Abstract

Tree species in the arid and semi-arid regions use various strategies to combat drought stress. Ziziphus nummularia, native to the Thar Desert in India, is highly drought-tolerant. To identify the most drought-tolerant ecotype of Z. nummularia, one ecotype each from semi-arid (Godhra, annual rainfall > 750 mm), arid (Bikaner, 250–350 mm) and hyper-arid (Jaisalmer, < 150 mm) regions was selected along with two other Ziziphus species; Z. mauritiana and Z. rotundifolia, and screened for parameters contributing to drought tolerance. Among these, Z. nummularia (Jaisalmer) (CIAHZN-J) was the most drought-tolerant. The tolerance nature of CIAHZN-J was associated with increased membrane stability, root length and number, length of hairs and thorns, root dry/fresh weight ratio, seed germination (at −0.5 MPa), proline content (31 fold), catalase and sugar content (2 to 3 fold). Apart from these characteristics, it also exhibited the longest duration to reach highest cumulative drought stress rating, maintained higher relative water content for a longer period of time with reduced leaf size, leaf rolling and falling of older leaves, and displayed sustained shoot growth during drought stress. To determine drought tolerance in Ziziphus, we developed a morphological symptom-based screening technique in this study. Additionally, transcriptome profiling of CIAHZN-J in response to drought revealed the up-regulation of genes involved in sugar metabolism and transport, ABA biosynthesis, osmo-regulation, ROS homeostasis and maintaining water potential. Expression profiles and semi-quantitative reverse transcription PCR results further correlated with the physiological and biochemical mechanisms. In conclusion, CIAHZN-J is an excellent genetic stock for the identification of drought-responsive genes and can also be deployed in crop improvement programmes for drought tolerance.

中文翻译：

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干旱和超干旱生态型枣树在干旱条件下明显的形态生理和生化特征表明其与半干旱生态型相比具有更高的耐受性

摘要

干旱和半干旱地区的树种使用各种策略来对抗干旱压力。Ziziphus nummularia原产于印度塔尔沙漠，具有很强的耐旱性。为了确定Z. nummularia最耐旱的生态型，半干旱（Godhra，年降雨量 > 750 mm）、干旱（Bikaner，250-350 mm）和超干旱（Jaisalmer，< 150 mm）各有一个生态型区域与其他两个Ziziphus物种一起被选择；Z. mauritiana和Z. rotundifolia，并筛选了有助于耐旱性的参数。其中，麻花(Jaisalmer) (CIAHZN-J) 是最耐旱的。CIAHZN-J 的耐受性与膜稳定性、根长度和数量、毛和刺长度、根干/鲜重比、种子发芽（在 -0.5 MPa）、脯氨酸含量（31 倍）、过氧化氢酶和含糖量（2 到 3 倍）。除了这些特征外，它还表现出达到最高累积干旱胁迫等级的最长持续时间，在较长时间内保持较高的相对含水量，叶片尺寸减小，叶片滚动和老叶脱落，并在干旱期间表现出持续的枝条生长压力。确定Ziziphus的耐旱性，我们在这项研究中开发了一种基于形态学症状的筛查技术。此外，CIAHZN-J 响应干旱的转录组分析揭示了参与糖代谢和转运、ABA 生物合成、渗透调节、ROS 稳态和维持水势的基因的上调。表达谱和半定量逆转录PCR结果进一步与生理和生化机制相关。总之，CIAHZN-J 是鉴定干旱响应基因的优良遗传资源，也可用于作物改良项目以提高耐旱性。