羌塘国家级自然保护区地表土壤冻结天数时空变化特征

利用1981—2018年羌塘自然保护区周边5个气象台站的地表逐日最低温度和平均气温资料,采用线性回归和Mann-Kendall非参数检验方法,分析了近38 a以及全球变暖1.5℃和2℃阈值时羌塘自然保护区地表土壤冻结天数的时空变化特征。结果表明:(1)近38 a近地表土壤冻结开始日期呈推迟趋势,变化率为7.72 d·10 a^-1,冻结终止日期以8.17d·10 a^-1的速率显著提早;冻结持续时间和冻结天数均呈显著缩短趋势,平均每10年分别缩短14.69和11.19 d;同时段内,自然保护区大部分土壤冻结参数的变化率均大于青藏高原。(2)在年代际变化上,自然保护区呈现土壤冻结开始日期推迟、冻结终止日期提前、冻结持续时间和冻结天数缩短的变化特征。(3)土壤冻结参数在21世纪初均发生了气候突变,较青藏高原土壤冻融时间的突变点偏晚。(4)在全球变暖1.5℃时,RCP4.5和RCP8.5情景下的自然保护区土壤冻结参数变化值相同,冻结开始日期推迟25 d,冻结终止日期提早22 d,冻结持续时间和冻结天数分别缩短46和28 d;变暖2.0℃时,RCP4.5和RCP8.5情景下的土壤冻结开始日期推迟35和33 d,冻结终止日期提早30和29 d,冻结持续时间减少64和62 d,冻结天数缩短40和39 d。     

冬季升温对高山生态系统碳氮循环过程的影响

全球温度升高是目前面临的重要环境问题,但存在明显的季节差异性,即冬季升温幅度显著高于夏季的季节非对称性趋势,这在高纬度和高海拔地区更加显著。冬季升温会直接影响积雪覆盖与冰冻层厚度,并引起冻融交替循环的增加,而冬季植物处于休眠状态,这会直接影响土壤中有效氮的吸收与损失,引起土壤有效氮可利用性的变化。然而,关于冬季增温对后续生长季节植物活动、土壤碳氮循环过程的影响等方面的研究仍存在诸多不确定。综述了冬季升温对积雪覆盖与冻融交替循环改变对高山生态系统物质循环的影响,以及冬季升温对土壤碳氮循环、微生物与酶活性的影响,并由此引起的植物物候期、群落结构、生产与养分循环与凋落物分解等生理、生态过程方面的研究进展。在未来的研究中,应针对不同生态系统特点选择合适的冬季增温方式,加强非极地苔原地区关于冬季升温的研究,注重关注冬季升温对植物-土壤微生物之间反馈作用的影响,重点关注冬季升温对生态系统的延滞效应。     

Evolution of herbs: key to the conundrum might be tolerance not avoidance

草本植物的进化：解决难题的关键在于忍耐而非逃避 木本植物延续了其祖先被子植物的生长形态,而草本植物则不断地从中进化演变。虽然关于驱动草本植物习性进化的因素已有许多假设,但是通过舍弃地上生物质从而避免冬季冻害的能力常常被认为是促使其进化的主要力量。然而,鉴于草本植物在反复干扰中依旧能够轻松存活,我们提出了不可预测的干扰可能比季节性霜冻更为重要的假设。我们通过比较草本植物和木本植物应对3种模拟干扰(容易预测的冬季冰冻、不易预测的春季冰冻和食草作用)的能力来验证这一假设。通过比较20种不同植物在同质园实验中的表现,我们评估了这些干扰对植物死亡和再生方面的影响。研究结果表明,在冬季冰冻条件下,比起木本植物,草本植物在存活率上并没有优势。在不易预测的春季冰冻条件下,草本植物比木本植物的存活率更高。而在模拟食草作用的条件下,草本植物的这种生存优势更大。在不可预测的条件下,草本植物相较于木本植物的生存优势表明,草本植物的生长形式可能是对不可预测的干扰的适应,这种逆境忍耐通过其损失地上生物质也能够生存的能力得以实现。因此,哺乳动物的食草行为或火灾等原因或许最有可能是木本植物向草本植物过渡的因素。     

