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Fine Structure of and Embryoid Development from Embryogenic Ovular Callus of 'Shamouti' Orange (Citrus sinensis Osb.)
Authors:BUTTON, J.   KOCHBA, J.   BORNMAN, C. H.
Abstract:A morphologically, anatomically and physiologically unique callushas been developed from unfertilized ovules of Shamouti orange.The callus, which is suspected to be of nueellar origin, isnot made up of the normal unorganized parenchymatous tissue,but solely of numerous proembryoids which vary between 0.1 and1.0 mm in diameter. Adventive embryogenesis in this tissue isautonomous and is in fact depressed by the inclusion of growthregulators in the medium, despite having been in culture formore than 2 years. Embryogenesis occurs in single cells on the periphery and withinexisting proembryoids. Cells destined to form new proembryoidsare surrounded by greatly thickened cell walls which lack plasmodesmata.Cell divisions occur within the thickened walls to give riseto globular proembryoids which are freed from encasing thickwalls as these degenerate. Proembryoids may enlarge into spherical pseudobulbils up to4 mm in diameter with an epidermal cell layer but no vascularization.Such structures rarely develop into plantlets but do form furtherproembryoids from surface cells. Alternatively, proembryoidsmay develop into heart-shaped, torpedo, and cotyledonary embryoids,and thence into plantlets with varying degrees of organ fasciation. Since plantlets are derived from single, usually surface cells,this system holds great promise for the production of solidgenetic mutants by irradiation.
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