Organ‐specific responses of tomato growth and phenolic metabolism to nitrate limitation

Phenolic compounds are secondary metabolites involved in plant innate chemical defence against pests and diseases. Their concentration varies depending on plant tissue and also on genetic and environmental factors, e.g. availability of nutrient resources. This study examines specific effects of low (LN) and high (HN) nitrogen supply on organ (root, stem and leaf) growth and accumulation of major phenolics [chlorogenic acid (CGA); rutin; kaempferol rutinoside (KR)] in nine hydroponically grown tomato cultivars. LN limited shoot growth but did not affect root growth, and increased concentrations of each individual phenolic in all organs. The strength of the response was organ‐dependent, roots being more responsive than leaves and stems. Significant differences were observed between genotypes. Nitrogen limitation did not change the phenolic content in shoots, whereas it stimulated accumulation in roots. The results show that this trade‐off between growth and defence in a LN environment can be discussed within the framework of the growth–differentiation balance hypothesis (i.e. GDBH), but highlight the need to integrate all plant organs in future modelling approaches regarding the impact of nitrogen limitation on primary and secondary metabolism.     

减弱UV-B辐射对烟草形态、光合及生理生化特性的影响

在地处低纬高原云南较高海拔烟区的通海县大田条件下,通过大棚覆盖不同透明膜的方式梯度减弱UV-B辐射,研究了外界环境30.39%(T1)、70.08%(T2)和75.74%(T3)强度的UV-B辐射对烟草品种K326形态、光响应特性和部分生理生化特征的影响。结果显示:减弱UV-B辐射促进了K326节间距和茎高的伸长,使叶片增大、变薄,尤以T2处理植株的叶片、茎围和节间距最大,而K326发育进程由T1至T3逐渐加快。在减弱UV-B辐射下,K326净光合速率(Pn)、最大净光合速率(Amax)和蒸腾速率(Tr)较高,但水分利用效率(WUE)、暗呼吸速率(Rd)、光补偿点(LCP)和光饱和点(LSP)较低。其中T1的Rd和LCP最低,并极大地降低了表观量子效率(AQY),T2的LSP最低而Pn最高,而T3的Amax、LCP和AQY最高。减弱UV-B辐射后烟叶叶绿素含量提高,而类黄酮、比叶重、类胡萝卜素含量和面积含水量下降,鲜重含水量和自然水分饱和亏却上升;T3处理下丙二醛含量最大,鲜重含水量和自然水分饱和亏则T2最大。结果表明,适当高强度的UV-B辐射对促进K326正常生长发育和提高其对UV-B辐射的适应性有重要作用。     

Induced responses in Nicotiana attenuata affect behavior and growth of the specialist herbivore Manduca sexta

Many plants employ induced responses against generalist herbivores. Specialist herbivores, however, may employ several mechanisms to overcome the negative effects of induced plant defenses. Here we test how the behavior and development of specialist Manduca sexta larvae are affected by induced responses in their natural host plant Nicotiana attenuata. On a spatial scale relevant to both the plant and the herbivore, we first determined how methyl jasmonate (MeJA)-induced responses, such as increased nicotine production, affect the tendency of larvae to leave induced plants. When larvae were allowed to move between two plants planted in one pot, they left an MeJA-treated plant faster than a control plant. When both plants in the pot were MeJA-treated, the larvae developed more slowly than when both plants were uninduced, or when the larvae had the opportunity to move to an uninduced neighbor. The sooner larvae moved from an MeJA-treated plant to an untreated neighbor, the larger the body mass they attained. This demonstrates that M. sexta larvae can compensate behaviorally for the deleterious effects of induced plant responses. These effects were observed in plants grown under both low and high N supply rates, though the effects were more pronounced under high N. To examine the consequences of the timing and the direction of the host plant switching behavior for larval development, neonate larvae were fed leaves excised from induced and uninduced plants. Larvae confined to MeJA-treated leaves had higher mortality rates and grew slower than larvae fed only control leaves. This demonstrates that MeJA-induced responses decrease growth and development of specialist herbivores that do not have the behavioral option of moving to an uninduced plant. The sooner the larvae were switched to MeJA-treated leaves, the slower their development compared to larvae fed only uninduced leaves. In contrast, the sooner larvae fed MeJA-treated leaves were switched to control leaves, the faster they developed. Again the effects of MeJA treatment were stronger in plants grown under high N supply. We propose that induced plants growing in close competition with an uninduced conspecific may offset the fitness costs of these induced responses and perhaps obtain a fitness benefit by motivating herbivores to move to their neighboring competitors. Received: 25 March 1999 / Accepted: 8 October 1999     

Mechanisms of optimal defense patterns in Nicotiana attenuata: flowering attenuates herbivory-elicited ethylene and jasmonate signaling

