Physiology of manganese toxicity and tolerance in Vigna unguiculata (L.) Walp.

Mechanisms of silicon-mediated alleviation of abiotic stresses in higher plants: A review

“…This finding has been supported by subsequent experiments (Horst and Marschner, 1978;Horiguchi and Morita, 1987;Shi et al, 2005b). Horst et al (1999) observed that Si lowered the apoplastic Mn concentration in cowpea, suggesting that Si may modify the cation binding capacity of the cell wall. Iwasaki et al (2002a,b) found that the Mn concentration in the apoplastic washing fluids of plants with a continuous supply of 1.44 mM Si and 50 mM Mn and not showing Mn toxicity symptoms was higher than that of plants grown at 10 mM Mn without Si supply which showed distinct Mn toxicity symptoms, suggesting that Si supply alleviates Mn toxicity not only by decreasing the concentration of soluble apoplastic Mn through enhanced adsorption of Mn on the cell walls, but also a role of soluble Si in the apoplast in the detoxicification of apoplastic Mn is indicated.…”

Synchrotron-based Techniques Shed Light on Mechanisms of Plant Sensitivity and Tolerance to High Manganese in the Root Environment

“…Hughes and Williams (1988) concluded that the eukaryotic cell pumps Mn into almost any vesicular partition of the cell rather than leave it in the cytoplasm, where high levels are toxic (Führs et al, 2008). High Mn in the veins further suggests the absence of an effective Mn sink in soybean leaves, with excess Mn remaining in or moving to the walls of cells in the interveinal regions where necrosis occurs through oxidation of phenolics and high peroxidase activity in the apoplast (Horst et al, 1999). Oxidation of Mn(II) to Mn(III) would be a likely consequence, as would be callose formation through cellular injury.…”

“…These lesions have been shown in cowpea (Vigna unguiculata) to contain oxidized Mn and callose , which forms as a reaction to high intracellular Ca (Kartusch, 2003). The necrotic lesions result mainly from oxidized phenolics and increased peroxidase activity in the apoplast (Horst et al, 1999). With a critical solution concentration for toxicity (10% growth reduction) of no more than 9 mM Mn, Edwards and Asher (1982) found that cotton (Gossypium hirsutum), bean (Phaseolus vulgaris), cowpea, and soybean (Glycine max) were the most sensitive species of 13 crop and pasture plants grown for 18 to 31 d at constant Mn in solution culture.…”

Can silicon partially alleviate micronutrient deficiency in plants? a review

“…In cowpea, a lower amount of Mn in the apoplast was obtained when Si was added to the media. This could be explained through the metal adsorption on cell walls mediated by the Si deposits as for Zn (Horst et al 1999), but also because soluble Si in the apoplast may affect Mn-oxidation state promoting its precipitation (Iwasaki et al 2002). Cucumber plants treated with Si presented more than 90 % of the Mn bound to the cell wall, in comparison with untreated plants, in which 50 % of the Mn was in the symplast and 50 % in the apoplast (Rogalla and Römheld 2002;Wiese et al 2007).…”