The Role of Hydrogen Peroxide-Producing and Hydrogen Peroxide-Consuming Peroxidases in the Leaf Apoplast of Cowpea in Manganese Tolerance

Abstract

The apoplast is considered the leaf compartment decisive for manganese (Mn) toxicity and tolerance in cowpea (Vigna unguiculata). Particularly apoplastic peroxidases (PODs) were proposed to be key enzymes in Mn toxicity-induced processes. The presented work focuses on the characterization of the role of hydrogen peroxide (H 2 O 2 )-producing (NADH peroxidase) and H 2 O 2 -consuming peroxidase (guaiacol POD) in the apoplastic washing fluid (AWF) of leaves for early stages of Mn toxicity and genotypic differences in Mn tolerance of cowpea. Leaf AWF of the Mn-sensitive cultivar (cv) TVu 91 but not of the Mntolerant cv 1987 showed an increase of guaiacol-POD and NADH-peroxidase activities at elevated AWF Mn concentrations. two-dimensional resolutions of AWF proteins revealed that cv TVu 91 expressed more and additional proteins at high Mn treatment, whereas Mn-tolerant cv TVu 1987 remained nearly unaffected. In both cultivars, NADH-peroxidase activity and accompanied H 2 O 2 formation rate in vitro were significantly affected by Mn 21 , p-coumaric acid, and metabolites occurring in the AWF. The total phenol concentration in the AWF was indicative of advanced stages of Mn toxicity but was rather unrelated to early stages of Mn toxicity and genotypic differences in Mn tolerance. The NADH oxidation by AWF PODs was significantly delayed or enhanced in the presence of the protein-free AWF from cv TVu 1987 or cv TVu 91, respectively. High-performance liquid chromatography analysis of AWF indicates the presence of phenols in cv TVu 1987 not observed in cv TVu 91. We conclude from our studies that the H 2 O 2 -producing NADH peroxidase and its modulation by stimulating or inhibiting phenolic compounds in the leaf apoplast play a major role for Mn toxicity and Mn tolerance in cowpea.

A Distinct Endosomal Ca2+/Mn2+ Pump Affects Root Growth through the Secretory Process

“…The method was modified from that used to extract apoplastic wall fluid from leaves (Rathmell and Sequeira, 1974;Fecht-Christoffers et al, 2006). Arabidopsis roots (0.1-0.5 g fresh weight) were rinsed in DI water and then excised into 10 mM Na phosphate buffer (pH 6.0).…”

The Potato-Specific Apyrase Is Apoplastically Localized and Has Influence on Gene Expression, Growth, and Development

“…This method has already been used not only for the determination of apoplastic metabolites but also for the extraction of apoplastic proteins (Boudart et al, 2005;Fecht-Christoffers et al, 2006). Pools of AWF from leaves from eight 6-week-old wild-type potato plants with reasonably low activity of UGPase, a soluble cytosolic enzyme with high activity and an almost identical molecular mass to that of apyrase, were prepared to analyze apyrase activity.…”

Malate Synthesis and Secretion Mediated by a Manganese-Enhanced Malate Dehydrogenase Confers Superior Manganese Tolerance in Stylosanthes guianensis

“…Therefore, it has been suggested that leaf chloroplasts might be primary targets of Mn toxicity, which could result in impairment of thylakoid structure and disruption of the electron transport chain in photosynthesis of plants (González et al, 1998;Lidon et al, 2004). In addition, Mn toxicity might also cause reactive oxygen species accumulation and brown spot formation in leaves, and may thereby inhibit plant growth more severely (Fecht-Christoffers et al, 2006). Although soil amelioration (e.g.…”

“…In cowpea (Vigna unguiculata), compartmentalization of Mn in leaf apoplasts is considered as a primary response to Mn toxicity (Horst et al, 1999). Furthermore, accumulation of peroxidases in leaf apoplasts can modulate Mn oxidation, and thereby affect Mn tolerance in cowpea (Fecht-Christoffers et al, 2006). In addition, increased cell wall binding capacity of Mn and decreased hydroxyl radical accumulation in leaf apoplasts have been suggested to alleviate Mn toxicity with silicon (Si) application (Dragiši c Maksimovi c et al, 2012).…”