Future climate CO₂ (eCO₂) and contamination with nano-sized heavy metals (HM-NPs) represent concurrent challenges threatening plants. The interaction between eCO₂ and HM-NPs is rarely investigated, and no study has addressed their synchronous impact on the metabolism of the multifunctional stress-related metabolites, such as sugars and amino acids. Moreover, the characteristic responses of C3 and C4 plant systems to the concurrent impact of eCO₂ and HM-NPs are poorly understood. Herein, we have assessed the impact of eCO₂ (620 ppm) and/or HgO-NPs (100 mg/Kg soil) on growth, physiology and metabolism of sugars and amino acids, particularly proline, in C3 (wheat) and C4 (maize) plant systems. Under Hg-free conditions, eCO₂ treatment markedly improved the growth and photosynthesis and induced sugars levels and metabolism (glucose, fructose, sucrose, starch, sucrose P synthase and starch synthase) in wheat (C3) only. In contrast, HgO-NPs induced the uptake, accumulation and translocation of Hg in wheat and to less extend in maize plants. Particularly in wheat, this induced significant decreases in growth and photosynthesis and increases in photorespiration, dark respiration and levels of tricarboxylic acid cycle organic acids. Interestingly, the co-application of eCO₂ reduced the accumulation of Hg and recovered the HgO-NPs-induced effects on growth and metabolism in both plants. At stress defense level, HgO-NPs induced the accumulation of sucrose and proline, more in maize, via upregulation of sucrose P synthase, ornithine amino transferase, ∆¹-pyrroline-5-carboxylate (P5C) synthetase and P5C reductase. The co-existence of eCO₂ favored reduced sucrose biosynthesis and induced proline catabolism, which provide high energy to resume plant growth. Overall, despite the difference in their response to eCO₂ under normal conditions, eCO₂ induced similar metabolic events in C3 and C4 plants under stressful conditions, which trigger stress recovery.

未来的气候CO ₂（eCO ₂）和纳米级重金属（HM-NPs）的污染代表着同时威胁植物的挑战。很少研究eCO ₂和HM-NP之间的相互作用，也没有研究涉及它们对多功能应激相关代谢物（如糖和氨基酸）的代谢的同步影响。此外，人们对C3和C4植物系统对eCO ₂和HM-NP并发影响的特征响应知之甚少。在此，我们评估了eCO ₂的影响（620 ppm）和/或HgO-NP（100 mg / Kg土壤）对C3（小麦）和C4（玉米）植物系统中糖和氨基酸（尤其是脯氨酸）的生长，生理和代谢的影响。在无汞条件下，eCO ₂处理仅显着改善了小麦（C3）的生长和光合作用，并诱导了糖水平和新陈代谢（葡萄糖，果糖，蔗糖，淀粉，蔗糖P合酶和淀粉合酶）。相反，HgO-NPs诱导了小麦中Hg的吸收，积累和转运，而在玉米植物中则较少。特别是在小麦中，这会导致生长和光合作用的显着下降，以及光呼吸，暗呼吸和三羧酸循环有机酸含量的增加。有趣的是，eCO ₂的共同应用减少了Hg的积累并恢复了HgO-NPs诱导的对两株植物生长和代谢的影响。在胁迫防御水平上，HgO-NPs通过上调蔗糖P合酶，鸟氨酸氨基转移酶，∆ ^1-吡咯啉-5-羧酸盐（P5C）合成酶和P5C还原酶诱导玉米中蔗糖和脯氨酸的积累。eCO ₂的共存有利于减少蔗糖的生物合成并诱导脯氨酸分解代谢，从而为恢复植物生长提供了高能量。总体而言，尽管在正常条件下它们对eCO ₂的响应有所不同，但在压力条件下eCO _2会在C3和C4植物中诱导相似的代谢事件，从而触发压力恢复。