山櫻花和楊梅種子之休眠及解除機制

Mechanisms of dormancy and dormancy-break in seeds of Prunus campanulata (Rosaceae) and Myrica rubra (Myricaceae)

陳舜英(Shun-Ying Chen)

指導教授 ： 郭幸榮

共同指導教授 ： 簡慶德(Ching-Te Chien)

國立臺灣大學/生物資源暨農學院/森林環境暨資源學研究所/博士(2008年)

https://doi.org/10.6342/NTU.2008.01754

摘要

成熟的新鮮山櫻花種子具有休眠性，需要4-6星期暖溫和8星期低溫的組合層積處理以解除休眠，獲得最高的發芽率。然而，若將內果皮和種皮剝除，則不需要經過層積處理，就可以使種子發芽。新鮮種子利用激勃素GA3處理，僅對部分的種子有促進發芽的效果。但是，如果預先將內果皮去除 (種皮仍保留)，然後用GA3處理，可有效地促進發芽。每粒新鮮種子內在的離層酸ABA含量高低，依序為內果皮 ＞ 種皮 ＞ 胚，其中內果皮和種皮的ABA總含量大約是胚的6.2倍。不論是經過暖溫、低溫或暖低溫層積處理後的種子，其ABA含量均大幅減少，約為新鮮種子含量的1/6-1/12。經測定內在GA4含量發現，已解除休眠的種子胚中GA4含量較高，但仍在休眠中的種子含量則低。Fluridone是類胡蘿素 (carotenoid) 生合成的抑制劑，用Fluridone處理後可以有效解除山櫻花種子的休眠，使種子迅速發芽。Paclobutrazol是GA生合成的抑制劑，會完全抑制山櫻花種子的發芽，但若以Paclobutrazol加GA4處理，則可逆轉此抑制作用而恢復種子發芽 (但GA3則無此效果)。因此認為，山櫻花種子的休眠性主要來自外層的內果皮與種皮 (非胚本身的問題)，而休眠的解除需要內果皮與種皮中的ABA含量降低和胚中的GA4含量增加，以促進發芽。
成熟的新鮮楊梅種子具有休眠性，需要8星期暖溫和12星期低溫的組合層積處理促進發芽。外加GA3處理可以有效地解除種子的休眠。新鮮種子以5.2 mM GA3處理後，放在30/20℃溫度下發芽，20星期後的發芽率達70% 以上。將新鮮種子的內果皮和種皮剝除，可以有效促進種子發芽，且添加GA3可加速發芽。剝除內果皮 (種皮仍保留)，再用GA1或GA4處理的發芽效果比GA3處理更好。種子經5.2 mM GA3處理後3星期和5星期後，利用GC-MS-SIM定量其內果皮、種皮與胚等部位的內在GA1, GA3, GA4, GA7和GA20含量，結果顯示，種子以5.2 mM GA3處理後，內果皮和種皮中的GA１含量增加，且胚根已伸長的種子之內果皮和胚中的GA１也大量增加。因此推測，種子在發芽期間GA3會轉變成GA1，進而參與種子的發芽。經定量暖溫、低溫或暖低溫層積處理後的種子ABA含量，發現新鮮楊梅種子中的ABA含量以內果皮 >> 種皮 > 胚，且內果皮中的含量比種皮和胚加起來還高出132倍以上。種子不論經過暖溫、低溫或暖低溫層積，ABA含量皆降低，約為新鮮種子含量的1/9-1/14。此外，觀察暖溫、低溫或暖低溫層積處理後的種子胚部GAs含量發現，除了胚根已伸長的種子胚中的GA4含量增加外，其他各處理的GA1, GA3, GA7和GA20含量都很低。研究結果推論，楊梅種子的休眠解除，除了需要ABA含量的降低外，在種子發芽時更需要GA4和/或GA1參與。另外，楊梅種子能乾燥儲藏在 -20℃長達42個月，活力仍維持與原來一樣，應屬於乾儲型種子。
山櫻花和楊梅種子的休眠性質均屬於生理休眠，種子的休眠解除和發芽皆需要伴隨著種皮和內果皮的內在荷爾蒙ABA含量的降低和胚內GA4含量的增加。