蛋白酶抑制剂对含水生菜种子耐冻性的影响

选取生菜(Lactuca sativa)种子作为试材,外源添加蛋白酶抑制剂2-硝基苯甲酸[5,5'-Dithiobis-(2-nitrobenzoic acid),DTNB]对种子吸胀处理,通过程序降温,分析2-硝基苯甲酸对低温下种子发芽率及生理活性的影响。结果表明,低温下含水生菜种子的致死温度为–20 ℃;外源添加2-硝基苯甲酸2 mmol·L–1时种子发芽率最高,即对种子活性的保护效果显著;在此浓度下种子内SOD活性比对照提高1.38倍,羟基自由基清除能力提高1.17倍;与对照组相比产生两种新的蛋白11 S种子贮藏球蛋白Jug r4和11 S种子贮藏球蛋白2,均属于球蛋白家族,可提高含水种子的耐冻性;低温下种子内积累更小分子量的球蛋白多肽,对种子具有低温保护效果。综上,低温条件下生菜种子产生一定的抗冷反应,外源添加2 mmol·L–1 2-硝基苯甲酸可提高含水种子发芽率及生理活性,产生抗冻蛋白,积累更小分子量的球蛋白多肽进而提高种子抗冻性。     

Co-expression of monodehydroascorbate reductase and dehydroascorbate reductase from Brassica rapa effectively confers tolerance to freezing-induced oxidative stress

Plants are exposed to various environmental stresses and have therefore developed antioxidant enzymes and molecules to protect their cellular components against toxicity derived from reactive oxygen species (ROS). Ascorbate is a very important antioxidant molecule in plants, and monodehydroascorbate reductase (MDHAR; EC 1.6.5.4) and dehydroascorbate reductase (DHAR; EC 1.8.5.1) are essential to regeneration of ascorbate for maintenance of ROS scavenging ability. The MDHAR and DHAR genes from Brassica rapa were cloned, transgenic plants overexpressing either BrMDHAR and BrDHAR were established, and then, each transgenic plant was hybridized to examine the effects of co-expression of both genes conferring tolerance to freezing. Transgenic plants co-overexpressing BrMDHAR and BrDHAR showed activated expression of relative antioxidant enzymes, and enhanced levels of glutathione and phenolics under freezing condition. Then, these alteration caused by co-expression led to alleviated redox status and lipid peroxidation and consequently conferred improved tolerance against severe freezing stress compared to transgenic plants overexpressing single gene. The results of this study suggested that although each expression of BrMDHAR or BrDHAR was available to according tolerance to freezing, the simultaneous expression of two genes generated synergistic effects conferring improved tolerance more effectively even severe freezing.     

Cryo‐Immunoelectron Microscopy of Adherent Cells Improved by the Use of Electrospun Cell Culture Substrates

Electrospun nanofibres are an excellent cell culture substrate, enabling the fast and non‐disruptive harvest and transfer of adherent cells for microscopical and biochemical analyses. Metabolic activity and cellular structures are maintained during the only half a minute‐long harvest and transfer process. We show here that such samples can be optimally processed by means of cryofixation combined either with freeze‐substitution, sample rehydration and cryosection‐immunolabelling or with freeze‐fracture replica‐immunolabelling. Moreover, electrospun fibre substrates are equally suitable for complementary approaches, such as biochemistry, fluorescence microscopy and cytochemistry.     

