Influence of exogenous carbohydrates on superoxide dismutase activity in Trifolium repens L. explants cultured in vitro

Ireneusz Ślesak 1*, Wojciech Hałdaś 2, and Halina Ślesak 2

1Institute of Plant Physiology, Polish Academy of Sciences,
ul. Niezapominajek 21, 30-239 Cracow, Poland
2 Department of Plant Cytology and Embryology, 
Jagiellonian University, ul. Grodzka 52, 31-044 Cracow, Poland

*e-mail: i.slesak@ifr-pan.krakow.pl

Received November 24, 2005; revision accepted April 25, 2006

The effect of four sugars (sucrose, glucose, fructose, maltose) used as carbon source in liquid medium on superoxide dismutase (SOD) activity was studied. Little is known about how different soluble sugars used in plant tissue culture can affect SOD activity, an antioxidant enzyme involved in regulating the level of reactive oxygen species (ROS) in plant cells. In extracts of 15-day old cotyledons and hypocotyls of Trifolium repens L., four SOD forms were detected by native PAGE and activity staining: MnSOD, FeSOD, Cu/ZnSOD I and Cu/ZnSOD II. Activity of FeSOD and Cu/ZnSOD II was significantly lower in cotyledons cultured on media supplied with different carbohydrates than in control cotyledons cultured on medium without sugars, or was absent altogether. FeSOD was absent in hypocotyls obtained from seedlings grown on sterile filter paper (SFP); those cultured on sucrose-supplemented medium showed weak FeSOD activity. FeSOD appeared to be the most labile SOD form in T. repens cotyledons. MnSOD activity was highest in cotyledons cultured on sucrose-, fructose- and maltose-based media. Cu/ZnSOD I activity was highest in cotyledons cultured on medium with glucose and fructose. Sucrose strongly inhibited both FeSOD and Cu/ZnSOD II activity. The results indicated that various carbohydrates affect the activity of SOD forms in T. repens cotyledons. The decrease in activity of FeSOD and Cu/ZnSOD II, putatively located in chloroplasts, might suggest an inhibitory effect of some carbohydrates on photosynthesis in cotyledons of T. repens. On the other hand, supply of sucrose, fructose and maltose increased the activity of the putative mitochondrial form of MnSOD. This result might indicate sugar-induced production of ROS during respiration in mitochondria.

Key words: Trifolium repens, plant tissue culture, SOD pattern.