Max Planck Institute of Molecular Plant Physiology, Potsdam-Golm, Germany.
Luxembourg Institute of Health, Strassen, Luxembourg.
Nat Plants. 2022 May;8(5):574-582. doi: 10.1038/s41477-022-01140-y. Epub 2022 Apr 28.
Many plants accumulate transitory starch reserves in their leaves during the day to buffer their carbohydrate supply against fluctuating light conditions, and to provide carbon and energy for survival at night. It is universally accepted that transitory starch is synthesized from ADP-glucose (ADPG) in the chloroplasts. However, the consensus that ADPG is made in the chloroplasts by ADPG pyrophosphorylase has been challenged by a controversial proposal that ADPG is made primarily in the cytosol, probably by sucrose synthase (SUS), and then imported into the chloroplasts. To resolve this long-standing controversy, we critically re-examined the experimental evidence that appears to conflict with the consensus pathway. We show that when precautions are taken to avoid artefactual changes during leaf sampling, Arabidopsis thaliana mutants that lack SUS activity in mesophyll cells (quadruple sus1234) or have no SUS activity (sextuple sus123456) have wild-type levels of ADPG and starch, while ADPG is 20 times lower in the pgm and adg1 mutants that are blocked in the consensus chloroplastic pathway of starch synthesis. We conclude that the ADPG needed for starch synthesis in leaves is synthesized primarily by ADPG pyrophosphorylase in the chloroplasts.
许多植物在白天通过在叶片中积累短暂性淀粉储备来缓冲碳水化合物供应对不断变化的光照条件的影响，并为夜间的生存提供碳和能量。人们普遍认为，短暂性淀粉是在叶绿体中由 ADP-葡萄糖（ADPG）合成的。然而，ADP 葡萄糖是由 ADPG 焦磷酸化酶在叶绿体中合成的共识受到了一个有争议的提议的挑战，该提议认为 ADPG 主要在细胞质中合成，可能是由蔗糖合酶（SUS）合成的，然后被导入叶绿体。为了解决这个长期存在的争议，我们批判性地重新检查了似乎与共识途径相冲突的实验证据。我们表明，当采取预防措施避免在叶片取样过程中产生人为变化时，拟南芥突变体（缺乏质体中 SUS 活性的四倍体 sus1234 或根本没有 SUS 活性的六倍体 sus123456）具有与野生型相同水平的 ADPG 和淀粉，而在 pgm 和 adg1 突变体中 ADPG 降低了 20 倍，这些突变体在淀粉合成的共识叶绿体途径中受阻。我们得出结论，叶片中淀粉合成所需的 ADPG 主要由叶绿体中的 ADPG 焦磷酸化酶合成。
