超干处理对几种芸苔属植物种子生理生化和细胞超微结构的效应

Physiological, Biochemical and Ultrastructural Studies on Ultradried Seeds of Some Brassica Species

几种芸苔属植物种子经过超干处理后,发芽力和活力不受影响,耐藏性大为提高。超干及老化后种子的脱氢酶、超氧物歧化酶、过氧化物酶、过氧化氢酶等酶系统保持完好;丙二醛和挥发性醛类物质等劣变产物相应减少;电导率测定表明,细胞膜系统的完整性良好;透射电镜(TEM)和扫描电镜(SEM)观察表明,细胞超微结构及功能保持完好。不同干燥方法和不同干燥剂的系列实验证实,生石灰的脱水效果并不亚于冰冻真空干燥法,且经济实用。

The seed moisture content (MC) of B. pekinensis, B. campestris and B. oleracca var. capilata were decreased from 6.1%～8.6% to 1%～2% by different ultradrying methods. Ultradrying treatment did not induce any significant changes in seed germination percentage and vigor index. After accelerated aging, the germination percentage and vigor index of ultradried seeds (UD)were higher than control. This indicated that the storability of UD was significantly improved (Table 1, 2, 4). As compared with different ultradrying methods, the effect of direct desiccating by lime at room temperature was as good as freeze-drying. Thus, it could be used instead of vacuum freeze-drying (Table 3,4; Fig. 1). When seeds were soaked without any treatment the conductivity of UD of B. campestris was higher than control due to the imbibition injury. When the seeds were soaked after PEG treatment, the conductivity of UD of B. campestris was lower than Control. This revealed the integrity of the membrane system in UD. The imbibition injury could be caused by rapid water uptake. But this could be avoided by PEG treatment (Fig. 2). After accelerated aging, the conductivity of control was higher than UD (Fig. 3). It has been shown that the function of membrane system in UD could be maintained more perfectly than control during storage. The higher activity of DHase of aged UD indicated a higher vigor level than aged control seeds. The higher activities of SOD, peroxidase and catalase indicated that UD had a higher self-defence ability against the attack of free radicals than control (Fig. 4). This is in accord with the fact that the content of MDA and volatile aldehydes of aged UD were lower than aged control seeds, indicating a lower deterioration in UD seeds during storage. SEM observation indicated that the cells in the UD seeds were morphologically intact and not broken by a sharp decrease in water content (Plate Ⅰ. 1,2). Nor did the rapid increasing of MC under high water potential during rehydration cause any damage to the cells (Plate Ⅰ. 3,4). TEM observation indicated that the ultrastructure of radicle tip cells was perfect after ultradrying. Mitochondria, plastid and endoplasmic reticulum were all normally developed. Plasmodesmata were observed in some cells. Obviously, the cells were in vigorous status (Plate Ⅰ. 5,6,7). After accelerated aging, the ultrastructure of UD radicle tip cells changed little (Plate Ⅰ. 8—10), but aging damage was very obvious in control. Mitochondrial cristae disappeared, and their double membranes became indistinct. The endoplasmic reticulum were swollen and became discontinuous. Nuclear membrane was disintegrated. Plastid was disappeared after disintegrated. Plasmodesmata also disappeared. Overall, the cells were greatly deteriorated (Plate Ⅱ. 11, 12, 13). Based on the results mentioned above, it was concluded that ultradrying did not influence seed vigor in some Brassica species, and greatly improved their storability. Some mechanisms of seed ultradrying storage were discussed.