Fat Mobilization in Seeds

Since fats are stored in oil bodies, it is reasonable to expect that the enzyme responsible for their degradation should be closely associated with these structures. During the first 11 days after imbibition a peanut cotyledon may decrease in dry weight from 345 mg to 143 mg, with a concomitant decrease in fat content of 55%. This represents hydrolysis of 9.4 pmoles of triglyceride per cotyledon per day. Even so, less than 1% of the total lipase activity of a peanut cotyledon has been found associated with the oil body and 99% is associated as an acid lipase (pH 4.6) with a particulate fraction [76]. This fraction has been claimed to be mitochondrial, but that is unlikely. The precise location of the acid lipase is still undetermined but it could be associated with the glyoxysomes. 

Lipases have been reported to be present in dry seeds of some species, e.g. Scots pine Firms sylvestris), Douglas fir Pseudotsuga menziesii), castor bean, but at a low level, or absent in others e.g. apple Pyrus mains). In most cases there appears to be a rise in lipase activity following imbibition, but whether this is due to de novo synthesis of the enzyme or activation of existing lipases has not been determined. A decline in lipase activity with declining triglyceride reserves has been widely reported. 

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