拟南芥角果衰老过程中膜脂的变化

角果发育对某些物种的生殖发育具有重要的作用。拟南芥种子附着在角果里,角果在早期发育时进行光合作用,角果成熟后开裂散落种子之前,其细胞会经历一个衰老的过程。一般植物细胞在衰老过程中要经历膜脂降解的过程,但是角果细胞衰老过程仍未知。通过比较角果衰老过程中拟南芥野生型(WS)及与膜脂代谢密切相关的磷脂酶Dδ缺失突变体(PLDδ KO)中膜脂分子的组成情况、膜脂含量、相对含量及双键指数值,结果发现,在拟南芥角果衰老过程中：(i)质体膜脂和质体外膜脂显著下降;(ii)不同膜脂降解速率不一样,质体膜脂的降解比质体外膜脂的降解快;(iii)总的双键指数DBI下降;(iv)磷脂酶Dδ缺失突变体(PLDδ KO)的角果膜脂组成的基本水平和变化样式与野生型(WS)非常相似。结果说明,角果在衰老过程中发生了膜脂的激烈降解。据此推测：(i) 膜脂水解产物可能转移到种子中用于储藏脂三酰甘油的合成;(ii) 质体膜脂相对含量下降和质体外膜脂相对含量上升导致了总的DBI下降;(iii) PLDδ参与了角果衰老中的膜脂代谢。     

超干种子耐贮藏性的细胞学及生理生化基础

种子超干贮藏是近年来种子生物学研究和植物种质资源保存领域的研究热点。本文综述了种子超干贮藏研究的进展 ,包括 :(1)超干种子的细胞和亚细胞结构变化 ;(2 )超干处理对种子水分状态的影响以及与劣变反应速率的关系 ;(3)超干种子中的自由基伤害和有毒物质的积累 ;(4)超干种子中的内源抗氧剂 ;(5 )糖类物质以及两性物质对极度脱水种子细胞的保护。此外 ,还对此领域的研究进行了展望     

细胞内分子运动与种子和花粉耐贮藏性的关系

近年来国际上一些学者采用电子顺磁共振(electron paramagnetic resonance,EPR)、饱和迁移电子顺磁共振波谱(saturation transfer electron paramagnetic resonance spectroscopy,ST-EPRS)和极性分子探针标记等技术成功地测定了种子和花粉细胞内的分子运动(molecular mobility).依据分子运动速率确定种子和花粉的最佳贮藏条件,已成为一种新的方法,这对于植物种质资源长期保存的研究具有重要的理论和实践意义.文章对近年来花粉和种子的耐贮藏性与细胞内分子运动变化的研究进展作一综述.     

植物种质资源的保存

传统的保存植物种质资源的方法是建立种子库。采用低温保存可大大延缓正常性种子的寿命,但采用此法仍难以保存顽拗性种子。和种子库相比,采用植物细胞、组织或器官,能最大限度地抑制生理代谢强度,降低劣变发生频率,达到长期保存种质的目的。     

桃花粉低温和超低温保存方法比较研究

桃(Prunus persica(L.)Batsch)是我国重要的无性繁殖作物种质资源,目前主要保存于3个国家无性繁殖作物种质圃。随着以茎尖、花粉、休眠芽为保存载体的超低温保存技术的发展,超低温保存已成为无性繁殖作物重要备份保存方式。本研究以15份桃种质花粉为研究对象,开展含水量、回湿处理和保存温度(4℃低温保存和液氮超低温保存)对保存后花粉离体萌发率的影响研究。研究结果:明确了桃种质花粉超低温保存的含水量;揭示了回湿处理对部分桃种质花粉超低温保存产生显著影响;超低温保存后花粉离体萌发率最高可达83%;4℃低温保存和超低温保存比较研究结果表明,超低温保存4年后14份桃种质花粉离体萌发率仍可保持30%以上,11份桃种质花粉离体萌发率与保存前花粉离体萌发率相比无显著变化甚至显著提高,而4℃低温保存的花粉离体萌发率降至0。该研究为国家种质库建立花粉规模化超低温保存提供技术支撑。     

