Cao Xu, Shen Qiudi, Ma Sang, Liu Li, Cheng Jialing
College of Biotechnology, Jiangsu University of Science and Technology, Zhenjiang, China.
Key Laboratory of Silkworm and Mulberry Genetic Improvement, Ministry of Agricultural and Rural Areas, Sericultural Research Institute, Chinese Academy of Agricultural Sciences, Zhenjiang, China.
Front Plant Sci. 2020 Aug 28;11:1310. doi: 10.3389/fpls.2020.01310. eCollection 2020.
Although mulberry cultivars Wubu, Yu711, and 7307 display distinct anatomical, morphological, and agronomic characteristics under natural conditions, it remains unclear if they differ in drought tolerance. To address this question and elucidate the underlying regulatory mechanisms at the whole-plant level, 2-month old saplings of the three mulberry cultivars were exposed to progressive soil water deficit for 5 days. The physiological responses and transcriptional changes of in different plant tissues were analyzed. Drought stress led to reduced leaf relative water content (RWC) and tissue water contents, differentially expressed , decreased chlorophyll and starch, increased soluble sugars and free proline, and enhanced activities of antioxidant enzymes in all plant parts of the three cultivars. Concentrations of hydrogen peroxide (HO), superoxide anion (O ), and malonaldehyde (MDA) were significantly declined in roots, stimulated in leaves but unaltered in wood and bark. In contrast, except the roots of 7307, soluble proteins were repressed in roots and leaves but induced in wood and bark of the three cultivars in response to progressive water deficit. These results revealed tissue-specific drought stress responses in mulberry. Comparing to cultivar Yu711 and 7307, Wubu showed generally slighter changes in leaf RWC and tissue water contents at day 2, corresponding well to the steady transcript levels, foliar concentrations of chlorophyll, O , MDA, and free proline. At day 5, Wubu sustained higher tissue water contents in green tissues, displayed stronger responsiveness of transcription, lower concentrations of soluble sugars and starch, lower foliar MDA, higher proline and soluble proteins, higher ROS accumulation and enhanced activities of several antioxidant enzymes. Our results indicate that whole-plant level responses of transcription, osmoregulation through proline and soluble proteins and antioxidative protection are important mechanisms for mulberry to cope with drought stress. These traits play significant roles in conferring the relatively higher drought tolerance of cultivar Wubu and could be potentially useful for future mulberry improvement programmes.
虽然桑树品种吴堡、豫711和7307在自然条件下表现出明显的解剖学、形态学和农艺学特征，但它们在耐旱性方面是否存在差异仍不清楚。为了解决这个问题并阐明全株水平上潜在的调控机制，对这三个桑树品种2月龄的树苗进行了5天的渐进性土壤水分亏缺处理。分析了不同植物组织中的生理反应和转录变化。干旱胁迫导致三个品种所有植物部位的叶片相对含水量（RWC）和组织含水量降低、差异表达、叶绿素和淀粉含量降低、可溶性糖和游离脯氨酸含量增加，以及抗氧化酶活性增强。根中过氧化氢（HO）、超氧阴离子（O）和丙二醛（MDA）的浓度显著下降，叶片中受到刺激，但木材和树皮中未发生变化。相比之下，除7307的根外，随着水分亏缺的加剧，三个品种的根和叶中可溶性蛋白受到抑制，而木材和树皮中则被诱导。这些结果揭示了桑树组织特异性的干旱胁迫响应。与豫711和7307品种相比，吴堡在第2天叶片RWC和组织含水量的变化通常较小，这与转录水平、叶绿素、O、MDA和游离脯氨酸的叶浓度稳定相对应。在第5天，吴堡绿色组织中的组织含水量持续较高，转录反应更强，可溶性糖和淀粉浓度较低，叶MDA含量较低，脯氨酸和可溶性蛋白含量较高，ROS积累较高，几种抗氧化酶活性增强。我们的结果表明，转录的全株水平反应、通过脯氨酸和可溶性蛋白进行的渗透调节以及抗氧化保护是桑树应对干旱胁迫的重要机制。这些性状在赋予吴堡品种相对较高的耐旱性方面发挥着重要作用，并且可能对未来的桑树改良计划具有潜在的用途。
