Postgerminative growth and lipid catabolism in oilseeds lacking the glyoxylate cycle

The glyoxylate cycle is regarded as essential for postgerminative growth an d seedling establishment in oilseed plants. We have identified two allelic Arabidopsis mutants, icl-1 and icl-2 which lack the glyoxylate cycle becaus e of the absence of the key enzyme isocitrate lyase. These mutants demonstr ate that the glyoxylate cycle is not essential for germination. Furthermore , photosynthesis can compensate for the absence of the glyoxylate cycle dur ing postgerminative growth, and only when light intensity or day length is decreased does seedling establishment become compromised. The provision of exogenous sugars can overcome this growth deficiency. The icl mutants also demonstrate that the glyoxylate cycle is important for seedling survival an d recovery after prolonged dark conditions that approximate growth in natur e. Surprisingly, despite their inability to catalyze the net conversion of acetate to carbohydrate, mutant seedlings are able to break down storage li pids. Results suggest that lipids can be used as a source of carbon for res piration in germinating oilseeds and that products of fatty acid catabolism can pass from the peroxisome to the mitochondrion independently of the gly oxylate cycle. However, an additional anaplerotic source of carbon is requi red for lipid breakdown and seedling establishment. This source can be prov ided by the glyoxylate cycle or, in its absence, by exogenous sucrose or ph otosynthesis.