Purpose: To evaluate the effects of polyethylene glycol (PEG) 6000 pretreatment on growth and physiological responses of eukaryotic microalga Chlorella vulgaris exposed to ionizing irradiation.

Materials and methods: The microalgal cells pretreated with different PEG concentrations (0, 5, 10 and 20%) and then exposed to 300 Gray gamma irradiation at a dose rate of 0.5 Gy s⁻¹. The various growth and physiological parameters including algal growth, cell size, the degree of electrolyte leakage (EL) and lipid peroxidation, the content of pigments and proline and the activity of antioxidant enzymes under gamma-free or 300 Gray gamma irradiation conditions were examined.

Results: The results showed that PEG stimulated a higher growth and cell size under both stress-free and gamma-stress conditions. The maximum growth and cell size was reported when the algae was pretreated with 10% PEG. A relative increase of catalase activity was observed in all samples after exposing to gamma irradiation. However, the highest value was recorded for the gamma-radiated algae pretreated with 10% PEG. In the absence of PEG, gamma irradiation induced a significant reduction in ascorbate peroxidase activity, but with PEG pretreatment, the enzyme activity remained constant or even increased after gamma irradiation. On the other hand, although gamma irradiation stress generally suppressed the activity of superoxide dismutase in all cells, pretreating the algae with PEG could diminish this suppressing effect at all applied concentrations. Compared to the PEG-free controls, a lower rate of chlorophylls and membrane integrity loss was shown in the PEG-treated algae when exposed to gamma stress. Total carotenoid content in PEG-treated algae was also similar under both gamma-free and gamma-radiated conditions. A PEG-independent increase in proline accumulation was reported under gamma-irradiation treatment.

Conclusions: Overall, the results suggested that PEG pretreatment could improve gamma-irradiation tolerance in C. vulgaris probably by stimulating a range of enzymatic and non-enzymatic reactive oxygen species scavenging systems. The microalgae may also consume PEG to break down and use it as an alternative source of carbon during stress which should be further studied in detail.

目的：评价聚乙二醇（PEG）6000预处理对暴露于电离辐射下的真核微藻小球藻的生长和生理响应的影响。

材料和方法：用不同的PEG浓度（0％，5％，10％和20％）预处理的微藻细胞，然后以0.5 Gy s ^-1的剂量率暴露于300 Grayγ辐射。在无γ或300 Grayγ辐射条件下，检查了藻类生长，细胞大小，电解质渗漏程度（EL）和脂质过氧化作用，色素和脯氨酸的含量以及抗氧化酶的活性等各种生长和生理参数。

结果：结果表明，在无压力和伽玛压力条件下，PEG都能刺激更高的生长和细胞大小。当用10％PEG预处理藻类时，报告了最大的生长和细胞大小。暴露于伽马射线照射后，所有样品中均观察到过氧化氢酶活性的相对增加。但是，记录了用10％PEG预处理的γ辐射藻类的最高值。在没有PEG的情况下，γ射线照射会导致抗坏血酸过氧化物酶活性显着降低，但是使用PEG预处理，在γ射线照射后，酶活性保持恒定甚至升高。另一方面，尽管γ射线照射应力通常会抑制所有细胞中超氧化物歧化酶的活性，但在所有应用浓度下，用PEG预处理藻类都可能减弱这种抑制作用。与不含PEG的对照相比，当暴露于γ胁迫时，在PEG处理的藻类中显示出较低的叶绿素比率和膜完整性损失。在无γ和γ辐射条件下，PEG处理的藻类中总类胡萝卜素含量也相似。据报道在γ射线照射下脯氨酸积累的PEG非依赖性增加。

结论：总体而言，结果表明PEG预处理可能通过刺激一系列酶促和非酶促活性氧清除系统来提高寻常棒杆菌的伽马辐照耐受性。微藻还可能消耗PEG来分解，并在压力期间将其用作碳的替代来源，应进一步详细研究。