A role for β‐sitosterol to stigmasterol conversion in plant–pathogen interactions

Upon inoculation with pathogenic microbes, plants induce an array of metabolic changes that potentially contribute to induced resistance or even enhance susceptibility. When analysing leaf lipid composition during the Arabidopsis thaliana–Pseudomonas syringae interaction, we found that accumulation of the phytosterol stigmasterol is a significant plant metabolic process that occurs upon bacterial leaf infection. Stigmasterol is synthesized from β‐sitosterol by the cytochrome P450 CYP710A1 via C22 desaturation. Arabidopsis cyp710A1 mutant lines impaired in pathogen‐inducible expression of the C22 desaturase and concomitant stigmasterol accumulation are more resistant to both avirulent and virulent P. syringae strains than wild‐type plants, and exogenous application of stigmasterol attenuates this resistance phenotype. These data indicate that induced sterol desaturation in wild‐type plants favours pathogen multiplication and plant susceptibility. Stigmasterol formation is triggered through perception of pathogen‐associated molecular patterns such as flagellin and lipopolysaccharides, and through production of reactive oxygen species, but does not depend on the salicylic acid, jasmonic acid or ethylene defence pathways. Isolated microsomal and plasma membrane preparations exhibited a similar increase in the stigmasterol/β‐sitosterol ratio as whole‐leaf extracts after leaf inoculation with P. syringae, indicating that the stigmasterol produced is incorporated into plant membranes. The increased contents of stigmasterol in leaves after pathogen attack do not influence salicylic acid‐mediated defence signalling but attenuate pathogen‐induced expression of the defence regulator flavin‐dependent monooxygenase 1. P. syringae thus promotes plant disease susceptibility through stimulation of sterol C22 desaturation in leaves, which increases the stigmasterol to β‐sitosterol ratio in plant membranes.     

剑叶龙血树内生真菌的分离及体外抑菌活性筛选

为研究剑叶龙血树内生真菌资源多样性,初步探讨和筛选具有抑菌活性的特异性菌株以及进一步开发剑叶龙血树内生真菌的抗菌活性化合物。该文采用植物组织分离法从剑叶龙血树茎和叶中分离内生真菌,对内生真菌进行液体发酵7 d,经乙酸乙酯萃取后制得粗提物,并采用牛津杯扩散法,以10种常见病原菌和5种临床耐药菌为靶标检测其发酵粗提物的抑菌活性,对有较好抑菌活性的内生真菌进行分子鉴定。结果表明:(1)从剑叶龙血树茎、叶中共分离得到345株内生真菌,294株对一种以上指示菌有抑制活性;(2)其中84株内生真菌对5株临床耐药菌均有不同程度的抑制活性,占所分离菌株总数的24.35%,75%的内生真菌对金黄色葡萄球菌有抑制活性。这说明剑叶龙血树中存在多种有抑菌活性的内生真菌,为剑叶龙血树内生菌抗菌活性成分挖掘及新型抗菌药物筛选奠定了基础。     

Population genetic structure of the endemic rosewoods Dalbergia cochinchinensis and D. oliveri at a regional scale reflects the Indochinese landscape and life‐history traits

Indochina is a biodiversity hot spot and harbors a high number of endemic species, most of which are poorly studied. This study explores the genetic structure and reproductive system of the threatened endemic timber species Dalbergia cochinchinensis and Dalbergia oliveri using microsatellite data from populations across Indochina and relates it to landscape characteristics and life‐history traits. We found that the major water bodies in the region, Mekong and Tonle Sap, represented barriers to gene flow and that higher levels of genetic diversity were found in populations in the center of the distribution area, particularly in Cambodia. We suggest that this pattern is ancient, reflecting the demographic history of the species and possible location of refugia during earlier time periods with limited forest cover, which was supported by signs of old genetic bottlenecks. The D. oliveri populations had generally high levels of genetic diversity (mean H_e = 0.73), but also strong genetic differentiation among populations (global G_ST = 0.13), while D. cochinchinensis had a moderate level of genetic diversity (mean H_e = 0.55), and an even stronger level of differentiation (global G_ST = 0.25). These differences in genetic structure can be accounted for by a higher level of gene flow in D. oliveri due to a higher dispersal capacity, but also by the broader distribution area for D. oliveri, and the pioneer characteristics of D. cochinchinensis. This study represents the first detailed analysis of landscape genetics for tree species in Indochina, and the found patterns might be common for other species with similar ecology.     

