Environmental Biophysics and Molecular Ecology Program, Institute of Marine and Coastal Sciences, Rutgers, The State University of New Jersey, New Brunswick, NJ 08901, USA.
Photosynth Res. 2011 Sep;108(2-3):215-24. doi: 10.1007/s11120-011-9682-9. Epub 2011 Sep 6.
Using a novel, pulsed micro-second time-resolved photoacoustic (PA) instrument, we measured thermal dissipation and energy storage (ES) in the intact cells of wild type (WT) Chlamydomonas reinhardtii, and mutants lacking either PSI or PSII reaction centers (RCs). On this time scale, the kinetic contributions of the thermal expansion component due to heat dissipation of absorbed energy and the negative volume change due to electrostriction induced by charge separation in each of the photosystems could be readily distinguished. Kinetic analysis revealed that PSI and PSII RCs exhibit strikingly different PA signals where PSI is characterized by a strong electrostriction signal and a weak thermal expansion component while PSII has a small electrostriction component and large thermal expansion. The calculated ES efficiencies at ~10 μs were estimated to be 80 ± 5 and 50 ± 13% for PSII-deficient mutants and PSI-deficient mutants, respectively, and 67 ± 2% for WT. The overall ES efficiency was positively correlated with the ratio of PSI to PSI + PSII. Our results suggest that the shallow excitonic trap in PSII limits the efficiency of ES as a result of an evolutionary frozen metabolic framework of two photosystems in all oxygenic photoautotrophs.
利用一种新颖的纳秒级时间分辨光声（PA）仪器，我们测量了野生型（WT）莱茵衣藻完整细胞中的热耗散和能量存储（ES），以及缺乏 PSI 或 PSII 反应中心（RCs）的突变体。在这个时间尺度上，可以很容易地区分由于吸收能量的热耗散引起的热膨胀分量的动力学贡献，以及由于每个光系统中的电荷分离引起的电致伸缩引起的负体积变化。动力学分析表明，PSI 和 PSII RCs 表现出明显不同的 PA 信号，其中 PSI 的特征是强电致伸缩信号和弱热膨胀分量，而 PSII 具有小的电致伸缩分量和大的热膨胀。在 ~10 μs 时估算的 ES 效率分别为 PSII 缺陷突变体和 PSI 缺陷突变体的 80 ± 5%和 50 ± 13%，WT 为 67 ± 2%。整体 ES 效率与 PSI 与 PSI + PSII 的比值呈正相关。我们的结果表明，由于所有产氧光合自养生物中两个光系统的代谢框架被冻结，PSII 中的浅激子陷阱限制了 ES 的效率。
