低夜温后不同光强对榕树叶片PSⅡ功能和光能分配的影响

研究了自然低夜温后全光照与遮荫对榕树叶片PSⅡ功能及光能分配的影响。结果表明低夜温后全光照条件下叶片吸收光能分配于光化学反应部分减少,而热耗散部分和反应中心过剩光能则增加,从而导致了PSⅡ功能的下降,遮荫条件下光能分配于光化学反应的程度增加．虽然用于热耗散的比例下降了,但反应中心过剩光能相对较少,从而有利于PSⅡ功能的恢复。     

长柄双花木光合功能对光强的适应

在光强较高的纯林和阔叶林内,长柄双花木净光合速率呈“双峰曲线”,并伴随有胞间CO2的下降和气孔限制值的增大;随着日间光强的增大,叶片PQ还原程度和非光化学猝灭（NPQ）增加,ΦPSⅡ则下降,但后者午后随着光强的下降可得到完全恢复;叶片吸收光能分配于光化学反应的比例随着光强的增大而迅速减少;而天线色素热耗散部分及反应中心过剩的光能则显著增加,在午后光强减弱后两者均可恢复到早晨的初始水平。在低照度光的竹林内,净光合速率呈现“单峰曲线”,叶片PQ还原程度、NPQ以及ΦPSⅡ均无明显变化,叶片吸收光能也主要用于光化学反应,热耗散及过剩光能比例均较低。     

两种杜鹃花属植物对长期遮阴后全光照环境的生理响应及其光保护机制

植物通过提高光能利用能力和光保护途径以响应环境光强的增加, 但不同植物对环境光强增加的生理响应存在差异, 从而导致植物对光环境的适应性不一致。为探讨植物对光环境变化的生理响应及其适应机制, 该文以遮阴条件下培养1年的2种杜鹃属(Rhododendron)植物比利时杜鹃(R. hybrida)和杜鹃(R. simsii)为材料, 对其由遮阴后转入全光照下培养5天时的叶片叶绿素荧光参数及其快速光曲线变化进行了比较研究, 以期从叶片吸收光能分配和光保护机制的角度探讨这2种植物对光环境变化的适应机制。结果表明: 全光照降低了喜阴植物比利时杜鹃叶片的光化学反应和热耗散能力, 且其吸收光能分配于光化学反应和调节性能量耗散部分的比例减少, 导致光系统II反应中心过量激发能积累, 造成了叶片光抑制甚至光破坏。杜鹃作为耐阴喜光植物对光环境变化具有较强的适应性, 具有较高的光化学反应、热耗散和环式电子传递能力等内在生理特性; 在遮阴和全光照两种光环境下均能维持较高的吸收光能在光化学反应和调节性能量耗散部分的分配比例, 从而保护了光合机构的正常运行, 是其全光照强光未造成叶片光抑制的原因。     

遮阴对绣球光合特性和叶绿素荧光参数的影响北大核心CSCD

为了从光合作用机制及叶片吸收光能分配的角度解释绣球(Hydrangea macrophylla)对不同光环境的适应机制,探讨绣球对光环境变化的生理响应和适应性,该文以盆栽的绣球品种‘无尽夏新娘’为材料,设置遮阴(遮光率为50%、75%)两种处理,并以全光照为对照,经过60天的处理,测定其光合-光响应曲线、气体交换参数、叶绿素荧光参数。结果表明:遮阴60天后,绣球的暗呼吸速率、光补偿点和光饱和点均有所下降,而表观量子效率(AQY)上升,说明绣球能够通过这些途径提高对弱光的利用能力并降低呼吸消耗,以维持植株正常生长,从而表现出了极强的适应能力;在50%的遮阴处理下,绣球叶片的净光合速率、胞间CO2浓度、蒸腾速率和水分利用效率均与其全光照和75%遮阴处理下差异显著;遮阴导致光系统II(PSII)最大光化学效率(Fv/Fm)增加,3种光照处理下呈显著差异,全光照下Fv/Fm低于50%遮阴处理,初始荧光水平高于50%遮阴处理,推断此条件下的绣球叶片发生了光抑制;而随着光照的减弱,非光化学淬灭系数在降低,说明遮阴降低了绣球叶片PSII天线色素吸收光能以热的形式耗散的比例,绣球叶片吸收的能量约70%用于热耗散,约20%用于非光化学反应,仅有4%的能量用于光化学反应,说明绣球处于饱和光环境下时,主要通过提高叶片吸收光能向热耗散等PSII调节性能量耗散途径的分配,削弱反应中心过量激发能的积累。     