Floral volatiles with colour cues from two cucurbitaceous plants causing attraction of Aulacophora foveicollis

Aulacophora foveicollis Lucas (Coleoptera: Chrysomelidae) is an important phytophagous pest of two cucurbitaceous plants, Momordica cochinchinensis Spreng and Solena amplexicaulis (Lam.) Gandhi. The volatile organic compound profiles from flowers of M. cochinchinensis and S. amplexicaulis were identified and quantified by gas chromatography‐mass spectrometry (GC‐MS) and GC‐flame ionization detector (FID) analyses. Twenty nine and 28 compounds were identified in volatiles of M. cochinchinensis and S. amplexicaulis flowers, respectively. Methyl jasmonate and 3‐octanol were the predominant volatiles of M. cochinchinensis flowers, whereas 1‐octadecanol and 1‐hexanol were most found in the headspace of S. amplexicaulis flowers. Aulacophora foveicollis were more attracted by the flower volatiles of M. cochinchinensis than by those of S. amplexicaulis in a glass Y‐tube olfactometer. A mixture of 1‐heptanol, linalool oxide, 1‐octanol, and nonanal in the proportions present in the headspace of both flower types elicited attraction in the insect. From 25 cm distance, A. foveicollis displayed a preference for artificial flowers of 6.5 cm diameter of S. amplexicaulis flower colour (white) over M. cochinchinensis flower colour (white‐yellow). Finally, a synthetic blend (0.43 μg 1‐heptanol + 1.44 μg linalool oxide + 0.14 μg 1‐octanol + 1.77 μg nonanal dissolved in 25 μl methylene chloride) attracted more beetles when applied in a white artificial flower than when applied in a white‐yellow artificial flower from 40 cm distance. This finding may be helpful in the development of traps for pest management strategies.     

A comparative study of aluminium and nutrient concentrations in mistletoes on aluminium‐accumulating and non‐accumulating hosts

Mistletoes offer a unique model to study interactions among Al and nutrients in vascular plants, because they grow and reproduce on hosts with distinct Al uptake strategies. We investigated Al distribution and nutrient relations of mistletoes on Al‐accumulating and non‐accumulating hosts. We hypothesised that mistletoes would exhibit similar leaf nutrient and Al concentrations as their host plants, but a strong compartmentalisation of Al when growing on Al‐accumulators. We measured concentrations of N, P, K, Ca, Mg, Cu, Fe, Mn, Zn in leaves and Al in leaves, seeds and branches of Phthirusa ovata and Psittacanthus robustus infecting Miconia albicans, an Al‐accumulator, and Ph. ovata infecting Byrsonima verbascifolia, a non‐Al‐accumulator. High leaf concentrations of Al in Ph. ovata only occurred while parasitizing the Al‐accumulating host; there was no accumulation in branches or seeds. In P. robustus, large concentrations of Al were found in leaves, branches and seeds. Mistletoe seed viability and leaf nutrient concentrations were not affected by Al accumulation. Passive uptake of Al, Ca, Mg, Mn and Cu in mistletoes was evidenced by significant correlations between mistletoes and host leaf concentrations, but not of N, P and K. Al was retranslocated to different plant organs in P. robustus, whereas it was mostly restricted to leaves in Ph. ovata. We suggest that Al might have some specific function in P. robustus, which only parasitizes Al‐accumulator hosts, while the host generalist Ph. ovata can be considered a facultative Al‐accumulator.     

