Effect of d-mannose on antioxidant defense and oxidative processes in etiolated wheat coleoptiles

Effect of d-mannose treatment on different antioxidants, phenolics, protease activity, lipid peroxidation, DNA damage and cell death was investigated in coleoptiles of etiolated wheat seedlings. Modulations in these biochemical parameters were monitored up to 96 h after treatment at 24 h intervals. With accelerating effect on initial signs of cell death, i.e., appearance of long DNA fragmentation and no effect on initiation of terminal stage, i.e., internucleosomal nDNA fragmentation, mannose treatment (1 % = 56 mM) diminished the antioxidant activities in wheat coleoptiles. Mannose treatment decreased the catalase activity at all intervals, while APX and POD activities decreased at 72 h. Peroxidation of lipids increased at 72 h after mannose treatment. Levels of most of antioxidants, i.e., SOD, peroxidases and phenolics were raised during initial time period (24–48 h) of mannose treatment probably as an attempt to counter the stress effect. Protease activity gradually increased and protein content decreased with time in both treated and non-treated coleoptiles. Sharp decrease in CAT, APX and peroxidase activities and increase in lipid peroxidation at 72 h overlaps with apoptotic internucleosomal nDNA fragmentation in this organ. This coincidence points towards the importance of compromised antioxidant defense and involvement of reactive oxygen species in initiation of terminal stage of programmed cell death in wheat coleoptile. In conclusion, accelerating effect on DNA fragmentation and lipid peroxidation along with diminished antioxidant activities at the time of internucleosomal nDNA fragmentation, provide evidence for pro-apoptotic effect of d-mannose in wheat coleoptile.