Germination of Alfalfa ( Medicago sativa L.) Seeds and Desiccated Somatic Embryos : I. Mobilization of Storage Reserves

Abstract

Desiccated somatic embryos lack the vigor that is accociated with seeds, and this reduces the feasibility of using artificial seeds as a means of plant propagation. Although desiccated somatic embryos of alfalfa (Medicago sativa L.) are characterized by faster imbibition than in seeds, radicle and shoot emergence are slower. To determine the physiological basis for this low vigor, the utilization of storage proteins and carbohydrates was compared between alfalfa somatic embryos and seeds during the first days after imbibition. Mature somatic embryos contained comparable quantities of storage proteins and carbohydrates to seeds, and these reserves were rapidly and extensively degraded within a few days of imbibition. Therefore, low vigor does not appear to be a consequence of inadequate or unavailable storage reserves. However, the hydrolysis products of the storage reserves, especially the free amino acids asparagine and glutamine, were lower in the seedlings from somatic embryos than seeds. Therefore, although the storage reserves in the dry somatic embryos were quantitatively similar to seeds and although they were rapidly hydrolysed after imbibition, the relatively low quantity of amino acids and sugars available for biosynthetic activity in these seedlings may limit their vigor.