植物光破坏防御机制研究进展

光破坏防御机制是植物为应对复杂多变的自然环境而产生的保护措施,这些措施从形态、生理和生化等方面反映了植物对环境的适应能力。本文根据光抑制的机理,对近年来植物的光破坏防御机制以及高等植物叶黄素循环机制的研究现状进行综述,认为叶黄素循环防御机制是植物光保护作用的重要措施之一。     

光合作用光抑制的研究进展

概述了植物光合作用光抑制的研究进展,包括造成光抑制和光氧化的活性氧的产生和作用机理,光抑制的作用部位,以及光保护机制等,着重从三个方面讨论了植物抗光抑制的保护机理：与光系统Ⅱ天线以及叶黄素循环相关的热耗散途径,包括光呼吸、H2O-H2O循环和环式电子传递在内的电子传递途径,以及活性氧清除机制等。     

光合作用光抑制的研究进展

概述了植物光合作用光抑制的研究进展,包括造成光抑制和光氧化的活性氧的产生和作用机理,光抑制的作用部位,以及光保护机制等,着重从三个方面讨论了植物抗光抑制的保护机理：与光系统Ⅱ天线以及叶黄素循环相关的热耗散途径,包括光呼吸、H2O-H2O循环和环式电子传递在内的电子传递途径,以及活性氧清除机制等。     

植物叶片花青素的光破坏防御机制研究进展

植物花青素广泛分布在植物的根、茎、叶、花和果实等器官中,是植物形态建成过程中或响应逆境而产生的一种次生代谢物质.植物叶片中的花青素具有特殊的化学结构和光谱特性,在光破坏防御机制方面发挥了重要的作用,已经成为植物光合生理生态的研究热点.本文综述了近年来植物叶片花青素与光合作用的研究进展,从叶片花青素的分布、光谱特性及其与光合色素的关系等方面说明花青素对植物光合作用的影响,重点介绍了叶片花青素通过光吸收、抗氧化剂和渗透调节等在植物光破坏防御机制方面的作用,展望了今后的主要研究方向     

植物环境响应启动子的诱导元件及转录因子

光、温度、水分等环境因素影响植物的生长发育,植物可以通过启动子中顺式作用元件与转录因子的相互协调作用,对这些信号产生响应,调控基因表达。本文综述了光、温度、水分诱导表达启动子中的顺式作用元件及相关转录因子研究的最新进展,从分子水平上探讨了环境因子诱导的基因表达调控,对研究植物适应环境的机制具有一定的意义。     

紫外诱导植物产生DNA损伤的修复机制

日光中的紫外线可以诱导生物体的DNA产生损伤,产生的损伤主要有两种：环丁烷嘧啶二聚体（CPD）和6-4光产物（即6-4嘧啶二聚体）.这些损伤如果不经修复则可能会导致生物体死亡.最近的研究证明,植物可以通过多种途径来修复紫外诱导的DNA损伤,包括6-4光产物和CPD的光修复作用.此外,植物还可以通过一般的核酸切除修复（NER）以及旁路聚合酶（bypass polymerase）来修复损伤.     

光敏色素光转化生理学特性研究进展(英文)

植物主要光受体光敏色素调节植物的多种光调控,使其作出最适宜的光生长,如:光形态建成.光敏色素接受光信号的生物功能基于其红光吸收型(Pr)和具有生理活性的远红光吸收型(Pfr)之间的光可逆式光转化.依据光生物学的标准该转化过程与光合作用相比是一个低能光反应过程,而且其间产生的中间过渡态和光敏色素的亚库可能反过来影响光转化的过程而最终表现出生理功能.在此,主要综述了近年来运用时间分辨动力学特别是差分荧光和光化学,研究光敏色素及其中间过度态光生物物理和光生物化学特性的若干进展,讨论了光信号转导的原初光反应的机理.     