Injured and uninjured leaf photosynthetic responses after mechanical injury on <Emphasis Type="Italic">Nerium oleander</Emphasis> leaves,and <Emphasis Type="Italic">Danaus plexippus</Emphasis> herbivory on <Emphasis Type="Italic">Asclepias curassavica</Emphasis> leaves

Insect herbivory has variable effects on plant physiology; so greater understanding is needed about how injury alters photosynthesis on individual injured and uninjured leaves. Gas exchange and light-adapted leaf chlorophyll fluorescence measurements were collected from uninjured and mechanical partial leaf defoliation in two experiments with Nerium oleander (Apocynaceae) leaves, and one experiment with Danaus plexippus herbivory on Asclepias curassavica (Asclepiadaceae) leaves. Gas exchange impairment (lower photosynthetic rate (P _n ), stomatal conductance (g _s)) indicates water stress in a leaf, suggests stomatal limitations causing injury P _n impairment. The same pattern of gas exchange impairment also occurred on uninjured leaves opposite from injured leaves in both N. oleander experiments. This is an interesting result because photosynthetic impairment is rarely reported on injured leaves near injured leaves. No photosynthetic changes occurred in uninjured A. curassavica leaves opposite from D. plexippus-fed leaves. Partially defoliated leaves that had P _n and g _s reductions lacked any significant changes in intercellular leaf [CO₂], C _i. These results neither support, nor are sufficient to reject, stomatal limitations to photosynthesis. Manually imposed midrib vein severance in N. oleander experiment #1 significantly increased leaf C _i, indicating mesophyll limitations to photosynthesis. Maximal light-adapted leaf photochemical efficiency () and also non-photochemical quenching (q _N) were reduced by mechanical or insect herbivory to both study species, suggesting leaf trouble handling excess light energy not used for photochemistry. Midrib injury on N. oleander leaves and D. plexippus herbivory on A. curassavica leaves also reduced effective quantum yield (ΦPSII) and photochemical quenching (q _P); so reduced plastoquinone pools could lead to additional PSII reaction center closure.     

Seasonal occurrence of amaranth Lepidopteran defoliators and effect of attractants and amaranth lines in their management

Lepidopteran defoliators are the most important pests of cultivated amaranths causing severe losses in cultivated fields worldwide. Leaf‐webbers, whose larvae fold, web or glue amaranth leaves using their silken webs as they feed and leaf‐worms which cause windowing but do not glue or fold leaves are mainly reported. Sustainable management strategies for these pests are still lacking given the adverse effects of synthetic pesticides. Field experiments were conducted during two seasons at two different sites in Central Kenya, to assess amaranth lepidopteran pests and their natural enemies’ population dynamics, evaluate the efficacy of phenylacetaldehyde (PAA) floral lure as attractant and the effects of three amaranth lines (Abuk1, Abuk2 and Abuk8) on the pests’ abundance and damage. Abundance of leaf‐webbers (p = .537), leaf‐worms (p = 1) and their associated parasitoids (p = .083) did not differ between the dry and wet seasons. The parasitoids Atropha tricolor and Apanteles sp. caused parasitism of 6.2% and 33.3% on Spoladea recurvalis and Choristoneura sp., respectively. PAA incorporated traps attracted moths that were largely unrelated to the damaging larvae observed on the crops with only 0.5% of total trap catches being S. recurvalis. Sub‐sites in which PAA were incorporated had significantly higher number of leaf‐webber larvae on the crops compared to control sub‐sites (p = .014). Amaranth lines studied had significant (p = .007) effect on lepidopteran defoliators’ abundance and damage, with fewer leaf‐webbers and lower severity of damage recorded on Abuk2 compared to Abuk8. The implication of these findings for the control of lepidopteran defoliators in East Africa is discussed.     

