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1.
The indirect effect of ants on plants through their mutualism with honeydew-producing insects has been extensively investigated. Honeydew-producing insects that are tended by ants impose a cost on plant fitness and health by reducing seed production and/or plant growth. This cost is associated with sap intake and virus transmissions but may be overcompesated by tending ants if they deter or prey on hebivorous insects. The balance between cost and benefits depends on the tending ant species. In this study we report other indirect effects on plants of the mutualism between aphids and ants. We have found that two Lasius ant species, one native and the other invasive, may change the composition of volatile organic compounds (VOCs) of the holm oak (Quercus ilex) blend when they tend the aphid Lachnus roboris. The aphid regulation of its feeding and honeydew production according to the ant demands was proposed as a plausible mechanism that triggers changes in VOCs. Additionally, we now report here that aphid feeding, which is located most of the time on acorns cap or petiole, significantly increased the relative content of linolenic acid in acorns from holm oak colonized by the invasive ant. This acid is involved in the response of plants to insect herbivory as a precursor or jasmonic acid. No effect was found on acorn production, germination or seedlings quality. These results suggest that tending-ants may trigger the physiological response of holm oaks involved in plant resistance toward aphid herbivory and this response is ant species-dependent.Key words: tended aphid, invasive ants, linolenic acid, jasmonic acid, monoterpene emissionsTo achieve an indirect effect it is necessary to have a minimun of three species, two focal species that interact directly and an associate species whose presence promotes an indirect effect on one or both focal species. In general, indirect effects of a third species are defined by how and to what degree a pairwise species interaction is influenced by the presence and density of this third species.1 There are several examples of interactions presenting indirect effects: apparent competition,1 facilitation,2 tri-trophic level interactions,3 cascading effects4 and exploitative competition. 5 But, indirect effects have been studied most extensively in the context of trophic cascades when top predators are removed6 or added7 and in the context of mutualisms.8–10 Usually, indirect effects are investigated as changes in abundance of the focal species occur. However, indirect effects may result in biologically significant changes in a species that are not reflected only to its abundance.11 There are many examples of changes in physiology, behavior, morphology and/or genotypic composition of the focal species.11,12 These changes on density and/or morphological, physiological and behavioral traits of the focal species are not mutually exclusive, and all can act at the same time.13 The magnitude and direction of both direct and indirect effects should influence the relative resilience of communities to perturbation, which in turn will affect species coexistence and community evolution.14 In this regard, indirect effects had been postulated as one of the main forces structuring communities2 and shaping the evolution of communities.14In terrestrial communities ants interact with plants both directly and indirectly. They can disperse or consume seeds, feed from specialized plant structures such as food bodies and extrafloral nectaries, act as or deter pollinitators, prey on herbivorous insects and/or develop mutualisms with honeydew-producing insects indirectly modifying plant fitness.15–17 Additionally, through their nesting activities in soil, ants increase soil nutrient content available to plants, may change water infiltration and soil holding-capacity and modify biodiversity and abundance of soil organisms related to the decomposition process.18,19 As a consequence of their activities, ants may thus change behavior, density, physiology or fitness of other species.12,22,23 In the case of ants that tend honeydew-producing insects, evidence shows that their attention may change some traits of insect life history, 22 their abundance or physiology.18 For the plant, the net outcome of the mutualism between ants and honeydew-producing insects will depend on the balance between the costs for plant fitness via consumption of plant sap and transmission of plant pathogens and the benefit of ants deterring herbivorous insects.18,23 As a consequence, plant seed production, pod production or even plant growth may decrease when the cost of honeydew-producing insects exceed the benefit provided