關鍵字

山櫻花 ； 楊梅 ； 種子休眠與發芽 ； 離層酸 ； 激勃素 ； 巴克素 ； 氟啶酮 ； 種子層積處理

並列摘要

Intact seeds (seed + endocarp) from freshly harvested fruits of Prunus campanulata were dormant and required 4-6 weeks of warm followed by 8 weeks of cold stratification for maximum germination percentage. Removing both endocarp and seed coat, however, promoted germination in a high percentage of non-stratified seeds. Treatment of intact, non-stratified seeds with gibberellic acid (GA3) was only partially effective in breaking dormancy. However, GA3 promoted germination of non-stratified seeds in which the endocarp (but not the seed coat) had been removed. The order of abscisic acid (ABA) concentration in fresh seeds was endocarp > seed coat > embryo, and its concentration in endocarp plus seed coat was about 6.2-fold higher than that in the embryo. Total ABA contents of seeds subjected to warm and/or cold moist stratification were reduced 6- to 12-fold. A higher concentration of GA4 was detected in embryos of non-dormant than in those of dormant seeds. Fluridone, a carotenoid biosynthesis inhibitor, was efficient in breaking dormancy of Prunus seeds. Paclobutrazol, a GA biosynthesis inhibitor, completely inhibited seed germination, and the inhibitory effect could be partially reversed by GA4, but not by GA3. Thus, dormancy in P. campanulata seeds is imposed by the covering layers. Dormancy break is accompanied by a decrease in ABA content of the covering layers and germination by an increase of embryonic GA4 content.
Intact seeds (with hard endocarp) from freshly harvested fruits of Myrica rubra were dormant and required 8 weeks of warm stratification followed by 12 weeks of cold stratification for germination. Exogenous application of gibberellic acid (GA3) to intact fresh seeds also was effective in breaking dormancy. Thus, germination increased to >70% for seeds treated with 5.2 mM GA3 and incubated at 30/20oC for 20 weeks. Removing endocarp and endocarp plus seed coat of fresh seed promoted germination, and addition of GA3 to the embryo accelerated germination. GA1 and GA4 were more effective than GA3 in promoting germination of endocarp-removed seeds. Endogenous levels of GA1, GA3, GA4, GA7 and GA20 were quantified by GC-MS-SIM in endocarp, seed coat and embryo of fresh seeds treated with 5.2 mM GA3. GA3 level decreased in endocarp during incubation, whereas GA1 level increased in endocarp and seed coat. Further, a high level of GA1 was detected in endocarp and embryo of radicle emerged seeds. We speculate that GA3 was converted to GA1 during incubation and thus that GA1 is involved in seed germination. Levels of endogenous abscisic acid (ABA) were measured in fresh and in warm and/or cold stratified seeds. The order of ABA level in fresh seeds was endocarp >> seed coat > embryo, and its level in endocarp was about 132-fold higher than that in the seed coat and embryo. Total ABA content of seeds subjected to warm and/or cold stratification was about 8.7- to 14.0-fold lower than that of fresh seeds. Low levels of endogenous GA1, GA3, GA7 and GA20 but elevated levels of GA4 were found in embryo of warm and/or cold stratified seeds. These observations, coupled with the fact that GA stimulated germination of dormant Myrica seeds, provide evidence that endogenous ABA decreased dormancy break and that endogenous gibberellins, especially GA4 and/or GA1 are involved in germination. Seeds that were dried to 8.6% of moisture content could be survived at -20℃ for 42 months without loss of germinability. Thus, seeds of M. rubra exhibited orthodox storage behavior.
Seeds of P. campanulata and M. rubra are classified as physiological dormancy. Dormancy break and germination of both seeds are accompanied by a decrease of ABA content in endocarp and seed coat, and by an increase of GA4 content in embryo.

並列關鍵字

Prunus campanulata ； Myrica rubra ； seed dormancy and germination ； abscisic acid ； gibberellins ； Fluridone ； Paclobutrazol ； seed stratification

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