Laboratory of Crop Physiology, Department of Plant Biology, Institute of Biology, University of Campinas (UNICAMP), PO Box 6109, Campinas 13083-970, Brazil.
Laboratory of Plant Physiology "Coaracy M. Franco", Center R&D in Ecophysiology and Biophysics, Agronomic Institute (IAC), PO Box 28, Campinas 13012-970, Brazil.
Tree Physiol. 2021 Aug 11;41(8):1372-1383. doi: 10.1093/treephys/tpab008.
Carbon allocation between source and sink organs determines plant growth and is influenced by environmental conditions. Under water deficit (WD), plant growth is inhibited before photosynthesis and shoot growth tends to be more sensitive than root growth. However, the modulation of the source-sink relationship by rootstocks remains unsolved in citrus trees under WD. Citrus plants grafted on Rangpur lime are drought tolerant, which may be related to a fine coordination of the source-sink relationship for maintaining root growth. Here, we followed 13C allocation and evaluated physiological responses and growth of Valencia orange trees grafted on three citrus rootstocks (Rangpur lime, Swingle citrumelo and Sunki mandarin) under WD. As compared with plants on Swingle and Sunki rootstocks, ones grafted on Rangpur lime showed higher stomatal sensitivity to the initial variation of water availability and less accumulation of non-structural carbohydrates in roots under WD. High 13C allocation found in Rangpur lime roots indicates this rootstock has high sink demand associated with high root growth under WD. Our data suggest that Rangpur lime rootstock used photoassimilates as sources of energy and carbon skeletons for growing under drought, which is likely related to increases in root respiration. Taken together, our data revealed that carbon supply by leaves and delivery to roots are critical for maintaining root growth and improving drought tolerance, with citrus rootstocks showing differential sink strength under WD.
碳在源器官和汇器官之间的分配决定了植物的生长，并且受到环境条件的影响。在水分亏缺（WD）下，光合作用之前植物的生长受到抑制，并且 shoot 生长往往比 root 生长更敏感。然而，在 WD 下柑橘树的砧木对源-汇关系的调节仍然没有解决。嫁接在莱姆上的柑橘植物耐旱，这可能与维持根生长的源-汇关系的精细协调有关。在这里，我们跟踪了 13C 的分配，并评估了在 WD 下嫁接在三种柑橘砧木（莱姆、甜橙和温州蜜柑）上的 Valencia 甜橙树的生理响应和生长。与嫁接在 Swingle 和 Sunki 砧木上的植物相比，嫁接在莱姆砧木上的植物对水分供应初始变化的气孔敏感性更高，并且在 WD 下根部的非结构性碳水化合物积累较少。在莱姆砧木根部发现的高 13C 分配表明，该砧木具有与 WD 下高根生长相关的高汇需求。我们的数据表明，莱姆砧木根利用光合作用产物作为能量和碳骨架的来源，在干旱条件下生长，这可能与根呼吸的增加有关。总之，我们的数据表明，叶片提供的碳供应和向根部的输送对于维持根生长和提高耐旱性至关重要，而柑橘砧木在 WD 下表现出不同的汇强度。