by tending ants.18,23Recently, we have described the changes that two tending ant species may exert indirectly on monoterpene emissions of holm oak (Quercus ilex) saplings through its mutualism with Lachnus roboris aphids.24 One of these tending ant species was Lasius neglectus, an invasive ant species that displaces the local ant Lasius grandis. We found that aphids feeding on holm oak increased the emission of total volatile organic carbon (VOCs) by 31%. In particular, aphids feeding elicited the emission of a new monoterpene, Δ3-carene, and increased the emission of myrcene (mean ± SE; sapling alone: 0.105 ± 0.011 µg g−1 h−1; sapling plus not tended aphid: 0.443 ± 0.057 µg g−1 h−1) and γ-terpinene (sapling alone: 0.0013 ± 0.0001; sapling plus not tended aphid: 0.0122 ± 0.0022 µg g−1 h−1) (Mann-Whitney, sapling alone vs. sapling plus not tended aphids, U4,4 = 0, p < 0.05 for both compounds). Changes of VOC emission in response to aphid infestation were noticed also in boreal trees.24 When the aphids became tended by the invasive ant, L. neglectus, VOCs emissions increased only 19% because myrcene, the main compound of the blend, decreased significantly (25 When our data was recalculated on leaf area basis (nmol m−2 s−1), the general pattern was the same independently of the units, but the differences among treatments were not statistically significant (26 These slight differences in the statitiscal significance of the differences of VOC emissions depending on the reference unit may be due to differences in leaf morphology, i.e., changes of leaf area and mass. However, in our study, all holm oaks showed a similar leaf morphology among treatments (Kruskal-Wallis, leaf mass: H3,20 = 2.16, p = 0.53; leaf area: H3,20 = 2.64, p = 0.45) (24,27 This lack of consistence of aphid effect on leaf area and mass limits the development of a clear pattern linking aphids feeding, leaf area or mass and VOC emissions. On the other hand, to achieve statistical significance of emitted VOCs among treatments, values should differ strongly given the high variability of VOC emission within treatments.26 Under this scenario, we recommend giving the values of leaf morphology and to give VOC emissions on both unit bases to facilite comparisons among different studies.
Open in a separate windowThe emission rate were compared first by Kruskal-Wallis test. Values given above were calculated as µg g−1 h−1, while values below were calculated as nmols m−2 s−1. At the last row, leaf morphology is shown for each treatment. Different letters indicate statistical differences of multiple non parametrical post hoc comparisons (Dunn''s test, p < 0.05).The tended aphid, Lachnus roboris, feed most of the time on the petiole or on the cap of acorns of holm oaks.28 Therefore, acorn quantity and quality (lipid content) and seedlings quality could be affected by tending ants through their mutualism with aphids. We analyzed lipid content as an estimator of acorn quality. Lipids and starches are synthetized in acorns from carbohydrates translocated from leaves.29 However, before being used for metabolic functions, lipid content of acorns must be transformed into glucids and then can be used as respiratory substrate during germination.29 As a consequence, when aphids suck sap from acorns they may act as a sink of translocated carbohydrates, thus decreasing the amount that reaches the seeds.30During two consecutive years, we counted all acorns from one branch (8–11 cm diameter) for each one of 6 holm oaks colonized by L. neglectus and 6 holm oaks colonized by L. grandis that we studied. We followed them at different stages of their development (July, September and December). Among holm oaks, the loss of acorn production varied between 87.9–96.8%. Acorn production (acorns that started to develop and reached maturity) did not differ between the tree colonized by one or another ant species (mean number of acorns per branch ± SE, 2003: L. neglectus trees: 2.67 ± 1.38, L. grandis trees: 2.67 ± 2.01; Mann Whitney, U = 15, p = 0.69; 2004: L. neglectus trees: 35.83 ± 19.23, L. grandis trees: 49.80 ± 27.99; Mann Whitney, U = 12, p = 0.66). The only work in which researchers evaluated the effect of ants on acorn production was conducted by Ito and Higashi.31 These authors showed that the acorn production of Quercus dentata in the presence of the tending ant Formica yessensis did not differ either. However, there was a significantly lower proportion of infested acorns with weevil larvae when Formica yessensis were tending aphids.31 So, ants may indirectly increase the probability that acorns reach the maturity in healthy conditions, improving in this way one component of the fitness of the oak. In the case of