遮阴对绣球光合特性和叶绿素荧光参数的影响

为了从光合作用机制及叶片吸收光能分配的角度解释绣球(Hydrangea macrophylla)对不同光环境的适应机制,探讨绣球对光环境变化的生理响应和适应性,该文以盆栽的绣球品种‘无尽夏新娘’为材料,设置遮阴(遮光率为50%、75%)两种处理,并以全光照为对照,经过60天的处理,测定其光合-光响应曲线、气体交换参数、叶绿素荧光参数。结果表明:遮阴60天后,绣球的暗呼吸速率、光补偿点和光饱和点均有所下降,而表观量子效率(AQY)上升,说明绣球能够通过这些途径提高对弱光的利用能力并降低呼吸消耗,以维持植株正常生长,从而表现出了极强的适应能力;在50%的遮阴处理下,绣球叶片的净光合速率、胞间CO2浓度、蒸腾速率和水分利用效率均与其全光照和75%遮阴处理下差异显著;遮阴导致光系统II(PSII)最大光化学效率(Fv/Fm)增加,3种光照处理下呈显著差异,全光照下Fv/Fm低于50%遮阴处理,初始荧光水平高于50%遮阴处理,推断此条件下的绣球叶片发生了光抑制;而随着光照的减弱,非光化学淬灭系数在降低,说明遮阴降低了绣球叶片PSII天线色素吸收光能以热的形式耗散的比例,绣球叶片吸收的能量约70%用于热耗散,约20%用于非光化学反应,仅有4%的能量用于光化学反应,说明绣球处于饱和光环境下时,主要通过提高叶片吸收光能向热耗散等PSII调节性能量耗散途径的分配,削弱反应中心过量激发能的积累。     

不同生态习性热带雨林树种的幼苗对光能的利用与耗散

研究了生长于100％、25％和8％光照条件下的热带雨林先锋树种团花、演替顶极阶段的冠层树种绒毛番龙眼和中下层树种滇南风吹楠幼苗的光合能力及光能分配特性对光强的响应。与绒毛番龙眼和滇南风吹楠相比,团花具有较高的最大光合速率和最大电子传递速率,从光能分配对光强的响应曲线可以看出,随着光强的增加,3个树种幼苗叶片吸收的光能分配到光化学反应的比例减少,分配到热耗散的比例增加,光能在光化学反应与热耗散之间的分配呈显著负相关,与其它两个种相比,100％光下的团花幼苗将较多的光能分配到光化学反应中,热耗散较弱且未达到饱和。过剩光能少,没有引起长期光抑制,绒毛番龙眼和滇南风吹楠将叶片吸收的较多光能分配到热耗散中,但生长于100％光下的幼苗过剩光能仍然较多,导致幼苗遭受长期光抑制,结果表明,不同生态习性热带雨林树种幼苗更新对光环境的要求与这些幼苗对光能的利用和耗散特性密切相关。     

遮荫和全光下生长的棉花光合作用和叶绿素荧光特征

 遮荫条件下（遮荫下光强相当于自然光强的40％左右）棉花(Gossypium hirsutum)叶片光合速率明显降低,仅为自然光强下生长叶片的30%～40％,叶片中RuBP羧化酶活性降低,而表观量子效率(AQY)较高。不同光照条件下生长的棉花叶片对短时间持续光强的光合诱导过程有明显的差异,由弱光转到强光下,自然光强下生长的叶片的Pn、Gs、ΦPSⅡ及非光化学猝灭系数(NPQ)都能在较短的时间内达到最大值,而遮荫叶片需要的时间较长;遮荫下生长的棉花叶片的实际光化学效率,随光强的增加下降幅度较大,而自然光照下生长的叶片下降幅度较小;自然光照下生长的叶片的NPQ随光强的升高达到较高水平,而遮荫叶片在较低的光强下即达到最大值,此时NPQ较低,遮荫叶片依赖于叶黄素循环的能量耗散水平较低。遮荫叶片较低的光合速率以及过剩光能耗散能力是其转入自然强光后光抑制严重的主要原因。     

