Abstract:

【Objective】The study explored the changes of water content, storage substance content, and enzyme activity during the germination process of Pinus bungeana seeds, in order to reveal the physiological mechanism of temperature that affects the seed germination. 【Method】Seed germination was performed at various temperatures to study the effects of temperature on the extent of germination. Physiological indicators, such as the content of water, soluble sugar, starch, soluble protein, crude fat and the activities of amylase, protease and acid phosphatase were measured during the germination process. 【Result】A high germination percentage (approximately 90%) was obtained when the seeds were cultured at 15 and 20 ℃. As the culture temperature continued to rise to 25 and 30 ℃, the radicle protrusion and seed germination were seriously hindered, resulting in a sharp drop in germination percentage to <10%. At 20 ℃, the change of water content during germination could be characterized into three stages: rapid increase, period of retardation, and another rapid increase. During germination, the catabolism and anabolism of substances occurred vigorously in the seeds. The soluble sugar content initially decreased and then gradually increased. As starch began to hydrolyze with a decreased content after six days of cultivation, the crude fat and soluble protein were degraded into small molecules as catalyzed by the corresponding enzymes for embryo utilization after 10 days of cultivation. At 25 ℃, the water absorption process of seeds stayed in the retardation period throughout. At this incubation temperature, the activities of acid phosphatase, amylase, and protease in seeds was inhibited due to the excessive temperature, thus affecting the degradation of crude fat, soluble protein and soluble starch. In addition, the soluble sugar content was slightly decreased to keep the ‘still’ state of the seeds with low consumption. 【Conclusion】The suitable temperature range for seed germination of P. bungeana was 15-20 ℃. However, if the temperature continued to rise, seed germination was hindered and thermal inhibition occurred. At the favorable temperature of 20 ℃, seeds would preferentially use the nutrients stored in the embryo when germination occurred. Carbohydrates are first decomposed and utilized, followed by the mobilization of proteins and lipids. Degradation of a large amount of fat began after the radicle broke through the seed coat. At a high temperature of 25 ℃, the activity of enzymes in the seeds was inhibited, resulting in the catabolism of macromolecular substances was hindered. Ultimately, the embryo could not absorb and utilize enough nutrients to complete the germination process.

Key words: Pinus bungeana, seed germination, temperature, substance metabolism, enzyme activity