Evaluating Drosophila suzukii immunomarking for mark‐capture research

Drosophila suzukii Matsumura (Diptera: Drosophilidae) utilizes ‘Himalaya’ blackberry, Rubus armeniacus Focke (Rosaceae), as a host and may invade berry and stone fruit crops from field margins containing this invasive weed. Laboratory and semi‐field studies were conducted to determine (1) the persistence of protein marks including 10% chicken egg whites (egg albumin protein), 20% bovine milk (milk casein protein), and 20% soy milk (soy trypsin inhibitor protein) on topically sprayed D. suzukii, (2) protein retention on blackberry leaves, and (3) D. suzukii acquisition of protein after exposure to marked blackberry leaves for up to 14 days after application. All flies and leaves were assayed for the presence of the protein marks using protein‐specific enzyme‐linked immunosorbent assays. Egg albumin, milk casein, and soy trypsin proteins persisted on 94, 49, and 25% of the topically marked D. suzukii, respectively, throughout the 14‐day study period. Egg albumin was retained on 100% of treated leaves for 14 days, regardless of environmental conditions. At least 50% of flies exposed residually to egg albumin‐treated leaves were marked for 3 days, regardless of exposure time and environmental conditions. However, increasing fly exposure time to treated leaves in April and June appeared to improve protein mark acquisition. Acquisition of protein by flies from treated leaves for milk casein was inconsistent, and poor for soy trypsin, despite detectable levels on treated leaves. Egg albumin had the longest and most consistent persistence on flies, leaves, and flies exposed to leaves in laboratory and semi‐field studies, under a variety of environmental conditions and exposure times.     

盐胁迫对3种华南园林植物元素特性的影响

为筛选耐盐园林植物,研究了盐胁迫下狗牙花(Ervatamia divaricate)、红背桂(Excoecaria cochinchinensis)和花叶假连翘(Duranta erecta)的养分积累和分配规律。结果表明,盐胁迫增加了所有植物器官的Na和叶片K含量、狗牙花和红背桂各器官的Cl和N含量,但降低了所有植物枝干、红背桂和花叶假连翘根的K含量;各植物的P含量变化各异。盐胁迫增加了所有植物Na和Cl的积累量,并富集于枝干和叶片;狗牙花和花叶假连翘各器官的N、P和K积累量及红背桂各器官的P和K积累量随着Na Cl的浓度增加而下降。总之,盐胁迫使植物Na和Cl含量和积累量升高,而各器官生物量以及N、P和K积累量下降。3种植物中,狗牙花和花叶假连翘能更好地适应华南地区盐胁迫环境。     

Characterization of Fusarium spp. associated with pineapple fruit rot and leaf spot in Peninsular Malaysia

Pineapple (Ananas comosus) is one the important fruit crops planted in Malaysia, and this study was conducted to determine Fusarium spp. associated with diseases of the fruit crop as Fusarium is prevalent in tropical countries. Our objective was to identify and characterize Fusarium spp. associated with pineapple fruit rot and leaf spot mainly found on the fruits and leaves in Peninsular Malaysia. Fusarium isolates (n = 108) associated with pineapple fruit rot and leaf spot were characterized by morphological, molecular and phylogenetic analyses, a mating study and pathogenicity testing. TEF‐1α sequence analysis identified Fusarium proliferatum, Fusarium verticillioides, Fusarium sacchari and Fusarium sp. Mating was successful only between tester strains of F. proliferatum and F. verticillioides. Sexual crosses with standard tester strains showed that 82 isolates of F. proliferatum produced fertile crosses with mating population D (Gibberella intermedia) and three isolates of F. verticillioides were fertile with the tester strain of mating population A (Gibberella moniliformis). All isolates were pathogenic, causing pineapple fruit rot and leaf spot, thus fulfilling Koch's postulates.     

Identification and Characterization of two new Fungal Pathogens of Polygonatum odoratum (Angular Solomon's seal) in Italy

Polygonatum odoratum (Mill.) Druce (Angular Solomon's seal) is a well‐known ornamental plant and herbal drug, which is used in traditional medicine. Severe leaf spots were observed in wild Angular Solomon's seal plants in a public park in Trento, Italy. A combination of morphological and molecular characteristics, including sequence data of ITS‐rDNA, large subunit (LSU), beta tubulin (TUB) and glyceraldehyde 3‐phosphate dehydrogenase (GAPDH) led to identification of two species, namely Phoma odoratissimi and Colletotrichum dematium s. str., isolated from these leaf spots. Pathogenicity of the isolates was confirmed on wounded leaves of Po. odoratum; indeed, both species induced leaf spot symptoms on inoculated leaves within 10 days of inoculation. This is the first report of leaf spot disease caused by Ph. odoratissimi and C. dematium s. str. on Po. odoratum, which can be considered a new host for both the species examined in this study. In addition, isolation of Ph. odoratissimi represents a new record for the mycobiota of Italy.     

