Apoplastic hydrogen peroxide in the growth zone of the maize primary root under water stress. I. Increased levels are specific to the apical region of growth maintenance

Abstract

Previous work on the adaptation of maize (Zea mays L.) primary root growth to water stress showed that cell elongation is maintained in the apical region of the growth zone but progressively inhibited further from the apex. Cell wall proteomic analysis suggested that levels of apoplastic reactive oxygen species (ROS), particularly hydrogen peroxide (H2O2), may be modified in a region-specific manner within the growth zone of water-stressed roots. Apoplastic ROS may have wall loosening or tightening effects and may also have other growth regulatory functions. To gain an understanding of how apoplastic ROS levels change under water stress, cerium chloride staining was used in conjunction with transmission electron microscopy to examine the spatial distribution of apoplastic H2O2. The results revealed that apoplastic H2O2 levels increased specifically in the apical region of the growth zone under water stress, correlating spatially with the maintenance of cell elongation. The basal regions of the growth zone of water-stressed roots and the entire growth zone of well-watered roots exhibited relatively low levels of apoplastic H2O2. The increase in apoplastic H2O2 in the apical region under water stress probably resulted, at least in part, from a pronounced increase in oxalate oxidase activity in this region. By contrast, well-watered roots showed negligible oxalate oxidase activity throughout the growth zone. The results show that changes in apoplastic ROS levels in the root growth zone under water-deficit conditions are regulated in a spatially-specific manner, suggesting that this response may play an important role in maize root adaptation to water stress.

Genetic variability of oxalate oxidase activity and elongation in water-stressed primary roots of diverse maize and rice lines

“…1). Except for lines M162W, B73 and P39, all the temperate lines exhibited oxalate oxidase activity within the apical 3 mm region (as previously observed for FR697 13 ), with some lines showing more pronounced staining than other lines. In addition, all the temperate lines showed oxalate oxidase activity in the basal region (beyond 6 mm from the apex).…”

“…Although a correlation between the occurrence of increased oxalate oxidase activity and root growth maintenance under water deficit conditions was not apparent, it should be emphasized that the results do not necessarily imply that the maize and rice lines that lack an oxalate oxidase response also lack the response of increased apoplastic ROS levels in the apical region of the growth zone. 13 Oxalate oxidase might not be a major contributor to apoplastic H 2 O 2 production in these lines, and increased ROS levels could be achieved by increased activity of other ROS-producing enzymes. These alternative hypotheses could be tested by measuring apoplastic ROS levels in the rice and contrasting maize lines under water stress conditions.…”

“…11,12 In particular, several transcripts and proteins related to reactive oxygen species (ROS) production, including putative oxalate oxidases, increased in abundance in the apical region and oxalate oxidase activity was shown to increase markedly in the apical few mm. 13 Oxalate oxidase activity also increased, although to a lesser extent, beyond approximately 8 mm from the apex (beyond the growth zone). Oxalate oxidases catalyze the conversion of oxalate to CO 2 and hydrogen peroxide (H 2 O 2 ), and in cereals are known to be cell wall localized.…”

Boron Supply and Water Deficit Consequences in Young Paricá (<i>Schizolobium parahyba</i> var.<i> amazonicum</i>) Plants

“…The isolated effect of water deficit caused an increase in the H2O2 production in leaf and root tissues, being a response linked to oxidative stress and induced by the superoxide dismutase (SOD), which is an enzyme that acts in mechanism tolerance against the reactive species of oxygen (ROS), dismutating superoxide (O2 -) to H2O2 (Scandalios, 2005;Voothuluru and Sharp, 2013). Similar results on H2O2 accumulation were found by Anjum et al (2008) when the leaves of Vigna radiata were evaluated, corroborating with the data of this research.…”

ROS as Key Players of Abiotic Stress Responses in Plants

“…These pathways were also found to play important roles in the response of plants to abiotic stresses. For example, oxalate oxidase was shown to be involved in ROS production in root cells during drought stress (Voothuluru and Sharp 2013). In addition, recent studies uncovered a role for peroxidase-dependent ROS in the regulation of root growth and response to potassium deficiency (Kim et al 2010;Jia 2011;Kwasniewski et al 2013).…”