Spatial and Temporal Changes in Endogenous Polyamine Levels Associated with Somatic Embryogenesis from Different Hypocotyl Segments of Eggplant ( Solanum melongena L.)

Abstract

Summary In Solanum Melongena L. Cv. Pusa Purple Long, Significant Differences Were Observed For Embryogenic Potential Within A Single Explant (Hypocotyl System). Terminal Hypocotyl Segments (Apical and Basal) Yielded A Higher Number Of Somatic Embryos Than The Medial (Sub-Apical and Sub-Basal) Segments. High Levels Of Conjugated Spermidine Along With High Levels Of Total Polyamines (Primarily Free Fraction) Could Be Correlated With The Formation Of Somatic Embryos In Terminal Segments. Temporal Changes In Endogenous Levels Of Free, Conjugated and Bound Putrescine, Spermidine and Spermine Were Analyzed At Critical Stages Of Somatic Embryogenesis From Four Different Hypocotyl Segments. Within 3 Days Of Culture, There Was A Sharp Decline In Free (and Total) Putrescine and An Increase In Conjugated Spermidine Levels. All Hypocotyl Segments Attained Similar Levels Of Free Spermidine, Irrespective Of Their Subsequent Embryogenic Response. As The Tissues Become Committed For Embryogenesis, Free, Conjugated and Total Putrescine and Spermidine Reach Uniformly Minimal Levels For All Segments. Just Before The Onset Of Embryogenesis, There Was A Dramatic Increase In All Fractions Of Putrescine, and In Free and Conjugated (Along With Total) Spermidine Levels. Intermediate Levels Of Conjugated and Total Putrescine and Spermidine Were Reached In Tissues With Good Embryogenic Potential: tissues with poor embryogenic potential attained lower or higher levels. After the embryos were formed, their levels fell sharply, and continued to decline. Free putrescine, however, reached another peak when embryos had fully matured. The changes in bound putrescine and spermidine, and in spermine (all forms) could not be correlated with somatic embryogenesis.