向光素调节植物向光性及其与光敏色素/隐花色素的相互关系

蓝光受体向光素(PHOT1/PHOT2)调节蓝光诱导的植物运动反应, 包括植物向光性、叶绿体运动、气孔运动和叶片伸展等。其中, 向光素介导的植物向光性能够促使植物弯向光源, 确保其以最佳取向捕获光源, 优化光合作用。光敏色素和隐花色素作为光受体也参与植物的向光性调节。该文综述了向光素介导的拟南芥(Arabidopsis thaliana)下胚轴向光弯曲信号转导及其与光敏色素、隐花色素协同作用的分子机制, 以期为改造植物光捕获能力及提高光利用效率提供理论基础。     

植物的向性运动及机理简介

高等植物不能象动物一样自由移动整体的位置 ,但植物体的器官在空间可以产生移动 ,以适应环境的变化 ,这就是植物的运动。高等植物的运动主要有两种类型 :向性运动 (tropicmovement)和感性运动 (nasticmove ment)。植物向性运动是指在刺激方向和诱导所产生运动的方向之间有固定关系的运动。依外界因素的不同 ,向性运动主要包括向光性、向重力性、向触性、向化性和向水性等。向性运动大多是生长性运动 ,是不可逆的运动过程。1　向光性 (Phototropism)植物随光的方向而弯曲的能力称为向光性 ,向光性是植物为捕获更多光能而建立起来的对不良光…     

叶黄素循环及其在光保护中的分子机理研究

植物的生命活动离不开充足的光照 ,但是当光照过强时 ,叶片吸收的光能超过了光合电子传递所需 ,过剩的光能便会对光合器官产生潜在的危害 ,引起光合作用的光抑制或光破坏。依赖于叶黄素循环的热耗散被认为是光保护的主要途径。本文着重介绍近年来有关植物叶黄素循环在酶学方面的分子调控、它的主要功能以及依赖于叶黄素循环的热耗散在光保护中的分子机理等 ,并对需进一步研究的问题作了探讨     

How do insect herbivores cope with the extreme oxidative stress of phototoxic host plants?

Plants of the Asteraceae and Hypericaceae possess secondary compounds that induce photooxidation in insect herbivores that consume them. One of the well-established modes of action of these substances is peroxidation of membrane lipids. Some herbivores counteract these defences by avoidance of light and tissues rich in phototoxins or the ability to detoxify these secondary substances. The cytochrome P-450 polysubstrate monooxygenase systems involved, the metabolic products, and a new putative toxin pump have been described. Dietary antioxidants (β-carotene, vitamin E, ascorbate) are additional defences against phototoxicity. They reduce mortality in herbivores exposed to phototoxins and some specialist herbivores have high constitutive levels. Adapted specialist insects also have higher constitutive levels of superoxide dismutase (SOD) and respond to phototoxins in their diet by the induction of catalase (CAT), glutathione reductase (GR), and increased levels of reduced glutathione (GSH). Artificial inhibition of the enzymes SOD and CAT had little effect on phototoxicity but inhibition of GSH synthesis in herbivores enhanced photooxidative effects of administered phototoxins on lipid peroxidation. While insects have many mechanisms to overcome plant photooxidants, the Asteraceae appear to have adopted a strategy of counterattack. We suggest and provide preliminary evidence that a second group of secondary substances, the sesquiterpene lactones, occurring in the Asteraceae can attack key antioxidant defences to synergise phototoxins. © 1995 Wiley-Liss, Inc.     

Influence of light on plant allelochemicals: A synergistic defense in higher plants

Plant phototoxins are broad-spectrum biocides which adversely affect an array of potential plant enemies, including among others disease-causing pathogens, nematodes, insect herbivores, and competing plant species. Thus far, plants which contain these broad-spectrum allelochemicals have been found to occur in open habitats (i.e., in full sunlight) where a defensive mechanism mediated by light would seem to operate most effectively. The levels of available light in shaded environments, although considerably lower than full sun (1–10% of full sun), are equivalent to the intensities of light used to kill phototoxin-treated insects in laboratory studies. This suggests that phototoxic reactions might mediate important organismal interactions in shaded environments as well. In this study, more than 230 Costa Rican rainforest plants were bioassayed for phototoxic metabolites in an effort to ascertain their prevalence among plants growing in moderate to extreme shade. Microbial bioassays, employing Bacillus cereus (a gram positive bacterium), Escherichia coli (a gram negative bacterium), and Saccharomyces cerevisiae (a yeast) were used to rapidly and sensitively indicate phototoxic action and potential for insecticidal action. Tissue extracts from 12 plant families tested positive for phototoxins. This is the first report of phototoxins occurring in eight of those families (Acanthaceae, Campanulaceae, Gesnariaceae, Loganiaceae, Malpigaceae, Phytolaccaceae, Piperaceae, and Sapotaceae). The presence of phototoxins in rainforest plants suggests that phototoxic plant allelochemicals may function as important defenses in low-light, as well as high-light, environments.     