the larvae of weevils, wasps and moth species that infest holm oak acorns32 during their development, they do not move to other acorn as in the case reported by Ito and Higashi.31 This behavior prevents ant predation during the move from one acorn to another.Lipid content of acorn cotyledons was analyzed by gas cromatography-flame ionization detector (FID) after performing the derivatization of lipid acids to methyl esters with BF3 in methanol.33 Acorn quality only differed in the content of linolenic acid, which was significantly higher in acorns from oaks colonized by the invasive ant Lasius neglectus (Fig. 1). Linolenic acid acts as a precursor for the synthesis of jasmonic acid,34 a signaling molecule involved in responses associated with insect herbivory.35 The increase of linolenic acid suggests that a local response to aphid feeding was triggered during acorn development. In boreal trees, aphid feeding increased up to 50% the emission of methyl salicylate, a defence compound of plants, that acts as aphid repellent and an attractor of foraging predators and parasitoids.24Open in a separate windowFigure 1Mean (±SE) of the percentage of each fatty acid relative to the total amount of fatty acids of acorns from holm oaks colonized by invasive ants L. neglectus (in grey) or by native ants L. grandis (in white). Asterisk shows significant differences of linolenic content (Mann Whitney, U = 7.5, p = 0.026).We then performed a germination test at the second year when enough acorns reached maturity. We picked mature acorns from trees colonized by the invasive or by the native ant. Those acorns with visual evidence of being infested by insect larvae were discarded as non-viable. From the group of healthy acorns, we chose randomly between 6 to 18 acorns per tree comprising in total 94 or 97 acorns for holm oaks colonized by L. neglectus or L. grandis, respectively. We performed a laboratory germination test at 20–25°C under natural light conditions. Acorns were planted in nursery flats of 300 cc filled with commercial compost (70% organic matter, pH = 6.5), watered twice a week and inspected daily from January to April until emergency. After 90 days, acorn viability (germination + seedling emergence) was 89% and 87% for acorns from holm oaks colonized by the invasive or by native ant, respectevily. Puerta-Piñeiro et al. obtained a 90% acorn viability when acorns where sown in sterilized river sand. On the other hand, Leiva and Fernαndez-Alés37 sowed 20 acorns per 7l pots filled with peat and obtained 59% of acorn viability. In our test, we sowed acorns in separate flats under a less competitive environment. The mean time of seedling emergence was 47.8 ± 13.1 days for acorns from holm oaks colonized by L. neglectus and 47.3 ± 14.1 days for acorns from holm oaks colonized by L. grandis. We randomly chose 10 one-month-old seedlings to calculate their quality using the Dickson index.38 This index indicates the potentiality of a seedling to survive and to grow by combining the ratio between root biomass and total biomass with the height and the diameter of the sapling. Seedlings with a higher quality have a higher index. Seedlings showed a very low and similar Dickson index (Mann-Whitnney, L. neglectus: 0.072 ± 0.015; L. grandis: 0.075 ± 0.015, U = 44, p = 0.68, n = 10 seedlings). The low values of Dickson index of the two treatments suggest that from the chosen acorns, emerged seedlings had, per se, a low quality. Only a long term experiment, i.e., at least 10 years to achieve at least two masting years with reproductive holm oaks that never had been infested with aphids, and another group that was infested, could reveal if the effect of aphid feeding on acorns really affect holm oak fitness.We conclude that ants, through their mutualism with tended aphids, may promote considerable changes of holm oaks VOCs emission and acorn quality. However, there was no effect on seedling quality in spite of the decrease of linolenic acid content of acorns from holm oaks where aphids were tended by the invasive ant. These results indicate that the physiological response of acorns to aphid feeding tended by invasive or local ants does not necessary imply a low quality of seedlings as we previously expected. Under natural conditions, the emission of mature holm oak doubled those of saplings from a plantation.39 So considering that we performed our experiment using 4-year-old saplings, it is probable that the indirect effect of ants on VOCs emissions and acorn quality could be magnified when aphid outbreaks occur in mature holm oak forest. Taking into account the contribution of monoterpenes and isoprene emitted by mediterranean and boreal forests to atmospheric VOC pools40 and the species richness of aphids in the north hemisphere,41 we suggest, in agreement with Blande et al., that aphid infestations should be considered in future models of biogenic VOC emissions from forests. 相似文献
