低溫層積與吉貝素處理對臺灣青楓種子休眠解除之影響

Abstract

種子休眠在種子發芽時機的調控上扮演重要的角色，是植物適應環境的重要生理現象。槭樹屬植物是北半球重要的樹種，其種子普遍具有生理休眠的特性，因此國外學者針對多種槭樹屬植物種子休眠解除的方法，與解除過程中生理與生化變化進行詳盡的研究。然而，臺灣六種原生槭樹屬植物中，只有臺灣紅榨槭的種子休眠解除機制較有系統深入的研究。因此，本研究以廣泛分布於臺灣本島中低海拔的青楓種子為材料，探討低溫層積與外加吉貝素（GA）處理對種子休眠解除的效果，並利用化學定量分析與植物解剖技術研究休眠解除過程中種子內植物荷爾蒙與儲存物質的變化，同時也量測種子經GA處理發芽後在溫室內苗木的形質生長表現，以期進一步評估解除種子休眠在林產業育苗上的應用性。 研究結果顯示，具休眠性的青楓種子胚胎發育完整，果皮與種皮不影響水分的滲透，低溫層積處理12週可以有效提升種子的發芽率，並使種子提早發芽，顯示其休眠種類為生理休眠。種子對於外加的GA4處理較GA3敏感，但兩者皆只稍微提升種子的發芽率，但無法使種子發芽提早。低溫層積與外加GA處理皆可使種子內離層酸（ABA）的含量顯著下降；但低溫層積處理後，種子內GAs的總含量並無顯著提升；外加GA3或GA4處理後，種子內該GA的含量極高，然隨著培養過程逐漸減少，但其他GAs的含量則沒有顯著變化。青楓新鮮種子以液胞中的蛋白質與油粒體中的脂質為其主要的儲存物質；低溫層積處理過程中與外加GA處理後，子葉內之蛋白質與脂質在種子發芽前皆無顯著的減少，胞器亦無明顯變化，唯GA4處理之種子其子葉內脂質開始代謝的時間稍微提早，可能與GA4促進脂質酶的活化有關。種子經低溫層積處理發芽後苗木的生長狀況與存活率皆較GA處理之種子佳。 總結來說，低溫層積處理在青楓種子休眠解除與苗木生長上有較好的表現，應用性較高。在種子休眠與發芽調控中，對植物荷爾蒙ABA與GA的敏感性或生合成的能力比此兩者在種子內含量的變化來的重要。子葉內的儲存物質主要是提供發芽與其後的苗木生長所需，而在種子休眠解除過程中的變化不明顯。

Seed dormancy is important in regulating the timing of germination, and is a critical characteristic evolved for adapting to the environments. Acer species, which consist of important members in ecosystems of north hemisphere, commonly exhibit physiological dormancy. Therefore, the mechanism of seed dormancy of Acer receives considerable attention. However, among 6 native Acer species in Taiwan, only Acer morrisonense that grows at high elevation was studied systematically. Acer serrulatum is a famous ornamental tree distributed from low to medium elevations. This study aims to investigate the effects of cold stratification and exogenous gibberellin (GA) treatments on seed dormancy break of A. serrulatum. During dormancy break, biochemical analysis was applied to quantify the amounts of plant hormones in seeds, and plant anatomical techniques were used to observe the changes of storage substances. Seedling height and weight were also measured to evaluate the effects of seed pretreatments on seedling growth. Our results showed that the seeds of A. serrulatum have fully developed embryos, and the pericarps and the seed coats do not block the entrance of water, showing no evidence of morphological or physical dormancy. Cold stratification for 12 weeks effectively increased seed germination percentage and reduced germination time, indicating that the seed has physiological dormancy. Both GA3 and GA4 treatments slightly increased seed germination percentage but not germination speed. After cold stratification or GA treatment, the content of abscisic acid (ABA) in seeds reduced significantly. However, cold stratification did not elevate the content of GAs. GA3 or GA4 treatments only increased the GA content of the same type and then reduced subsequently during incubation. The main storage organelles, protein storage vacuole (PSV) and lipid body (LB), in the seeds of A. serrulatum were found. Before seed germination, amounts of the storage substances appeared unchanged, except the seeds treated with GA4, whose lipid content in cotyledon decreased slightly. It is possible that GA4 activates lipase which hydrolyzes lipid. The survival rate and growth performance of seedlings were better in seeds treated with cold stratification than those with GA3 and GA4. In summary, cold stratification is the better method in breaking A. serrulatum’s seed dormancy and their subsequence to increase seedling growth, and is therefore a proper procedure in nursery practices. Regarding the hormone regulation during dormancy-break, the sensitivity or metabolism capability of ABA and GA to seeds is more important than their content in seeds. Moreover, while the seed reserves remained stable during dormancy break, it might play an important role in early seedling growth.