Early responses to manganese (Mn) excess and its relation to antioxidant performance and organic acid exudation in barley cultivars

Abstract

Manganese (Mn) is an essential micronutrient for plants, and is necessary for biochemical and physiological processes. The objective of this research was to determine the early responses to Mn excess and its relation to antioxidant performance mechanisms and organic acid exudation in commercial barley cultivars. We determined early responses to Mn excess in four barley cultivars (Barke, Tatoo, Scarlett, Sebastian), which were subjected to increasing Mn concentrations (2.4-150-350-750-1500 µM Mn), pH 4.8, under nutrient solution during seven days. Results showed that plant growth parameters: biomass, length and relative growth rate (RGR) were negatively altered with the higher Mn treatments. Antioxidant performance such as antioxidant activity (AA) and antioxidant enzymes such as superoxidase dismutase (SOD) were activated in presence of excess Mn. Oxalate was the major organic acid roots exudate, and the cultivar Sebastian had the highest oxalate exudation. In conclusion, Tatoo and Sebastian are proposed as the most Mn tolerant cultivars given that the biomass parameters were not affected by increasing Mn doses, showing major oxalate exudation. It is suggested that the mechanisms associated to Mn alleviation could be attributed to SOD, AA and organic acid production, mainly oxalate, in tolerant cultivars (Sebastian, Tatoo) together to significant decrease of total phenols (TP) in shoot of sensitive cultivars (Barke and Scarlett). Non-enzymatic barriers were not related to early responses, and an enzymatic barrier and oxalate exudation were considered as early indicators of Mn stress, projecting that the tolerance of Mn-tolerant cultivars could increase under field conditions.

The Optimization of Medium Conditions and Auxins in the Induction of Adventitious Roots of Pokeweed (Phytolacca americana L.) and Their Phytochemical Constituents

“…The opposite position between the parameters of root growth and phytochemicals clearly exhibited the negative correlation, which was also observed in Lactuca sativa [ 65 ] and Hordeum vulgare [ 66 ]. The negative correlations may be indirectly resulted from the solidification states of the culture.…”

Genotypic differences in reaction of barley root system on Mn and Fe toxicity

“…In contrast, other studies shown that the antioxidant system decreases its activity due to the effects of Mn [19] and these contrasting antioxidant responses when facing excess Mn are directly influenced by Mn resistance and sensitivity mechanisms in plants [18]. Millaleo et al [18] on example of four barley cultivars showed that Mnresistant varieties increased AOA and sensitive cultivars decreased AOA. According to these observations, all barley varieties studied by us are considered as potentially resistant to manganese ions, but differ in resistance to iron ions: cv.…”

“…In the case of manganese, an increase in antioxidant activity was observed in all cultivars studied; and in iron influence, a significant change was observed only in three cultivars, of which two cultivars had an increase in this parameter. Since it is known that antioxidant performance such as antioxidant activity (AOA) and antioxidant enzymes such as superoxide dismutase (SOD) were activated in presence of excess Mn [18], probably in different barley genotypes disorders are associated with different biochemical reactions (increase in synthesis of enzymes, secondary metabolites, lipid peroxidation of membranes). In contrast, other studies shown that the antioxidant system decreases its activity due to the effects of Mn [19] and these contrasting antioxidant responses when facing excess Mn are directly influenced by Mn resistance and sensitivity mechanisms in plants [18].…”

“…Since it is known that antioxidant performance such as antioxidant activity (AOA) and antioxidant enzymes such as superoxide dismutase (SOD) were activated in presence of excess Mn [18], probably in different barley genotypes disorders are associated with different biochemical reactions (increase in synthesis of enzymes, secondary metabolites, lipid peroxidation of membranes). In contrast, other studies shown that the antioxidant system decreases its activity due to the effects of Mn [19] and these contrasting antioxidant responses when facing excess Mn are directly influenced by Mn resistance and sensitivity mechanisms in plants [18]. Millaleo et al [18] on example of four barley cultivars showed that Mnresistant varieties increased AOA and sensitive cultivars decreased AOA.…”

Advances in Plant–Soil Feedback Driven by Root Exudates in Forest Ecosystems

“…These chemicals were used as chelating agents to reduce metal toxicity in plants [113]. In the case of certain variable-valence metals, their solubility and phytotoxicity are often influenced by their redox status [114,115]. Therefore, plants have the capacity to oxidize metals including Mn by releasing oxygen and oxides to reduce their toxic effects [116].…”