Table 1
Means and standard error of the emission rates of the main compounds emitted by Quercus ilex saplings (n = 4 for T1 and T2 and n = 8 for T3) infested with untended aphids (T1) or infested with aphids tended by the native ant Lasius grandis (T2) or by the invasive ant Lasius neglectus (T3)Emission rates: µg g−1 h−1 above and nmol m−2 s−1 below | |||
Compound | T1 | T2 | T3 |
Non tended | Tended by native ant | Tended by invasive ant | |
α-Thujene | 0.007 ± 0.004a | 0.015 ± 0.005a | 0.005 ± 0.001a |
0.006 ± 0.004a | 0.006 ± 0.003a | 0.009 ± 0.008a | |
α-Pinene | 0.391 ± 0.182a | 2.072 ± 0.033b | 0.551 ± 0.105a |
0.244 ± 0.139a | 0.532 ± 0.082a | 0.244 ± 0.127a | |
Camphene | 0.007 ± 0.003a | 0.047 ± 0.014b | 0.012 ± 0.004ab |
0.005 ± 0.003a | 0.014 ± 0.004a | 0.007 ± 0.004a | |
Sabinene | 0.084 ± 0.042a | 0.387 ± 0.045b | 0.075 ± 0.017a |
0.100 ± 0.076a | 0.210 ± 0.097a | 0.128 ± 0.107a | |
β-Pinene | 0.227 ± 0.105a | 1.454 ± 0.269b | 0.306 ± 0.075a |
0.159 ± 0.097a | 0.322 ± 0.134a | 0.179 ± 0.097a | |
Myrcene | 0.443 ± 0.057a | 0.482 ± 0.044a | 0.093 ± 0.020b |
0.101 ± 0.034a | 0.119 ± 0.026a | 0.060 ± 0.034a | |
Δ3-Carene | 0.003 ± 0.002a | 0.018 ± 0.001b | 0.010 ± 0.003ab |
0.001 ± 0.001a | 0.004 ± 0.001a | 0.002 ± 0.001a | |
α-Terpine | 0.004 ± 0.001a | 0.003 ± 0.001a | 0.001 ± 0.000a |
0.001 ± 0.000a | 0.004 ± 0.003a | 0.001 ± 0.001a | |
γ-Terpinene | 0.012 ± 0.002a | 0.011 ± 0.004a | 0.013 ± 0.005a |
0.003 ± 0.001a | 0.013 ± 0.010a | 0.006 ± 0.003a | |
Terpinolene | 0.001 ± 0.000a | 0.002 ± 0.001a | 0.005 ± 0.002a |
0.001 ± 0.000a | 0.002 ± 0.001a | 0.001 ± 0.001a | |
Leaf mass (g) | 0.001 ± 0.000a | 0.002 ± 0.001a | 0.005 ± 0.002a |
Leaf area (m2) | 0.104 ± 0.005a | 0.146 ± 0.026a | 0.113 ± 0.006a |
2.
Riboflavin significantly enhanced the efficacy of simulated solar disinfection (SODIS) at 150 watts per square meter (W m−2) against a variety of microorganisms, including Escherichia coli, Fusarium solani, Candida albicans, and Acanthamoeba polyphaga trophozoites (>3 to 4 log10 after 2 to 6 h; P < 0.001). With A. polyphaga cysts, the kill (3.5 log10 after 6 h) was obtained only in the presence of riboflavin and 250 W m−2 irradiance.Solar disinfection (SODIS) is an established and proven technique for the generation of safer drinking water (11). Water is collected into transparent plastic polyethylene terephthalate (PET) bottles and placed in direct sunlight for 6 to 8 h prior to consumption (14). The application of SODIS has been shown to be a simple and cost-effective method for reducing the incidence of gastrointestinal infection in communities where potable water is not available (2-4). Under laboratory conditions using simulated sunlight, SODIS has been shown to inactivate pathogenic bacteria, fungi, viruses, and protozoa (6, 12, 15). Although SODIS is not fully understood, it is believed to achieve microbial killing through a combination of DNA-damaging effects of ultraviolet (UV) radiation and thermal inactivation from solar heating (21).The combination of UVA radiation and riboflavin (vitamin B2) has recently been reported to have therapeutic application in the treatment of bacterial and fungal ocular pathogens (13, 17) and has also been proposed as a method for decontaminating donor blood products prior to transfusion (1). In the present study, we report that the addition of riboflavin significantly enhances the disinfectant efficacy of simulated SODIS against bacterial, fungal, and protozoan pathogens.Chemicals and media were obtained from Sigma (Dorset, United Kingdom), Oxoid (Basingstoke, United Kingdom), and BD (Oxford, United Kingdom). Pseudomonas aeruginosa (ATCC 9027), Staphylococcus aureus (ATCC 6538), Bacillus subtilis (ATCC 6633), Candida albicans (ATCC 10231), and Fusarium solani (ATCC 36031) were obtained from ATCC (through LGC Standards, United Kingdom). Escherichia coli (JM101) was obtained in house, and the Legionella pneumophila strain used was a recent environmental isolate.B. subtilis spores were produced from culture on a previously published defined sporulation medium (19). L. pneumophila was grown on buffered charcoal-yeast extract agar (5). All other bacteria were cultured on tryptone soy agar, and C. albicans was cultured on Sabouraud dextrose agar as described previously (9). Fusarium solani was cultured on potato dextrose agar, and conidia were prepared as reported previously (7). Acanthamoeba polyphaga (Ros) was isolated from an unpublished keratitis case at Moorfields Eye Hospital, London, United