唐菖蒲花粉低温保存过程中的生理生化特征

以唐菖蒲切花栽培品种嫦娥粉花粉为实验材料,比较其花粉各项生理生化指标在-80℃和4℃贮藏过程中(360 d)的变化,以探讨2种保存条件下花粉保存效果出现显著性差异的生理生化原因.结果表明:唐菖蒲花粉在2种保存温度条件下,随保存时间的延长,各项生理生化指标表现出显著差异.与4℃保存处理相比,-80℃保存处理抑制了花粉中MDA的积累,增强了超氧化物歧化酶(SOD)和过氧化物酶(POD)的活性,减轻了花粉膜质过氧化和膜系统受伤害程度,同时提高了花粉可溶性蛋白质和可溶性糖的含量,增强了花粉的抗冻能力,从而使低温保存花粉活力维持在相对较高水平,这或许是-80℃条件下花粉保存效果较好的部分生理生化原因.     

农业其它

962282 番茄花粉的冷冻保存[会,英]/Sacks, E.J.…//Hortscience.-1995,30(4).-797～[译自DBA,1996,15(2),96-00958] 开发了冷冻保存番茄花粉的方法,以促进杂交进程和长期种质保存。用组织试纸包被含有花粉的明胶胶囊,置于装有无水硫酸钙干燥剂的密封玻璃     

棉花花粉水合和萌发时超微结构的变化：着重论述内质网和被膜小泡

棉花(Gossypium hirsutum L.)花粉在授粉后水合至萌发时期的营养细胞中贮藏的大量淀粉粒和脂体被动用。超微结构的观察表明,首先是造粉质体中的淀粉粒降解,尔后是脂体。在花粉水合至萌发时期,营养细胞中内质网和高尔基体十分活跃,并含丰富的被膜小泡。内质网的构型发生明显的变化:花粉刚水合时内质网潴泡高度扩张,不同程度扩张的内质网潴泡连续成网状并折迭形成许多囊袋状结构单位,其中包含造粉质体、脂体和被膜小泡群;其后,内质网潴泡形成的囊袋状结构消失,变为分支互通的网状结构;至萌发时,内质网潴泡略为扩张,有些连续成简单的网状,有些呈游离的囊泡状。被膜小泡始终是成群地分布,并与脂体联结,当脂体降解时一些被膜小泡与之融合。根据棉花花粉在水合至萌发时期,营养细胞质中存在独特形态的内质网系统和含丰富的被膜小泡,它们的动态行为及与淀粉和脂体的转化和降解之间的密切关系,讨论了这两种细胞器可能的功能。     

植物遗传资源的离体保存

近年来国内外遗传资源学界越来越重视植物遗传资源的离体(细胞和组织培养)保存,因为它可解决营养繁殖材料,产生顽拗型种子的作物和有特殊问题的作物的种质保存问题.现在离体保存研究已涉及330个属648个种(Withers 1986).我国不少学者从事马铃薯、甘薯和草莓等作物的离体保存研究工作,取得了很大进展.国际植物遗传资源委员会(IBPGR)专门设立了离体贮藏咨询委员会,并建立了离体保存数据库.IBPGR和国际热带农业中心(CIAT)正合作拟定中短期离体基因库的运行规范.对植物遗传资源的离体研究内容包括:(1)种质收集;(2)消除病原,确定病害指数和检疫;(3)     

苏铁属花粉萌发及保存条件研究

以不同浓度梯度的蔗糖与硼酸组合在不同pH条件下用悬浮培养法测定德保苏铁、叉叶苏铁、元江苏铁和越南篦齿苏铁花粉的活力;将元江苏铁和越南篦齿苏铁花粉分别保存在不同低温、不同湿度的环境中,研究温度和湿度对保存花粉的影响。结果表明:(1)最适合苏铁属植物花粉萌发的培养液配方为蔗糖(1%～2.5%)+硼酸(100～500 mg/L),pH6.0～7.0;(2)在室温下,将苏铁花粉密封保存在有干燥剂的容器中,可存活30 d以上;(3)在0℃条件下,不加干燥剂,花粉可保存4个月以上;(4)用液氮保存后的越南篦齿苏铁花粉进行人工授粉,结实率高达90.3%,与用新鲜花粉人工授粉的结实率无明显差异;(5)将花粉含水率降低到15.5%～13.2%后,能在液氮中进行长期保存,表明花粉液氮保存可以作为苏铁花粉长期和超长期保存的方法。     

