Similar attractiveness of maize volatiles induced by Helicoverpa armigera and Pseudaletia separata to the generalist parasitoid Campoletis chlorideae

Campoletis chlorideae Uchida (Hymenoptera: Ichneumonidae), a major larval endoparasitoid of Helicoverpa armigera (Hübner) (Lepidoptera: Noctuidae), also attacks many other noctuid caterpillars. We investigated the attractiveness of H. armigera‐ and Pseudaletia separata (Lepidoptera: Noctuidae)‐infested maize [Zea mays L. (Poaceae)] plants to C. chlorideae, and analyzed the volatiles emitted from infested plants and undamaged plants. Considering the reported specific induction of plant volatiles by elicitors in the caterpillar regurgitant, we also tested the response of the parasitoid to mechanically damaged plants treated with caterpillar regurgitant or water and measured the volatiles released by these plants. In wind‐tunnel bioassays, C. chlorideae was strongly attracted to herbivore‐induced maize volatiles. Mechanically damaged plants, whether they were treated with caterpillar regurgitant or water, were more attractive to the parasitoid than undamaged plants. The parasitoid did not distinguish between maize seedlings infested by the two noctuid insects, nor did they show a difference in attraction to mechanically damaged plants treated with caterpillar regurgitant or water. Coupled gas chromatography–mass spectrometer (GC‐MS) analysis revealed that 15 compounds were commonly emitted by herbivore‐infested and mechanically damaged maize plants, whereas only two compounds were released in minor amounts from undamaged plants. Infestation by H. armigera specifically induced four terpenoids, β‐pinene, β‐myrcene, D‐limonene, and (E)‐nerolidol, which were not induced by infestation of P. separata and mechanical damage, plus caterpillar regurgitant or water. Two compounds, geranyl acetate and β‐sesquiphellandrene, were also induced by the infestation of H. armigera, but not by the infestation of P. separata. All treated maize plants released volatiles in significantly larger total amounts than did undamaged plants. Maize plants infested by H. armigera emitted greater amounts of volatiles than plants infested by P. separata. The treatment with caterpillar regurgitant resulted in larger amounts of volatile emission than the treatment with water did in mechanically damaged plants. The amounts of emissions of individual compounds were also different between differently treated plants.     

Aboveground Whitefly Infestation Modulates Transcriptional Levels of Anthocyanin Biosynthesis and Jasmonic Acid Signaling-Related Genes and Augments the Cope with Drought Stress of Maize

Up to now, the potential underlying molecular mechanisms by which maize (Zea mays L.) plants elicit defense responses by infestation with a phloem feeding insect whitefly [Bemisia tabaci (Genn.)] have been barely elucidated against (a)biotic stresses. To fill this gap of current knowledge maize plants were infested with whitefly and these plants were subsequently assessed the levels of water loss. To understand the mode of action, plant hormone contents and the stress-related mRNA expression were evaluated. Whitefly-infested maize plants did not display any significant phenotypic differences in above-ground tissues (infested site) compared with controls. By contrast, root (systemic tissue) biomass was increased by 2-fold by whitefly infestation. The levels of endogenous indole-3-acetic acid (IAA), jasmonic acid (JA), and hydrogen peroxide (H₂O₂) were significantly higher in whitefly-infested plants. The biosynthetic or signaling-related genes for JA and anthocyanins were highly up-regulated. Additionally, we found that healthier plants were obtained in whitefly-infested plants under drought conditions. The weight of whitefly-infested plants was approximately 20% higher than that of control plants at 14 d of drought treatment. The drought tolerance-related genes, ZmbZIP72, ZmSNAC1, and ZmABA1, were highly expressed in the whitefly-infected plants. Collectively, our results suggest that IAA/JA-derived maize physiological changes and correlation of H₂O₂ production and water loss are modulated by above-ground whitefly infestation in maize plants.     

The influence of kinetin on the endogenous content of indoleacetic acid in swelling seeds of Phaseolus, Zea and Pinus and young plants of Phaseolus

Treatment of different plant materials, seeds of Phaseolus vulgaris, Zea mays and Pinus silvestris and young plants of Phaseolus, with kinetin increased the level of extractable IAA. For seeds this increase was most pronounced in bean seeds, which contained the lowest amount of endogenous IAA and cytokinins, and lower in maize seeds with high endogenous content of IAA and cytokinins. – For young bean plants the kinetin treatment significantly increased the extractable amounts of IAA from all parts of the plant, hypocotyls, cotyledons, epicotyls and primary leaves, when the cut plants were placed for 24 h in kinetin solution. For plants sprayed with kinetin solution only the primary leaves showed a significantly higher level of extractable IAA, which could be explained by the fact that the plants were growing very close together, so that the primary leaves received most of the kinetin during spraying.     