Kingdom, in 1991. Trophozoites were maintained and cysts prepared as described previously (8, 18).Assays were conducted in transparent 12-well tissue culture microtiter plates with UV-transparent lids (Helena Biosciences, United Kingdom). Test organisms (1 × 106/ml) were suspended in 3 ml of one-quarter-strength Ringer''s solution or natural freshwater (as pretreated water from a reservoir in United Kingdom) with or without riboflavin (250 μM). The plates were exposed to simulated sunlight at an optical output irradiance of 150 watts per square meter (W m−2) delivered from an HPR125 W quartz mercury arc lamp (Philips, Guildford, United Kingdom). Optical irradiances were measured using a calibrated broadband optical power meter (Melles Griot, Netherlands). Test plates were maintained at 30°C by partial submersion in a water bath.At timed intervals for bacteria and fungi, the aliquots were plated out by using a WASP spiral plater and colonies subsequently counted by using a ProtoCOL automated colony counter (Don Whitley, West Yorkshire, United Kingdom). Acanthamoeba trophozoite and cyst viabilities were determined as described previously (6). Statistical analysis was performed using a one-way analysis of variance (ANOVA) of data from triplicate experiments via the InStat statistical software package (GraphPad, La Jolla, CA).The efficacies of simulated sunlight at an optical output irradiance of 150 W m−2 alone (SODIS) and in the presence of 250 μM riboflavin (SODIS-R) against the test organisms are shown in Table Table1.1. With the exception of B. subtilis spores and A. polyphaga cysts, SODIS-R resulted in a significant increase in microbial killing compared to SODIS alone (P < 0.001). In most instances, SODIS-R achieved total inactivation by 2 h, compared to 6 h for SODIS alone (Table (Table1).1). For F. solani, C. albicans, ands A. polyphaga trophozoites, only SODIS-R achieved a complete organism kill after 4 to 6 h (P < 0.001). All control experiments in which the experiments were protected from the light source showed no reduction in organism viability over the time course (results not shown).
Open in a separate windowaConditions are at an intensity of 150 W m−2 unless otherwise indicated.bThe values reported are means ± standard errors of the means from triplicate experiments.cAdditional experiments for this condition were performed using natural freshwater.The highly resistant A. polyphaga cysts and B. subtilis spores were unaffected by SODIS or SODIS-R at an optical irradiance of 150 W m−2. However, a significant reduction in cyst viability was observed at 6 h when the optical irradiance was increased to 250 W m−2 for SODIS-R only (P < 0.001; Table Table1).1). For spores, a kill was obtained only at 320 W m−2 after 6-h exposure, and no difference between SODIS and SODIS-R was observed (Table (Table1).1). Previously, we reported a >2-log kill at 6 h for Acanthamoeba cysts by using SODIS at the higher optical irradiance of 850 W m−2, compared to the 0.1-log10 kill observed here using the lower intensity of 250 W m−2 or the 3.5-log10 kill with SODIS-R.Inactivation experiments performed with Acanthamoeba cysts and trophozoites suspended in natural freshwater gave results comparable to those obtained with Ringer''s solution (P > 0.05; Table Table1).1). However, it is acknowledged that the findings of this study are based on laboratory-grade water and freshwater and that differences in water quality through changes in turbidity, pH, and mineral composition may significantly affect the performance of SODIS (20). Accordingly, further studies are indicated to evaluate the enhanced efficacy of SODIS-R by using natural waters of varying composition in the areas where SODIS is to be employed.Previous studies with SODIS under laboratory conditions have employed lamps delivering an optical irradiance of 850 W m−2 to reflect typical natural sunlight conditions (6, 11, 12, 15, 16). Here, we used an optical irradiance of 150 to 320 W m−2 to obtain slower organism inactivation and, hence, determine the potential enhancing effect of riboflavin on SODIS.In conclusion, this study has shown that the addition of riboflavin significantly enhances the efficacy of simulated SODIS against a range of microorganisms. The precise mechanism by which photoactivated riboflavin enhances antimicrobial activity is unknown, but studies have indicated that the process may be due, in part, to the generation of singlet oxygen, H2O2, superoxide, and hydroxyl free radicals (10). Further studies are warranted to assess the potential benefits from riboflavin-enhanced SODIS in reducing the incidence of gastrointestinal infection in communities where potable water is not available. 相似文献
TABLE 1.
