Tetraploids are usually more tolerant to environmental stresses than diploids. Citrus plants face numerous abiotic stresses, including salinity, which negatively affect growth and yield. Double diploid citrus rootstocks have been shown to be more tolerant to abiotic stresses than their diploid relatives. In this study, we evaluated the antioxidative and osmotic adjustment mechanisms of diploid (2x) and double diploid (4x) volkamer lemon (Citrus volkameriana Tan. and Pasq.) rootstocks, which act against salt stress (75 and 150 mM). Results indicated that, under salt stress, all physiological variables (photosynthesis, stomatal conductance, transpiration rate, and leaf greenness) decreased, and these decreases were more noticeable in 2x plants than in 4x plants. On the other hand, accumulation of oxidative markers (malondialdehyde and hydrogen peroxide) was greater in the leaves and roots of 2x seedlings than in 4x seedlings. Similarly, the activities of antioxidative enzymes (peroxidase, ascorbate peroxidase, glutathione reductase, and catalase) were higher in the leaves and roots of 4x plants than in 2x plants. However, superoxide dismutase activity was higher in the roots of 2x seedlings than 4x seedlings. Double diploid plants affected by salt stress accumulated more osmolytes (i.e. proline and glycine betaine) in their leaves and roots than that by 2x plants. Total protein content, antioxidant capacity, and total phenolic content were also higher in 4x plants than 2x plants under salinity. At 150 mM, both 2x and 4x plants showed more symptoms of stress than those at 75 mM. Sodium content was the highest in the roots of 2x plants and in the leaves of 4x plants, while chloride content peaked in the leaves of 2x plants and in the roots of 4x plants. Overall, our results demonstrate that the active antioxidative defence mechanisms of 4x plants increase their tolerance to salinity compared to their corresponding 2x relatives. Thus, the use of newly developed tetraploid rootstocks may be a strategy for enhancing crop production in saline conditions.

中文翻译：

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四倍体与二倍体 volkamer 柠檬幼苗更好的耐盐性与强大的抗氧化和渗透调节机制有关

四倍体通常比二倍体更能耐受环境压力。柑橘植物面临许多非生物胁迫，包括盐分，这会对生长和产量产生负面影响。双二倍体柑橘砧木已被证明比其二倍体亲属更能耐受非生物胁迫。在这项研究中，我们评估了二倍体 (2x) 和双二倍体 (4x) volkamer 柠檬（Citrus volkameriana Tan. 和 Pasq.）砧木的抗氧化和渗透调节机制，它们可以对抗盐胁迫（75 和 150 mM）。结果表明，在盐胁迫下，所有生理变量（光合作用、气孔导度、蒸腾速率和叶绿度）均下降，并且这些下降在 2x 植物中比在 4x 植物中更明显。另一方面，氧化标记物（丙二醛和过氧化氢）的积累在 2x 幼苗的叶子和根中比在 4x 幼苗中更大。同样，抗氧化酶（过氧化物酶、抗坏血酸过氧化物酶、谷胱甘肽还原酶和过氧化氢酶）在 4x 植物的叶子和根中的活性高于 2x 植物。然而，2x 幼苗根部的超氧化物歧化酶活性高于 4x 幼苗。受盐胁迫影响的双二倍体植物在其叶和根中积累的渗透物（即脯氨酸和甘氨酸甜菜碱）比受 2x 植物影响的植物更多。在盐度下，4x 植物的总蛋白质含量、抗氧化能力和总酚含量也高于 2x 植物。在 150 mM 时，2x 和 4x 植物都比 75 mM 的植物表现出更多的胁迫症状。钠含量在 2x 植物的根和 4x 植物的叶子中最高，而氯化物含量在 2x 植物的叶子和 4x 植物的根中达到峰值。总的来说，我们的结果表明，与相应的 2x 亲属相比，4x 植物的主动抗氧化防御机制提高了它们对盐度的耐受性。因此，使用新开发的四倍体砧木可能是在盐碱条件下提高作物产量的一种策略。