缺铁使大豆叶片激发能的耗散增加

缺铁叶片的光合速率大幅度下降。这种降低可能不是色素含量降低的结果 ;而且缺铁对PSII复合物的活性影响很小 ;较高的PQ还原程度显示缺铁叶片PSII受体侧电子传递受阻 ,这可能是导致光合速率下降的主要因素。强光下缺铁叶片的天线转化效率比正常叶片低 ,用于光化学反应的激发能很少。缺铁导致大豆叶片激发能耗散增加。通过抑制剂处理和叶黄素组分的分析 ,可以认为在耗散过剩激发能的过程中 ,缺铁叶片充分启动了叶黄素循环     

遮荫对异株荨麻光合特性和荧光参数的影响

系统研究了全光照和不同程度的遮荫(43%,58%,73%,87%,97%)对异株荨麻光合特性和荧光参数的影响。结果表明,异株荨麻的光补偿点和光饱和点均较低,且随着遮荫程度的提高,其值以及暗呼吸速率均依次降低。净光合速率日变化曲线呈单峰型,光合速率高峰值和日平均光合速率均随着遮荫程度的提高而明显下降。蒸腾速率和气孔导度的日变化与光合速率的日变化趋势一致,遮荫对蒸腾作用和气孔导度均有显著的影响,随着遮荫程度的提高,蒸腾速率和气孔导度均显著下降。在各光照条件下,蒸腾速率与气孔导度呈显著正相关。蒸腾速率和气孔导度与光合速率的相关性随遮荫条件的不同而异,全光照条件下蒸腾速率与光合速率呈显著正相关,而所有遮荫条件下相关性不显著。气孔导度与光合速率在所有光照下相关性均不显著。各遮荫条件下叶片总叶绿素、叶绿素a、叶绿素b含量均显著高于全光照的,且随遮荫程度的提高叶绿素含量呈上升趋势,而叶绿素a/b的值则随着遮荫程度的提高而下降。叶绿素荧光参数PSⅡ内禀光能转化效率(Fv/Fm)和潜在活性(Fv/Fo)日变化呈单谷曲线。各遮荫条件下Fv/Fm和Fv/Fo值均高于全光照的,且随着遮荫程度的提高其值均依次增加。这说明,异株荨麻是一种耐荫性很强的植物,遮荫可使其降低光补偿点、光饱和点、净光合速率、暗呼吸速率以及叶绿素a/b,但增加总叶绿素、叶绿素a、叶绿素b含量、光能利用率以及PSⅡ原初光能转化效率和潜在活性,以增强在弱光条件下的生长发育能力。     

