Institute of Biomaterials and Biomolecular Systems, Department of Plant Biotechnology, University of Stuttgart, Pfaffenwaldring 57, Stuttgart, 70569, Germany.
Institute of Electrical Engineering and Informatics, DHBW Ravensburg, Marienplatz 2, Ravensburg, 88212, Germany.
Plant J. 2018 Jun;94(5):776-789. doi: 10.1111/tpj.13898. Epub 2018 Apr 16.
Whole-plant carbon balance comprises diurnal fluctuations of photosynthetic carbon gain and respiratory losses, as well as partitioning of assimilates between phototrophic and heterotrophic organs. Because it is difficult to access, the root system is frequently neglected in growth models, or its metabolism is rated based on generalizations from other organs. Here, whole-plant cuvettes were used for investigating total-plant carbon exchange with the environment over full diurnal cycles. Dynamics of primary metabolism and diurnally resolved phloem exudation profiles, as proxy of assimilate transport, were combined to obtain a full picture of resource allocation. This uncovered a strong impact of periodicity of inter-organ transport on the efficiency of carbon gain. While a sinusoidal fluctuation of the transport rate, with minor diel deflections, minimized respiratory losses in Arabidopsis wild-type plants, triangular or rectangular patterns of transport, found in mutants defective in either starch or sucrose metabolism, increased root respiration at the end or beginning of the day, respectively. Power spectral density and cross-correlation analysis revealed that only the rate of starch synthesis was strictly correlated to the rate of net photosynthesis in wild-type, while in a sucrose-phosphate synthase mutant (spsa1), this applied also to carboxylate synthesis, serving as an alternative carbon pool. In the starchless mutant of plastidial phospho-gluco mutase (pgm), none of these rates, but concentrations of sucrose and glucose in the root, followed the pattern of photosynthesis, indicating direct transduction of shoot sugar levels to the root. The results demonstrate that starch metabolism alone is insufficient to buffer diurnal fluctuations of carbon exchange.
整株植物的碳平衡包括光合作用碳增益和呼吸损失的昼夜波动，以及同化产物在光养器官和异养器官之间的分配。由于根系难以获取，因此在生长模型中，根系经常被忽略，或者其代谢是根据其他器官的概括来评估的。在这里，使用整株植物培养皿来研究整个植物与环境的总植物碳交换在整个昼夜周期内的情况。初级代谢的动态和昼夜解析的韧皮部渗出液剖面作为同化产物运输的替代物，结合起来获得资源分配的全貌。这揭示了器官间运输周期性对碳增益效率的强烈影响。虽然在拟南芥野生型植物中，运输率的正弦波动，昼夜偏移较小，使呼吸损失最小化，但在淀粉或蔗糖代谢缺陷的突变体中发现的三角形或矩形运输模式，分别在白天结束或开始时增加了根呼吸。功率谱密度和互相关分析表明，只有淀粉合成率与野生型的净光合作用率严格相关，而在蔗糖-磷酸合酶突变体（spsa1）中，这也适用于羧化作用合成，作为替代的碳库。在质体磷酸葡糖变位酶（pgm）的无淀粉突变体中，没有这些速率，但根中的蔗糖和葡萄糖浓度遵循光合作用的模式，表明直接将茎部的糖水平传递到根部。结果表明，淀粉代谢本身不足以缓冲碳交换的昼夜波动。