To defend themselves against herbivore attack, plants produce secondary metabolites, which are variously inducible and constitutively deployed, presumably to optimize their fitness benefits in light of their fitness costs. Three phytohormones, jasmonates (JA) and their active forms, the JA-isoleucine (JA-Ile) and ethylene (ET), are known to play central roles in the elicitation of induced defenses, but little is known about how this mediation changes over ontogeny. The Optimal Defense Theory (ODT) predicts changes in the costs and benefits of the different types of defenses and has been usefully extrapolated to their modes of deployment. Here we studied whether the herbivore-induced accumulation of JA, JA-Ile and ET changed over ontogeny in Nicotiana attenuata, a native tobacco in which inducible defenses are particularly well studied. Herbivore-elicited ET production changed dramatically during six developmental stages, from rosette through flowering, decreasing with the elongation of the first corollas during flower development. This decrease was largely recovered within a day after flower removal by decapitation. A similar pattern was found for the herbivore-induced accumulation of JA and JA-Ile. These results are consistent with ODT predictions and suggest that the last steps in floral development control the inducibility of at least three plant hormones, optimizing defense-growth tradeoffs.     

Abscisic acid is involved in the response of grape (Vitis vinifera L.) cv. Malbec leaf tissues to ultraviolet-B radiation by enhancing ultraviolet-absorbing compounds, antioxidant enzymes and membrane sterols

We investigated the interactions of abscisic acid (ABA) in the responses of grape leaf tissues to contrasting ultraviolet (UV)-B treatments. One-year-old field-grown plants of Vitis vinifera L. were exposed to photosynthetically active radiation (PAR) where solar UV-B was eliminated by using polyester filters, or where PAR was supplemented with UV-B irradiation. Treatments combinations included weekly foliar sprays of ABA or a water control. The levels of UV-B absorbing flavonols, quercetin and kaempferol were significantly decreased by filtering out UV-B, while applied ABA increased their content. Concentration of two hydroxycinnamic acids, caffeic and ferulic acids, were also increased by ABA, but not affected by plus UV-B (+UV-B) treatments. Levels of carotenoids and activities of the antioxidant enzymes, catalase, ascorbate peroxidase and peroxidase were elevated by +ABA treatments, but only if +UV-B was given. Cell membrane β -sitosterol was enhanced by ABA independently of +UV-B. Changes in photoprotective compounds, antioxidant enzymatic activities and sterols were correlated with lessened membrane harm by UV-B, as assessed by ion leakage. Oxidative damage expressed as malondialdehyde content was increased under +UV-B treatments. Our results suggest that the defence system of grape leaf tissues against UV-B is activated by UV-B irradiation with ABA acting downstream in the signalling pathway.     

唐古特白刺叶黄酮类及酚酸类成分的分离鉴定

从蒺藜科植物唐古特白刺（ＮｉｔｒａｒｉａｔａｎｇｕｔｏｒｕｍＢｏｒ．）叶中分得８个黄酮类及酚酸类化合物,经理化常数测定和波谱学方法确定了它们的化学结构,分别为：３甲氧基４羟基反式桂皮酸（１）、对羟基反式肉桂酸（２）、３羟基４甲氧基苯甲酸（３）、邻羟基苯甲酸（４）、３,５二甲醚山柰黄素７ＯβＤ葡萄糖甙（５）、３甲醚山柰黄素７ＯβＤ葡萄糖甙（６）、异鼠李素７ＯβＤ葡萄糖甙（７）、异鼠李素３ＯβＤ芸香糖甙（８）。以上化合物均为首次从该植物中得到,可以作为白刺属化学分类学的特征性化合物。     

额济纳绿洲胡杨（Populus euphratica）酚类物质含量和分布及其与土壤水分的关系

采用分光光度法测定了额济纳绿洲胡杨(Populus euphratica)的披针形叶、卵圆形叶、嫩枝、枝(D《5 mm)、枝(5～10 mm)、主干树皮、根(D《2 mm)、根(2～5 mm)和根(5～10 mm)9类器官中的总酚、黄酮和缩合单宁含量.结果表明,总酚含量较高的器官为皮(27.93 mg/s),叶、根、枝中总酚含量分别为17.64 mg/g(两类叶均值)、16.72mg/g(三类根均值)、12.19 mg/g(三类枝均值);黄酮含量较高的器官为皮(51.30 mg/g),叶、根、枝中黄酮含量分别为28.45 mg/g(两类叶均值)、39.99 mg/g(三类根均值)、23.67 mg/g(三类枝均值);根中缩合单宁含量较高,三类根均值为22.10 mg/g,皮、叶、枝中缩合单宁含量分别为8.41 mg/g、4.03 mg/g(两类叶均值)、4.47 mg/g(三类枝均值).披针形叶和卵圆形叶中酚类物质含量没有显著性差异(P》0.05);随着枝不断成熟,嫩枝、枝(D《5mm)、枝(5～10mm)中酚类物质逐渐减少;随着根直径减少,根中缩合单宁逐渐增加,细根(D《2mm)中的缩合单宁含量最高(25.95 mg/g).分析胡杨各器官中酚类物质含量与土壤水分的关系,结果表明卵圆形叶中酚类物质含量与土壤水分含量成显著负相关关系(P《0.05,总酚:r=-0.949;黄酮:r=-0.923;缩合单宁:r=-0.944).研究揭示了极端干旱地区胡杨各器官中酚类物质的变化规律,及其与环境因子的相互作用关系.     

