Abstract
Salinization of soils is one of the main sources of soil degradation worldwide, particularly in arid and semiarid ecosystems. High salinity results in osmotic stress and it can negatively impact plant grow and survival. Some plant species, however, can tolerate salinity by accumulating osmolytes like proline and maintaining low Na+ concentrations inside the cells. Another mechanism of saline stress tolerance is the association with symbiotic microorganism, an alternative that can be used as a biotechnological tool in susceptible crops. From the immense diversity of plant symbionts, those found in extreme environments such as Antarctica seems to be the ones with most potential since they (and their host) evolved in harsh and stressful conditions. We evaluated the effect of the inoculation with a consortium of plant growth-promoting rhizobacteria (PGPB) and endosymbiotic fungi isolated from an Antarctic plant on saline stress tolerance in different crops. To test this we established 4 treatments: (i) uninoculated plants with no saline stress, (ii) uninoculated plants subjected to saline stress (200 mM NaCl), (iii) plants inoculated with the microorganism consortium with no saline stress, and (iv) inoculated plants subjected to saline stress. First, we assessed the effect of symbiont consortium on survival of four different crops (cayenne, lettuce, onion, and tomato) in order to obtain a more generalized response of this biological interaction. Second, in order to deeply the mechanisms involved in salt tolerance, in lettuce plants we measured the ecophysiological performance (Fv/Fm) and lipid peroxidation to estimate the impact of saline stress on plants. We also measured proline accumulation and NHX1 antiporter gene expression (involved in Na+ detoxification) to search for possible mechanism of stress tolerance. Additionally, root, shoot, and total biomass was also obtained as an indicator of productivity. Overall, plants inoculated with microorganisms from Antarctica increased the fitness related traits in several crops. In fact, three of four crops selected to assess the general response increased its survival under salt conditions compared with those uninoculated plants. On the other hand, saline stress negatively impacted all measured trait, but inoculated plants were significantly less affected. In control osmotic conditions, there were no differences in proline accumulation and lipid peroxidation between inoculation treatments. Interestingly, even in control salinity, Fv/Fm was higher in inoculated plants after 30 and 60 days. Under osmotic stress, Fv/Fm, proline accumulation and NHX1 expression was significantly higher and lipid peroxidation lower in inoculated plants compared to uninoculated individuals. Moreover, inoculated plants exposed to saline stress had a similar final biomass (whole plant) compared to individuals under no stress. We conclude that Antarctic extremophiles can effectively reduce the physiological impact of saline stress in a salt-susceptible crops and also highlight extreme environments such as Antarctica as a key source of microorganism with high biotechnological potential.
Highlights
As a result of the global demand for processed food, intensive agricultural practices had altered the natural dynamics of the soil around the world, leading in many cases to the degradation of edaphic properties that are fundamental for crop productivity (Godfray et al, 2010)
The consortium of microorganisms used in our study was composed by two halotolerant plant growth-promoting rhizobacteria (PGPR) of the genus Arthrobacter sp. and Planoccocus sp. and two root-fungal endophytes; identifies as Penicillium chrysogenum and Penicillium brevicompactum
In our study we showed evidence suggesting the importance of symbiont microorganisms from Antarctica improving salt tolerance in crops
Summary
As a result of the global demand for processed food, intensive agricultural practices had altered the natural dynamics of the soil around the world, leading in many cases to the degradation of edaphic properties that are fundamental for crop productivity (Godfray et al, 2010). Several key aspects of intensive agricultural systems, like assisted irrigation, are one of the main drivers of soil saline accumulation (Allbed and Kumar, 2013). This process, known as soil salinization, represents one of the major forms of land degradation and was proposed to be a global problem for food security in the upcoming decades (Food and Agriculture Organization of the United Nations, 2009). Alternative practices that allow the utilization of degraded soils for crop production could became necessary in the near future One of these practices, plantmicrobe symbiosis, is highlighted as one of the most promising tools in such context (Paul and Lade, 2014; Joshi et al, 2015). The mechanistic analysis of this kind of interactions, and their evaluation for crop production, must be of primary interest in the upcoming years
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