Decrease in Manganese Superoxide Dismutase Leads to Reduced Root Growth and Affects Tricarboxylic Acid Cycle Flux and Mitochondrial Redox Homeostasis    

Abstract

Superoxide dismutases (SODs) are key components of the plant antioxidant defense system. While plastidic and cytosolic isoforms have been extensively studied, the importance of mitochondrial SOD at a cellular and whole-plant level has not been established. To address this, transgenic Arabidopsis (Arabidopsis thaliana) plants were generated in which expression of AtMSD1, encoding the mitochondrial manganese (Mn)SOD, was suppressed by antisense. The strongest antisense line showed retarded root growth even under control growth conditions. There was evidence for a specific disturbance of mitochondrial redox homeostasis in seedlings grown in liquid culture: a mitochondrially targeted redox-sensitive green fluorescent protein was significantly more oxidized in the MnSOD-antisense background. In contrast, there was no substantial change in oxidation of cytosolically targeted redox-sensitive green fluorescent protein, nor changes in antioxidant defense components. The consequences of altered mitochondrial redox status of seedlings were subtle with no widespread increase of mitochondrial protein carbonyls or inhibition of mitochondrial respiratory complexes. However, there were specific inhibitions of tricarboxylic acid (TCA) cycle enzymes (aconitase and isocitrate dehydrogenase) and an inhibition of TCA cycle flux in isolated mitochondria. Nevertheless, total respiratory CO 2 output of seedlings was not decreased, suggesting that the inhibited TCA cycle enzymes can be bypassed. In older, soil-grown plants, redox perturbation was more pronounced with changes in the amount and/or redox poise of ascorbate and glutathione. Overall, the results demonstrate that reduced MnSOD affects mitochondrial redox balance and plant growth. The data also highlight the flexibility of plant metabolism with TCA cycle inhibition having little effect on overall respiratory rates.

Unraveling the Tapestry of Networks Involving Reactive Oxygen Species in Plants

“…Since then researchers have taken advantage of this tool to monitor the redox state involved in glutathione metabolism (Meyer et al, 2007) or the removal of ROS by manganese superoxide dismutase in mitochondria (Morgan et al, 2008), and additional papers are anticipated. Other valuable methods for in vivo monitoring of ROS were also introduced, including autoluminescence (Havaux et al, 2006) and biophotone imaging (Kobayashi et al, 2007) as well as luciferase imaging (Shao et al, 2007).…”

The Arabidopsis Class II Sirtuin Is a Lysine Deacetylase and Interacts with Mitochondrial Energy Metabolism

“…For mitochondria isolation, Arabidopsis (Arabidopsis thaliana; ecotype Columbia [Col-0]) seedlings were grown in liquid culture as described in Morgan et al (2008). For growth on plates, Arabidopsis seeds were treated and grown the same way except that the medium was supplemented with 0.8% (w/v) phytoagar.…”

“…Mitochondria were isolated from 10-d-old Arabidopsis seedlings grown in liquid cultures as described before (Morgan et al, 2008). The integrity of the outer membrane was determined by the latency of cytochrome c oxidation before and after addition of Triton-X100 (Sweetlove et al, 2007).…”

“…Gels were either transferred to nitrocellulose membranes for western-blot analysis or stained with Coomassie colloidal blue. Protein spots were excised from gels and trypsin digested as described before (Morgan et al, 2008) and analyzed using LC-MS/MS as described below.…”

Identification of key genes involved in root development of tomato using expressed sequence tag analysis

“…Hsp70 was involved in instrumenting root-shoot communication in cucumber plants (Li et al 2014) whereas expression of hsp81-2 was found high in roots of Arabidopsis thaliana (Yabe et al 1994). In addition, a gene encoding for superoxide dismutase (SOD) is major component of plant defence system but decrease in manganese superoxide dismutase leads to reduced root growth (Morgan et al 2008). Other identified genes like glutathione peroxidase, cinnamic acid 4-hydroxylase and ACC oxidase have been involved in root metabolism and growth (Passaia et al 2013;Dennis and Kennedy 1986).…”