3.4. Effect of pre-treatments on germination
Seeds soaked in water at room temperature were permeable to water. This indicated that the cause of dormancy of this plant might not be attributed to the seed coat as a physical barrier to water absorption. The dormancy was broken after a 12-h soaking (Table 1). It seems that the soaking treatment may have promoted the leaching of germination inhibitors on the seed coat (Xia and Kermode, 2002). It was noticed that longer soaking tended to slightly decrease germination. It may be due to water trapped in tissue between the embryo and seed coat creating an oxygen barrier as in the case of Datura ferox and D. stramonium seeds (Reisman-Berman et al., 1989). Norton (1986) concluded that
anoxia caused by prolonged soaking of seeds may result in irreversible injury due to accumulation of toxic metabolites. Pre-washing in running water for 60 min was able to increase germination to 72.5% (Table 1). Pre-washing treatment was able to overcome the seed dormancy in this plant, which may be due to the presence of inhibitors on the seed coat. Pre-heating at 40 ℃ for only 1 day was able to break dormancy of these seeds (Table 1). Bewley and Black (1982) noted that high temperature frequently enhanced the degradation of the seed tissues. As a result, the energy supply to embryonic axis may increase and diffusion in and out of the seeds by such substances as water, oxygen, inhibitors and carbon dioxide, may be easier, and hence, it promotes germination. The effects of pre-chilling varied with time of pre-chilling. Prechilling for 1 day was able to break dormancy and increased germination to 65.8% (Table 1). Duration of moist chilling to release embryo dormancy is influenced by factors such as covering structures and inhibitors (Khan, 1997). The ability of pre-chilling to release dormancy was probably due to various metabolisms that occur during these treatments, such as increasing the level and responsiveness of endogenous gibberellins (Hilhorst and Karssen, 1992), but substantial decreasing in ABA level (Bewley and Black, 1982). When seeds were germinated with GA3 and KNO3 at various concentrations, it was found that the germination percentages
were significantly higher when compared to control (Table 1). The highest germination percentage was obtained in the concentrations 0.02–0.03 and 0.1–0.2% for GA3 (30–34%) and KNO3 (16–20%). At higher concentration, seed germination seems to be decreased slightly. However, the germination found in this study was lower than that reported by Ochuodho et al. (2004). This may be related to the fact that the present seed lots had not been in storage before being subjected to the treatments, compared to the seeds used by Ochuodho et al. (2004) which were 1–2 years old. A longer period of storage has positively affected the dormancy condition of cleome seed lot and thus improved its germination (Chweya and Mnzava, 1997).
In conclusion, cleome seeds exhibit seed dormancy, which could be overcome within 3 months under room temperature storage. Of all the dormancy breaking methods tested, it is suggested that pre-heating at 40 ℃ for 1–5 days is more effective and efficient to break dormancy of cleome seed than the other
treatments. However, as seed companies usually keep large stock of seeds, further studies on storability of pre-heated seeds are necessary, especially for commercial varieties (Boonsong Ekpong, 2009).
3.4. 前處理對發芽的影響
在室溫下水可以滲透到浸潤在水中的種子內。這顯示植物休眠的原因可能是種皮阻礙了吸水。浸泡12小時之後打破休眠（見表 1）。看來浸泡處理可能促進種皮將抑制發芽的物質過濾掉(Xia and Kermode, 2002)。再浸泡發現發芽率略有下降。這可能是由於水被限制在胚和種皮組織之間而導致Datura ferox和曼陀羅的種子不透氧(Reisman-Berman et al., 1989)。Norton (1986)認為長時間浸泡造成種子缺氧，有毒代謝物的累積可能會導致不可逆的損害。淋洗60分鐘萌芽率才得以增加到72.5%（見表 1）。預措處理能克服植物種子休眠的問題，這可能是種皮內的抑制物質。只需要40℃預熱一天就能打破種子休眠（見表 1）。Bewley 和 Black (1982) 指出不斷的高溫易使種子組織退化。供應能量胚軸可能會增長和擴散，使水、氧氣、抑制劑、和二氧化碳這些物質更容易進出種子，因此可以促進發芽。預冷的影響隨著預冷的時間而不相同。預冷一天能打破休眠和提高發芽率達65.8％（見表 1）。持續的潮濕低溫對解除胚休眠的影響因素，包括結構和抑制物質(Khan, 1997)。預冷能夠解除休眠的原因，可能是由於處理期間各種代謝的發生，例如像是內源性激勃素含量的增加和反應(Hilhorst 和 Karssen, 1992)，但是ABA的含量大幅下降(Bewley 和 Black, 1982)。種子使用不同的濃度的激勃素和硝酸鉀處理後發芽，結果發現，發芽率均明顯的高於對照組（見表 1）。處理濃度0.02-0.03和0.1-0.2％激勃素（30-34％）和硝酸鉀（16-20％）的發芽率最高。高濃度處理組的發芽率以乎略有下降。然而，這次的發芽率比Ochuodho等人在 2004年的研究報告結果低。原因可能是因為這次實驗處理的種子是未經貯藏的，而Ochuodho等人在2004年所使用的是貯藏1-2年的種子。長期貯藏顯然對白花菜種子的休眠狀態有影響，因此提高了它的發芽率 (Chweya 和 Mnzava, 1997)。
我們的結論是，在室溫貯存3個月即可解除白花菜種子的休眠。所有打破白花菜休眠的方法，以40℃預熱1-5天比其他的處理方式更有效。然而，由於種子公司經常貯存大量種子，進一步研究預熱種子的耐貯性是必要的，尤其是商業品種(Boonsong Ekpong, 2009)。
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