高温培养条件下爪哇伪枝藻的生理特性和超微结构特征

摘要

Soil biological crusts distribute widely in arid environment, and high temperature stress is a critical environmental factor on algal survival in these areas. During summer and autumn, temperature of desert biological crusts rise rapidly under the intense sun radiation. Scytonema javanicum Born et Flah is one of the important dominant species in biological soil crust and distributes at the outermost layer of biological soil crust. Consequently, S. javanicum are often suffered from high temperature. It is necessary to take into account the survival of S. javanicum in the desert environment. However, the impact of high temperature on desert algae was rarely reported. So, S. javanicum was used as experimental material, the effect of different high temperature (25 ℃ as control, 35℃, 40 ℃ and 45 ℃) on physiological, biochemical characteristics, and cell structure were studied in the laboratory in order to illuminate the tolerance and adaptation mechanisms of desert algae under high temperature. The results showed that chlorophyll a synthesis increased while carotenoid synthesis decreased under 35 ℃; on the contrary, carotenoid synthesis accelerated while chlorophyll a synthesis retarded under 40 ℃, contents of carotenoid in 40 ℃ were significant higher than those in control and 35℃ treaments. Changes of photosynthetic pigment content in S. javanicum under different temperatures generated variance in photosynthesis efficiency. As for the short term (6h) treatments, the maximum photochemical efficiency (Fv/Fm) and actual photochemical efficiency (ΦPSⅡ) of S. javanicum were significantly promoted under 35℃, while Fv/Fm and <ΦPSⅡ were inhibited under 40 ℃. For 45 ℃ treatments, photosynthetic activity of S. javanicum could not be detected after 2h, whose photosynthetic organs were irreversibly damaged and could not be restored. As to the long term (15d) treatments, there was no significant difference between 35℃ treatments and controls in Fv/Fm and <ΦPSⅡ of 5. javanicum. However, the maximum photochemical efficiency (Fv/Fm) and actual photochemical efficiency (ΦPSⅡ) of S. javanicum were noticeably restrained in 40 ℃ treatments. With the increasing of temperature, lipid peroxidation in S. javanicum increased gradually, and content of malondialdehyde (MDA) also enhanced. MDA contents of S. javanicum in 40℃ treatments were significant higher than those in control and 35 ℃ treatments. At the same time, with the temperature increasing, the membrane structures in cells of S. javanicum were more and more fragile. And the polysaccha-rides, as osmotic regulation substances, play important roles in preventing the damages of high temperature on membrane. Accordingly, the higher the temperature was, the more the contents of extracellular polysaccharides and intracel-lular soluble sugar outside and inside S. javanicum. Especially, content of extracellular polysaccharides outside S. javanicum in 40 ℃ treatments was almost 8 times than that of controls. Photographs of transmission electron microscope (TEM) sections of S. javanicum showed that cell structures were not damaged in 35 ℃ treatments, cellular morphologies were more stable, while the ultrastructures of algal cells were significantly damaged in 40 ℃, the protoplasts were flocculent and vacuolar finally. All these results confirmed that S. javanicum could withstand appropriate high temperature (35℃). This study has some theoretical significance in understanding the tolerance and adaptability of S. javanicum to high temperatures, and has actual guidance value in controlling desertification by use of desert cyanobacteria.%荒漠生物结皮广泛分布于干旱区环境,高温是影响生物结皮中藻类生存的重要环境因子.在实验室培养条件下,以生物结皮形成和发育中的重要优势种爪哇伪枝藻(Scytonemajavanicum Born et Flah)为材料,研究高温胁迫对伪枝藻生理生化特性和细胞结构的影响.设置了25℃(对照)、35℃、40℃和45℃等不同高温处理,测定了短期(6h)和长期(15d)高温条件下,S.javanicum的光合活性、光合色素、多糖含量和丙二醛含量以及细胞超微结构的变化.结果表明,S.javanicum最大光化学量子产量Fv/Fm和PSII有效光化学量子产量ΦPSII在35℃下表现出最大值.40℃高温明显抑制藻体叶绿素a合成,35℃处理促进了叶绿素α合成(高于对照值),而40℃处理明显促进了藻体类胡萝卜素合成,高于对照处理和35℃处理.随温度升高,S.javanicum 丙二醛、胞内可溶性糖和胞外多糖含量呈现出逐渐增大的趋势.透射电镜切片显示,40℃高温明显破坏了藻体细胞超微结构,如原生质体出现絮状形态和空泡化,35℃处理则有利于细胞形态结构的保持和稳定.以上结果初步证实了S.javanicum能够较好地耐受适当的高温(35℃).研究对于了解S.javanicum对高温环境的耐受程度及对高温的适应性具有一定的理论意义,并对利用荒漠蓝藻治理荒漠化具有实际指导价值.