Drought is one of the major constraints for soybean production in Brazil. In this study we investigated the physiological traits of two soybean parental genotypes under progressive soil drying and rewetting. The plants were evaluated under full irrigation (control) conditions and under water deficit imposed by suspending irrigation until the plants reached predawn leaf water potentials (Ψam) of -1.0 MPa (moderate) and -1.5 MPa (severe). Physiological analyses showed that these genotypes exhibit different responses to water deficit. The Embrapa 48 genotype reached moderate and severe water potential two days after the BR16 genotype and was able to maintain higher levels of A, ETR and ΦPSII even under deficit conditions. This result was not related to changes in gs, 13C isotopic composition and presence of a more efficient antioxidant system. In addition, Fv/Fm values did not decrease in Embrapa 48 genotype in relation to irrigated condition showing that stress was not causing photochemical inhibition of photosynthesis. The greater reduction in the relative growth of the shoots, with concomitant greater growth of the root system under drought, indicates that the tolerant genotype is able to preferentially allocated carbon to the roots, presenting less damage to photosynthesis. Therefore, the physiological responses revealed that the tolerant genotype postponed leaf dehydration by a mechanism involving a more efficient use and translocation of water from root to shoot to maintain cell homeostasis and photosynthetic metabolism under stress.

中文翻译：

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用生理学方法破译巴西热带稀树草原大豆基因型的耐旱性。

干旱是巴西大豆生产的主要制约因素之一。在这项研究中，我们调查了两种大豆亲本基因型在逐步土壤干燥和再湿润下的生理特性。在完全灌溉（对照）条件下和通过暂停灌溉施加的水分亏缺条件下对植物进行评估，直到植物达到-1.0 MPa（中度）和-1.5 MPa（严重）的黎明前叶水势（）am）。生理分析表明，这些基因型对水分缺乏表现出不同的反应。Embrapa 48基因型在BR16基因型两天后达到中度和重度水势，即使在缺乏条件下也能够维持较高水平的A，ETR和ΦPSII。此结果与gs，13C同位素组成的变化以及更有效的抗氧化剂系统的存在无关。此外，相对于灌溉条件，Embrapa 48基因型的Fv / Fm值未降低，表明胁迫并未引起光合作用的光化学抑制。芽的相对生长的减少越大，干旱条件下根系的生长也就越大，这表明耐性基因型能够优先向根部分配碳，对光合作用的损害较小。因此，生理反应表明，该耐受基因型通过一种机制来推迟叶片脱水，该机制涉及更有效地利用和从根部转移水到芽，以维持胁迫下的细胞稳态和光合代谢。与灌溉条件相关，Embrapa 48基因型的Fv / Fm值未降低，表明胁迫并未引起光合作用的光化学抑制。芽的相对生长的减少越大，干旱条件下根系的生长也就越大，这表明耐性基因型能够优先向根部分配碳，对光合作用的损害较小。因此，生理反应揭示了该耐受基因型通过一种机制来推迟叶片脱水，该机制涉及更有效地利用和从根部到茎部转移水以维持胁迫下的细胞稳态和光合代谢。与灌溉条件相关，Embrapa 48基因型的Fv / Fm值未降低，表明胁迫并未引起光合作用的光化学抑制。芽的相对生长的减少越大，干旱条件下根系的生长也就越大，这表明耐性基因型能够优先向根部分配碳，对光合作用的损害较小。因此，生理反应表明，该耐受基因型通过一种机制来推迟叶片脱水，该机制涉及更有效地利用和从根部转移水到芽，以维持胁迫下的细胞稳态和光合代谢。表明耐性基因型能够优先向根部分配碳，对光合作用的损害较小。因此，生理反应表明，该耐受基因型通过一种机制来推迟叶片脱水，该机制涉及更有效地利用和从根部转移水到芽，以维持胁迫下的细胞稳态和光合代谢。表明耐性基因型能够优先将碳分配给根，对光合作用的损害较小。因此，生理反应表明，该耐受基因型通过一种机制来推迟叶片脱水，该机制涉及更有效地利用和从根部转移水到芽，以维持胁迫下的细胞稳态和光合代谢。