Synthesis of CuPF6‐(S)‐BINAP loaded resin and its enantioselectivity toward phenylalanine enantiomers

A type of resin‐anchored CuPF₆‐(S )‐BINAP was synthesized and identified. The PS‐CuPF₆‐(S )‐BINAP resin was used to adsorb the phenylalanine enantiomers. The results showed that the adsorption capacity of PS‐CuPF₆‐(S )‐BINAP resin toward L‐phenylalanine was higher than that of resin toward D‐phenylalanine. PS‐CuPF₆‐(S )‐BINAP resin exhibited good enantioselectivity toward L‐phenylalanine and D‐phenylalanine. The influence of phenylalanine concentration, pH, adsorption time, and temperature on the enantioselectivity of the resin were investigated. The results showed that the enantioselectivity of the resin increased with increasing the phenylalanine concentration, pH, and adsorption time, while it decreased with an increase in temperature. The causes for these influences are discussed. The highest enantioselectivity (α = 2.81) was obtained when the condition of phenylalanine concentration was 0.05 mmol/mL, pH was 8, adsorption time was 12 h, and temperature 5°C. The desorption test for removing D/L‐phenylalanine on PS‐CuPF₆‐(S )‐BINAP resin was also investigated. The desorption ratios of D‐phenylalanine and L‐phenylalanine at pH of 1 were 95.7% and 94.3%, respectively. This result indicated that the PS‐CuPF₆‐(S )‐BINAP resin could be regenerated by shaking with an acidic solution. The reusability of the PS‐CuPF₆‐(S )‐BINAP resin was also assessed and the resin exhibited considerable reusability.     

Feeding of fall armyworm,Spodoptera frugiperda,on Bt transgenic cotton and its isoline

Studies on insect food intake and utilization are important for determining the degree of insect/plant association and host species’ resistance, and also for helping design pest management programs by providing estimates of potential economic losses, techniques for mass breeding of insects, and identifying physiological differences between species. We studied the feeding and development of fall armyworm, Spodoptera frugiperda (JE Smith) (Lepidoptera: Noctuidae), on transgenic (Bt) and non‐transgenic (non‐Bt) cotton. The larvae of S. frugiperda fed on Bt cotton had a longer development period (23.0 days) than those fed on non‐Bt cotton (20.2 days). Survivorship of S. frugiperda larvae fed on Bt cotton (74.1%) was lower than that of larvae fed on non‐Bt cotton (96.7%). Pupal weight of larvae fed on Bt cotton (0.042 g) was lower than that of larvae fed on non‐Bt cotton (0.061 g). The cotton cultivar significantly affected food intake, feces production, metabolization, and food assimilation by S. frugiperda larvae. However, it did not affect their weight gain. Intake of Bt‐cotton leaf (0.53 g dry weight) per S. frugiperda larva was lower than the intake of non‐Bt‐cotton leaf (0.61 g dry weight). Larvae fed on Bt‐cotton leaves produced less feces (0.25 g dry weight) than those fed on non‐Bt‐cotton leaves (0.37 g dry weight). Weight gain per S. frugiperda larva fed on Bt‐cotton leaves (0.058 g dry weight) was similar to the weight gain for larvae fed on non‐Bt‐cotton leaves (0.056 g dry weight). The cotton cultivar significantly affected the relative growth, consumption, and metabolic rates, as well as other nutritional indices: the figures were lower for larvae fed on Bt‐cotton leaves than for larvae fed on non‐transgenic cotton leaves.     

