Interruption of Jasmonic Acid Biosynthesis Causes Differential Responses in the Roots and Shoots of Maize Seedlings against Salt Stress
Interruption of Jasmonic Acid Biosynthesis Causes Differential Responses in the Roots and Shoots of Maize Seedlings against Salt Stress
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JA生物合成的中断导致玉米幼苗根部和芽部对盐胁迫的不同反应
DOI：
10.3390/ijms20246202
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发表时间：
2019-12-01
影响因子：
5.6
通讯作者：
Yan, Yuanxin
中科院分区：
文献类型：
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作者：
Ahmad, Ramala Masood;Cheng, Cheng;Yan, Yuanxin
茉莉酸(Jas)和茉莉酸及其分支是脂类衍生的内源激素，在植物的发育过程和不同的防御反应中发挥关键作用。在过去的几十年里，Jas因其在模式植物抵御不同环境胁迫的植物防御中的重要作用而受到广泛研究。然而，这种植物激素在单子叶植物中抵抗非生物胁迫的作用还没有得到很好的研究。本研究以茉莉酸生物合成突变体opr7opr8为材料，研究了茉莉酸在0~300 mM盐胁迫下玉米幼苗盐胁迫反应中的作用。叶片气孔观察表明，盐胁迫下，opr7opr8的气孔开度大于野生型(WT)(B73)，表明JA对盐胁迫下保卫细胞的运动有积极的调节作用。叶绿素含量和叶片衰老的研究结果表明，与对照相比，opr7opr8在盐胁迫下表现出延缓叶片衰老的表现，表明茉莉酸在盐诱导的细胞死亡和随后的叶片衰老中发挥了作用。此外，从地上部和根部的长度、地上部和根部的鲜重和干重等形态参数来看，盐处理7d后，opr7opr8的地上部比对照重且长，但根比对照短而粗。此外，离子分析表明，与对照相比，opr7opr8在叶片中积累的钠较少，但对钾的积累较多，而在根中积累的钠和钾较少，说明茉莉酸缺乏对根系造成更高的盐分胁迫，但对叶片的胁迫较小。活性氧(ROS)分析表明，在盐处理下，opr7opr8在叶片中产生的H_2O_2少于WT，而在根中产生更多的H_2O_2，相应地，ROS清除酶超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)也表现出类似的变化，即在盐处理下，opr7opr8在地上部的酶活性低于WT，而在根中的活性高于WT。在渗透调节方面，在100和300 mM盐处理下，opr7opr8在地上部产生的脯氨酸较少，但在所有盐处理下根中产生的脯氨酸比对照根多。此外，还对盐胁迫下脱落酸(ABA)生物合成相关基因的表达进行了研究。结果表明，与对照相比，盐胁迫下ABA生物合成关键酶ZEP1、NCED5、AO1和VP10的表达水平显著降低。综上所述，我们得出结论：玉米幼苗缺茉莉酸降低了地上部对盐胁迫的反应，但夸大了根对盐胁迫的反应。此外，由于突变体opr7opr8在根中的钠含量高于WT，而在地上部的钠含量显著低于WT，因此内源JA对钠离子从根到地上部的运输起到了正向调节作用。此外，茉莉酸可能是盐胁迫下叶片ABA生物合成的正向调节因子。
Jasmonates (JAs) together with jasmonic acid and its offshoots are lipid-derived endogenous hormones that play key roles in both developmental processes and different defense responses in plants. JAs have been studied intensively in the past decades for their substantial roles in plant defense comebacks against diverse environmental stresses among model plants. However, the role of this phytohormone has been poorly investigated in the monocotyledonous species against abiotic stresses. In this study, a JA biosynthesis mutant opr7opr8 was used for the investigation of JA roles in the salt stress responses of maize seedlings, whose roots were exposed to 0 to 300 mM NaCl. Foliar stomatal observation showed that opr7opr8 had a larger stomatal aperture than wild type (WT) (B73) under salinity stress, indicating that JA positively regulates guard cell movement under salt stress. The results regarding chlorophyll content and leaf senescence showed that opr7opr8 exhibited delayed leaf senescence under salt stress as compared to WT, indicating that JA plays a role in salt-inducing cell death and subsequent leaf senescence. Moreover, the morphological parameters, including the length of the shoots and roots, and the fresh and dry weights of the shoots and roots, showed that after 7 days of salt treatment, opr7opr8 had heavier and longer shoots than WT but slighter and shorter roots than WT. In addition, ion analysis showed that opr7opr8 accumulated less sodium but more potassium in the leaves than WT but more sodium and less potassium in the roots than WT, suggesting that JA deficiency causes higher salt stress to the roots but less stress to the leaves of the seedlings. Reactive oxygen species (ROS) analysis showed that opr7opr8 produced less H2O2 than WT in the leaves but more H2O2 in the roots under salt treatment, and correspondingly, ROS-scavenging enzymes superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) showed a similar variation, i.e., opr7opr8 has lower enzymatic activities in the shoots but higher activities in the roots than WT under salt treatment. For osmotic adjustment, opr7opr8 produced less proline in the shoots at 100 and 300 mM NaCl treatments but more in the roots than the WT roots under all salt treatments. In addition, the gene expression for abscisic acid (ABA) biosynthesis under salt stress was investigated. Results showed that the expression levels of four key enzymes of ABA biosynthesis, ZEP1, NCED5, AO1, and VP10, were significantly downregulated in the shoots as compared to WT under salt treatment. Putting all the data together, we concluded that JA-deficiency in maize seedlings reduced the salt-stress responses in the shoots but exaggerated the responses in the roots. In addition, endogenous JA acted as a positive regulator for the transportation of sodium ions from the roots to the shoots because the mutant opr7opr8 had a higher level of sodium in the roots but a significantly lower level in the shoots than WT. Furthermore, JA may act as a positive regulator for ABA biosynthesis in the leaves under salt stress.