化率的波动以及与之相关的荧光参数，这些波动与光合作用的三磷酸磷酸利用（TPU）限制有关。然而，这些波动的机制还知之甚少。在这里，我们利用最近开发的动态同化技术（DATs）来测量二氧化碳同化的速率，以增加我们对引起波动所需的生理条件的理解。我们发现，仅 TPU 限制条件是不够的，而且植物必须快速进入 TPU 限制才能引起波动。我们发现，二氧化碳的斜坡会引起与斜坡速度成正比的强度波动，并且斜坡引起的波动比二氧化碳浓度阶跃引起的波动后果更糟。最初的过冲是由可用磷酸盐的暂时过剩引起的。在过冲过程中，植物的表现优于稳态 TPU 和核酮糖 1,5-二磷酸再生对光合作用的限制，但不能超过 RuBisCO 的限制。我们进行了额外的光学测量，这些测量支持 PSI 还原和 NADP+和 ATP 可用性波动在支持波动中的作用。