Genetic relationships among Eriobotrya species revealed by genome‐wide RAD sequence data

Restriction site‐associated DNA sequencing (RAD‐seq) was used to illuminate the genetic relationships among Eriobotrya species. The raw data were filtered, and 221 million clean reads were used for further analysis. A total of 1,983,332 SNPs were obtained from 23 Eriobotrya species and two relative genera. We obtained similar results by neighbor‐joining and maximum likelihood phylogenetic trees. All Eriobotrya plants grouped together into a big clade, and two out‐groups clustered together into a single or separate clade. Chinese and Vietnam accessions were distributed throughout the dendrogram. There was nonsignificant correlation between genotype and geographical distance. However, clustering results were correlated with leaf size to some extent. The Eriobotrya species could be divided into following three groups based on leaf size and phylogenetic analysis: group A and group B comprised of small leaves with <10 cm length except E. stipularis (16.76 cm), and group C can be further divided into two subgroups, which contained medium‐size leaves with a leaf length ranged from 10 to 20 cm and a leaf length bigger than 20 cm.     

Selective herbivory by brushtail possums: Determining the age of ingested leaves using n‐alkanes

Abstract Leaves often decline in nutritional quality as they age, and selective feeding on young leaves may be nutritionally important for herbivores. Preference by mammalian herbivores for young leaves has rarely been measured in the field owing to technical difficulties. We measured preferences with respect to leaf age of an arboreal folivore, the brushtail possum (Trichosurus vulpecula Kerr), feeding on southern rata (Metrosideros umbellata Cav.; Myrtaceae) in a new application of the alkane technique. We characterized the cuticle waxes (n‐alkanes) of rata leaves that were less than 1 year old (‘1‐year’), between 1 and 2 years (‘2‐year’) and greater than 2 years old (‘>2‐year’). Simulations showed that the method accurately discriminated between 1‐year and other age groups but slightly overestimated the importance of rare components of the diet. This bias was larger when discriminating between 2‐year and >2‐year leaves apparently because they had more‐similar alkane profiles. Metrosideros umbellata leaf formed 20.8% of the diet of a population of possums from Rakiura, New Zealand, sampled in autumn 2002 (n = 33). Of the M. umbellata component, alkane analyses showed that 1‐year leaves formed 88.7 ± 3.9% of the diet despite making up only 39.5 ± 2.2% of the leaf biomass on rata trees (n = 14). The foliar concentrations of the macronutrients N, P and K all declined significantly with leaf age (P < 0.0001). Lignin content did not measurably increase with leaf age, suggesting that digestibility per se did not determine the preference of brushtail possums for young rata leaves. This study provides the first quantitative evidence that possums discriminate by leaf age and that the resulting diet is enriched in macronutrients.     

2,6‐Dimethoxy‐1,4‐Benzoquinone Enhances Resistance Against the Rice Blast Fungus Magnaporthe oryzae

We investigated the effect of 2,6‐dimethoxy‐1,4‐benzoquinone (DMBQ) on induced resistance to Magnaporthe oryzae in rice. DMBQ concentrations greater than 50 μg/ml inhibited spore germination and appressorium formation in M. oryzae. When rice leaves pretreated with 10 μg/ml DMBQ, which did not show antifungal activity against spore germination and appressorium formation of M. oryzae, were inoculated with M. oryzae spores 5 days after DMBQ pretreatment, blast lesion formation was inhibited compared with control leaves pretreated with distilled water. In addition, infection‐inhibiting activity against M. oryzae was significantly enhanced in rice leaf sheaths pretreated with 10 μg/ml DMBQ. H₂O₂ generation was observed in rice leaves pretreated with DMBQ, and PAL, POX, CHS and PR10a were significantly expressed in these leaves. These results suggested that DMBQ can protect rice from blast disease caused by M. oryzae.     