The role of sugar, vitrification and membrane phase transition in seed desiccation tolerance

In a search for the mechanism of desiccation tolerance, a comparison was made between orthodox (desiccation-tolerant) soybean ( Glycine max [L.] Merrill) and recalcitrant (desiccation-intolerant) red oak ( Quercus rubra L.) seeds. During the maturation of soybean seeds, desiccation tolerance of seed axes is correlated with increases in sucrose, raffinose and stachyose. In cotyledons of mature oak seeds, sucrose levels are equal to those in mature soybeans, but oligosaccharides are absent. By using the thermally stimulated current method, we observed the glassy state in dry soybean seeds during maturation. Oak cotyledons showed the same phase diagram for the glass transition as did mature soybeans. By using X-ray diffraction, we found the maturation of soybeans to be associated with an increased ability of membranes to retain the liquid crystalline phase upon drying, whereas the mature oak cotyledonary tissue existed in the gel phase under similar dry conditions. These findings lead to the conclusion that the glassy state is not sufficient for desiccation tolerance, whereas the ability of membranes to retain the liquid crystalline phase does correlate with desiccation tolerance. An important role for soluble sugars in desiccation tolerance is confirmed, as well as their relevance to membrane phase changes. However, the presence of soluble sugars does not adequately explain the nature of desiccation tolerance in these seeds.     

Air-drying kinetics affect yeast membrane organization and survival

The plasma membrane (PM) is a key structure for the survival of cells during dehydration. In this study, we focused on the concomitant changes in survival and in the lateral organization of the PM in yeast strains during desiccation, a natural or technological environmental perturbation that involves transition from a liquid to a solid medium. To evaluate the role of the PM in survival during air-drying, a wild-type yeast strain and an osmotically fragile mutant (erg6Δ) were used. The lateral organization of the PM (microdomain distribution) was observed using a fluorescent marker related to a specific green fluorescent protein-labeled membrane protein (Sur7-GFP) after progressive or rapid desiccation. We also evaluated yeast behavior during a model dehydration experiment performed in liquid medium (osmotic stress). For both strains, we observed similar behavior after osmotic and desiccation stresses. In particular, the same lethal magnitude of dehydration and the same lethal kinetic effect were found for both dehydration methods. Thus, yeast survival after progressive air-drying was related to PM reorganization, suggesting the positive contribution of passive lateral rearrangements of the membrane components. This study also showed that the use of glycerol solutions is an efficient means to simulate air-drying desiccation.     

Desiccation enhances phosphorylation of PSII and affects the distribution of protein complexes in the thylakoid membrane

Desiccation has significant effects on photosynthetic processes in intertidal macro‐algae. We studied an intertidal macro‐alga, Ulva sp., which can tolerate desiccation, to investigate changes in photosynthetic performance and the components and structure of thylakoid membrane proteins in response to desiccation. Our results demonstrate that photosystem II (PSII) is more sensitive to desiccation than photosystem I (PSI) in Ulva sp. Comparative proteomics of the thylakoid membrane proteins at different levels of desiccation suggested that there were few changes in the content of proteins involved in photosynthesis during desiccation. Interestingly, we found that both the PSII subunit, PsbS (Photosystem II S subunit) (a four‐helix protein in the LHC superfamily), and light‐harvesting complex stress‐related (LHCSR) proteins, which are required for non‐photochemical quenching in land plants and algae, respectively, were present under both normal and desiccation conditions and both increased slightly during desiccation. In addition, the results of immunoblot analysis suggested that the phosphorylation of PSII and LHCII increases during desiccation. To investigate further, we separated out a supercomplex formed during desiccation by blue native‐polyacrylamide gel electrophoresis and identified the components by mass spectrometry analysis. Our results show that phosphorylation of the complex increases slightly with decreased water content. All the results suggest that during the course of desiccation, few changes occur in the content of thylakoid membrane proteins, but a rearrangement of the protein complex occurs in the intertidal macro‐alga Ulva sp.     

