共生与非共生爪哇伪枝藻对高温胁迫的响应

研究以自由生长的爪哇伪枝藻(Free-living S. javanicum, fs)和分离自地衣的爪哇伪枝藻(Symbiotic S. javanicum, ss)为研究对象, 探究了不同生长状态爪哇伪枝藻对高温(45℃)胁迫的响应。结果发现在高温胁迫下, 爪哇伪枝藻光合活性、叶绿素a及类胡萝卜素含量下降; 丙二醛(MDA)、胞外多糖及可溶性蛋白含量上升。在高温处理下, 与fs相比, ss光合活性下降较慢, 且高温处理后ss的叶绿素a及类胡萝卜素含量也明显高于fs。高温处理下, 与fs相比, ss的MDA含量和增长速度均较低; 并且在面临高温胁迫时, ss能够更快的分泌胞外多糖和可溶性蛋白质, 从而在一定程度上达到自我保护的目的。研究结果表明, 在暴露于高温胁迫时, 相较于自由生长状态, 来自地衣的爪哇伪枝藻具有更高的自我保护效率。     

低温驯化和外源糖对爪哇伪枝藻冷胁迫的影响

低温是影响荒漠藻类生存的重要环境因子.研究了低温驯化和外源糖对爪哇伪枝藻冷胁迫的作用.实验测定了低温和外源糖处理下伪枝藻某些生理活性指标的变化.结果表明,低温胁迫导致伪枝藻生物量和光合活性的显著降低,低温驯化和外源糖在一定程度上对藻细胞叶绿素α含量和光合活性具有促进作用,低温驯化明显提高了细胞内可溶性蛋白的含量,而对丙二醛的含量影响不大.研究还发现,低温驯化明显降低了细胞膜的相对透性,而外源糖对细胞膜的相对透性影响不大.此外,低温驯化促进了伪枝藻胞外多糖的大量合成.研究结果初步证实了低温驯化和外源糖类对于提高伪枝藻的冷胁迫耐受性具有调节作用.     

发状念珠藻对盐胁迫的响应

探讨了发状念珠藻(NostocflagelliformeBornetFlah)对盐胁迫的耐受适应机制,采用含不同浓度NaCl(0、01、02、04、06、08、10mol/L)的BG110培养液处理具有正常生理活性的丝状体,25±05℃,40μmol/m2/s下照光培养12h,测定藻体光合作用、呼吸作用等生理活性以及体内一些物质的含量,结果表明:随培养液中NaCl浓度的升高藻体光合作用、呼吸作用以及PSⅡ活性(Fv/Fm)降低;质膜透性不断增大,丙二醛含量升高,自由水含量、自由水/束缚水比值下降,类胡萝卜素、可溶性糖含量增加,脯氨酸含量变化不大。由此可知,盐胁迫下发状念珠藻正常生理活性受到抑制而表现出一定的抗逆能力;该藻对盐胁迫具有一定的耐受能力,类胡萝卜素的增加有助于清除藻体内的氧自由基,可溶性糖可能是其主要渗透调节物质之一,脯氨酸在盐胁迫中的渗透调节作用不大。       

盐胁迫对葛仙米生理生化特性的影响

受盐胁迫的葛仙米其光系统II(PSII)反应中心的激发捕获效率(Fv/Fm)随着盐度的升高而降低,盐度高时,藻体FV/Fm随处理时间延长而迅速下降。外源脯氨酸对FV/Fm由于盐胁迫而降低的缓解作用并不十分明显,内源脯氨酸含量并不因为盐度的上升而增加。受胁迫藻体的膜脂过氧化产物丙二醛则由于胁迫加重而上升。另外,随着外界盐度的上升,葛仙米SOD的活性却呈现出典型的“V”形变化,这可能与藻体在不同盐度时所承受的实际胁迫有关。     

