黄瓜幼苗子叶在低温下的光抑制及其恢复

用ＰＡＭ脉冲调制荧光仪测定叶绿素荧光的变化研究了黄瓜幼苗子叶在ＰＦＤ为５０和１００μｍｏｌｍ＾－２Ｓ＾－１,温度为４、７、１０、１５℃下 挑抑制及其恢复。结果表明,黄瓜幼苗子叶Ｆｖ／Ｆｍ随着温度的下降和ＰＦＤ的增加而下降,并且增加等量的ＰＦＤ在４℃下比在１０℃下引起更大的Ｆｖ／Ｆｍ下降。在黑暗条件下光抑制有轻微恢复,但完全发电和需光照,且恢复起始时的光照十分重要。     

黄瓜幼苗的冷锻炼与低温引起的光抑制

黄瓜幼苗的冷锻炼与低温引起的光抑制李晓萍,陈贻竹,李平,郭俊彦（中国科学院华南植物研究所,广州５１０６５０）关键词：低温引起的光抑制,荧光猝灭,冷锻炼,黄瓜幼苗低温使植物利用光能的能力降低从而引起或加剧光抑制（ｈａｓ等１９８３）。在光抑制中常以叶绿素...     

低温与光对黄瓜幼苗子叶光合电子传递活性的影响

25～30℃和30 μmol m~(-2)s~(-1)光下培养的黄瓜幼苗,在黑暗下经 1～7℃处理24h或5℃处理24～72h,光合电子传递活性受不同程度的抑制;其抑制部位主要在PSⅡ氧化侧;随温度的降低和时间的延长,抑制部位可发展至PSⅡ及之后的电子递体上,但尚未影响PSⅠ的活性。160μmol m~(-2)s~(-1)的光强加重低温对电子传递活性的抑制,光强越高,则加重的程度越高;抑制部位从PSⅡ氧化侧发展至PSⅡ反应中心以及PSⅠ。     

低温对黄瓜幼苗子叶光合强度和叶绿素荧光的影响

低温胁迫时间延长和低温胁迫强度增加,黄瓜幼苗子叶光合速率和Chl荧光递减。高氧浓度可加剧低温下光合速率和Chl荧光的降低,相反,这种降低可被抗氧化剂抑制。低温下光合速率和Chl荧光的递减与子叶电解质泄漏和丙二醛(MDA)含量的递增呈一定的负相关。     

冷锻炼对甜椒叶片光合作用及其低温光抑制的影响

以冷敏感植物甜椒 (CapsicumannuumL .)抗冷性不同的两个品种为试材 ,利用CIRAS 1光合测定系统和FMS2调制式荧光仪 ,在控温控光条件下分析比较了冷锻炼苗与未经锻炼苗的叶片光合特性、叶绿素荧光参数对温度的响应。结果表明 ,随着温度的降低 ,无论是否经过锻炼 ,低温主要通过抑制碳同化能力来影响光合作用 ,并使光能过剩 ,导致低温光抑制。提高环境CO2 浓度以增强暗反应对光能的利用 ,低温光抑制减轻。 5d的亚适温锻炼过程中甜椒叶片已发生一定程度的光抑制 ,但锻炼苗叶片能在低温下维持较高的光系统II光化学效率(ФPSII)、光化学猝灭系数 (qP)和光适应下光系统II最大光化学效率 (Fv′/Fm)值 ;冷锻炼提高了两品种低温下对光抑制的抗性 ,而且对抗冷品种的作用效果更明显     

低温光抑制恢复过程中黄瓜叶片PSⅡ活性及其电子传递对PSⅠ的影响

以“津春4号”黄瓜为试材,通过测定黄瓜叶片叶绿素荧光快速诱导动力学曲线和对820 nm光的吸收曲线,结合叶绿素荧光淬灭分析,研究低温光胁迫(4℃,200 μmol·m-2·s-1)6 h后,黄瓜叶片在常温(25℃)不同光强(0、15、200μmol·m-2·s-1)下PS Ⅰ和PS Ⅱ活性的恢复,以及恢复过程中PS Ⅰ与PS Ⅱ的相互作用.结果表明:低温光胁迫6h后,PS Ⅰ和PS Ⅱ发生不同程度的光抑制.在常温恢复阶段,PS Ⅱ活性快速恢复且对光强不敏感;PS Ⅰ活性在弱光下(15 μmol·m-2·s-1)快速恢复,在较强光(200 μmol·m-2·s-1)下恢复较慢.在低温光抑制恢复过程中,常温下PS Ⅱ活性恢复较快可能导致PS Ⅱ向PS Ⅰ的线性电子传递过快,进而抑制PS Ⅰ的活性恢复.因此,在进行黄瓜抗冷性育种时,不应该仅追求较高的PS Ⅱ抗性和较快的PS Ⅱ恢复速度,还应该注意两个光系统活性的协调.在生产中,应当在低温逆境发生及其之后较长一段时间内采取措施降低叶表面光照强度,以利于对植株光合机构的保护和光合活性的恢复.     