Efficacies of simulated SODIS for 6 h alone and with 250 μM riboflavin (SODIS-R)Organism | Conditiona | Log10 reduction in viability at indicated h of exposureb | |||
---|---|---|---|---|---|
1 | 2 | 4 | 6 | ||
E. coli | SODIS | 0.0 ± 0.0 | 0.2 ± 0.1 | 5.7 ± 0.0 | 5.7 ± 0.0 |
SODIS-R | 1.1 ± 0.0 | 5.7 ± 0.0 | 5.7 ± 0.0 | 5.7 ± 0.0 | |
L. pneumophila | SODIS | 0.7 ± 0.2 | 1.3 ± 0.3 | 4.8 ± 0.2 | 4.8 ± 0.2 |
SODIS-R | 4.4 ± 0.0 | 4.4 ± 0.0 | 4.4 ± 0.0 | 4.4 ± 0.0 | |
P. aeruginosa | SODIS | 0.7 ± 0.0 | 1.8 ± 0.0 | 4.9 ± 0.0 | 4.9 ± 0.0 |
SODIS-R | 5.0 ± 0.0 | 5.0 ± 0.0 | 5.0 ± 0.0 | 5.0 ± 0.0 | |
S. aureus | SODIS | 0.0 ± 0.0 | 0.0 ± 0.0 | 6.2 ± 0.0 | 6.2 ± 0.0 |
SODIS-R | 0.2 ± 0.1 | 6.3 ± 0.0 | 6.3 ± 0.0 | 6.3 ± 0.0 | |
C. albicans | SODIS | 0.2 ± 0.0 | 0.4 ± 0.1 | 0.5 ± 0.1 | 1.0 ± 0.1 |
SODIS-R | 0.1 ± 0.0 | 0.7 ± 0.1 | 5.3 ± 0.0 | 5.3 ± 0.0 | |
F. solani conidia | SODIS | 0.2 ± 0.1 | 0.3 ± 0.0 | 0.2 ± 0.0 | 0.7 ± 0.1 |
SODIS-R | 0.3 ± 0.1 | 0.8 ± 0.1 | 1.3 ± 0.1 | 4.4 ± 0.0 | |
B. subtilis spores | SODIS | 0.3 ± 0.0 | 0.2 ± 0.0 | 0.0 ± 0.0 | 0.1 ± 0.0 |
SODIS-R | 0.1 ± 0.1 | 0.2 ± 0.1 | 0.3 ± 0.3 | 0.1 ± 0.0 | |
SODIS (250 W m−2) | 0.1 ± 0.0 | 0.1 ± 0.1 | 0.1 ± 0.1 | 0.0 ± 0.0 | |
SODIS-R (250 W m−2) | 0.0 ± 0.0 | 0.0 ± 0.0 | 0.2 ± 0.0 | 0.4 ± 0.0 | |
SODIS (320 W m−2) | 0.1 ± 0.1 | 0.1 ± 0.0 | 0.0 ± 0.1 | 4.3 ± 0.0 | |
SODIS-R (320 W m−2) | 0.1 ± 0.0 | 0.1 ± 0.1 | 0.9 ± 0.0 | 4.3 ± 0.0 | |
A. polyphaga trophozoites | SODIS | 0.4 ± 0.2 | 0.6 ± 0.1 | 0.6 ± 0.2 | 0.4 ± 0.1 |
SODIS-R | 0.3 ± 0.1 | 1.3 ± 0.1 | 2.3 ± 0.4 | 3.1 ± 0.2 | |
SODIS, naturalc | 0.3 ± 0.1 | 0.4 ± 0.1 | 0.5 ± 0.2 | 0.3 ± 0.2 | |
SODIS-R, naturalc | 0.2 ± 0.1 | 1.0 ± 0.2 | 2.2 ± 0.3 | 2.9 ± 0.3 | |
A. polyphaga cysts | SODIS | 0.4 ± 0.1 | 0.1 ± 0.3 | 0.3 ± 0.1 | 0.4 ± 0.2 |
SODIS-R | 0.4 ± 0.2 | 0.3 ± 0.2 | 0.5 ± 0.1 | 0.8 ± 0.3 | |
SODIS (250 W m−2) | 0.0 ± 0.1 | 0.2 ± 0.3 | 0.2 ± 0.1 | 0.1 ± 0.2 | |
SODIS-R (250 W m−2) | 0.4 ± 0.2 | 0.3 ± 0.2 | 0.8 ± 0.1 | 3.5 ± 0.3 | |
SODIS (250 W m−2), naturalc | 0.0 ± 0.3 | 0.2 ± 0.1 | 0.1 ± 0.1 | 0.2 ± 0.1 | |
SODIS-R (250 W m−2), naturalc | 0.1 ± 0.1 | 0.2 ± 0.2 | 0.6 ± 0.1 | 3.4 ± 0.2 |
3.