失水-吸水过程中集球藻的生理生化特性研究

荒漠结皮藻类广泛分布于干旱、半干旱地区,经常面临生存水源的短缺。以一种从荒漠结皮中分离的典型绿藻-集球藻(Palmellococcus sp.)为材料,研究其在失水-吸水过程中的某些生理生化特性。即在温室模拟条件下设置相对湿度分别为0%(极度失水)、43%(适度失水)和98%(水合,对照),测定不同失水处理对集球藻光合活性、膜脂过氧化产物丙二醛含量、细胞内可溶性物质含量和抗氧化酶活性的影响,并测定蒸馏水、BBM培养基、0.2 g/L蔗糖溶液、0.2 g/L蓝藻多糖、0.2 g/L脯氨酸和2.5 mmol/L氯霉素及50μmol/L敌草隆进行吸水处理时对失水藻体光合活性的恢复效果。结果表明,与对照处理相比,集球藻在失水过程中光合活性迅速降低,SOD和CAT活性大量升高,细胞内可溶性糖含量和可溶性蛋白含量明显增加,并且膜脂丙二醛含量出现大量积累。不同的失水-吸水处理发现,外源蔗糖和胞外多糖吸水对集球藻的光合活性有较好的恢复作用,添加脯氨酸和氯霉素吸水时光合活性也获得了一定程度的恢复,采用敌草隆吸水时则出现光合活性的明显抑制。研究结果对于更好地理解荒漠结皮绿藻对干旱的生理适应机制提供了有意义的参考。     

几种固沙荒漠藻的温度适应性

蓝藻结皮在干旱和半干旱区广泛分布,它们在环境状态的维持和改良过程中发挥着重要的作用。在荒漠藻固沙技术的应用过程中,温度不仅影响藻类在培养池中的培养,还影响接种后藻类的生长。因此,摸清优势固沙藻类的温度生长特征及对不同温度的生长适应性,对于接种蓝藻固沙技术的应用具有积极的意义。实验分3部分:研究了室温培养条件下3种荒漠优势蓝藻-具鞘微鞘藻(Microcoleus vaginatus)、爪哇伪枝藻(Scytonema javanicum)、纤细席藻(Phormidium tenue)的生长曲线,在不同温度(2、5、10、15、25、35℃)、开放式载体培养状态下3种蓝藻的生长状况及形态观察,以及爪哇伪枝藻在不同温度(10、15、20、25、30℃)培养条件下的光合活性、光合色素含量和伪枝藻素含量的变化。实验结果表明:(1)在液体培养基中,纤细席藻生长速率最快,高于具鞘微鞘藻和爪哇伪枝藻;(2)开放式载体培养条件下,藻株的生长速率低于液体培养,因此荒漠优势藻类的培养优先选择液体培养,具鞘微鞘藻和爪哇伪枝藻不易被细菌污染,纤细席藻容易受到细菌污染,在培养该藻株时要考虑添加抗生素类药物抑制细菌过度繁殖;(3)爪哇伪枝藻短期培养(18d)宜选择相对较高的培养温度(25-30℃),而长期培养(30d)宜选择相对较低的培养温度(15-20℃)。       

壬基酚对三角褐指藻的毒性效应及其机理

为了探讨壬基酚(Nonylphenol,NP)对海洋微藻的生态毒性效应,实验选择三角褐指藻(Phaeodactylum triconutum Bohlin)作为受试对象,设置7 个NP 质量浓度梯度(0、0.2、0.4、0.6、0.8、1.0 和2.0 mg·L^-1),测定了不同浓度处理下三角褐指藻的生长情况、光合色素含量、可溶性蛋白含量、丙二醛(MDA)含量及最大光能转化效率(Fv/Fm)以及24 h,48 h,72 h,96 hEC₅₀ 等指标。结果表明,NP 对三角褐指藻的96 h EC50 为0.84 mg·L^-1;当NP 暴露浓度在0.4 mg·L^-1 以上时对三角褐指藻生长表现抑制效应,而且随着NP 质量浓度的增加,生长抑制效应加强,当暴露浓度≥1.0mg·L^-1 时即可造成藻细胞大量死亡,当NP暴露浓度≥2.0mg·L^-1 时,藻细胞基本不能生长。三角褐指藻的细胞密度、可溶性蛋白含量、光合色素含量以及Fv/Fm 等指标随NP 暴露浓度质量浓度的增加而下降的幅度更加显著,暴露处理24 h,MDA 含量随NP 质量浓度的增加而上升,表明较高质量浓度的NP 胁迫,使藻细胞膜脂过氧化程度增强,可能会导致细胞膜结构的破坏和功能的丧失。NP 对三角褐指藻的生长具有明显的毒性效应,并可以造成抗氧化酶系统和光合系统的损伤。     

