Does the glyoxylate cycle have an anaplerotic function in plants?

摘要

Studies of growth and metabolism in an Arabidopsis mutant lacking the glyoxylate cycle, and consideration of enzyme synthesis and metabolism in carbohydrate-deprived plant cells have led Peter Eastmond and Ian Graham [1] to the conclusion that the glyoxylate cycle serves an anaplerotic function in plants. I question the validity of that conclusion and argue for further research on this important aspect of plant metabolism. In microorganisms, the glyoxylate by-pass of the tricarboxylic acid (TCA) cycle provides the means to grow on C2 compounds by converting them into C4 dicarboxylic acids [2]. This is achieved through the activity of two unique enzymes, isocitrate lyase (ICL) and malate synthase (MS). The oxaloacetate supplied by the by-pass maintains the TCA cycle by replacing intermediates that are removed for biosynthesis. This is an archetypal anaplerotic ('topping up') reaction. Bacterial and fungal mutants lacking ICL are unable to grow on acetate as the sole carbon source [3,4].