弱光胁迫影响夏玉米光合效率的生理机制初探

大田条件下, 以普通夏玉米(Zea mays) ‘泰玉2号’为材料, 于授粉后1-20天遮光55% (+S), 以大田自然光照条件下生长的玉米作为对照(-S), 研究了遮光及恢复过程中玉米植株的光合性能、叶绿体荧光参数、叶黄素循环以及光能分配的变化, 初步揭示夏玉米开花后弱光条件下光适应的生理机制, 为玉米高产稳产提供理论依据。结果表明, 遮光后玉米穗位叶叶绿素含量及可溶性蛋白含量均减少, RuBP羧化酶和PEP羧化酶活性显著降低, 导致穗位叶净光合速率(P_n)迅速下降, 光饱和点也明显降低; 恢复初期P_n迅速升高, 光合关键酶活性有所增强。遮光后植株的最大光化学效率(F_v/F_m)、实际光化学效率(Ф_PSII)显著降低, 非光化学淬灭(NPQ)则显著升高, 而恢复初期植株穗位叶Ф_PSII有所升高, 表明突然暴露在自然光下的光合电子传递速率明显加快, 这与其光合速率及光合酶活性的趋势保持一致; 遮光处理对穗位叶叶黄素循环库的大小(紫黄质+花药黄质+玉米黄质(V + A + Z))影响不显著, 但使叶黄素循环的脱环氧化状态(A + Z)/(V + A + Z)增加; 遮光后植株分配于光化学反应的光能明显减少, 天线耗散光能比率显著增加, 恢复过程中植株主要以过剩非光化学反应的形式耗散过剩的光能。遮光后及恢复初期, 玉米植株的PSII原初光化学活性明显下降, 限制了光合碳代谢的电子供应从而抑制了光合作用, 主要依赖叶黄素循环途径进行能量耗散, 而在光照转换后遮光的玉米叶片在适应自然光过程中的光保护机制不断完善, 光合能力逐渐得到 恢复。     

Geometrical similarity analysis of photosynthetic light response curves, light saturation and light use efficiency

Light absorption and use efficiency (LAUE mol mol⁻¹, daily gross photosynthesis per daily incident light) of each leaf depends on several factors, including the degree of light saturation. It is often discussed that upper canopy leaves exposed to direct sunlight are fully light-saturated. However, we found that upper leaves of three temperate species, a heliophytic perennial herb Helianthus tuberosus, a pioneer tree Alnus japonica, and a late-successional tree Fagus crenata, were not fully light-saturated even under full sunlight. Geometrical analysis of the photosynthetic light response curves revealed that all the curves of the leaves from different canopy positions, as well as from the different species, can be considered as different parts of a single non-rectangular hyperbola. The analysis consistently explained how those leaves were not fully light-saturated. Light use optimization models, called big leaf models, predicted that the degree of light saturation and LAUE are both independent of light environment. From these, we hypothesized that the upper leaves should not be fully light-saturated even under direct sunlight, but instead should share the light limitation with the shaded lower-canopy leaves, so as to utilize strong sunlight efficiently. Supporting this prediction, within a canopy of H. tuberosus, both the degree of light saturation and LAUE were independent of light environment within a canopy, resulting in proportionality between the daily photosynthesis and the daily incident light among the leaves.     

Blue light regeneration of bacteriorhodopsin bleached by continuous light

Photobleaching of bacteriorhodopsin (BR) by continuous light has recently been demonstrated. This bleaching consists of at least two subsequent product states. One of them is absorbing maximally in the blue spectral region. Our present study shows that upon illumination of the bleached sample with blue light a back photoprocess appears, resulting in regeneration of the original BR state. From a technical point of view, the observed phenomenon is similar to the reverting effect of blue light on the photocycle. An important difference is that the photobleached state of BR is much more stable than any of the photocycle intermediates, and may provide an advantage for several technical applications.     

Shedding a little light on light chains

Myosin II regulatory light chains have an important role in the organization and function of the contractile machinery at cytokinesis. Two recent reports provide new insights into these important proteins.     

Analysis of light regime in continuous light distributions in photobioreactors

Maximum photobioreactor (PBR) efficiency is a must in applications such as the obtention of microalgae-derived fuels. Improving PBR performance requires a better understanding of the "light regime", the varying irradiance that microalgal cells moving in a dense culture are exposed to. We propose a definition of light regime that can be used consistently to describe the continuously varying light patterns in PBRs as well as in light/dark cycles. Equivalent continuous and light/dark regimes have been experimentally compared and the results show that continuous variations are not well represented by light/dark cycles, as had been widely accepted. It has been shown that a correct light regime allows obtaining photosynthetic rates higher than the corresponding to continuous light, the so-called "flashing light effect" and that this is possible in commercial PBRs. A correct PBR operation could result in photosynthetic efficiency close to the optimum eight quanta per O(2).     