春季不同程度低水位对四种沉水植物生理的影响

为了解不同沉水植物对春季低水位的生理响应, 在2014年春季开展为期3个月的控制实验, 研究不同程度的春季低水位, 包括极低水位(水深18 cm)、较低水位(36 cm)和低水位(54 cm)对3种乡土沉水植物微齿眼子菜、穗花狐尾藻和菹草的最大光化学量子产量(Fv/Fm)、总叶绿素含量和可溶性糖含量的影响, 并与外来种伊乐藻作对比。结果显示, 随着水位的降低, 微齿眼子菜、菹草和伊乐藻Fv/Fm显著升高, 而穗花狐尾藻的Fv/Fm无显著变化; 在3种水位下伊乐藻的Fv/Fm都明显高于其他3种植物。微齿眼子菜和菹草总叶绿素含量也随着水位降低有升高趋势, 而穗花狐尾藻和伊乐藻的总叶绿素含量随水位没有显著变化。所有水位下微齿眼子菜总叶绿素含量最高, 穗花狐尾藻最低, 菹草只在低水位下显著低于伊乐藻。微齿眼子菜、菹草和伊乐藻的可溶性糖含量随着水位的降低而下降, 穗花狐尾藻的可溶性糖含量随着水位的降低有升高趋势。在低水位和较低水位下穗花狐尾藻和菹草的可溶性糖含量分别是所有植物中的最小和最大, 但在极低水位下4种沉水植物的可溶性糖含量无明显差异。以上结果表明, 春季极低水位对微齿眼子菜、伊乐藻和菹草不产生胁迫,但对穗花狐尾藻产生了胁迫; 伊乐藻潜在光合能力强于乡土种, 在春季浅水区具备较强的入侵性。     

高、低温胁迫对牡丹叶片PSⅡ功能和生理特性的影响

以牡丹‘肉芙蓉’离体叶片为试材,以25 ℃为对照,研究了强光(1400 μmol·m-2·s-1)下高温(40℃)和低温(15℃)处理对牡丹叶片PSⅡ光化学活性和生理特性的影响.结果表明:随处理时间的延长,各处理叶片的PSⅡ最大光化学效率(Fv/Fm)、PSⅡ实际光量子效率(φPsⅡ)和光下开放的PSⅡ反应中心激发能捕获效率(Fv’/Fm’)均持续降低.暗恢复4h后,对照和15℃处理叶片的Fv/Fm基本上完全恢复,而40℃处理叶片仅恢复到处理前的75.5％,即使15 h后也不能完全恢复;强光下40℃处理使PSⅠ和PSⅡ间的激发能分配严重偏离平衡状态.强光下40 ℃处理抑制了超氧化物歧化酶活性,加剧了O2、H2O2、丙二醛的产生,导致叶绿素和可溶性蛋白含量不断下降.说明强光下40℃高温胁迫对牡丹叶片光合机构造成了不可逆的破坏,而15℃低温处理对其光合机构的影响相对较弱.     

