Evidence That Putrescine Modulates the Higher Plant Photosynthetic Proton Circuit

The light reactions of photosynthesis store energy in the form of an electrochemical gradient of protons, or proton motive force (pmf), comprised of electrical (Δψ) and osmotic (ΔpH) components. Both components can drive the synthesis of ATP at the chloroplast ATP synthase, but the ΔpH component also plays a key role in regulating photosynthesis, down-regulating the efficiency of light capture by photosynthetic antennae via the qE mechanism, and governing electron transfer at the cytochrome b6f complex. Differential partitioning of pmf into ΔpH and Δψ has been observed under environmental stresses and proposed as a mechanism for fine-tuning photosynthetic regulation, but the mechanism of this tuning is unknown. We show here that putrescine can alter the partitioning of pmf both in vivo (in Arabidopsis mutant lines and in Nicotiana wild type) and in vitro, suggesting that the endogenous titer of weak bases such as putrescine represents an unrecognized mechanism for regulating photosynthetic responses to the environment.

光合作用的光反应以质子电化学梯度——即质子动力势（proton motive force, pmf）——的形式储存能量，该梯度由电位分量（Δψ）与渗透分量（ΔpH）共同构成。两类分量均可驱动叶绿体ATP合酶催化ATP合成，但ΔpH分量在光合调控中发挥关键作用：它可通过qE机制下调光合天线系统的捕光效率，并调控细胞色素b6f复合物处的电子传递。环境胁迫下已观测到质子动力势向ΔpH与Δψ的差异化分配现象，该现象被认为是微调光合调控的潜在机制，但此类微调的具体分子机制尚未阐明。本研究证实，腐胺可在体内（拟南芥突变株系与烟草野生型中）与体外改变质子动力势的分配模式，这表明腐胺这类弱碱的内源性滴度，代表了一种此前未被认知的光合环境响应调控机制。