Many plant species can be induced to flower by responding to stress factors. The short-day plants Pharbitis nil and Perilla frutescens var. crispa flower under long days in response to the stress of poor nutrition or low-intensity light. Grafting experiments using two varieties of P. nil revealed that a transmissible flowering stimulus is involved in stress-induced flowering. The P. nil and P. frutescens plants that were induced to flower by stress reached anthesis, fruited and produced seeds. These seeds germinated, and the progeny of the stressed plants developed normally. Phenylalanine ammonialyase inhibitors inhibited this stress-induced flowering, and the inhibition was overcome by salicylic acid (SA), suggesting that there is an involvement of SA in stress-induced flowering. PnFT2, a P. nil ortholog of the flowering gene FLOWERING LOCUS T (FT) of Arabidopsis thaliana, was expressed when the P. nil plants were induced to flower under poor-nutrition stress conditions, but expression of PnFT1, another ortholog of FT, was not induced, suggesting that PnFT2 is involved in stress-induced flowering.Key words: flowering, stress, phenylalanine ammonia-lyase, salicylic acid, FLOWERING LOCUS T, Pharbitis nil, Perilla frutescensFlowering in many plant species is regulated by environmental factors, such as night-length in photoperiodic flowering and temperature in vernalization. On the other hand, a short-day (SD) plant such as Pharbitis nil (synonym Ipomoea nil) can be induced to flower under long days (LD) when grown under poor-nutrition, low-temperature or high-intensity light conditions.1–9 The flowering induced by these conditions is accompanied by an increase in phenylalanine ammonia-lyase (PAL) activity.10 Taken together, these facts suggest that the flowering induced by these conditions might be regulated by a common mechanism. Poor nutrition, low temperature and high-intensity light can be regarded as stress factors, and PAL activity increases under these stress conditions.11 Accordingly, we assumed that such LD flowering in P. nil might be induced by stress. Non-photoperiodic flowering has also been sporadically reported in several plant species other than P. nil, and a review of these studies suggested that most of the factors responsible for flowering could be regarded as stress. Some examples of these factors are summarized in 12–14
Open in a separate window 相似文献
Table 1
Some cases of stress-induced floweringStress factor | Species | Flowering response | Reference |
high-intensity light | Pharbitis nil | induction | 5 |
low-intensity light | Lemna paucicostata | induction | 29 |
Perilla frutescens var. crispa | induction | 14 | |
ultraviolet C | Arabidopsis thaliana | induction | 23 |
drought | Douglas-fir | induction | 30 |
tropical pasture Legumes | induction | 31 | |
lemon | induction | 32–35 | |
Ipomoea batatas | promotion | 36 | |
poor nutrition | Pharbitis nil | induction | 3, 4, 13 |
Macroptilium atropurpureum | promotion | 37 | |
Cyclamen persicum | promotion | 38 | |
Ipomoea batatas | promotion | 36 | |
Arabidopsis thaliana | induction | 39 | |
poor nitrogen | Lemna paucicostata | induction | 40 |
poor oxygen | Pharbitis nil | induction | 41 |
low temperature | Pharbitis nil | induction | 9, 12 |
high conc. GA4/7 | Douglas-fir | promotion | 42 |
girdling | Douglas-fir | induction | 43 |
root pruning | Citrus sp. | induction | 44 |
Pharbitis nil | induction | 45 | |
mechanical stimulation | Ananas comosus | induction | 46 |
suppression of root elongation | Pharbitis nil | induction | 7 |
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6.