念珠藻葛仙米生理生化特性对不同低温胁迫的响应

研究了不同培养温度下对念珠藻葛仙米的生长和相关生理生化特性的变化.结果表明,低温抑制葛仙米的生长,在2℃～5℃低温下其生长甚至完全停止;在10℃低温胁迫下,其生长延滞期变长,其后仍能保持正常生长.低温胁迫下,葛仙米光合系统II(PSII)的光合效率(Fv/Fm)的变化趋势与生长曲线相似;细胞电解质渗透率在低温胁迫初期尚能保持比较低的水平,但随着时间延长而升高;可溶性糖和还原性糖含量的变化则随胁迫加剧有不同程度升高.可溶性蛋白含量则在低温下保持比较低的水平.这些结果表明,低温对葛仙米的生长和光合作用具有抑制作用,但葛仙米也表现出了一定的抵抗低温胁迫的能力,并通过调节细胞膜的渗透性、重新合成低温适应调节物质(如总糖和可溶性糖等)来减少低温伤害,从而适应低温胁迫.     

高温培养条件下爪哇伪枝藻的生理特性和超微结构特征

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(Scytonema javanicum 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a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。     

Dehydration rate and time of desiccation affect recovery of the lichenic algae <Emphasis Type="Italic">Trebouxia erici</Emphasis>: alternative and classical protective mechanisms

The mechanisms involved in desiccation tolerance of lichens and their photobionts are still poorly understood. To better understand these mechanisms we have studied dehydration rate and desiccation time in Trebouxia, the most abundant chlorophytic photobiont in lichen. Our findings indicate that the drying rate has a profound effect on the recovery of photosynthetic activity of algae after rehydration, greater than the effects of desiccation duration. The basal fluorescence (F′_o) values in desiccated algae were significantly higher after rapid dehydration, than after slow dehydration, suggesting higher levels of light energy dissipation in slow-dried algae. Higher values of PSII electron transport were recovered after rehydration of slow-dried Trebouxia erici compared to rapid-dried algae. The main component of non-photochemical quenching after slow dehydration was energy dependent (q _E), whereas after fast dehydration it was photoinhibition (q _I). Although q _E seems to play a role during desiccation recovery, no significant variations were detected in the xanthophyll cycle components. Desiccation did not affect PSI functionality. Classical antioxidant activities like superoxide dismutase or peroxidase decreased during desiccation and early recovery. Dehydrins were detected in the lichen-forming algae T. erici and were constitutively expressed. There is probably a minimal period required to develop strategies which will facilitate transition to the desiccated state in this algae. In this process, the xanthophyll cycle and classical antioxidant mechanisms play a very limited role, if any. However, our results indicate that there is an alternative mechanism of light energy dissipation during desiccation, where activation is dependent on a sufficiently slow dehydration rate.     

Desiccation tolerance in the moss Polytrichum formosum: physiological and fine-structural changes during desiccation and recovery

