Linking waterlogging tolerance with Mn²⁺ toxicity: a case study for barley

Abstract

Vast agricultural areas are affected by flooding, causing up to 80% yield reduction and resulting in multibillion dollar losses. Up to now, the focus of plant breeders was predominantly on detrimental effects of anoxia, while other (potentially equally important) traits were essentially neglected; one of these is soil elemental toxicity. Excess water triggers a progressive decrease in soil redox potential, thus increasing the concentration of Mn(2+) that can be toxic to plants if above a specific threshold. This work aimed to quantify the relative contribution of Mn(2+) toxicity to waterlogging stress tolerance, using barley as a case study. Twenty barley (Hordeum vulgare) genotypes contrasting in waterlogging stress tolerance were studied for their ability to cope with toxic (1 mm) amounts of Mn(2+) in the root rhizosphere. Under Mn(2+) toxicity, chlorophyll content of most waterlogging-tolerant genotypes (TX9425, Yerong, CPI-71284-48 and CM72) remained above 60% of the control value, whereas sensitive genotypes (Franklin and Naso Nijo) had 35% less chlorophyll than 35% of controls. Manganese concentration in leaves was not related to visual Mn(2+) toxicity symptoms, suggesting that various Mn(2+) tolerance mechanisms might operate in different tolerant genotypes, i.e. avoidance versus tissue tolerance. The overall significant (r = 0.60) correlation between tolerance to Mn(2+) toxicity and waterlogging in barley suggests that plant breeding for tolerance to waterlogging traits may be advanced by targeting mechanisms conferring tolerance to Mn(2+) toxicity, at least in this species.

Waterlogging tolerance in barley is associated with faster aerenchyma formation in adventitious roots

“…Since excessive accumulation of metal ions in plants is a possible factor in triggering ROS production , selecting waterlogging-tolerant genotypes can partially be achieved through plant tolerance to toxic Mn 2+ and Fe 2+ which often is increased in waterlogged soils (Khabaz-Saberi et al 2005). This is consistent with our recent study with the demonstration of a significant correlation between Mn 2+ tolerance and waterlogging tolerance in barley (Huang et al 2014). In the light of above, we believe that using activity of enzymatic AO as biochemical markers will not be able to discover QTLs conferring waterlogging stress tolerance in barley.…”

Genomic and Genetic Studies of Abiotic Stress Tolerance in Barley

“…This variation could be harnessed to identify chromosomal regions not yet identified that are involved in Mn tolerance. Huang et al (2015) proposed that breeding for Mn tolerance could improve waterlogging tolerance in barley, which could be due to the decrease in soil redox potential under waterlogging, which in turn increases the soil Mn 2+ concentration and causes Mn-toxicity effects in plants. On the other hand, Leplat et al (2016) examined 248 barley varieties that were cultivated in six distinct environments prone to Mn deficiency, and identified several putative QTLs.…”

Waterlogging and submergence stress: affects and acclimation

“…This may lead to morphological damage and increased susceptibility to pests and diseases (Catling, 1992;Greenway & Setter, 1996). Partial submergence, often referred to as waterlogging, leads to reduced gas diffusion, growth of microorganisms and production of toxic substances such as Fe 2+ , Mn 2+ and H 2 S (Huang et al, 2015;Setter et al, 2009). Whether it is partial and/or fully submerged conditions, there occurs a limited supply of O 2 a condition generally called hypoxia.…”