In vitro enzymatic chlorophyll catabolism in wheat elicited by cereal aphid feeding

Chlorophyll degradation is a complex phenomenon that often accompanies insect feeding damage to plants. Loss of chlorophyll can be initiated by several reactions, including oxidative bleaching, chlorophyllase activity, and Mg-dechelatase activity. Extracts from the Russian wheat aphid [Diuraphis noxia (Mordvilko)], the bird cherry-oat aphid [Rhopalosiphum padi (L.)], and aphid-infested and uninfested wheat plants were assayed in vitro for activities involved in chlorophyll degradation. Although the initial infestation was the same (10 apterous adults) for both aphid species, D. noxia weight was significantly higher than R. padi after feeding for 12 days. Consequently, D. noxia feeding caused greater fresh leaf weight reduction than R. padi feeding. Chlorophyll degradation assays showed no activity from either D. noxia or R. padi extracts. Plant extract assays showed a significant difference in Mg-dechelatase activity, while no difference was detected in either the chlorophyllase or oxidative bleaching pathways among the aphid-infested or uninfested plant extracts. Diuraphis noxia-infested leaf extracts showed a greater increase of Mg-dechelatase activity than either R. padi-infested or the uninfested plants. The findings suggest that leaf chlorosis elicited by D. noxia feeding is different from the chlorophyll degradation that occurs in natural plant senescence. Aphid-elicited chlorosis might be the result of a Mg-dechelatase-driven catabolism of chlorophyll in challenged wheat seedlings, however, the factor(s) from D. noxia that elicited the increase of Mg-dechelatase activity still remain to be determined.     

Photoinhibition in Chilling Stressed Leguminosae: Comparison of Vicia Faba and Pisum Sativum

The concentrations of photosynthetic pigments decreased in both chilling stressed species but the ratios of chlorophyll (Chl) a/b and total carotenoids (Car)/Chls were depressed only in faba bean. The contents of + carotene and lutein+lutein-5,6-epoxide remained unaffected in both species, but the de-epoxidation state involving the components of xanthophyll cycle increased in pea. Under chilling stress the photosynthetic electron transport associated with photosystem 2, PS2 (with and without the water oxidising complex) decreased in both plant species, the inhibition being higher in faba bean. The intrachloroplast quinone pool also decreased in both stressed species, yet an opposite trend was found for cytochrome b _559LP. Under stress an increasing peroxidation of thylakoid acyl lipids was detected in pea, but higher protein/Chl ratio was detected in faba bean. Thus the acceptor side of PS2 is mostly affected in both chilling stressed species, but faba bean is more sensitive.     

Photosynthetic apparatus in primary leaves of barley seedlings grown under blue or red light of very low photon flux densities

Chlorophyll (Chl) a and Chl b contents, rate of CO₂ gas exchange, quenching coefficients of chlorophyll fluorescence, and endogenous phytohormones have been studied in primary leaves of barley seedlings cultivated under blue (BL) or red (RL) light. Photon flux densities (PFD) were between 0.3 and 12 mol m^-2 s^-1. Plants grown at PFD of 0.3 mol m^-2 s^-1 demonstrated in BL tenfold and in RL threefold decreased Chl content compared to plants grown at 12 mol m^-2 s^-1. Chl a/b ratio increased from 2.3–2.5 to 4.4–4.5 in BL, not in RL, following the decrease in PFD at plant cultivation from 12 to 0.3 mol m^-2 s^-1. Plants cultivated at weak BL demonstrated severalfold decreased rate of photosynthetic CO₂ uptake, whereas decrease in PFD of RL from 12 to 0.3 mol m^-2 s^-1 caused only 20% de cline in the rate of photosynthesis. Decrease in PFD during a plant cultivation reduced the maximum quantum yield of photosynthesis in BL, not in RL leaves. Light response curves of non-photochemical and photochemical quenching of chlorophyll fluorescence calculated on the basis of absorbed quanta were not affected by PFD of RL during plant cultivation. On the contrary, both non-photochemical quenching and accumulation of Q_A ^-, reduced primary acceptor of Photosystem II, occurred at lower amounts of absorbed quanta in leaves of BL plants grown at 0.3 than at 12 mol m^-2 s^-1. Two photoregulatory reactions were suggested to exert the light control of the development of photosynthetic apparatus in the range of low PFDs. The photoregulatory reaction saturating by very low PFDs of RL was supposed to be mediated by phytochrome. Phytochrome was proposed to enhance (as related to other pigment-protein complexes of thylakoids) the accu mulation of chlorophyll- b-binding light-harvesting complex of Photosystem II (LHC II). It acts independently of the pigment mediating the second photoregulatory reaction, as evidenced by the results of experiments with plant growth under mixed blue plus red light. The contents of cytokinins and indole-3-acetic acid in a leaf were not significantly affected by either light quality and PFD thus indicating those phytohormones not to be involved into photoregulatory processes.     