BACKGROUND AND AIMS: This study explores basic physiological features and time relations of recovery of photosynthetic activity and CO2 uptake following rehydration of a desiccation-tolerant moss in relation to the full temporal sequence of cytological changes associated with recovery to the normal hydrated state. It seeks reconciliation of the apparently conflicting published physiological and cytological evidence on recovery from desiccation in bryophytes. METHODS: Observations were made of water-stress responses and recovery using infrared gas analysis and modulated chlorophyll fluorescence, and of structural and ultrastructural changes by light and transmission electron microscopy. KEY RESULTS: Net CO2 uptake fell to zero at approx. 40 % RWC, paralleling the fluorescence parameter PhiPSII at 200 micromol m(-2) s(-1) PPFD. On re-wetting the moss after 9-18 d desiccation, the initially negative net CO2 uptake became positive 10-30 min after re-wetting, restoring a net carbon balance after approx. 0.3-1 h. The parameter Fv/Fm reached approx. 80 % of its pre-desiccation value within approx. 10 min of re-wetting. In the presence of the protein-synthesis inhibitors chloramphenicol and cycloheximide, recovery of Fv/Fm (and CO2 exchange) proceeded normally in the dark, but declined rapidly in the light. Though initial recovery was rapid, both net CO2 uptake and Fv/Fm required approx. 24 h to recover completely to pre-desiccation values. The fixation protocols produced neither swelling of tissues nor plasmolysis. Thylakoids, grana and mitochondrial cristae remained intact throughout the drying-re-wetting cycle, but there were striking changes in the form of the organelles, especially the chloroplasts, which had prominent lobes and lamellar extensions in the normally hydrated state, but rounded off when desiccated, returning slowly to their normal state within approx. 24 h of re-wetting. Sub-cellular events during desiccation and re-wetting were generally similar to those seen in published data from the pteridophyte Selaginella lepidophylla. CONCLUSIONS: Initial recovery of respiration and photosynthesis (as of protein synthesis) is very rapid, and independent of protein synthesis, suggesting physical reactivation of systems conserved intact through desiccation and rehydration, but full recovery takes approx. 24 h. This is consistent with the cytological evidence, which shows the thylakoids and cristae remaining intact through the whole course of dehydration and rehydration. Substantial and co-ordinated changes in other cell components, which must affect spatial relationships of organelles and metabolic systems, return to normal on a time span similar to full recovery of photosynthesis. Comparison of the present data with recently published results suggests a significant role for the cytoskeleton in desiccation responses.     

集球藻对盐胁迫的生理适应及细胞结构变化

盐胁迫是影响荒漠区土壤藻类生存的重要环境因子。集球藻是一种广泛分布于生物土壤结皮中的球状绿藻, 能够积累红色素(如虾青素)和油滴, 显示出其独特的生理特性和潜在的应用价值。目前对集球藻的生理、细胞结构以及色素积累的研究非常匮乏。以从荒漠生物结皮中分离的一种集球藻为材料, 在实验室条件下研究盐胁迫对集球藻生物量、光合活性、膜脂过氧化产物丙二醛含量、细胞可溶性蛋白质含量和可溶性糖含量以及细胞结构的影响。研究结果表明, 与对照处理相比, 盐胁迫导致集球藻生物量和光合活性的显著降低, 细胞可溶性蛋白和可溶性糖呈现一定的积累。同时盐处理导致集球藻膜脂丙二醛含量大量增加, SOD和CAT 活性升高。研究还表明, 对照处理下细胞结构完整, 细胞器形态清晰, 生长后期有大量脂肪体积累。在盐处理下藻体细胞形态结构出现阶段性破坏特征和脂肪体以及淀粉粒的积累, 此外细胞器结构模糊和消失, 细胞出现质壁分离和空泡化等。研究为更好地揭示集球藻在盐胁迫环境中的生理适应特性、微结构特征以及色素积累机制具有重要的科学意义, 并为该藻的基础和应用研究提供实验资料。       

Antioxidant metabolism in the intertidal red seaweed Stictosiphonia arbuscula following desiccation

Seaweeds grow in distinct vertical bands on the seashore and it is well known that their ability to recover physiological processes following desiccation is correlated to their shore position. Despite this, little is known of the cellular mechanisms by which intertidal seaweeds limit membrane damage during desiccation and subsequent rehydration. In this study, specimens of the intertidal red seaweed Stictosiphonia arbuscula were placed in sealed tanks and maintained at different relative humidities (control, RH 90-100%; moderate desiccation, RH 70-80% and severe desiccation, RH 40-50%) for 12, 24 or 48 h. Membrane damage and antioxidant metabolism was examined immediately following specimen rehydration. Amino acid leakage, through the plasmalemma, was greater for desiccated low-band specimens than high-band specimens, indicating greater membrane damage. In addition, low-band specimens produced more hydrogen peroxide and lipid hydroperoxides than high-band specimens. This indicates that, upon rehydration, high-band populations have a greater ability to reduce the build-up of hydrogen peroxide, limit lipid peroxidation and hence membrane and protein damage, than low-band populations. The greater ability to prevent or reduce the production of reactive oxygen species was not due to a larger antioxidant pool, but rather increased activity of the enzymes required to regenerate ascorbate and glutathione. These findings suggest that antioxidant metabolism is one of the defence mechanisms that protect S. arbuscula from cellular damage due to desiccation.     

