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

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 cutvars 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. © 2018, Sociedad Chilena de la Ciencia del Suelo. All rights reserved.