The Effect of Low Growth Temperature on Hill Reaction and Photosystem 1 Activities and Pigment Contents in Maize Inbred Lines and Their F1 Hybrids

Young plants of maize inbred lines CE777, CE704, and CE810 and their F₁ hybrids displaying a positive heterotic effect in various photosynthetic characteristics were exposed to low temperature during their early growth developmental stage. The photochemical activity of isolated mesophyll chloroplasts and the contents of photosynthetic pigments in leaves of stressed and non-stressed plants were compared with the aim to find out the possible changes in the relationship between parents and hybrids, and to determine the genetic basis of heterosis in F₁ generation. Strong decrease in the content of chlorophylls was observed for all genotypes examined when plants were subjected to low growth temperature. Similar change was recorded for Hill reaction activity (HRA) of inbred lines but not of their F₁ hybrids, and no significant response at all was found for photosystem 1 (PS1) activity or the total carotenoids content. The intraspecific variation due to differences between genotypes was found for most of photosynthetic characteristics examined. This variation was caused by the additive and dominance genetic effects. Positive dominance was the main cause of positive heterosis in HRA and in the contents of photosynthetic pigments and was much more pronounced in the stressed plants compared to the non-stressed ones. The maternal additive effects participated in the inheritance of contents of photosynthetic pigments in plants exposed to low temperature, too. This revised version was published online in June 2006 with corrections to the Cover Date.     

Relationships between leaf chlorophyll content and spectral reflectance and algorithms for non-destructive chlorophyll assessment in higher plant leaves

Leaf chlorophyll content provides valuable information about physiological status of plants. Reflectance measurement makes it possible to quickly and non-destructively assess, in situ, the chlorophyll content in leaves. Our objective was to investigate the spectral behavior of the relationship between reflectance and chlorophyll content and to develop a technique for non-destructive chlorophyll estimation in leaves with a wide range of pigment content and composition using reflectance in a few broad spectral bands. Spectral reflectance of maple, chestnut, wild vine and beech leaves in a wide range of pigment content and composition was investigated. It was shown that reciprocal reflectance (R lambda)-1 in the spectral range lambda from 520 to 550 nm and 695 to 705 nm related closely to the total chlorophyll content in leaves of all species. Subtraction of near infra-red reciprocal reflectance, (RNIR)-1, from (R lambda)-1 made index [(R lambda)(-1)-(RNIR)-1] linearly proportional to the total chlorophyll content in spectral ranges lambda from 525 to 555 nm and from 695 to 725 nm with coefficient of determination r2 > 0.94. To adjust for differences in leaf structure, the product of the latter index and NIR reflectance [(R lambda)(-1)-(RNIR)-1]*(RNIR) was used; this further increased the accuracy of the chlorophyll estimation in the range lambda from 520 to 585 nm and from 695 to 740 nm. Two independent data sets were used to validate the developed algorithms. The root mean square error of the chlorophyll prediction did not exceed 50 mumol/m2 in leaves with total chlorophyll ranged from 1 to 830 mumol/m2.     

Acclimation of Two Distinct Plant Species,Spring Barley and Norway Spruce,to Combined Effect of Various Irradiance and CO2 Concentration During Cultivation in Controlled Environment

The short-term acclimation (10-d) of Norway spruce [Picea abies (L.) Karst] to elevated CO₂ concentration (EC) in combination with low irradiance (100 mol m^–2 s^–1) resulted in stimulation of CO₂ assimilation (by 61 %), increased total chlorophyll (Chl) content (by 17 %), significantly higher photosystem 2 (PS2) photochemical efficiency (F_v/F_m; by 4 %), and reduced demand on non-radiative dissipation of absorbed excitation energy corresponding with enhanced capacity of photon utilisation within PS2. On the other hand, at high cultivation irradiance (1 200 mol m^–2 s^–1) both Norway spruce and spring barley (Hordeum vulgare L. cv. Akcent) responded to EC by reduced photosynthetic capacity and prolonged inhibition of F_v/F_m accompanied with enhanced non-radiative dissipation of absorbed photon energy. Norway spruce needles revealed the expressive retention of zeaxanthin and antheraxanthin (Z+A) in darkness and higher violaxanthin (V) convertibility (yielding even 95 %) under all cultivation regimes in comparison with barley plants. In addition, the non-photochemical quenching of minimum Chl a fluorescence (SV₀), expressing the extent of non-radiative dissipation of absorbed photon energy within light-harvesting complexes (LHCs), linearly correlated with V conversion to Z+A very well in spruce, but not in barley plants. Finally, a key role of the Z+A-mediated non-radiative dissipation within LHCs in acclimation of spruce photosynthetic apparatus to high irradiance alone and in combination with EC was documented by extremely high SV₀ values, fast induction of non-radiative dissipation of absorbed photon energy, and its stability in darkness.     