Desiccation induced changes in osmolytes production and the antioxidative defence in the cyanobacterium Anabaena sp. PCC 7120

Cells of Anabaena sp. PCC 7120, a low desiccation tolerant cyanobacterium, was subjected to prolonged desiccation and effect of loss of water was examined on production of osmolytes, and antioxidant response as well as on overall viability in terms of photosynthetic activity. During dehydration (22 h), the organism maintained about 98.5 % loss of cellular water, yet cells remained viable as about 30 % of photosynthetic O₂-evolution activity resumed upon hydrating (1 h) such cells. In desiccated state, cyanobacterial cells accumulated osmolytes within 1 h though their contents decreased thereafter. The highest levels of trehalose (179 nmol mg⁻¹ protein), sucrose (805 nmol mg⁻¹ protein) and proline (23.2 nmol mg⁻¹ protein) were attained within 1 h. Chlorophyll a and carotenoid contents also increased within 1 h but phycocyanin level showed opposite trend. The oxygen-evolving activity declined in desiccated cyanobacterial biomass while rehydration led to instant recovery, indicating that cells protect the photosynthetic machinery against desiccation. Notwithstanding, activities of antioxidant enzymes (catalase, peroxidase and superoxide dismutase) attained their peaks after 3 h of desiccation, though within 10 min of rehydration, their levels returned back close to basal activities of the cultured cells. We propose that onset of osmolyte production in conjunction with upshift of antioxidant enzymes apparently protects the cyanobacterial cells from desiccation stress.     

Effects of Dehydration and Rehydration on Photosynthesis of Detached Leaves of the Resurrective Plant Boea hygrometrica

Fluorescence induction kinetics was used to investigate the effects of dehydration and rehydration on photosynthesis of detached leaves of the desiccation-tolerant, resurrective plant Boea hygrometrica (Bunge) R. Br. In comparison with the desiccation-intolerant plant Chirita heterotricha Merr., the PSⅡphotochemical activity of Boea hygrometrica was characterized by a faster decline during dehydration and a much higher capacity of recovery during rehydration. By means of native PAGE, it was further shown that the thylakoid pigment-protein complexes of Boea hygrometrica were highly stable during dehydration and rehydration. These features may contribute to the extreme desiccation resistance of photosynthesis apparatus of resurrective plant Boea hygrometrica.     

Effects of dehydration rate on physiological responses and survival after rehydration in larvae of the anhydrobiotic chironomid

Strategies to combat desiccation are critical for organisms living in arid and semi-arid areas. Larvae of the Australian chironomid Paraborniella tonnoiri resist desiccation by reducing water loss. In contrast, larvae of the African species Polypedilum vanderplanki can withstand almost complete dehydration, referred to as anhydrobiosis. For successful anhydrobiosis, the dehydration rate of P. vanderplanki larvae has to be controlled. Here, we desiccated larvae by exposing them to different drying regimes, each progressing from high to low relative humidity, and examined survival after rehydration. In larvae of P. vanderplanki, reactions following desiccation can be categorized as follows: (I) no recovery at all (direct death), (II) dying by unrepairable damages after rehydration (delayed death), and (III) full recovery (successful anhydrobiosis). Initial conditions of desiccation severely affected survival following rehydration, i.e. P. vanderplanki preferred 100% relative humidity where body water content decreased slightly. In subsequent conditions, unfavorable dehydration rate, such as more than 0.7 mg water lost per day, resulted in markedly decreased survival rate of rehydrated larvae. Slow dehydration may be required for the synthesis and distribution of essential molecules for anhydrobiosis. Larvae desiccated at or above maximum tolerable rates sometimes showed temporary recovery but died soon after.     

