蕹菜萌發期間澱粉及蛋白分解酶基因表現之組織特異性

Abstract

蕹菜萌發期間種子內的不同組織酶基因表現之差異，與生理機能之關聯性為本文之研究重點。萌發0.5天種子內的胚乳，可測到相當高的澱粉分解酶(α-amylase)活性及大量澱粉分解酶mRNA的堆積，但隨後都急迫下降。顯然這些酶分子及其mRNA，很可能是在種子成熟時期所轉錄、轉譯的。而萌發期間子葉及胚軸都測不到澱粉分解酶mRNA的存在，因此推論澱粉分解酶基因在此萌發期間，無論是胚乳、子葉或胚軸組織皆不表現。蛋白分解酶(proteinase) mRNA在胚乳及胚軸組織，也是隨著種子的萌發而急速下降、消失。唯有子葉組織的酶基因在萌發期間有所表現。 細胞分裂素(benzyladenine)和吉貝素(gibberellic acid)的處理，並不影響胚乳組織α-amylase 的活性。細胞分裂素則對子葉的蛋白分解酶活性有短暫性的促進效果，此促進作用似乎與子葉的生長發育有關。從南方轉潰分析結果顯示，α-amylase及蛋白分解酶基因在基因組中皆為單份( single copy)基因。

Differential expression ofα-amylase and proteinase genes in relation to the physiological function of different tissues in the seed of water spinach during germination were studied. High levels ofα-amylase activity and its mRNA were detected in the endosperm of 0.5 day germinating seeds, but both of them decreased rapidly during germination. This enzyme and its mRNA are most likely to have been produced during seed maturation. Unlike endosperm, α-amylase mRNA was not detectable in either cotyledon or embryo axis during seed germination. These results indicate that theα-amylase genes are repressed in all tissues of water spinach seed during the observed period of germination. Similarily, proteinase mRNAs in the tissues of endosperm and embryo axis also decrease rapidly during germination, although the proteinase gene expresses in the germinating cotyledon. The activities of α-amylase in endosperm and cotyledon were not affected by treatment of either benzyladenine or gibberellic acid. A temporary increase in proteinase activity was observed by treatment with benzyladenine in germinating cotyledon which might be concerned with the growth and development of the tissue. Southern blot analysis indicates that the genome may contain a single copy for both α-amylase and proteinase genes.