Khalid Muhammad Fasih, Vincent Christopher, Morillon Raphael, Anjum Muhammad Akbar, Ahmad Shakeel, Hussain Sajjad
Department of Horticulture, Faculty of Agricultural Sciences and Technology, Bahauddin Zakariya University, Multan 60800, Pakistan.
Horticultural Sciences Department, Citrus Research and Education Centre, Institute of Food and Agricultural Sciences, University of Florida, Lake Alfred, FL 33850, USA.
Tree Physiol. 2021 Dec 4;41(12):2359-2374. doi: 10.1093/treephys/tpab074.
Water scarcity restricts citrus growth and productivity worldwide. In pot conditions, tetraploid plants tolerate water deficit more than their corresponding diploids. However, their tolerance mechanisms remain elusive. In this study, we focused on which mechanisms (i.e., hydraulic, osmotic or antioxidative) confer water-deficit tolerance to tetraploids. We exposed diploid and tetraploid Volkamer lemon rootstock (Citrus volkameriana Tan. and Pasq.) to quickly (fast) and slowly (slow) developing water-deficit conditions. We evaluated their physiological, antioxidative defense and osmotic adjustment responses, and mineral distribution to leaves and roots. Water-deficit conditions decreased the photosynthetic variables of both diploid and tetraploid plants. Moreover, the corresponding decrease was greater in diploids than tetraploids. Higher concentrations of antioxidant enzymes, osmoprotectants and antioxidant capacity were found in the leaves and roots of tetraploids than diploids under water deficit. Diploid plants showed fast response in slow water-deficit condition, but that response did not persist as the deficit intensified. Meanwhile, tetraploids had lower water loss, which slowed the onset of slow water deficit relative to diploids. This response allowed stronger photosynthesis, while antioxidant and osmoprotectant production allowed for further tolerance once desiccation began. Overall, our results concluded that Volkamer lemon tetraploid plants tolerate rapid and slow water deficit by maintaining their photosynthesis due to low conductance (stem or roots), which helps to avoid desiccation, and stronger biochemical defense machinery than their corresponding diploids.
水资源短缺限制了全球柑橘的生长和产量。在盆栽条件下，四倍体植物比相应的二倍体更能耐受水分亏缺。然而，它们的耐受机制仍然不清楚。在本研究中，我们聚焦于哪些机制（即水力、渗透或抗氧化机制）赋予四倍体植物水分亏缺耐受性。我们将二倍体和四倍体沃尔卡默柠檬砧木（Citrus volkameriana Tan. and Pasq.）置于快速（快）和缓慢（慢）发展的水分亏缺条件下。我们评估了它们的生理、抗氧化防御和渗透调节反应，以及叶片和根系中的矿物质分布。水分亏缺条件降低了二倍体和四倍体植物的光合变量。此外，二倍体植物的相应降幅大于四倍体植物。在水分亏缺条件下，四倍体植物叶片和根系中的抗氧化酶、渗透保护剂浓度和抗氧化能力均高于二倍体植物。在缓慢水分亏缺条件下，二倍体植物反应迅速，但随着亏缺加剧，这种反应并未持续。同时，四倍体植物水分损失较低，相对于二倍体植物，减缓了缓慢水分亏缺的发生。这种反应使光合作用更强，而抗氧化剂和渗透保护剂的产生使植物在开始脱水后具有更强的耐受性。总体而言，我们的结果表明，沃尔卡默柠檬四倍体植物通过低导度（茎或根）维持光合作用来耐受快速和缓慢的水分亏缺，这有助于避免脱水，并且其生化防御机制比相应的二倍体更强。