Specificity of root microbiomes in native‐grown Nicotiana attenuata and plant responses to UVB increase Deinococcus colonization

Plants recruit microbial communities from the soil in which they germinate. Our understanding of the recruitment process and the factors affecting it is still limited for most microbial taxa. We analysed several factors potentially affecting root microbiome structure – the importance of geographic location of natural populations, the microbiome of native seeds as putative source of colonization and the effect of a plant's response to UVB exposure on root colonization of highly abundant species. The microbiome of Nicotiana attenuata seeds was determined by a culture‐dependent and culture‐independent approach, and the root microbiome of natural N. attenuata populations from five different locations was analysed using 454‐pyrosequencing. To specifically address the influence of UVB light on root colonization by Deinococcus, a genus abundant and consistently present in N. attenuata roots, transgenic lines impaired in UVB perception (irUVR8) and response (irCHAL) were investigated in a microcosm experiment with/without UVB supplementation using a synthetic bacterial community. The seed microbiome analysis indicated that N. attenuata seeds are sterile. Alpha and beta diversities of native root bacterial communities differed significantly between soil and root, while location had only a significant effect on the fungal but not the bacterial root communities. With UVB supplementation, root colonization of Deinococcus increased in wild type, but decreased in irUVR8 and irCHAL plants compared to nontreated plants. Our results suggest that N. attenuata recruits a core root microbiome exclusively from soil, with fungal root colonization being less selective than bacterial colonization. Root colonization by Deinococcus depends on the plant's response to UVB.     

Solar ultraviolet-B radiation influence on Sphagnum bog and Carex fen ecosystems: first field season findings in Tierra del Fuego, Argentina

Stratospheric ozone depletion occurs over Tierra del Fuego, southern Argentina and Chile, in the austral spring and summer due to the precession of the Antarctic ‘ozone hole’ and the general erosion of the ozone layer. Plots receiving either near-ambient or reduced UV-B radiation were established using different louvered plastic film filters over Sphagnum bog and Carex fen ecosystems in October 1996. In the Sphagnum bog system, growth measurements during the late spring and summer showed no significant differences in the moss Sphagnum magellanicum, or the vascular plants (Empetrum rubrum, Nothofagus antarctica, and Tetroncium magellanicum) between near-ambient and attenuated UV-B radiation treatments. In the Carex fen system, leaf length and spike height did not differ in the two dominant species, Carex decidua and C. curta, between UV-B radiation treatments. The length of individual spikelets of C. curta under near-ambient UV-B radiation was less than under the reduced UV-B radiation treatment, but this was not evident in C. decidua. No differences in seed number, seed mass, or viability were seen in either Carex species between the UV-B treatments. Two important constituents of the microfauna that inhabit the Sphagnum bog are testate amoebae and rotifers. These both appeared to be more numerous under near-ambient UV-B radiation than under reduced UV-B radiation. The subtle responses of the Sphagnum and Carex ecosystems may become more apparent in subsequent years as the treatments are continued. Trophic-level changes, such as the differences in number of amoebae and rotifers, may be more sensitive to solar UV-B radiation than growth and productivity of the vegetation.     

Antibacterial activity of sphagnum acid and other phenolic compounds found in Sphagnum papillosum against food-borne bacteria

Aims:  To identify the phenolic compounds in the leaves of Sphagnum papillosum and examine their antibacterial activity at pH appropriate for the undissociated forms.
Methods and Results:  Bacterial counts of overnight cultures showed that whilst growth of Staphylococcus aureus 50084 was impaired in the presence of milled leaves, the phenol-free fraction of holocellulose of S. papillosum had no bacteriostatic effect. Liquid chromatography–mass spectrometry analysis of an acetone–methanol extract of the leaves detected eight phenolic compounds. Antibacterial activity of the four dominating phenols specific to Sphagnum leaves, when assessed in vitro as minimal inhibitory concentrations (MICs), were generally >2·5 mg ml⁻¹. MIC values of the Sphagnum- specific compound 'sphagnum acid' [ p -hydroxy-β-(carboxymethyl)-cinnamic acid] were >5 mg ml⁻¹. No synergistic or antagonistic effects of the four dominating phenols were detected in plate assays.
Conclusions:  Sphagnum -derived phenolics exhibit antibacterial activity in vitro only at concentrations far in excess of those found in the leaves.
Significance and Impact of the Study:  We have both identified the phenolic compounds in S. papillosum and assessed their antibacterial activity. Our data indicate that phenolic compounds in isolation are not potent antibacterial agents and we question their potency against food-borne pathogens.