甜瓜品種間同功異構酶變異性之研究 Ⅰ.四個甜瓜品種（PMR西施，黃金，新玉）間 peroxidase 及 shikimate dehydrogenase 變異性及其在 F1 純度鑑定之利用

Abstract

本試驗用洋香瓜系統PMR 和西施及東方甜瓜系統黃金香瓜和新玉等四種之自交系及其雜交後代，以電泳方法調查種子及幼苗子葉所含同功異構酶之變異性。在調查的十種酵素中，只有peroxidase（PRX）及shikimate dehydrogenase（SkDH）具有多型性。PMR屬於PRX-2B2B，而西施、黃金香瓜和新玉則屬於PRX-2A2A；PMR 和西施具有SkDH-SS型，而黃金香瓜和新玉則為SkDH-FF型。由PMR × 新玉的F2後裔分析SkDH之分離比，可以推斷此酵素為由一個基因座的兩個對偶基因（Skdh-F及Skdh-S）所控制，各表現出單一條帶，PRX-2亦由一個基因座的兩個對偶基因所控制，但各表現出三個條帶，其F1為混合型，具有四個條帶。兩系統間的F1可以用此兩種酵素的同功異構酶來鑑定其純度，但系統內品種間則酵素無差異，無法測定比較其純度。 Four melon Inbred lines, belonging to var, reticulatus and maukwa and their progenies were used for studying isozyme variation in either seeds or young cotyledons. Among ten enzymes investigated, two were found to be polymorphic. They are peroxidase (PRX) and shikimate dehydrogenase (SkDH). For PRX, variety PMR has the phenotype of 2B2B, while Hsi-Shih, Hwang-Jin, and Shin-Yuh belong to 2A2A type. For SkDH, varieties PMR and Hsi-Shih have the phenotype of SS, while Hwang-Jin and Shin-Yuh belong to FF type. Samples from selfing progeny of a PMR × Shin-Yuh cross were analysed for segregation in SkDH locus. The result showed that it was controlled by a single locus of two alleles, each encoded a single band of different mobility. Similarly, PRX-2 may also found to be controlled by a single locus of two alleles, each expressed different three-banded pattern. The two genes were named as Skdh and Prx-2, respectively. Hybrid between genotype Prx-2A2A and 2B2B revealed four banded patterns, which indicated the codominance nature of the enzymes. Seed purity in hybrid could be monitored between two parents having different isozyme patterns.