Nie Wenjing, He Qinghai, Ma Jinzhao, Guo Hongen, Shi Qinghua
Shandong Engineering Research Center of Functional Crop Germplasm Innovation and Cultivation Utilization, Yantai Engineering Research Center of Plant Stem Cell Targeted Breeding, Shandong Institute of Sericulture, Yantai 264001, China.
Shandong Academy of Agricultural Machinery Science, Jinan 250100, China.
Plants (Basel). 2024 Dec 27;14(1):54. doi: 10.3390/plants14010054.
Brassinosteroids (BRs) are recognized for their ability to enhance plant salt tolerance. While considerable research has focused on their effects under neutral salt conditions, the mechanisms through which BRs regulate photosynthesis under alkaline salt stress are less well understood. This study investigates these mechanisms, examining plant growth, photosynthetic electron transport, gas exchange parameters, Calvin cycle dynamics, and the expression of key antioxidant and Calvin cycle genes under alkaline stress conditions induced by NaHCO. The findings indicate that NaHCO stress substantially impairs cucumber growth and photosynthesis, significantly reducing chlorophyll content, net photosynthetic rate (Pn), stomatal conductance (Gs), transpiration rate (E), maximum photochemical efficiency (Fv/Fm), actual photochemical efficiency (ΦPSII), antenna conversion efficiency (Fv'/Fm'), and photochemical quenching coefficient (qP). This disruption suggests a severe dysregulation of the photosynthetic electron transport system, impairing electron transfer from photosystem II (PSII) to photosystem I (PSI) and subsequently the Calvin cycle. Application of exogenous 24-epibrassinolide (EBR) alleviated these effects, reducing leaf chlorosis and growth inhibition and significantly enhancing the expression of key genes within the antioxidant system (AsA-GSH cycle) and the Calvin cycle. This intervention also led to a reduction in reactive oxygen species (ROS) accumulation and improved photosynthetic performance, as evidenced by enhancements in Pn, Gs, E, Fv/Fm, ΦPSII, Fv'/Fm', and qP. Moreover, NaHCO stress hindered chlorophyll synthesis, primarily by blocking the conversion from porphobilinogen (PBG) to uroporphyrinogen III (UroIII) and by increasing chlorophyllase (Chlase) and decreasing porphobilinogen deaminase (PBGD) activity. Exogenous EBR countered these effects by enhancing PBGD activity and reducing Chlase activity, thereby increasing chlorophyll content under stress conditions. In summary, EBR markedly mitigated the adverse effects of alkaline stress on cucumber leaf photosynthesis by stabilizing the photosynthetic electron transport system, accelerating photosynthetic electron transport, and promoting the Calvin cycle. This study provides valuable insights into the regulatory roles of BRs in enhancing plant resilience to alkaline stress.
油菜素甾醇（BRs）因其增强植物耐盐性的能力而受到认可。虽然大量研究集中在它们在中性盐条件下的作用，但BRs在碱性盐胁迫下调节光合作用的机制尚不清楚。本研究调查了这些机制，研究了在由NaHCO诱导的碱性胁迫条件下植物的生长、光合电子传递、气体交换参数、卡尔文循环动态以及关键抗氧化剂和卡尔文循环基因的表达。研究结果表明，NaHCO胁迫严重损害黄瓜的生长和光合作用，显著降低叶绿素含量、净光合速率（Pn）、气孔导度（Gs）、蒸腾速率（E）、最大光化学效率（Fv/Fm）、实际光化学效率（ΦPSII）、天线转换效率（Fv'/Fm'）和光化学猝灭系数（qP）。这种破坏表明光合电子传递系统严重失调，损害了从光系统II（PSII）到光系统I（PSI）的电子传递，进而影响卡尔文循环。外源施加24-表油菜素内酯（EBR）减轻了这些影响，减少了叶片黄化和生长抑制，并显著增强了抗氧化系统（AsA-GSH循环）和卡尔文循环中关键基因的表达。这种干预还导致活性氧（ROS）积累减少，光合性能改善，Pn、Gs、E、Fv/Fm、ΦPSII、Fv'/Fm'和qP的提高证明了这一点。此外，NaHCO胁迫阻碍叶绿素合成，主要是通过阻断胆色素原（PBG）向尿卟啉原III（UroIII）的转化以及增加叶绿素酶（Chlase）活性和降低胆色素原脱氨酶（PBGD）活性。外源EBR通过增强PBGD活性和降低Chlase活性来对抗这些影响，从而在胁迫条件下增加叶绿素含量。总之，EBR通过稳定光合电子传递系统、加速光合电子传递和促进卡尔文循环，显著减轻了碱性胁迫对黄瓜叶片光合作用的不利影响。本研究为BRs在增强植物对碱性胁迫的耐受性中的调节作用提供了有价值的见解。