Role of leaf glandular trichomes of melon plants in deterrence of Aphis gossypii Glover

External characteristics of the leaf epidermis and their effects on behaviour of Aphis gossypii Glover were evaluated in two Cucumis melo L. genotypes, ‘Bola de Oro’ (aphid susceptible) and TGR‐1551 (aphid resistant) in order to explore their role in the early rejection of TGR‐1551 by this aphid. No differential effects of epicuticular waxes on aphid behaviour were observed. The type, distribution and number of trichomes on melon leaves were also studied. Pubescence in melon, measured as the number of non‐glandular trichomes per cm², was not sufficient to prevent aphid settling. However, there was a high density of type I glandular trichomes on leaves of the aphid‐resistant genotype. According to microscopic observations and stain testing, these trichomes store and secrete phenols and flavonoids. Free‐choice tests were conducted to determine the effect of these glandular trichomes on A. gossypii preference, revealing that aphids reject leaf disks of TGR‐1551 from the onset of the experiment. Additional experiments after removal of leaf type I glandular trichome exudates showed that A. gossypii preferred washed TGR‐1551 leaf disks over unwashed disks, while this effect was not observed in experiments using washed and unwashed ‘Bola de Oro’ leaf disks. These results suggest that a high density of glandular trichomes and chemicals secreted by them deter A. gossypii and disturb aphid settling on TGR‐1551.     

What happens in the pith stays in the pith: tissue‐localized defense responses facilitate chemical niche differentiation between two spatially separated herbivores

Herbivore attack is known to elicit systemic defense responses that spread throughout the host plant and influence the performance of other herbivores. While these plant‐mediated indirect competitive interactions are well described, and the co‐existence of herbivores from different feeding guilds is common, the mechanisms of co‐existence are poorly understood. In both field and glasshouse experiments with a native tobacco, Nicotiana attenuata, we found no evidence of negative interactions when plants were simultaneously attacked by two spatially separated herbivores: a leaf chewer Manduca sexta and a stem borer Trichobaris mucorea. T. mucorea attack elicited jasmonic acid (JA) and jasmonoyl‐l ‐isoleucine bursts in the pith of attacked stems similar to those that occur in leaves when M. sexta attacks N. attenuata leaves. Pith chlorogenic acid (CGA) levels increased 1000‐fold to levels 6‐fold higher than leaf levels after T. mucorea attack; these increases in pith CGA levels, which did not occur in M. sexta‐attacked leaves, required JA signaling. With plants silenced in CGA biosynthesis (irHQT plants), CGA, as well as other caffeic acid conjugates, was demonstrated in both glasshouse and field experiments to function as a direct defense protecting piths against T. mucorea attack, but not against leaf chewers or sucking insects. T. mucorea attack does not systemically activate JA signaling in leaves, while M. sexta leaf‐attack transiently induces detectable but minor pith JA levels that are dwarfed by local responses. We conclude that tissue‐localized defense responses allow tissue‐specialized herbivores to share the same host and occupy different chemical defense niches in the same hostplant.     

An oxygen isotope chronometer for cellulose deposition: the successive leaves formed by tillers of a C4 perennial grass

Multiannual time series of (palaeo)hydrological information can be reconstructed from the oxygen isotope composition of cellulose (δ¹⁸O_Cel) in biological archives, for example, tree rings, but our ability to temporally resolve information at subannual scale is limited. We capitalized on the short and predictable leaf appearance interval (2.4 d) of a perennial C₄ grass (Cleistogenes squarrosa), to assess its potential for providing highly time‐resolved δ¹⁸O_Cel records of vapour pressure deficit (VPD). Plants grown at low (0.63 kPa) or high (1.58 kPa) VPD were swapped between VPD environments and exposed to the new environment for 7 d with simultaneous ¹³CO₂ labelling. Then, leaves were sampled by age/position along individual tillers. Five leaves at different developmental stages were growing simultaneously. The period of most‐active leaf elongation, from 10 to 90% of final length, lasted 6.6 d, and ~80% of all carbon and oxygen incorporation in whole‐leaf cellulose occurred within 7 d. Cellulose deposition stopped at (or shortly after) full leaf expansion. The direction of change, low‐to‐high or high‐to‐low VPD, had no differential effect on new oxygen and carbon incorporation in cellulose. Successive leaves produced by tillers of C. squarrosa provide a δ¹⁸O_Cel record useful for reconstructions of short‐term hydrological dynamics.