Membrane phase behavior of Escherichia coli during desiccation, rehydration, and growth recovery

The membrane lipid bilayer is one of the primary cellular components affected by variations in hydration level, which cause changes in lipid packing that may have detrimental effects on cell viability. In this study, Fourier transform infrared (FTIR) spectroscopy was used to quantify changes in the membrane phase behavior, as identified by membrane phase transition temperature (T_m), of Escherichia coli during desiccation and rehydration. Extensive cell desiccation (1 week at 20%-40% RH) resulted in an increase in T_m from 8.4 ± 1.7 °C (in undried control samples) to 16.5 ± 1.3 °C. Fatty acid methyl ester analysis (FAME) on desiccated samples showed an increase in the percent composition of saturated fatty acids (FAs) and a decrease in unsaturated FAs in comparison to undried control samples. However, rehydration of E. coli resulted in a gradual regression in T_m, which began approximately 1 day after initial rehydration and plateaued at 12.5 ± 1.8 °C after approximately 2 days of rehydration. FAME analysis during progressive rehydration revealed an increase in the membrane percent composition of unsaturated FAs and a decrease in saturated FAs. Cell recovery analysis during rehydration supported the previous findings that showed that E. coli enter a viable but non-culturable (VBNC) state during desiccation and recover following prolonged rehydration. In addition, we found that the delay period of approximately 1 day of rehydration prior to membrane reconfiguration (i.e. decrease in T_m and increase in membrane percent composition of unsaturated FAs) also preceded cell recovery. These results suggest that changes in membrane structure and state related to greater membrane fluidity may be associated with cell proliferation capabilities.     

Ultrasonic acoustic emissions from excised stems of two Thryptomene species

ABA-dcficient ( aba-1 ) and ABA-insensitive ( abi3–1 ) double mutant seeds of Arabidopsis thaliana are desiccation-intolerant. Carbohydrates are supposed to fulfill a role in membrane protection during dehydration. Desiccation tolerance can be induced in douhle mutant seeds in vivo by supplying the ABA-analog LAB 173 711 to the plant root system. However. this does not lead to significant changes in the carbohydrate composition, in contrast, in vitro incubation of dissected immature seeds with ABA induced desiccation tolerance concomitant with an increase in the seed raffinose content. Thus, different desiccation tolerance-inducing treatments show contradictory effects on seed carbohydrate composition and accumulation. It is concluded that. although carbohydrates might be invohed in membrane protection or glass formation during dehydration, it is unlikely that they are the sole factor determining desiccation tolerance in Arabidopsis seeds     

Drought acclimation and lipid composition in Folsomia candida: implications for cold shock,heat shock and acute desiccation stress

Many of the physiological adaptations evolved in terrestrial invertebrates to resist desiccation have also been shown to enhance the survival of low temperatures. In this study we have examined temporal changes in the physiology of the collembolan Folsomia candida during acclimation to mild desiccation stress (98.2% RH), and how physiological changes correlate with resistance to subsequent cold shock, heat shock and acute desiccation stress. Drought-acclimation increased the resistance to cold and acute drought but reduced the resistance to heat shock. The composition of membrane phospholipid fatty acids (PLFA) changed during acclimation resulting in a higher degree of unsaturation by the end of the 192-h acclimation period. This resembles typical membrane alterations seen in ectothermic animals exposed to cold. Only small changes were seen in the neutral lipid fraction. The temporal changes in cold resistance and drought resistance correlated well with changes in PLFA composition and accumulation of sugars and polyols (’cryoprotectives’). It is proposed that the drought-induced PLFA desaturation, combined with the membrane protecting accumulation of cryoprotectives, are important physiological adaptations providing tolerance to both desiccation and cold.     