Food utilization and antioxidant enzyme activities of black swallowtail in response to plant phototoxins

Phototoxic compounds are widely distributed among plant families; due to their ability to bind covalently to DNA or to react with oxygen and generate toxic oxyradicals, these compounds are toxic to a variety of herbivorous organisms. Black swallowtail (Papilio polyxenes) larvae feed exclusively on phototoxic host plants in the Apiaceae and Rutaceae. In this study, we examined the toxicity of four phototoxins—three furanocoumarins and one β-carboline alkaloid—to P. polyxenes, as well as the inducibility of antioxidant enzyme defenses in response to these phototoxins. Neither the furanocoumarins nor the β-carboline alkaloid demonstrated any toxic effect on digestive efficiencies of P. polyxenes in the presence of light; harmine, the alkaloid, did significantly reduce growth and consumption rates. None of the compounds had a significant effect on antioxidant enzyme levels. These findings contrast with those reported in earlier studies for Trichoplusia ni, a generalist noctuid sensitive to both furanocoumarins and β-carboline alkaloids. Greater detoxicative metabolic capabilities, coupled with substantially higher constitutive levels of antioxidant enzyme activity, likely explain at least in part the absence of induced antioxidant enzyme responses in the specialist feeder on phototoxic plants. © 1993 Wiley-Liss, Inc.     

Phototoxicity of plant secondary metabolites: Insect and mammalian perspectives

Phototoxic chemicals produced by plants have been studied in a number of contexts, most notably as protective agents against mammalian and insect herbivores. Although there are commonalities in the responses of these two groups of herbivores to plant phototoxins, there are differences as well. Whereas a greater range of chemical classes has been demonstrated to display phototoxicity against insects, considerably more information is available on symptomology of phototoxicity and mechanisms of action in mammals. The commonalities include alterations in behavior following ingestion, notably photophobia, disruption of integumentary integrity following contact or ingestion, and metabolic detoxification following ingestion, in the case of furanocoumarins involving cytochrome P450 monooxygenases. Not yet known to exist in insects are phototoxin-mediated effects on sensory (particularly visual) systems and phototoxicity resulting from abnormal chlorophyll metabolism. In order to gain greater understanding of the ecological significance of phototoxin-mediated plant defense against both insects and mammals, there is a need for more studies centered on natural associations. © 1995 Wiley-Liss, Inc.     

Action of antioxidant enzymes and cytochrome P-450 monooxygenases in the cabbage looper in response to plant phototoxins

Effects of two biosynthetically distinct plant phototoxins—xanthototoxin, a furanocoumarin, and harmine, a β-carboline alkaloid, which are known to produce toxic oxygen species—on the food utilization efficiencies and enzymatic detoxification systems of the polyphagous cabbage looper. Trichoplusia ni (Lepidoptera: Noctuidae), were studied. Newly molted fifth-instar larvae were allowed 36 h to ingest diets containing these two phototoxins at 0.15% wet weight in the presence of near ultraviolet (UVA). The growth and development of the larvae, as well as the corresponding activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPOX), and glutathione reductase (GR) and the detoxification enzyme cytochrome P-450, were measured. Xanthotoxin reduced rates of relative growth and consumption and efficiencies of conversion of ingested and digested food to biomass. Harmine reduced rates of growth and consumption without affecting efficiencies of conversion. Specific activities of SOD, CAT, GPOX, and GR of whole-body homogenates in the absence of compounds were 0.88 units, 153μmol H₂O₂ decomposed·mg protein^?1·min—¹, 38.3 nmol NADPH oxidized·mg protein^?1·min^?1, and 0.56 nmol NADPH oxidized·mg protein^?1·min^?1, respectively. SOD activity was induced 2.9-fold and 3.8-fold by dietary xanthotoxin and harmine, respectively. CAT and GPOX activities were induced 1.2-fold by harmine only, and GR activity was not changed by either chemical. The P-450 activity toward xanthotoxin in the microsomal fraction of midguts was low (0.15 nmol xanthotoxin metabolized·mg protein^?1·min^?1) and was not induced by xanthotoxin ingestion. These studies indicate that P-450 and antioxidant enzyme systems may be independent but consequential, the induction of antioxidant enzymes by phototoxins occurring when low P-450 activity toward the phototoxin permits the accumulation of oxidative stress from unmetabolized phototoxin, which in turn induces antioxidant enzymes.     

