Established and proposed roles of xanthine oxidoreductase in oxidative and reductive pathways in plants

Xanthine oxidoreductase (XOR) is among the most-intensively studied enzymes known to participate in the consumption of oxygen in cells. However, it attracted the attention of researchers due its participation in free radical production in vivo, mainly through the production of superoxide radicals. In plants, XOR is a key enzyme in purine degradation where it catalyzes the oxidation of hypoxanthine to xanthine and of xanthine to uric acid. Both reactions are accompanied by electron transfer to either NAD+ with simultaneous formation of NADH or to molecular oxygen, which results in formation of superoxides. Characterization of plant XOR mutants and isolated XOR proteins from various plant species provided evidence that the enzyme plays significant roles in plant growth, leaf senescence, fruit size, synthesis of nitrogen storage compounds, and plant-pathogen interactions. Moreover, the ability of XOR to carry out redox reactions as NADH oxidase and to produce reactive oxygen species and nitric oxide, together with a possible complementary role in abscisic acid synthesis have raised further attention on the importance of this enzyme. Based on these established and proposed functions, XOR is discussed as regulator of different processes of interest in plant biology and agriculture.The authors acknowledge the support of the research grants AGL2010-16167 to J.F.M. from the Spanish Ministry of Science and Innovation and Bi 1075/5-1 to F.B. by the Deutsche Forschungsgemeinschaft. R.E. received a JAE-Doctor grant from the Spanish Research Council (CSIC).

The effect of molybdenum on the molecular control of cold tolerance in cauliflower (Brassica oleracea var. botrytis) artificial seeds

Molybdenum (Mo) was used to improve the cold tolerance of cauliflower microshoots/artificial seeds. The optimal stage to introduce Mo to the micropropagation system was found to be the microshoots liquid culture stage, since its use within artificial seed capsules or conversion media had negative effects on conversion rate and viability. Mo was found to improve the cold tolerance of both acclimated and non-acclimated microshoots/artificial seeds. The capacity of Mo to up-regulate CBF/DREB1 in cauliflower microshoots was confirmed. Moreover, this study is the first to confirm the ability of this element to upregulate CBF/DREB1 without any low temperature treatment. Mo significantly increased the accumulation of 23 kDa polypeptide when it was used at 15 ppm concentration. However, Mo had a negative effect on the accumulation of dehydrin proteins which suggest that this group of proteins have no significant role in the cold tolerance of cauliflower microshoots. The study could help in improving the understanding of the abiotic stress network in plants and in improving the quality and efficiency of cauliflower artificial seed production systems