Lhc proteins and the regulation of photosynthetic light harvesting function by xanthophylls

Photoprotection of the chloroplast is an important component of abiotic stress resistance in plants. Carotenoids have a central role in photoprotection. We review here the recent evidence, derived mainly from in vitro reconstitution of recombinant Lhc proteins with different carotenoids and from carotenoid biosynthesis mutants, for the existence of different mechanisms of photoprotection and regulation based on xanthophyll binding to Lhc proteins into multiple sites and the exchange of chromophores between different Lhc proteins during exposure of plants to high light stress and the operation of the xanthophyll cycle. The use of recombinant Lhc proteins has revealed up to four binding sites in members of Lhc families with distinct selectivity for xanthophyll species which are here hypothesised to have different functions. Site L1 is selective for lutein and is here proposed to be essential for catalysing the protection from singlet oxygen by quenching chlorophyll triplets. Site L2 and N1 are here proposed to act as allosteric sites involved in the regulation of chlorophyll singlet excited states by exchanging ligand during the operation of the xanthophyll cycle. Site V1 of the major antenna complex LHC II is here hypothesised to be a deposit for readily available substrate for violaxanthin de-epoxidase rather than a light harvesting pigment. Moreover, xanthophylls bound to Lhc proteins can be released into the lipid bilayer where they contribute to the scavenging of reactive oxygen species produced in excess light. This revised version was published online in June 2006 with corrections to the Cover Date.     

Absorption spectra of chlorophyll a and b in Lhcb protein environment

The spectral forms of the two chlorophyll species in higher plant Photosystem II antenna proteins have been experimentally determined within their protein environment. Recombinant CP29 and LHC II antenna proteins missing individual chromophores were obtained by over-expression in bacteria without any changing of the primary protein sequence and in vitro reconstitution. Difference absorption spectroscopy with respect to the corresponding proteins binding the complete pigment complement yielded the spectral shape and extinction of single chlorophyll a and b. A functional relation of their absorption was given by Gaussian subband decomposition covering the entire Q_x and Q_y optical region together with the absolute value of the molar extinction coefficient. With respect to analogous determinations reported in the literature for organic solvents, this information is valuable for further understanding the in-protein chlorophyll excited states and excited state dynamics: in particular, for the calculation of Förster transfer rates by means of chlorophyll–chlorophyll overlap integral employing the Stepanov relation for emission and single chromophore transition energies according to the results of mutational analysis of chlorophyll binding sites [Bassi et al. (1999) Proc Natl Acad Sci USA 96: 10056–10061; Remelli et al. (1999) J Biol Chem 274: 33510–33521].     

宽胫夜蛾成虫触角和下唇须感器的超微形态

触角和下唇须是昆虫头部的重要感觉器官,其上被有多种类型的感器。宽胫夜蛾Protoschinia scutosa是一种重要的农业害虫,但其触角和下唇须感器研究较少。本研究利用扫描电子显微镜观察了宽胫夜蛾的触角和下唇须感器的类型、分布和超微形态。宽胫夜蛾的雌雄触角均为丝状,雌虫触角鞭节明显短于雄虫。雌雄触角均分布有8种类型感器,分别为Bhm氏鬃毛、鳞形感器、毛形感器、刺形感器、耳形感器、锥形感器、腔锥形感器和栓锥形感器。其中,毛形感器数量最多,且雄性毛形感器的数量明显多于雌性。宽胫夜蛾的下唇须为长管状,雌雄下唇须长度无显著差异。共观察到5种类型感器,即毛形感器、钟形感器、鳞形感器、刺形感器和棒形感器。毛形感器分布在下唇须基部第1节和端部第3节的陷窝器内,钟形感器位于第1节毛形感器簇之中,鳞形感器在各节均有分布,刺形感器和棒形感器只见于第3节。并对宽胫夜蛾的触角和下唇须感器的功能进行初步的推测和讨论。为昆虫感器功能分析、分类学和行为学研究提供依据。