**Plant Metabolomics in a Changing World: Metabolite Responses to Abiotic Stress Combinations Responses to Abiotic Stress Combinations**

**Plant Metabolomics in a Changing World: Metabolite** 

DOI: 10.5772/intechopen.71769

Tiago F. Jorge and Carla António Tiago F. Jorge and Carla António Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.71769

#### **Abstract**

Climate change constitutes a real threat to the global landscape. Current climate models predict an increased occurrence of coastal floods associated to sea level rise and longterm droughts associated to changes in the intra- and inter-year rainfall variability. Under natural environmental conditions, plants are routinely exposed to abiotic stresses, and must develop different strategies to cope with this multitude of climate change factors. Mass spectrometry (MS)-based plant metabolomics approaches are finding an increasing number of applications to investigate the molecular and biochemical mechanisms that underlie plant responses to changing environments. These studies provide a promising basis for facilitating our understanding of the plant's flexibility to reconfigure central metabolic pathways (i.e., carbon, nitrogen and energy metabolism) as well as the degree by which plants tolerate and/or are susceptible to a climate change scenario. In this chapter, we will provide an update on the recent MS-based metabolomics strategies to study plant responses to drought, salt and heat stress as well as combinations thereof. We will describe how these stresses activate and coordinate several different signalling pathways, for example, through the synthesis of osmolytes.

**Keywords:** plant metabolomics, drought stress, salinity stress, heat stress, stress combination, climate change, mass spectrometry

### **1. Introduction**

Climate change can be defined as a statistically significant variation in the weather pattern or in its variability during a long-term period [1]. The causes of climate change have been mainly associated to (i) internal environmental processes and (ii) anthropogenic activities that lead to changes in the chemical composition of the atmosphere [1]. Natural climate variability itself is not enough to explain the unforeseen weather changes in the last decades. In fact,

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© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

since the industrial revolution that human-kind activities (e.g., fossil fuel burning) have also contributed to the release of significant amounts of greenhouse gases (GHGs) namely CO<sup>2</sup> , CH<sup>4</sup> , N<sup>2</sup> O as well as fluorinated gases to the atmosphere [1]. Indeed, climate change assessments have reported that the global atmospheric CO<sup>2</sup> concentration has increased from 270 to 401 μL L−1 since the industrial revolution, and consequently, the average global temperatures to rise by 0.85°C. Moreover, global warming has been reported to be highly correlated with ocean thermal expansion and loss of glacier mass, which ultimately reflected the observed global mean sea level rise of 0.19 ± 0.02 m over the period 1901–2010 [2]. By the end of the twenty-first century, unmatched climate changes are envisaged with CO<sup>2</sup> concentrations of at least 700 μL L−1 and global temperatures are expected to rise at least 4°C. Consequently, higher surface temperatures, longer and frequent heat waves and intense extreme precipitation events are very likely to occur in many regions around the globe. The consequences from climate change cannot be totally avoided, but without additional mitigation efforts beyond those already in place today, warming by the end of the twenty-first century will lead to very high risk of severe and irreversible impacts globally [2].

applied stress alone. Additionally, when different stresses are combined, they might require synergistic or antagonistic responses that are largely controlled by, sometimes, opposing signalling pathways [16, 17]. In this chapter, we will provide an update on recent studies of plant responses to drought, salt and heat stress as well as combinations thereof. We will describe how these abiotic stress combinations activate and coordinate several different signalling pathways, for example, through the synthesis of osmolytes, in order to ensure plant survival.

Plant Metabolomics in a Changing World: Metabolite Responses to Abiotic Stress Combinations

http://dx.doi.org/10.5772/intechopen.71769

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Over the past decade, plant metabolomics has undoubtedly become a powerful research tool to study the biochemical mechanisms underlying plant growth and development in the context of plant metabolite responses to abiotic stress, particularly drought, flooding, salinity and extreme temperatures (heat and cold). In fact, metabolomics itself, together with the other *omics* technologies (genomics, transcriptomics and proteomics) has accelerated our understanding of the complex molecular interactions in biological systems [18–24] (**Figure 1**). Moreover, unlike other *omics* tools, metabolomics has the advantage of not being dependent on the availability of organism-specific genome information for data analysis [25–27]. The main goal of plant metabolomics is to provide a non-biased characterisation of the total metabolite pool of a plant tissue in response to its environment. This metabolite pool includes a wide range of metabolites with diverse physical properties, from ionic inorganic compounds to biochemically derived hydrophilic carbohydrates, organic and amino acids, and a range of hydrophobic lipid-related compounds. Indeed, it is estimated that more than 200,000 different primary and secondary metabolites exist in the plant kingdom over a large dynamic range in concentrations that can vary from femtomolar to millimolar [28]. While, primary metabolites are fundamental for plant growth and development, being highly conserved in their molecular structures and abundances throughout the plant kingdom, secondary metabolites help plants communicating with the environment and widely differ across species. Due to such metabolite diversity, current plant metabolomics studies often combine multiple analytical tools in an effort to acquire more comprehensive metabolite coverage from a complex biological plant sample. One powerful analytical tool is nuclear magnetic resonance (NMR); however, due

**Figure 1.** *Omics* technologies have accelerated our understanding of the complex molecular interactions in biological

**2. Metabolomics—a key** *omics* **tool to study plant responses to** 

**abiotic stress**

systems.

Extreme climate change events expose plants to stressful environmental conditions that are outside of their physiological limits, and beyond the range by which they are already adapted [3]. Studies aiming at assessing the impact of climate change in plant ecosystems revealed that plant community responses occur at three sequential levels in which (i) climate change immediately impacts plant individuals at the morpho-physiological level, (ii) the community response is affected because of demographic changes in species abundances and (iii) the mortality or loss of species leads to their replacement by novel species within the community [4–6]. Although some studies have contributed to a better understanding of plant ecosystem responses to climate change, this research field is still emerging. A comprehensive discussion on this topic falls outside the scope of this chapter, and detailed information can be found elsewhere [4–13].

Responses by individual plant species to climate change have been indirectly studied through the assessment of the strategies and mechanisms by which they cope with adverse environmental conditions, that is, abiotic stresses. Abiotic stresses in plants comprise a multitude of environmental factors such as water (drought, flooding and submergence), temperature (high and low), light (high and low), radiation (UV-B and UV-A), salinity and nutrients, heavy metals, among others. These environmental (stress)factors negatively affect plant growth and development, and trigger a series of high-complex adaptive responses initiated by stress perception, signal transduction and the activation of many stress-related genes and metabolites [14, 15]. However, under natural environmental conditions, plants are routinely exposed to a combination of different abiotic stresses, and therefore, must develop different strategies to cope with a multitude of environmental factors. The latter gains more relevance under climate change scenarios, and therefore, there has been an increasing interest in understanding the molecular and biochemical mechanisms that underlie plant responses to abiotic stress combinations [16, 17].

Many studies, at both physiological and biochemical levels, have been performed to study plant responses to different stress combinations namely drought, salt, extreme temperatures and biotic stresses. Interestingly, these studies demonstrated that a plant response to a combined stress is unique, and should not be regarded as the sum of the responses from each applied stress alone. Additionally, when different stresses are combined, they might require synergistic or antagonistic responses that are largely controlled by, sometimes, opposing signalling pathways [16, 17]. In this chapter, we will provide an update on recent studies of plant responses to drought, salt and heat stress as well as combinations thereof. We will describe how these abiotic stress combinations activate and coordinate several different signalling pathways, for example, through the synthesis of osmolytes, in order to ensure plant survival.