低温下壳聚糖处理对黄瓜幼苗生理生化特性的影响

50 mg/L的壳聚糖处理减轻了低温对黄瓜幼苗膜的伤害,低温(6℃)处理4 d后,幼苗膜透性和MDA含量明显低于对照,并且显著减缓了低温导致的光合速率、实际光化学效率(ФPS Ⅱ)、光化学猝灭系数(qP)和1光系数(F’v /Em’)的下降;同时,处理使抗氧化酶SOD、POD、CAT和APX活性提高,可溶性蛋白和脯胺酸含量增加.因此,壳聚糖处理增强了黄瓜幼苗的抗冷性,保护了膜系统,提高了活性氧清除能力,减轻了低温对光合机构的破坏.     

低温弱光处理及恢复期间黄瓜叶片的光抑制与类囊体膜中脂肪酸组成的变化

低温导致黄瓜叶片严重的光抑制,同时类囊体膜不饱和脂肪酸含量下降.低温弱光处理后恢复期间,Vv/Fm和多聚不饱和脂肪酸含量都迅速恢复,暗示两者之间可能有一定的联系.     

水淹对水芹叶片结构和光系统II光抑制的影响

通过探讨在水淹条件下水芹(Oenanthe javanica)叶片结构的变化以及出水对其光系统II功能和光抑制的影响, 阐明水芹光合机构在水淹条件下及出水后死亡的可能原因。结果表明: 水淹条件下新生沉水功能叶光系统II(PSII)最大光化学效率(Fv/Fm) 、电子传递活性与对照叶片差异很小, 但水淹使气生功能叶的Fv/Fm显著降低; 植株总生物量呈负增长趋势; 活体弱光条件下, 沉水叶出水后2小时叶片相对含水量(RWC)和Fv/Fm无显著变化; 中等光强和强光条件下其RWC和Fv/Fm迅速降低; 离体条件下, 5小时的中等光强对沉水叶的Fv/Fm影响不显著, 在随后的弱光下能恢复到出水时的初始状态; 强光能使沉水叶的Fv/Fm大幅降低, 且弱光下不能恢复到出水时的初始水平; 在解剖结构上, 水芹沉水叶的叶片总厚度、上下表皮厚度和气孔大小都显著低于气生叶, 而且沉水叶没有明显的栅栏组织分化, 但是沉水叶上表皮的气孔密度显著高于气生叶。研究结果表明, 水淹使水芹原气生叶PSII功能迅速衰退, 但对新生沉水叶片影响很小。水芹植株出水后, 沉水叶片结构变化使其在光下保水能力下降, 而强光导致了光合机构的光抑制和反应中心失活。田间条件下两者共同作用则加剧了对叶片光合机构的破坏, 进而致使其死亡。     

低温胁迫对以野生黄瓜(棘瓜)为砧木的黄瓜嫁接苗生理生化指标的影响

在5℃低温胁迫条件下,对以野生黄瓜——棘瓜(Sicyos angulatus L．)和以黑籽南瓜为砧木的黄瓜嫁接苗以及自根苗的抗冷性生理生化指标的变化规律作了研究。结果表明,以棘瓜为砧木的黄瓜嫁接苗叶片的SOD、POD、CAT活性以及Pro、可溶性糖含量均高于后两者,MDA含量低于后两者。说明利用棘瓜嫁接的黄瓜苗可以忍受更长时间或更大强度的低温。     

Photoinhibition and recovery of photosynthesis in intact barley leaves at 5 and 20°C

Photoinhibition of photosynthesis and its recovery were studied in intact barley ( Hordeum vuigare L. cv. Gunilla) leaves grown in a controlled environment by exposing them to two temperatures, 5 and 20°C, and a range of photon flux densities in excess of that during growth. Additionally, photoinhibtion was examined in the presence of chloramphenicol (CAP, an inhibitor of chloroplast protein synthesis) and of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). Susceptibility to photoinhibition was much higher at 5 than at 20°C. Furthermore, at 20°C. CAP exacerbated photoinhibition strongly, whereas CAP had little additional effect (10%) at 5°C. These results support the model that net photoinhibition is the difference between the inactivation and repair of photosystem II (PSII); i.e. the degradation and synthesis of the reaction centre protein, Dl. Furthermore, the steady-state extent of photoinhibition was strongly dependent on temperature and the results indicated this was manifested through the effects of temperature on the repair process of PSII. We propose that the continuous repair of PS II at 20°C conferred at least some protection from photoinhibition. At 5°C the repair process was largely inhibited, with increased photoinhibition as a consequence. However, we suggest where repair is inhibited by low temperature, some protection is alternatively conferred by the photoinhibited reaction centres. Providing they are not degraded, such centres could still dissipate excitation energy non-radiatively, thereby conferring protection of remaining photochemically active centres under steady-state conditions.
A fraction of PS II centres were capable of resisting photoinhibition when the repair process was inhibited by CAP. This is discussed in relation to PS II heterogeneity. Furthermore, the repair process was not apparently activated within 3 h when barley leaves were transferred to photoinhibitory light conditions at 20°C.     