Photochemical Efficiency of PSⅡand Membrane Lipid Peroxidation in Leaves of indica and japonica Rice (Oryza sativa) Under Chilling Temperature and Strong Light Stress Conditions

Relationships between fluorescence parameters and membrane lipid peroxidation in leaves of indica and japonica rice (Oryza sativa L.) during later growth stage were studied under chilling temperature and strong light stress conditions. Results showed that D1 protein contents of PSⅡ in photosynthetic app aratus dropped, the generation of antheraxanthin (A) and zeaxanthin (Z)of xanthophyll cycle were inhibited partly, PSⅡ photochemical efficiency （Fv/Fm）and non photochemical quenching (qN) were also decreased obviously. In addition, endogenous active oxygen scavenger—superoxide dismutase (SOD) reduced, superoxide anion radical (O[SX(B-*3)-[]·[SX]]2) and malondialdehyde (MDA) accumulated, as a result, photooxidation of leaves occurred under chilling temperature and strong light stress conditions. Obvious differences in the changes of the above mentioned physiological parameters between indica and japonica rice were observed. Experiments in leaves treated with inhibitors under chilling temperature and strong light conditions showed that indica rice was more sensitive to chilling temperature with strong light and subjected to photooxidation more than japonica rice. Notable positive correlation between D1 protein contents and Fv/Fm or (A+Z)/(A+Z+V), and a marked negative correlation between Fv/Fm and MDA contents were obtained by regression analysis in indica and japonica rice during chilling temperature and strong light conditions. According to the facts mentioned above, it was inferred that PSⅡ photochemical efficiency（Fv/Fm） was the key index to forecast for the prediction of photooxidation under stress circumstances and the physiological basis were the synthetic capacity of D1 protein and the protection of xanthophyll cycle.     

Three-stage Transformation of Chlorophyll Transient Fluorescence Pattern Under Sustained Dehydration and the Discovery of Critical Water Content in Seaweeds (in English)

The chlorophyll fluorescence kinetics of marine red alga Grateloupia turuturu Yamada, green alga Ulva pertusa Kjellm and brown alga Laminaria japonica Aresch during natural sustained dehydration were monitored and investigated. The pulse amplified modulation (PAM) system was used to analyze the distinct fluorescence parameters during thallus dehydration. Results proved that the fluorescence kinetics of different seaweed all showed three patterns of transformation with sustained water loss. These were: 1) peak kinetic pattern (at the early stage of dehydration fluorescence enhanced and quenched subsequently, representing a normal physiological state). 2) plateau kinetic pattern (with sustained water loss fluorescence enhanced continuously but quenching became slower, finally reaching its maximum). 3) Platform kinetic pattern (fluorescence fell and the shape of kinetic curve was similar to plateau kinetic pattern). A critical water content (CWC) could be found and defined as the percentage of water content just prior to the fluorescence drop and to be a significant physiological index for evaluation of plant drought tolerance. Once thallus water content became lower than this value the normal peak pattern can not be recovered even through rehydration, indicating an irreversible damage to the thylakoid membrane. The CWC value corresponding to different marine species were varied and negatively correlated with their desiccation tolerance, for example. Laminaria japonica had the highest CWC value (around 90%) and the lowest dehydration tolerance of the three. In addition, a fluorescence “burst” was found only in red algae during rehydration. The different fluorescence parameters Fo , Fv and Fv/ Fm were measured and compared during water loss. Both Fo and Fv increased in the first stage of dehydration but Fv / Fm kept almost constant. So the immediate response of in vivo chlorophyll fluorescence to dehydration was an enhancement. Later with sustained dehydration Fo increased continuously while Fv decreased and tended to become smaller and smaller. The major changes in fluorescence (including fluorescence drop during dehydration and the burst during rehydration) were all attributed to the change in Fo instead of Fv . This significance of Fo indicates that it is necessary to do more research on Fo as well as on its relationship with the state of thylakoid membrane.