Ultrastructural and Biochemical Changes in Cotyledon Reserve Tissues3

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Abstract
Changes in major protein, lipid and carbohydrate reserves during the germination of Citrus limon (L.) Burm. f. seeds have been studied. The rate of release of amino acids and soluble sugars has been evaluated. Mobilization of protein reserves began 4 d after the onset of imbibition. The main period of hydrolysis occurred between 8 d and 24 d after the start of germination. Ultrastructural studies showed the presence of protein bodies in quiescent cotyledon cells. These bodies virtually disappeared 14 d after the start of germination. The nitrogenous compounds that were liberated and subsequently translocated were predominantly in the form of asparagine, arginine, and proline. The cotyledons had a lipid content representing 51.7% of their dry weight. Lipid reserves in quiescent cotyledons were laid down in the form of oil-bodies. These organelles rapidly disappeared as germination progressed, and were replaced by vacuoles. The starch content of quiescent cotyledons is very low, but it increased considerably up to 20 d after germination started.