Decreased reactive oxygen species concentration in the elongation zone contributes to the reduction in maize leaf growth under salinity

Abstract

Reactive oxygen species (ROS) in the apoplast of cells in the growing zone of grass leaves are required for elongation growth. This work evaluates whether salinity-induced reductions in leaf elongation are related to altered ROS production. Studies were performed in actively growing segments (SEZ) obtained from leaf three of 14-d-old maize (Zea mays L.) seedlings gradually salinized to 150 mM NaCl. Salinity reduced elongation rates and the length of the leaf growth zone. When SEZ obtained from the elongation zone of salinized plants (SEZs) were incubated in 100 mM NaCl, the concentration where growth inhibition was approximately 50%, O2*- production, measured as NBT formazan staining, was lower in these than in similar segments obtained from control plants. The NaCl effect was salt-specific, and not osmotic, as incubation in 200 mM sorbitol did not reduce formazan staining intensity. SEZs elongation rates were higher in 200 mM sorbitol than in 100 mM NaCl, but the difference could be cancelled by scavenging or inhibiting O2*- production with 10 mM MgCl2 or 200 microM diphenylene iodonium, respectively. The actual ROS believed to stimulate growth is *OH, a product of O2*- metabolism in the apoplast. SEZ(s) elongation in 100 mM NaCl was stimulated by a *OH-generating medium. Fusicoccin, an ATPase stimulant, and acetate buffer pH 4, could also enhance elongation in these segments, although both failed to increase ROS activity. These results show that decreased ROS production contributes to the salinity-associated reduction in grass leaf elongation, acting through a mechanism not associated with pH changes.

Cadmium-induced early changes in O2 •−, H2O2 and antioxidative enzymes in soybean (Glycine max L.) leaves

“…•-level by abiotic stresses (Rodriguez et al 2004). It can be argued that this decrease in O 2 •-content in WP leaves could be due to an enhanced SOD activity.…”

Cell Wall Proteome in the Maize Primary Root Elongation Zone. II. Region-Specific Changes in Water Soluble and Lightly Ionically Bound Proteins under Water Deficit

“…Recent studies suggest that generation of hydroxyl radicals from H 2 O 2 (by either the Fenton reaction or peroxidase activity) can play a direct role in cell wall loosening via polysaccharide cleavage (Fry, 1998;Fry et al, 2001;Liszkay et al, 2003), and there is evidence for this activity in the elongation zone of leaves (Rodriguez et al, 2002) and primary roots (Liszkay et al, 2004) of well-watered maize. Further, there is evidence that salinity-induced inhibition of leaf expansion in maize is associated with reduced apoplastic ROS production (Rodriguez et al, 2004(Rodriguez et al, , 2007. However, to our knowledge, up-regulation of this mechanism of wall loosening in the response of root growth to water stress has not been investigated.…”

Role of Reactive Oxygen Species during Cell Expansion in Leaves

“…Loosening of the cell wall is in part regulated by two classes of proteins (expansins and xyloglucan endotransglucosylases/ hydrolases) that act on the interaction between xyloglucans, the major hemicellulose polymer, and the cellulose network (Park and Cosgrove, 2012). Studies on leaf expansion in maize under saline conditions revealed a decreased O 2 2 -derived _ OH production in the apoplast and a consequent reduction in leaf growth (Rodríguez et al, 2004). Interestingly, it was found that _ OH promotes cell elongation by loosening the cell wall through oxidative cleavage of polymers like xyloglucan and pectin (Fry, 1998;Müller et al, 2009).…”

“…Although during abiotic stress ROS levels rise, this does not necessarily apply to the growth zone of the leaf. For instance, studies on leaf expansion in maize (Zea mays) under saline conditions revealed that not an increase in ROS but a decrease caused retarded leaf growth (Rodríguez et al, 2004). Moreover, exposure of maize to salinity or drought causes an increase in the antioxidant capacity of the leaf and thereby restricts cell expansion (Bernstein et al, 2010;Kravchik and Bernstein, 2013;Avramova et al, 2015).…”