Resilience to Freezing in the Vegetative Cells of the Microalga Lobosphaera incisa (Trebouxiophyceae,Chlorophyta)

The chlorophyte microalga Lobosphaera incisa was isolated from the snowy slopes of Mt. Tateyama in Japan. This microalga stores exceptionally high amounts of the omega-6 LC-PUFA arachidonic acid in triacylglycerols, and therefore represents a potent photosynthetic source for this essential LC-PUFA. Assuming that freezing tolerance may play a role in adaptation of L. incisa to specific ecological niches, we examined the capability of L. incisa to tolerate extreme sub-zero temperatures. We report here, that the vegetative cells of L. incisa survived freezing at −20°C and −80°C (over 1 month), without cryoprotective agents or prior treatments. Cells successfully recovered upon thawing and proliferated under optimal growth conditions (25°C). However, cells frozen at −80°C showed better recovery and lower cellular ROS generation upon thawing, compared to those preserved at −20°C. Photosynthetic yield of PSII, estimated by F_v/F_m, temporarily decreased at day 1 post freezing and resumed to the original level at day 3. Interestingly, the thawed algal cultures produced a higher level of chlorophylls, exceeding the control culture. The polar metabolome of the vegetative cells comprised a range of compatible solutes, dominated by glutamate, sucrose, and proline. We posit that the presence of endogenous cryoprotectants, a rigid multilayer cell wall, the high LC-PUFA content in membrane lipids, and putative cold-responsive proteins may contribute to the retention of functionality upon recovery from the frozen state, and therefore for the survival under cryospheric conditions. From the applied perspective, this beneficial property holds promise for the cryopreservation of starter cultures for research and commercial purposes.     

Differences in NMR Spectra between Some α- and γ-Glutamyl Dipeptides

A methanol-utilizing phototrophic bacterium, strain M402, was isolated from surface water of an acidic hot spring. The isolated strain was identified as Rhodopseudomonas acidophila from its morphological and physiological characters. Profiles of the utilization of non-aromatic compounds as carbon sources by this strain were in good agreement with those of some strains of R. acidophila reported by Pfennig [J. Bacteriol., 99, 597 (1969)]. However, strain M402 was found to be capable of utilizing vanillic acid, vanillin, vanillyl alcohol, ferulic acid, veratric acid, syringic acid, syringal-dehyde and benzyl alcohol as carbon sources under anaerobic-light conditions. Although Pfennig did not refer to these abilities of his strains, these notable characters of strain M402 seem to be additional new characters of R. acidophila.     

Polyethylene glycol‐based low generation dendrimers functionalized with β‐cyclodextrin as cryo‐ and dehydro‐protectant of catalase formulations

Polyethylene glycol (PEG)‐based low generation dendrimers are analyzed as single excipient or combined with trehalose in relation to their structure and efficiency as enzyme stabilizers during freeze‐thawing, freeze‐drying, and thermal treatment. A novel functional dendrimer (DG_o‐CD) based on the known PEG's ability as cryo‐protector and β‐CD as supramolecular stabilizing agent is presented. During freeze‐thawing, PEG and β‐CD failed to prevent catalase denaturation, while dendrimers, and especially DG_o‐CD, offered the better protection to the enzyme. During freeze‐drying, trehalose was the best protective additive but DG_o‐CD provided also an adequate catalase stability showing a synergistic behavior in comparison to the activities recovered employing PEG or β‐CD as unique additives. Although all the studied dendrimers improved the enzyme remaining activity during thermal treatment of freeze‐dried formulations, the presence of amorphous trehalose was critical to enhance enzyme stability. The crystallinity of the protective matrix, either of PEG derivatives or of trehalose, negatively affected catalase stability in the freeze‐dried systems. When humidified at 52% of relative humidity, the dendrimers delayed trehalose crystallization in the combined matrices, allowing extending the protection at those conditions in which normally trehalose fails. The results show how a relatively simple covalent combination of a polymer such as PEG with β‐CD could significantly affect the properties of the individual components. Also, the results provide further insights about the role played by polymer–enzyme supramolecular interactions (host–guest crosslink, hydrogen bonding, and hydrophobic interactions) on enzyme stability in dehydrated models, being the effect on the stabilization also influenced by the physical state of the matrix. © 2013 American Institute of Chemical Engineers Biotechnol. Prog., 29:786–795, 2013