Pea aphids (Acyrthosiphon pisum Harris) reduce secretion of extrafloral nectar in broad bean (Vicia faba)

1. Herbivores sometimes suppress plant defences. This study tested whether the presence of pea aphids (Acyrthosiphon pisum Harris) on broad bean (Vicia faba) led to decreased secretion of extrafloral nectar (EFN) which functions as an indirect plant defence against herbivores. 2. To determine effects of aphid infestation on EFN secretion, a comparison was done between EFN secretion in uninfested plants and that in plants infested by A. pisum and another aphid species (Aphis craccivora Koch). 3. When broad bean plants were infested by A. pisum, they secreted significantly smaller amounts of EFN than did uninfested plants and A. craccivora‐infested plants. There was no significant difference in EFN secretion between uninfested plants and A. craccivora‐infested plants. The number of extrafloral nectaries did not differ among the three treatments. 4. These results suggest that A. pisum reduced EFN production in broad bean plants.     

Auxin Physiology of Decapitated Stems of Phaseolus vulgaris L. Treated with Indol-3yl-acetic Acid

Physiological amounts of indol-3yl-acetic acid (IAA) were accumulatedby decapitated stems of Phaseolus vulgaris L. seedlings fromlanolin pastes, containing 0.1 per cent IAA, applied to thecut surfaces of the stumps. Both the levels and gradients ofextractable and diffusable IAA detected in the treated stumpscompared favourably with those reported for the whole plants.A considerable portion of IAA that entered the tissue was metabolizedto a compound that had chromatographic properties similar toindol-3yl-acetylaspartic acid. Two other metabolities were tentativelyidentified as indol-3yl-acetylaspartic acid indol-3yl-acetylglucose.The accumulated IAA appears to be transported as indol-3yl-aceticacid at an apparent velocity of 28 mm/h down the decapitatedinternodes.     

Epiphytic microorganisms and IAA synthesis

Summary Epiphytic microorganisms present on cotton plants synthesized 3-indoleacetic acid (IAA) from tryptophan. Microorganisms from the root zone synthesized 3 times the amount of IAA when compared with the shoot zone and the root zone contained a much higher number of microorganisms. IAA-synthesizing activity was eliminated when the tissues were treated with a weak solution of mercuric chloride. Various tests on the possible accumulation of IAA from external sources showed that IAA synthesized outside the plant does not accumulate in the plant. Although epiphytic microorganisms synthesize IAA in large amounts, they do not influence the IAA content of the plant due to (1) lack of available tryptophan, (2) destruction of the auxin by the microflora, and (3) the polar movement of the auxin.     

Can herbivore‐induced plant volatiles inform predatory insect about the most suitable stage of its prey?

The leaf beetle Plagiodera versicolora (Coleoptera: Chrysomelidae) is a specialist herbivore, all of whose mobile stages feed on the leaves of salicaceous plants. Both the larval and adult stages of the ladybird Aiolocaria hexaspilota (Coleoptera: Coccinellidae) are dominant natural enemies of the larvae of the leaf beetle. To clarify the role of plant volatiles in prey‐finding behaviour of A. hexaspilota, the olfactory responses of the ladybird in a Y‐tube olfactometer are studied. The ladybird adults show no preference for willow plants Salix eriocarpa that are infested by leaf beetle adults (nonprey) over that for intact plants but move more to the willow plants infested by leaf beetle larvae (prey) than to intact plants. Moreover, ladybird larvae show no preference for willow plants infested by leaf beetle larvae or adults over intact plants. Using gas chromatography‐mass spectrometry, six volatile compounds are released in larger amounts in the headspace of willow plants infested by leaf beetle larvae than in the headspace of willow plants infested by leaf beetle adults. In addition, the total amount of volatiles emitted from willow plants that are either intact or infested by leaf beetle adults is much smaller than that from willow plants infested by leaf beetle larvae. These results indicate that volatiles from S. eriocarpa infested by P. versicolora inform A. hexaspilota adults about the presence of the most suitable stage of their prey, whereas A. hexaspilota larvae do not use such information.     

Adaptation of chickpea to desiccation stress is enhanced by symbiotic rhizobia

This study examined the influence of three inoculant strains of Bradyrhizobium japonicum (Thal-8, Tal 620, Dulawala) on the ability of chickpea (Cicer arietinum (L.) to adapt to drought-stress. Strain Thal-8 was most effective in the root-nodule symbiosis and also partially alleviated decreased growth and yield imposed by drought stress. Strain Thal-8, in pure culture, also produced higher amounts of gibberellic acid (GA) and indole-3-acetic acid (IAA) and lower amounts of abscisic acid (ABA) than the other two test strains. Thal-8 increased the root biomass, GA and IAA contents of leaves of chickpea plants, including ICC 4948NN, a non-nodulating line. These results are consistent with the hypothesis that GA and IAA is produced by the Thal-8 strain and/or elevates levels of these phytohormones in chickpeas. This contributes to its high performance as a nitrogen-fixing microsymbiont. The growth-promoting response evoked by different strains of Bradyrhizobium correlated with higher ratios of GA and IAA relative to ABA phytohormones in the plants.     