Ultrastructural changes during recovery from anabiosis in the plant parasitic nematode, Ditylenchus

Ultrastructural changes after desiccation and rehydration of the anabiotic fourth-stage juveniles of the plant parasitic nematode Ditylenchus dipsaci (Kuhn) Filipjev are described and quantified. Anabiotic juveniles retain their structural integrity, although the cuticle decreases in thickness and the muscle cell sarcoplasm condenses. In contrast the structure of the non-anabiotic nematode Panagrellus silusae is completely disorganized by desiccation. Following rehydration of D. dipsaci there is a lag phase of 2-3 hr before the nematodes become active. During this period the juveniles undergo an ordered series of morphological changes. The lipid droplets within the intestinal cells coalesce and the cuticle increases in thickness. The muscle cell sarcoplasm expands, the spacing of the thick myofilaments increases and the mitochondria swell before recovering a more normal appearance. These morphological changes, together with earlier metabolic studies, indicate that repair occurs during the lag phase prior to recovery. This may involve membrane repair and the re-establishment of the ionic gradients essential for normal muscle and nerve function.     

Engineering desiccation tolerance in Escherichia coli

Recombinant sucrose-6-phosphate synthase (SpsA) was synthesized in Escherichia coli BL21DE3 by using the spsA gene of the cyanobacterium Synechocystis sp. strain PCC 6803. Transformants exhibited a 10,000-fold increase in survival compared to wild-type cells following either freeze-drying, air drying, or desiccation over phosphorus pentoxide. The phase transition temperatures and vibration frequencies (P==O stretch) in phospholipids suggested that sucrose maintained membrane fluidity during cell dehydration.     

Ultrastructural changes during desiccation of the anhydrobiotic nematode Ditylenchus dipsaci

Ultrastructural changes during desiccation of the anhydrobiotic nematode Ditylenchus dipsaci were followed and quantified after preparation of material at different levels of hydration using freeze substitution techniques. Some shrinkage was caused by processing in the more hydrated specimens but the changes observed correspond to those observed in live nematodes by light microscopy, indicating that the technique is useful for following changes during desiccation. The overall pattern of changes was a rapid decrease in the magnitude of the measured parameter during the first 5 min of desiccation, followed by a slower rate of decrease upon further desiccation. This was observed in the cuticle, the lateral hypodermal cords and the muscle cells and is consistent with the pattern of water loss of the nematode. The contractile region of the muscle cells, however, proved an exception and the muscle fibres appear to resist shrinkage and packing until water loss becomes severe. The mitochondria swell and then shrink during desiccation, which may indicate disruption of the permeability of the mitochondrial membrane. A decrease in the thickness of the cortical zone was the most prominent change in the cuticle and this may be related to the permeability slump which occurs during the first 5 min of desiccation.     

Roles of membrane structure and phase transition on the hyperosmotic stress survival of Geobacter sulfurreducens

Geobacter sulfurreducens is a delta-proteobacterium bacteria that has biotechnological applications in bioremediation and as biofuel cells. Development of these applications requires stabilization and preservation of the bacteria in thin porous coatings on electrode surfaces and in flow-through bioreactors. During the manufacturing of these coatings the bacteria are exposed to hyperosmotic stresses due to dehydration and the presence of carbohydrates in the medium. In this study we focused on quantifying the response of G. sulfurreducens to hyperosmotic shock and slow dehydration to understand the hyperosmotic damage mechanisms and to develop the methodology to maximize the survival of the bacteria. We employed FTIR spectroscopy to determine the changes in the structure and the phase transition behavior of the cell membrane. Hyperosmotic shock resulted in greatly decreased membrane lipid order in the gel phase and a less cooperative membrane phase transition. On the other hand, slow dehydration resulted in increased membrane phase transition temperature, less cooperative membrane phase transition and a small decrease in the gel phase lipid order. Both hyperosmotic shock and slow dehydration were accompanied by a decrease in viability. However, we identified that in each case the membrane damage mechanism was different. We have also shown that the post-rehydration viability could be maximized if the lyotropic phase change of the cell membrane was eliminated during dehydration. On the other hand, lyotropic phase change during re-hydration did not affect the viability of G. sulfurreducens. This study conclusively shows that the cell membrane is the primary site of injury during hyperosmotic stress, and by detailed analysis of the membrane structure as well as its thermodynamic transitions it is indeed possible to develop methods in a rational fashion to maximize the survival of the bacteria during hyperosmotic stress.