低温光照下与黄瓜子叶叶绿素降低有关的酶促反应

黄瓜子叶在低温光照下处理时,随着时间的延长,Chl含量和CAT活性显著下降,POD和AsA-POD在开始24h活性亦有下降趋势,随后POD活性显著增加,而AsA-POD活性仅稍有提高。Chl含量的减少和CAT活性降低之间呈正相关,与POD活性的增加呈负相关。低温、光照处理的黄瓜子叶内Chl的降低可被亚胺环己酮(CHM)延缓,被AsA、Vit E、没食子酸丙酯(PG)和DCMU抑制,但被H_2O_2,乙醇酸钠和甲基紫精(MV)加速。     

钙对亚适温弱光下黄瓜幼苗Ca2+分布及叶绿素荧光参数的影响

以'津优3号'黄瓜幼苗为试验材料,采用焦锑酸钙沉淀的电镜细胞化学方法,研究了CaCl2预处理对亚适温(昼/夜18℃/12℃)弱光(100 μmol·m-2·s-1)下黄瓜幼叶细胞中Ca2+分布、Ca2+-ATP酶活性及叶绿素荧光参数的影响.结果显示:正常温光条件(CK)下,黄瓜幼叶细胞Ca2+主要存在于液泡和液泡膜上,细胞质中含量较低;经亚适温和弱光处理7 d后,叶片细胞质和细胞膜中形成较大的钙沉淀颗粒,液泡中的Ca2+颗粒聚集成团,膜组织边缘模糊,Ca2+-ATPase活性降低;胁迫前用CaCl2预处理的细胞质中Ca2+颗粒略有增加,且分布较均匀,膜组织完整,Ca2+-ATPase活性与CK差异不显著;而经LaCl3、EGTA和CPZ预处理的Ca2+多呈大颗粒状聚积在细胞质、液泡膜或细胞壁上,Ca2+-ATPase活性大幅度下降.在7 d亚适温弱光处理后,各处理黄瓜叶片的Fv/Fm变化不大,而ΦPSⅡ、qP和ETR显著降低;与水预处理相比,叶片ΦPSⅡ、qP和ETR在CaCl2处理下显著增加,而在EGTA和CPZ处理下显著减小,LaCl3处理的无显著变化.研究表明,亚适温弱光处理能打破黄瓜幼苗细胞内的Ca2+平衡,使其膜组织受到一定程度破坏;CaCl2可维持胞内较高的Ca2+-ATP酶活性,保持Ca2+平衡,保护细胞膜组织结构完整,并参与了光合作用光能捕获和光合效率的调控,能有效减轻亚适温弱光对黄瓜幼苗光合作用的不良影响.     

Factors Limiting Photosynthetic Recovery in Sweet Pepper Leaves After Short-Term Chilling Stress Under Low Irradiance

The effects of chilling treatment (4 °C) under low irradiance, LI (100 mol m^–2 s^–1) and in the dark on subsequent recovery of photosynthesis in chilling-sensitive sweet pepper leaves were investigated by comparing the ratio of quantum yields of photosystem (PS) 2 and CO₂ assimilation, _PS2/_CO2, measured in normal air (21 % O₂, NA) and low O₂-air (2% O₂, LOA), and by analyzing chlorophyll (Chl) a fluorescence parameters. Chilling treatment in the dark had little effect on F_v/F_m and _PS2/_CO2, but it caused the decrease of net photosynthetic rate (P _N) under saturating irradiance after 6-h chilling treatment, indicating that short-term chilling alone did not induce PS2 photoinhibition. Furthermore, photorespiration and Mehler reaction also did not obviously change during subsequent recovery after chilling stress in the dark. During chilling treatment under LI, there were obvious changes in F_v/F_m and _PS2/_CO2, determined in NA or LOA. F_v/F_m could recover fully in 4 h at 25 °C, and _PS2/_CO2 increased at the end of the treatment, as determined in both NA and LOA. During subsequent recovery, _PS2/_CO2 in LOA decreased faster than in NA. Thus the Mehler reaction might play an important role during chilling treatment under LI, and photorespiration was an important process during the subsequent recovery. The recovery of PN under saturating irradiance determined in NA and LOA took about 50 h, implying that there were some factors besides CO₂ assimilation limiting the recovery of photosynthesis. From the progress of reduced P700 and the increase of the Mehler reaction during chilling under LI we propose that active oxygen species were the factors inducing PS1 photoinhibition, which prevented the recovery of photosynthesis in optimal conditions because of the slow recovery of the oxidizable P700.