‘曼赛龙柚''种子不同发育期高温耐性研究

全球变暖导致极端高温频发,植物种子不可避免地置身于高温胁迫环境之中。为探究种子高温耐性的生理基础,该文以中间型种子‘曼赛龙柚''(Citrus maxima ‘Mansailong'')为实验材料,对不同发育阶段的种子进行高温处理,并同步检测各个发育时期种子的形态变化、可溶性蛋白和热稳定蛋白含量以及细胞超显微结构的变化。结果表明:(1)在花后23周到49周的整个发育过程中,种子含水量明显降低,鲜重显著增加,干重与鲜重的百分比也有明显的提高,这些指标均是在花后31周前后快速变化,到花后41周趋于稳定。(2)种子在花后29周获得完全的成苗能力和初步的高温耐性,此后高温耐性逐渐增加,并在花后37～49周之间快速提高。与种子高温耐性的变化相似,种子中可溶性蛋白和热稳定蛋白含量在花后23～49周均呈连续升高趋势,相关性分析表明在整个发育过程中这两者的积累与种子的高温耐性呈显著正相关。(3)超显微结构观察发现,随着种子的发育,线粒体逐渐减少,胚轴细胞体积逐渐变小,细胞中脂质体逐渐增多并且排列趋于规则,同时液泡由小变大且后期的液泡中充斥着黑色絮状物。综上所述,‘曼赛龙柚''种子在花后41周达到生理成熟,没有明显的成熟脱水过程; 其高温耐性是在发育过程中获得并逐渐提高,直到种子发育的后期; 种子中可溶性蛋白和热稳定蛋白含量的增加及细胞超显微结构的变化对种子高温耐性的发育具有重要贡献。

High-temperature tolerance of Citrus maxima ‘Mansailong'' seeds at different developmental stages

The seeds are invariably exposed to high-temperature conditions since global warming frequently causes abnormally high temperature. In order to investigate the physiological basis of high-temperature tolerance in seeds, we used intermediate Citrus maxima ‘Mansailong'' seeds as the research material, heated the seeds at different developmental stages, and simultaneously detected changes in seed morphology, contents of soluble protein and heat-stable protein, and cellular ultrastructure. The results were as follows:(1)The seed moisture content dramatically dropped between 23 and 49 weeks after flowering(WAF), whereas the percentage of DW/FW and fresh weight increased significantly. All of these indicators began to change quickly from 31 WAF and stabilized around 41 WAF.(2)At 29 WAF, the seeds acquired full seedling formation ability and a preliminary tolerance to high temperature; from there, the high-temperature tolerance gradually grew and improved quickly between 37 and 49 WAF. The improvement in high-temperature tolerance was accompanied by a steady increase in contents of soluble protein and heat-stable protein of seeds, from 23 to 49 WAF. The results of the correlation analysis showed a substantial positive correlation between the accumulation of heat-stable protein and soluble protein and the ability of seeds to tolerate high temperature.(3)Ultrastructural observation showed that the number of mitochondria progressively dropped as the seed developed, the volume of the embryonic axis cells gradually decreased, and the number of lipid bodies in the cells gradually rose and their arrangement became more and more regular. In addition, the vacuoles enlarge at the same time, and at a later stage, they were packed with black floccules. In conclusion, the C. maxima ‘Mansailong'' seeds reach physiological maturity at 41 WAF without any noticeable maturation drying; the ability to tolerate high temperature is acquired during seed development and is further enhanced until a later stage; changes in cellural ultrastructure and an increase in contents of soluble protein and heat-stable protein of seeds are essential in helping the seeds develop their high-temperature tolerance.