Acclimation of Arabidopsis thaliana to the light environment: the existence of separate low light and high light responses

The capacity for photosynthetic acclimation in Arabidopsis thaliana (L.) Heynh. cv. Landsberg erecta was assessed during growth over a broad range of irradiance. Discontinuities in the response to growth irradiance were revealed for the light- and CO2-saturated rate of photosynthesis (Pmax) and the ratio of chlorophyll a to chlorophyll b (Chl a/b). Three separate phases in the response of Pmax and Chl a/b to growth light were evident, with increases at low and high irradiance ranges and a plateau at intermediate irradiance. By measuring all chlorophyll-containing components of the thylakoid membrane that contribute to Chl a/b we reveal that distinct strategies for growth at low and high irradiance underlie the discontinuous response. These strategies include, in addition to changes in the major light-harvesting complexes of photosystem II (LHCII), large shifts in the amounts of both reaction centres as well as significant changes in the levels of minor LHCII and LHCI components.     

Biogenesis and light regulation of the major light harvesting chlorophyll-protein of diatoms

The apoprotein of the major light harvesting pigment-protein complex from the diatom Phaeodactylum tricornutum (UTEX 646) is composed of two similar polypeptides of 17.5 and 18.0 kilodaltons (kD). The in vivo synthesis of these polypeptides is inhibited by the 80s protein synthesis inhibitor cycloheximide, but not by the 70s ribosome inhibitor chloramphenicol. When total poly(A)⁺ RNA was used in in vitro protein synthesis, a number of polypeptides were synthesized with a dominant product at 22 kD. When the polypeptides were immunoprecipitated with monospecific antibodies to the 17.5 and 18.0 polypeptides, a single protein zone of 22 kD was detected. Immunoprecipitation with preimmune serum failed to precipitate detectable levels of protein at any relative molecular weight (M_r). These findings indicate that the two apoprotein polypeptides of the diatom light harvesting pigment-protein are translated from polyadenylated message on cytoplasmic ribosomes as either a single or two (or more) similar M_r precursor proteins. These findings also suggest that this protein is encoded in the nucleus.

Photosynthetic light adaptation features of P. tricornutum UTEX 646 indicate that it responds to low light by increasing cell size and numbers of photosystem I and II reaction centers per cell, but does not change photosynthetic rate per cell or photosynthetic unit sizes significantly. When low light cells are exposed to higher photon flux densities, the in vivo incorporation of label into the apoprotein of the light harvesting complex decreases. In contrast, high light grown cells show rapid (<3 hour) increases in apoprotein synthesis when exposed to low light levels. This is the first demonstration of a specific role of photon flux density in regulating the synthesis of a major light harvesting pigment-protein during photosynthetic light adaptation.

     

Neuroendocrine effects of light

The light/dark cycle to which animals, and possibly humans, are exposed has a major impact on their physiology. The mechanisms whereby specific tissues respond to the light/dark cycle involve the pineal hormone melatonin. The pineal gland, an end organ of the visual system in mammals, produces the hormone melatonin only at night, at which time it is released into the blood. The duration of elevated nightly melatonin provides every tissue with information about the time of day and time of year (in animals that are kept under naturally changing photoperiods). Besides its release in a circadian mode, melatonin is also discharged in a pulsatile manner; the physiological significance, if any, of pulsatile melatonin release remains unknown. The exposure of animals including man to light at night rapidly depresses pineal melatonin synthesis and, therefore, blood melatonin levels drop precipitously. The brightness of light at night required to depress melatonin production is highly species specific. In general, the pineal gland of nocturnally active mammals, which possess rod-dominated retinas, is more sensitive to inhibition by light than is the pineal gland of diurnally active animals (with cone-dominated retinas). Because of the ability of the light/dark cycle to determine melatonin production, the photoperiod is capable of influencing the function of a variety of endocrine and non-endocrine organs. Indeed, melatonin is a ubiquitously acting pineal hormone with its effects on the neuroendocrine system having been most thoroughly investigated. Thus, in nonhuman photoperiodic mammals melatonin regulates seasonal reproduction; in humans also, the indole has been implicated in the control of reproductive physiology.Summary of a Plenary Lecture presented by the author in Vienna, August, 1990