A Quantitative Profiling Method of Phytohormones and Other Metabolites Applied to Barley Roots Subjected to Salinity Stress

Abstract

As integral parts of plant signaling networks, phytohormones are involved in the regulation of plant metabolism and growth under adverse environmental conditions, including salinity. Globally, salinity is one of the most severe abiotic stressors with an estimated 800 million hectares of arable land affected. Roots are the first plant organ to sense salinity in the soil, and are the initial site of sodium (Na+) exposure. However, the quantification of phytohormones in roots is challenging, as they are often present at extremely low levels compared to other plant tissues. To overcome this challenge, we developed a high-throughput LC-MS method to quantify ten endogenous phytohormones and their metabolites of diverse chemical classes in roots of barley. This method was validated in a salinity stress experiment with six barley varieties grown hydroponically with and without salinity. In addition to phytohormones, we quantified 52 polar primary metabolites, including some phytohormone precursors, using established GC-MS and LC-MS methods. Phytohormone and metabolite data were correlated with physiological measurements including biomass, plant size and chlorophyll content. Root and leaf elemental analysis was performed to determine Na+ exclusion and K+ retention ability in the studied barley varieties. We identified distinct phytohormone and metabolite signatures as a response to salinity stress in different barley varieties. Abscisic acid increased in the roots of all varieties under salinity stress, and elevated root salicylic acid levels were associated with an increase in leaf chlorophyll content. Furthermore, the landrace Sahara maintained better growth, had lower Na+ levels and maintained high levels of the salinity stress linked metabolite putrescine as well as the phytohormone metabolite cinnamic acid, which has been shown to increase putrescine concentrations in previous studies. This study highlights the importance of root phytohormones under salinity stress and the multi-variety analysis provides an important update to analytical methodology, and adds to the current knowledge of salinity stress responses in plants at the molecular level.

Insights Into Oxidized Lipid Modification in Barley Roots as an Adaptation Mechanism to Salinity Stress

“…Seeds of four Australian barley (H. vulgare L.) cultivars Mundah, Vlamingh, Keel, and Gairdner were provided by the University of Adelaide (SA, Australia). Cultivars were selected based on prior knowledge of their contrasting responses to salinity stress (Coventry et al, 2008;Cao et al, 2017;Yu et al, 2018). Barley seedlings (20 plants per variety and treatment) were grown in hydroponics for 5 weeks as previously described (Cao et al, 2017;Yu et al, 2018).…”

“…Cultivars were selected based on prior knowledge of their contrasting responses to salinity stress (Coventry et al, 2008;Cao et al, 2017;Yu et al, 2018). Barley seedlings (20 plants per variety and treatment) were grown in hydroponics for 5 weeks as previously described (Cao et al, 2017;Yu et al, 2018). Seeds were imbibed in deionized water with aeration for 16 h and then transferred to moistened filter paper for vernalization at 4°C.…”

Metabolomics 20 years on: what have we learned and what hurdles remain?

“…Although approaches to tackle this are likely to involve relatively complex strategies, we believe that they will be instrumental in helping us to ascertain the precise function of specific metabolites and the biological circumstances under which they play the most important role. First steps towards the latter have been made in an elegant study, in which the roles of flavonoids in the core pathway were tested in a range of mutants under conditions of oxidative and drought stress (Nakabayashi et al ., ; Cao et al ., ); however, these authors were only able to draw conclusions concerning the role of flavonoids as a compound class, and further studies are required to dissect the quantitative contributions of individual flavonoid species to the conferment of stress tolerance. We would argue that the identification of metabolite function on a metabolite‐by‐metabolite basis arguably represents the real grand challenge as metabolomics enters its third decade.…”

Metabolômica: Definições, Estado-Da-Arte E Aplicações Representativas

“…Estes estudos apresentaram resultados que contribuem para um melhor entendimento no que se refere à resposta ao estresse salino em plantas, em nível molecular, e como o estresse afeta a produção de fitohormô-nios, o crescimento, o desenvolvimento e o metabolismo de plantas. 257 …”