Abstract
This work demonstrated how reactive oxygen species (ROS) are involved in the regulation of rhizogenesis from hypocotyls of Mesembryanthemum crystallinum L. cultured on a medium containing 1-naphthaleneacetic acid (NAA). The increase of NADPH oxidase activity was correlated with an increase of hydrogen peroxide (H2O2) content and induction of mitotic activity in vascular cylinder cells, leading to root formation from cultured hypocotyls. Diphenylene iodonium (DPI), an inhibitor of NADPH oxidase, inhibited H2O2 production and blocked rhizogenesis. Ultrastructural studies revealed differences in H2O2 localization between the vascular cylinder cells and cortex parenchyma cells of cultured explants. We suggest that NADPH oxidase is responsible for H2O2 level regulation in vascular cylinder cells, while peroxidase (POD) participates in H2O2 level regulation in cortex cells. Blue formazan (NBT) precipitates indicating superoxide radical (O2 •−) accumulation were localized within the vascular cylinder cells during the early stages of rhizogenesis and at the tip of root primordia, as well as in the distal and middle parts of newly formed organs. 3,3′-diaminobenzidine (DAB) staining of H2O2 was more intense in vascular bundle cells and in cortex cells. In newly formed roots, H2O2 was localized in vascular tissue. Adding DPI to the medium led to a decrease in the intensity of NBT and DAB staining in cultured explants. Accumulation of O2 •− was then limited to epidermis cells, while H2O2 was accumulated only in vascular tissue. These results indicate that O2 •− is engaged in processes of rhizogenesis induction involving division of competent cells, while H2O2 is engaged in developmental processes mainly involving cell growth.
Highlights
Hypocotyls of M. crystallinum cultured on a medium supplemented with 2,4-dichlorophenoxy-acetic acid (2,4-D) exhibited high rhizogenic potential and induction of root formation was found to depend on high endogenous H2O2 and the activity of specific isoforms of some antioxidant enzymes (Konieczny et al 2014)
Auxins play a central role in the control of cell and plant growth, but oxidative stress caused by overproduction of reactive oxygen species (ROS) affects growth and development
Pasternak et al (2005) showed that oxidative stress initiates cell division and the formation of morphogenic cell clusters in the pericycle area of Arabidopsis seedlings but that in the absence of externally sourced auxin the oxidative stress had no effect on morphogenesis induction
Summary
M. Kozieradzka-Kiszkurno Department of Plant Cytology and Embryology, University of Gdańsk, Wita Stwosza 59 St., 80-308 Gdańsk, Poland. Z. Miszalski Malopolska Centre of Biotechnology, Jagiellonian University, Gronostajowa 7A St., 30-387 Kraków, Poland. R. Konieczny Department of Plant Cytology and Embryology, Institute of Botany, Jagiellonian University, Gronostajowa 9 St., 30-387 Kraków, Poland. Processes of organ development in vitro require the reinitiation of cell division and the modulation of cell differentiation in cultured explants. Explant cells acquire organogenic competence, the ability to recognize signals that commit them to a particular developmental program. Already competent but still quiescent cells re-enter the cell cycle, proliferate, and alter their developmental fate, the key step during de novo organogenesis. The last phase of organogenesis is cell differentiation and organ
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