Glutathione modulation of purine metabolism in cultured white spruce embryogenic tissue

Abstract

Changes in the glutathione redox state have been shown to affect plant growth and more specifically cell proliferation. Inclusion of reduced glutathione in the maintenance medium promotes the proliferation of white spruce embryogenic tissue. In this study we assessed the importance of the glutathione redox state in the modulation of purine nucleotide metabolism during the proliferation of white spruce embryogenic tissue. Purine nucleotide metabolism was investigated over the 7-day culture period by following the metabolic fate of 14 C -labeled 5-aminoimidazole-4-carboxamide-1-β- d-ribofuranoside (AICAR), adenine, adenosine, and inosine. Key enzymes involved in purine metabolism were also monitored during the culture period. The balance between the reduced (GSH) and oxidized (GSSG) forms of glutathione and ultimately the GSH:GSSG ratio could be correlated with the growth of the embryogenic tissue over time. Treatment of embryogenic tissue with 0.2 mM GSH gave higher uptake of both 14 C -adenine and 14 C -adenosine, especially during the rapid growth phase (Day 4) of the culture period, where a large proportion of these substrates was converted into nucleic acids and ATP. On the other hand, the majority of inosine was catabolized to CO 2 and ureides on all monitored days under all treatments, possibly due to the low activity of inosine kinase. Thus, there is a strong correlation between the glutathione redox state and purine metabolism in the proliferation of white spruce embryogenic tissue.