Pavan Umate 《Plant signaling & behavior》2011,6(3):335-338
The enzymes called lipoxygenases (LOXs) can dioxygenate unsaturated fatty acids, which leads to lipoperoxidation of biological membranes. This process causes synthesis of signaling molecules and also leads to changes in cellular metabolism. LOXs are known to be involved in apoptotic (programmed cell death) pathway, and biotic and abiotic stress responses in plants. Here, the members of LOX gene family in Arabidopsis and rice are identified. The Arabidopsis and rice genomes encode 6 and 14 LOX proteins, respectively, and interestingly, with more LOX genes in rice. The rice LOXs are validated based on protein alignment studies. This is the first report wherein LOXs are identified in rice which may allow better understanding the initiation, progression and effects of apoptosis, and responses to bitoic and abiotic stresses and signaling cascades in plants.Key words: apoptosis, biotic and abiotic stresses, genomics, jasmonic acid, lipidsLipoxygenases (linoleate:oxygen oxidoreductase, EC 1.13.11.-; LOXs) catalyze the conversion of polyunsaturated fatty acids (lipids) into conjugated hydroperoxides. This process is called hydroperoxidation of lipids. LOXs are monomeric, non-heme and non-sulfur, but iron-containing dioxygenases widely expressed in fungi, animal and plant cells, and are known to be absent in prokaryotes. However, a recent finding suggests the existence of LOX-related genomic sequences in bacteria but not in archaea.1 The inflammatory conditions in mammals like bronchial asthama, psoriasis and arthritis are a result of LOXs reactions.2 Further, several clinical conditions like HIV-1 infection,3 disease of kidneys due to the activation of 5-lipoxygenase,4,5 aging of the brain due to neuronal 5-lipoxygenase6 and atherosclerosis7 are mediated by LOXs. In plants, LOXs are involved in response to biotic and abiotic stresses.8 They are involved in germination9 and also in traumatin and jasmonic acid biochemical pathways.10,11 Studies on LOX in rice are conducted to develop novel strategies against insect pests12 in response to wounding and insect attack,13 and on rice bran extracts as functional foods and dietary supplements for control of inflammation and joint health.14 In Arabidopsis, LOXs are studied in response to natural and stress-induced senescence,15 transition to flowering,16 regulation of lateral root development and defense response.17The arachidonic, linoleic and linolenic acids can act as substrates for different LOX isozymes. A hydroperoxy group is added at carbons 5, 12 or 15, when arachidonic acid is the substrate, and so the LOXs are designated as 5-, 12- or 15-lipoxygenases. Sequences are available in the database for plant lipoxygenases (EC:1.13.11.12), mammalian arachidonate 5-lipoxygenase (EC:1.13.11.34), mammalian arachidonate 12-lipoxygenase (EC:1.13.11.31) and mammalian erythroid cell-specific 15-lipoxygenase (EC:1.13.11.33). The prototype member for LOX family, LOX-1 of Glycine max L. (soybean) is a 15-lipoxygenase. The LOX isoforms of soybean (LOX-1, LOX-2, LOX-3a and LOX-3b) are the most characterized of plant LOXs.18 In addition, five vegetative LOXs (VLX-A, -B, -C, -D, -E) are detected in soybean leaves.19 The 3-dimensional structure of soybean LOX-1 has been determined.20,21 LOX-1 was shown to be made of two domains, the N-terminal domain-I which forms a β-barrel of 146 residues, and a C-terminal domain-II of bundle of helices of 693 residues21 (Fig. 1). The iron atom was shown to be at the centre of domain-II bound by four coordinating ligands, of which three are histidine residues.22Open in a separate windowFigure 1Three-dimensional structure of soybean lipoxygenase L-1. The domain I (N-terminal) and domain II (C-terminal) are indicated. The catalytic iron atom is embedded in domain II (PDB ID-1YGE).21This article describes identification of LOX genes in Arabidopsis and rice. The Arabidopsis genome encodes for six LOX proteins23 (www.arabidopsis.org) (Locus Annotation Nomenclature A* B* C* AT1G55020 lipoxygenase 1 (LOX1) LOX1 859 98044.4 5.2049 AT1G17420 lipoxygenase 3 (LOX3) LOX3 919 103725.1 8.0117 AT1G67560 lipoxygenase family protein LOX4 917 104514.6 8.0035 AT1G72520 lipoxygenase, putative LOX6 926 104813.1 7.5213 AT3G22400 lipoxygenase 5 (LOX5) LOX5 886 101058.8 6.6033 AT3G45140 lipoxygenase 2 (LOX2) LOX2 896 102044.7 5.3177