栽培種大豆台南三號與爪哇大豆早期胚乳與胚胎發育之比較解剖研究

Abstract

栽培種大豆種子因具高經濟價值，其種子發育包含雌配子體、胚胎與胚乳發育之研究，相當豐富；然而對其親緣較近的其他屬植物之種子發育，我們所知甚少。爪哇大豆過去被歸類於大豆屬，於1977年由Lackey重新命名並建立爪哇大豆屬予以歸置，爪哇大豆屬內僅兩個物種，均為多年生。相較於栽培種大豆，爪哇大豆的種粒較小。 大豆為無胚乳種子 (Ex-albuminous seed)，其早期種子發育過程中，胚乳是一個暫時性儲存養分的結構。近年同為無胚乳種子的阿拉伯芥，其研究結果顯示，早期胚乳發育的結果將影響成熟種子的大小，然而胚乳發育對其他雙子葉植物種子大小的影響，卻鮮為人知。在本研究中，我們選用種子大小差距甚大的三種豆科植物，栽培種大豆台南3號（中種粒種子）及台南5號（大種粒種子） (Glycine max (L.) Merr. cv Tainan No. 3 & Tainan No. 5) 及其異源種爪哇大豆（小種粒種子） (Neonotonia wightii (Arn.) Lackey)，探討胚乳由游離核時期進入胚乳細胞化時期之發育過程對於成熟種子大小的影響。 結果顯示，爪哇大豆與栽培種大豆台南三號在早期胚乳與胚胎的發育過程皆相似，然而栽培種大豆早期發育各階段皆早於爪哇大豆。另比較不同種粒大小之豆科種子的早期胚乳發育，發現大種粒種子（台南五號）的游離核胚乳時期雖較短，但胚乳游離核數量較多，且胚乳體積較大，因此我們推測大種粒種子因為胚乳游離核快速分裂與胚乳體積快速增加，使胚乳得以在短時間內大量累積養分供給後續胚胎之發育，應是大種子之成因。

The development of the seed, especially in the female gametophyte, embryo and endosperm has been studied for cultivated soybean; however, little was known about these components of sexual reproduction in the sister genus of Glycine, such as Neonotonia. The genus Neonotonia was early grouped with the genus Glycine and has been established by Lackey in 1977. Neonotonia consists of only two species that are perennial and have smaller seeds compared to those of G. max. Seed of soybean is exalbuminous. In an exalbuminous seed, the endosperm is an ephemeral structure for nutrient storage during early seed development. Recently, the results of interploidy crosses and mutations of Arabidopsis thaliana suggested that the early endosperm development affected the mature seed size. However, little was known about whether the endosperm development also affected the seed size in other dicot plants. In this study, we chose three legumes (cultivated soybean Glycine max (L.) Merr. cv Tainan No. 3, Tainan No. 5 and Neonotonia wightii) those dramatically differ in mature seed size, and examined which cellular developmental processes resulted in the differences in seed size. The results show that the patterns of early embryogenesis and endosperm development are similar in Tainan No. 3 and N. wightii. Reproductive events, however, occur earlier in Tainan No. 3. Additionally, the duration of early reproductive events in cultivated soybeans (Tainan No. 3 & Tainan No. 5) is relatively shorter than N. wightii. The amount of nuclei in the cellularized endosperm of cultivated soybean is greater than N. wightii, and the area of endosperm of Tainan No. 5 is larger than those of Tainan No. 3 and N. wightii. We suggest that the rapid mitosis in an endosperm results in greater amount of nutrient accumulation for embryo development, and subsequently, big seeds.