Key message

A detailed study of the response of wheat plants, inoculated with drought-tolerant PGPR is studied which would be beneficial to achieve genetic improvement of wheat for drought tolerance.

Abstract

Drought stress, a major challenge under current climatic conditions, adversely affects wheat productivity. In the current study, we observed the response of wheat plants, inoculated with drought-tolerant plant growth-promoting rhizobacteria (PGPR) Bacillus megaterium (MU2) and Bacillus licheniformis (MU8) under induced drought stress. In vitro study of 90 rhizobacteria exhibited 38 isolates showed one or more plant growth-promoting properties, such as solubilization of phosphorus, potassium, and exopolysaccharide production. Four strains revealing the best activities were tested for their drought-tolerance ability by growing them on varying water potentials (− 0.05 to − 0.73 MPa). Among them, two bacterial strains Bacillus megaterium and Bacillus licheniformis showed the best drought-tolerance potential, ACC deaminase activities, IAA production, and antagonistic activities against plant pathogens. Additionally, these strains when exposed to drought stress (− 0.73 MPa) revealed the induction of three new polypeptides (18 kDa, 35 kDa, 30 kDa) in Bacillus megaterium. We determined that 10⁶ cells/mL of Bacillus megaterium and Bacillus licheniformis were enough to induce drought tolerance in wheat under drought stress. These drought-tolerant strains increased the germination index (11–46%), promptness index (16–50%), seedling vigor index (11–151%), fresh weight (35–192%), and dry weight (58–226%) of wheat under irrigated and drought stress. Moreover, these strains efficiently colonized the wheat roots and increased plant biomass, relative water content, photosynthetic pigments, and osmolytes. Upon exposure to drought stress, Bacillus megaterium inoculated wheat plants exhibited improved tolerance by enhancing 59% relative water content, 260, 174 and 70% chlorophyll a, b and carotenoid, 136% protein content, 117% proline content and 57% decline in MDA content. Further, activities of defense-related antioxidant enzymes were also upregulated. Our results revealed that drought tolerance was more evident in Bacillus megaterium as compared to Bacillus licheniformis. These strains could be effective bioenhancer and biofertilizer for wheat cultivation in arid and semi-arid regions. However, a detailed study at the molecular level to deduce the mechanism by which these strains alleviate drought stress in wheat plants needs to be explored.

中文翻译：

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半干旱条件下分离的抗旱巨大芽孢杆菌诱导小麦在干旱条件下的系统耐受性

关键信息

详细研究了接种耐旱 PGPR 的小麦植物的响应，这将有利于实现小麦的耐旱遗传改良。

抽象的

干旱胁迫是当前气候条件下的主要挑战，对小麦生产力产生不利影响。在目前的研究中，我们观察了小麦植物在诱导干旱胁迫下接种耐旱植物促生根际细菌 (PGPR)巨大芽孢杆菌(MU2) 和地衣芽孢杆菌(MU8) 的反应。对 90 种根际细菌的体外研究表明，38 种分离株显示出一种或多种植物生长促进特性，例如溶解磷、钾和产生胞外多糖。通过在不同的水势（- 0.05 到 - 0.73 MPa）上培养它们，测试了四种表现出最佳活性的菌株的耐旱能力。其中，巨大芽孢杆菌和地衣芽孢杆菌表现出最佳的耐旱潜力、ACC脱氨酶活性、IAA产生和对植物病原体的拮抗活性。此外，这些菌株在暴露于干旱胁迫 (- 0.73 MPa) 时揭示了巨大芽孢杆菌中三种新多肽 (18 kDa、35 kDa、30 kDa) 的诱导。我们确定 10 ^{6 个} 细胞/mL 的巨大芽孢杆菌和地衣芽孢杆菌足以诱导小麦在干旱胁迫下的耐旱性。这些耐旱菌株提高了发芽指数 (11-46%)、及时性指数 (16-50%)、幼苗活力指数 (11-151%)、鲜重 (35-192%) 和干重 (58- 226%) 的小麦在灌溉和干旱胁迫下。此外，这些菌株有效地在小麦根部定殖并增加了植物生物量、相对水分含量、光合色素和渗透质。暴露于干旱胁迫后，巨大芽孢杆菌通过提高 59% 的相对水分含量、260%、174% 和 70% 的叶绿素 a、b 和类胡萝卜素、136% 的蛋白质含量、117% 的脯氨酸含量和 57% 的 MDA 含量，接种小麦植株表现出更高的耐受性。此外，与防御相关的抗氧化酶的活性也被上调。我们的研究结果表明，与地衣芽孢杆菌相比，巨大芽孢杆菌的耐旱性更明显。这些菌株可作为干旱和半干旱地区小麦种植的有效生物增强剂和生物肥料。然而，需要在分子水平上进行详细研究，以推断这些菌株减轻小麦植株干旱胁迫的机制。