植物杀虫剂研究概况

简要综述不同资源类型的植物杀虫剂,通过其有效成份生物碱类、萜类、黄酮类、精油类、光活化毒素类等物质影响昆虫生长发育及消化系统、呼吸系统、代谢系统、神经肌肉系统等从而达到杀虫的目的。同时对其发展前景提出了展望。     

Antioxidant enzymes as biochemical defenses against phototoxin-induced oxidative stress in three species of herbivorous lepidoptera

Many secondary plant compounds are capable of photoactivation resulting in the production of toxic species of oxygen. One mechanism of defense for insects feeding on phototoxic plants may be the presence of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPOX), and glutathione reductase (GR). The activities of these enzymes were examined in larvae of three lepidoptera: Ostrinia nubilalis, Manduca sexta, and Anaitis plagiata. Highest levels of antioxidant enzyme activity were found in A. plagiata, a specialist feeder on Hypericum perforatum, which contains high levels of the phototoxin hypericin. Larvae of A. plagiata fed leaf discs treated with hypericin exhibited a short-term, concentration-dependent decline in enzyme activity. Longer term studies with A. palgiata fed either the photoxic H. perforatum, or the closely related but non-phototoxic H. calycinum, resulted in increased CAT and GR activity in larvae fed the phototoxic plant whereas SOD activity was not significantly different. These results suggest that CAT and GR may be inducible defenses against phototoxins.     

A qauntitative in vitro assay for the evaluation of phototoxic potential of topically applied materials

A quantitative in vitro method for phototoxic evaluation of chemicals has been developed and validated. The assay uses Saccharomyces cerevisiae, seeded in an agar overlay on top of a plate count agar base. 8-Methoxy psoralen is used as a reference standard against which materials are measured. Activity is quantified by cytotoxicity measured as zones of inhibition. Several known phototoxins (heliotropine, lyral, phantolid, and bergamot oil) and photoallergens (6-methyl coumarin and musk ambrette) are used to validate the assay. An excellent correlation is observed between in vivo studies employing Hartley albino guinea pigs and the in vitro assay for several fragrance raw materials and other chemicals. The in vitro assay exhibits a greater sensitivity from 2–500 fold. For three fragrance oils, the in vitro assay detects low levels of photobiological activity while the in vivo assay is negative. Although the in vitro assay does not discriminate between phototoxins and photoallergens, it can be used for screening of raw materials so that reduction in animal usage can be achieved while maintaining the protection of the consumer.Abbreviations C centigrade - cm centimeter - cm² square centimeter - ml milliliters - mm millimeters - 8-MOP 8-methoxy psoralen - mW milliwatt - nm nanometer - UVA ultraviolet radiation, 320–400 nm The first in a series of research papers on alternatives to animal toxicity studies.     

Colocalization of fluorescent markers in confocal microscope images of plant cells

This protocol describes the steps needed to perform quantitative statistical colocalization on two-color confocal images, specifically of plant cells. The procedure includes a calibration test to check the chromatic alignment of the confocal microscope. A software tool is provided to calculate the Pearson and Spearman correlation coefficients ('Pearson-Spearman correlation colocalization' ImageJ plug-in) across regions of interest within the image. Steps are included to help the user practice using the software. The result is a quantitative estimate of the amount of colocalization in the images. Manual masking takes about 1-15 min per image, depending on the detail required, and calculating the correlation coefficients is almost instantaneous. Examples of suitable dyes for such two-color colocalization include Oregon Green or Alexa Fluor 488 dyes in the green range (excited with 488-nm laser line) and Alexa Fluor 555 dye in the red range (excited with 543-nm laser line).     

Photoinhibition of photosynthesis: effect of O2 and selective excitation of the photosystems in intact Lemna gibba plants

Intact Lemna gibba plants were photoinhibited under anaerobic conditions on illumination with monochromatic light which selectively excited the photosystems. Photoinhibition was less when PS 1 was excited and greatest when mainly PS 2 was excited, which suggests that PS 2 was most damaged by photoinhibition induced in complete absence of O₂ and CO₂.The illumination of plants with monochromatic light exciting PS 1, at different O₂ concentrations (in CO₂ deficient conditions), showed that PS 1 photoinhibition was increased at the low O₂ concentrations. The damage to PS 1 was more evident at 2% O₂ than at the higher O₂ concentrations.CO₂ as well as O₂ at atmospheric concentration, (air), was necessary for complete protection of the plant from photoinhibition when both photosystems were excited either separately or together.Abbreviations I irradiance, photon fluence rate - PCO photosynthetic carbon oxidation cycle - PCR photosynthetic carbon reduction cycle - PS 1 photosystem 1 - PS 2 photosystem 2