Factors of germinability at low temperature in seeds of rat's tail radish (Raphanus sativus L.) introduced from northern Thailand

本文报道了一种名为Pakki-hood（Raphanus sativus L.）从泰国北方引进的品种在低温下具有发芽性。我们研究了几个因素，是在低温条件下种子发芽的主要障碍。在5℃下培养4d后，两个品种的种子穿透种皮的压力下降没有差异，这表明这一结果不能解释种子萌发对冷敏感性的差异。通过种皮的水分吸收不受温度的影响。在经历一个吸水滞后期后，20℃时种子含水量进一步增加。在5℃条件下，种子在6 d内不再吸水，而小白菜种子在4 d后吸水量略有增加，同时胚根伸长。全长cDNA包含一个1791 bp的开放阅读框，两侧是一个148 bp的3 '非翻译区和一个399 bp的5'非翻译区。在起始密码子上游177个核苷酸处发现一个推定的TATA盒。我们搜索了假定的顺式作用基序，发现四个MYB识别位点。RsNCED mRNA在萌发过程中不积累。发芽种子中的阿坝含量在Pakki-hood根伸长之前迅速下降，但在Shoguan中保持，这表明阿坝含量的维持与在低温下不能发芽有关。

One of rat's tail radishes, cv.Pakki-hood (Raphanus sativus L.) introduced from northern Thailand has germinability at low temperatures. We examined several factors that are the main barrier to germination of seeds under low temperature conditions. There was no difference in the decrease of pressure to penetrate seed coat of the both cultivars after 4 days incubation at 5℃, indicating that these finding cannot explain the difference in cold sensitivity in germination. Water uptake through the seed coat in was not affected by temperature. After a lag phase of water uptake, the water content of seeds showed a further increase at 20℃. At 5℃, no further water uptake took place in seeds of Shogoin within 6 days, while the uptake of water in the seed of Pakki-hood increased slightly after 4 days of imbibition, concurrent with radicle elongation.To identify the mechanisms involved in germination at low temperature in Pakki-hood, we cloned the gene for 9-cis-epoxycarotenoid dioxygenase (NCED). The full-length cDNA contains an open reading frame of 1791 bp, flanked by a 148-bp 3'-untranslated region and a 399-bp 5'-untranslated region. A putative TATA box was found 177 nucleotides upstream of the initiation codon. We searched for putative cis-acting motifs there and found four MYB-recognition sites. RsNCED mRNA was not accumulated during germination. The ABA content in germinating seeds decreased rapidly before elongation of roots of Pakki-hood, but it was maintained in Shogoin, suggesting that maintenance of ABA content is correlated with the inability to germinate at low temperatures.