种衣剂对低温处理下棉花胚根及幼苗外部形态和超微结构的影响

以棉种‘新陆中54号’为材料,用3种种衣剂(棉1、棉2、棉3)包衣棉种后播种于塑料营养盒内,25℃恒温培养,分别在第4天(棉种长出胚根)和第7天(棉株幼苗)均进行5、10、15、20℃共4个低温处理,与各低温下未包衣种子(对照,CK)进行比较,低温处理24h后,观察各处理棉花胚根、幼苗外部形态和超微结构的变化,以期通过模拟新疆早春"倒春寒"发生特点,考察种衣剂对提高棉花耐寒性的功效。结果表明:20℃下种衣剂处理与CK无差异,种子萌发正常,发芽率在92.24%~95.51%,3种种衣剂包衣处理胚根生长量为3.66~3.81cm,幼苗叶色浓绿,茎杆直立,胚根细胞中线粒体结构完整,叶肉细胞中线粒体、叶绿体结构规则;15℃低温下种衣剂处理棉种发芽率较CK提高4.45~6.98个百分点,胚根生长速度下降,但包衣处理生长量较CK提高25.27%~36.05%,幼苗叶色浓绿,棉苗直立,胚根细胞中线粒体内脊清晰,叶肉细胞中叶绿体、线粒体结构清晰,细胞器结构和数量明显优于CK;10℃低温下棉种发芽受到抑制,但包衣处理较CK发芽率提高0.73~4.25个百分点,19.15%~42.55%的幼苗叶片下垂萎蔫,保持正常温度后种衣剂处理棉苗很快恢复到正常形态,胚根细胞中线粒体、内质网数目多于CK,叶肉细胞中叶绿体轮廓清晰,内含物较少;5℃低温下各处理棉种发芽率均低于50.00%,CK幼苗叶色脱水失绿,萎蔫下垂,萎蔫率达74.47%,叶绿体膨胀成圆球形、轮廓模糊,包衣处理幼苗萎蔫率在60.42%~67.45%,叶肉细胞中叶绿体结构完整,呈椭球型,线粒体结构较规则、内含物浑浊。研究表明种衣剂能促进低温处理下种子萌发、提高发芽率和胚根生长速度、保护棉苗外部形态和细胞超微结构稳定,维持正常生长,增强幼苗抵御低温的危害能力。

Effect of Seed Coating Agents on External Morphology and Ultrastructure of Cotton Radicles and Seedlings under Low Temperature Treatments

In this study, 'Xinluzhong 54' cotton seeds coated with three different homemade seed coating agents (Mian 1, Mian 2 and Mian 3) were sown in plastic nutrition boxes and cultured at 25℃. On the 4th and 7th days when cotton seed radicles had grown into cotton seedlings, the coated cotton seeds were exposed to four low-temperature treatments at 5℃, 10℃, 15℃ and 20℃. The uncoated cotton seeds exposed to the same low-temperature treatments served as the control group (CK). The external morphologies and ultrastructures of the cotton radicles and seedlings were observed at 24 hours after low-temperature exposure to explore the effects of seed coating agents on improving the cold resistance of cotton by simulating the late spring cold climate in Xinjiang Province. The results showed that there was no significant difference between the coated and uncoated treatments at 20℃. Cotton seeds germinated normally at the germination rate of 92.24%-95.51%. The radicle growth lengths of the three different seed coating agents were 3.66-3.81cm, and the cotton seedlings grew well with dark green leaves and erect stems. The mitochondrial structure of radicle cells was complete, and the structures of mitochondria and chloroplasts in mesophyll cells were normal. Compared with the control, the seed germination rate of the coated seeds increased by 4.45-6.98 percentage points at 15℃. The radicle growth speed declined, but the growth amount increased by 25.27%-36.05%. The cotton seedlings grew well with dark green leaves and erect stems. Mitochondria cristae in radicle cells were clear. In addition, the structures of chloroplasts and mitochondria in mesophyll cells were clear, which were significantly better than after CK treatment. Cotton seed germination was inhibited at 10℃, but the germination rate of the coated seeds increased by 0.73-4.25 percentage points compared with that of the uncoated seeds. Radicle growth was limited, and the leaves were dark green. Approximately 19.15%-42.55% of the seedling leaves drooped and wilted. There were more mitochondria and endoplasmic reticula in the radicle cells of seedlings compared with that in seedlings from uncoated seeds. The outline of the chloroplast in mesophyll cells was clear with few inclusions. The Main 1 treatment was better than the other treatments. The cotton germination rate after different treatments was lower than 50.00% at 5℃. The seedling leaves in the uncoated group lost color and wilted with a wilting rate of 74.47%, whereas that of the coated treatment group was 60.42%-67.45%. The mitochondrial structure in the radicle cells was clear, and the mitochondrial structure in mesophyll cells was normal, while chloroplasts expanded into a spherical shape. The grana lamellar structure disintegrated, inclusions were turbid, and no significant difference was observed between coated and uncoated treatment groups. Our results show that seed coating agents can stimulate cotton seed germination, increase the seed germination rate and radicle growth speed under low-temperature treatments, protect the external morphology and cell ultrastructure stability of cotton radicles and seedlings, maintain normal growth, and enhance the ability of seedlings to resist damage from the low-temperature climate.