College of Horticulture, Gansu Agricultural University, Lanzhou, 730070, China.
Department of Horticulture, University for Development Studies, Tamale, Ghana.
BMC Plant Biol. 2022 Jul 8;22(1):329. doi: 10.1186/s12870-022-03717-3.
A biosynthetic precursor of tetrapyrrol, 5-aminolevulinic acid (ALA), is widely used in agricultural production, as an exogenous regulatory substance that effectively regulates plant growth. Previous studies have shown that heme and chlorophyll accumulate in plants under salt stress, when treated with exogenous ALA. In this study, we explored the regulatory role of heme in plants, by spraying 25 mg L ALA onto the leaves of cucumber seedlings treated with heme synthesis inhibitor (2,2'-dipyridyl, DPD) and heme scavenger (hemopexin, Hx), under 50 mmol L NaCl stress. The results showed that NaCl alone and DPD + Hx treatments to cucumber seedlings subjected to salt stress adversely affected their growth, by decreasing biomass accumulation, root activity, and root morphology. In addition, these treatments induced an increase in membrane lipid oxidation, as well as enhancement of anti-oxidase activities, proline content, and glutamate betaine. However, exogenous ALA application increased the plant growth and root architecture indices under NaCl stress, owing to a lack of heme in the seedlings. In addition, cucumber seedlings treated with DPD and Hx showed inhibition of growth under salt stress, but exogenous ALA effectively improved cucumber seedling growth as well as the physiological characteristics; moreover, the regulation of ALA in plants was weakened when heme synthesis was inhibited. Heme biosynthesis and metabolism genes, HEMH and HO1, which are involved in the ALA metabolic pathway, were upregulated under salinity conditions, when ferrochelatase activity was inhibited. Application of exogenous ALA increased the heme content in the leaves. Thus, exogenous ALA may supplement the substrates for heme synthesis. These results indicated that heme plays a vital role in the response of plants to salinity stress. In conclusion, heme is involved in ALA-mediated alleviation of damage caused to cucumber seedlings and acts as a positive regulator of plant adaption.
四吡咯生物合成前体物 5-氨基酮戊酸（ALA）在农业生产中被广泛用作一种有效的外源调节物质，可有效调节植物生长。先前的研究表明，在盐胁迫下，用外源 ALA 处理植物时，血红素和叶绿素会在植物中积累。在本研究中，我们通过向血红素合成抑制剂（2,2'-二吡啶，DPD）和血红素清除剂（血影蛋白，Hx）处理的黄瓜幼苗叶片喷洒 25mg L 的 ALA，来探索血红素在植物中的调节作用，在 50mmol L NaCl 胁迫下。结果表明，单独的 NaCl 和 DPD+Hx 处理对盐胁迫下的黄瓜幼苗的生长产生了不利影响，降低了生物量积累、根活力和根形态。此外，这些处理诱导膜脂氧化增加，以及抗氧化酶活性、脯氨酸含量和谷氨酸甜菜碱增强。然而，由于幼苗中缺乏血红素，外源 ALA 增加了 NaCl 胁迫下植物的生长和根系结构指数。此外，DPD 和 Hx 处理的黄瓜幼苗在盐胁迫下生长受到抑制，但外源 ALA 有效改善了黄瓜幼苗的生长以及生理特性；此外，当抑制亚铁螯合酶活性时，血红素合成的抑制削弱了 ALA 在植物中的调节作用。参与 ALA 代谢途径的血红素生物合成和代谢基因 HEMH 和 HO1 在盐胁迫条件下被上调，当亚铁螯合酶活性受到抑制时。外源 ALA 的应用增加了叶片中的血红素含量。因此，外源 ALA 可能补充血红素合成的底物。这些结果表明血红素在植物对盐胁迫的响应中起着重要作用。总之，血红素参与了 ALA 介导的对黄瓜幼苗的损伤缓解，并且是植物适应的正调节剂。