Morphogenesis of potato plants in vitro. II. Endogenous levels,distribution, and metabolism of IAA and cytokinins

The levels of endogenous IAA and cytokinins (zeatin, zeatin riboside, isopentenyladenine, and isopentenyladenosine) were determined in potato plants cultured in vitro under red light (R) and blue light (B) on medium with or without hormones. On medium without hormones in B, plants contained much higher cytokinin levels, particularly in leaves and roots, and also slightly elevated IAA levels. Kinetin in the medium in B changed the distribution of cytokinins and significantly increased IAA level in roots. In R, the presence of kinetin led to an increased cytokinin level in the whole plant, while the IAA level was slightly lower. IAA in the medium in B decreased cytokinin level in all plant parts, while the IAA level did not change significantly. In R, the presence of IAA in the medium led to a moderate increase of CK level and to a significant increase in IAA level, especially in roots. Uptake of 1-¹⁴C-IAA and of ³H-zeatin was generally higher in B than in R. Higher percentage of IAA taken up in B was converted to conjugates in the roots. Metabolism of ³H-zeatin was similar in R and B with only slight differences in metabolite amounts.Thus, in all experimental situations in which tuber formation was stimulated, IAA level in roots and stolons rose significantly, stressing the importance of an IAA gradient for tuber formation.     

Interaction of abscisic acid and indole-3-acetic acid-producing fungi with Salix leaves

The molds Botrytis cinerea, Cladosporium cladosporioides, and the yeast Aureobasidium pullulans, isolated from the leaves of three short-rotation Salix clones, were found to produce indole-3-acetic acid (IAA). Abscisic acid (ABA) production was detected in B. cinerea. The contents of IAA and ABA in the leaves of the Salix clones and the amounts of fungal propagules in these leaves were also measured, in order to evaluate whether the amounts of plant growth regulators produced by the fungi would make a significant contribution to the hormonal quantities of the leaves. The content of ABA, and to a lesser degree that of IAA, showed a positive correlation with the frequency of infection by the hormone-producing organisms. The amounts of hormone-producing fungi on leaves that bore visible colonies were, however, not sufficiently high to support the claim that either the fungal production of ABA or IAA would significantly contribute to the hormonal contents of the leaves of the Salix clones. It is therefore suggested that the effect of fungal IAA production on plants is limited to the rhizosphere and that B. cinerea, which is a known pathogen, induces ABA production by the mother plant as a response to physiological stress.Abbreviations ABA abscisic acid - ABA-Me abscisic acid methyl ester - GC-MS-SIM gas chromatography-selected ion monitoring-mass spectrometry - IAA indole-3-acetic acid - IAA-Me indole-3-acetic acid methyl ester Author for correspondence.     

Evidence that the mature leaves contribute auxin to the immature tissues of pea (<Emphasis Type="Italic">Pisum sativum</Emphasis> L.)

In plants such as the garden pea (Pisum sativum L.), it is widely thought that the auxin indole-3-acetic acid (IAA) is synthesised mainly in the immature tissues of the apical bud and then transported basipetally to other parts of the plant. Consistent with this belief are results showing that removal of the apical bud markedly reduces the IAA content in the stem. However, it has also been suggested that the mature leaves may synthesise substantial amounts of IAA, which enters the basipetal transport stream after being transported to the shoot apex in the phloem (Cambridge and Morris in Planta 99:583–588, 1996). To examine this theory, we defoliated pea plants and measured the effect on IAA content in the remaining shoot tissues. IAA levels were reduced in the internodes, and to a lesser extent in the apical bud, after defoliation, suggesting that mature leaves are indeed an important source of auxin for the shoot. Consistent with this idea, we have demonstrated that mature, fully expanded leaves are capable of de novo IAA synthesis. Furthermore, we report evidence for the presence of IAA in the phloem sap of pea. Together these results support those of Cambridge and Morris, suggesting that mature leaves are a source of the IAA in the basipetal transport stream.     

Tiller Bud Suppression in Reproductive Plants of Lolium multiflorum Lam. Cv. Westerwoldicum

The control of tiller bud growth during reproductive developmentwas investigated in experimental plants ofLolium multiflorumLam. cv. Westerwoldicum that were reduced to a main axis havinga developing but unemerged ear, elongating stem internodes,a series of expanded leaves, slow-growing tiller buds and aroot system. Isolation of the ear by excision of its base, ordecapitation so as to remove the ear together with the upperleaves, promoted the movement of ¹⁴C-assimilates to tiller buds,decapitation being the more effective treatment. Applicationof 0.1 per cent indol–3yl-acetic acid (IAA) to cut tissuesof decapitated plants diverted ¹⁴C-assimilates to upper internodesbut did not reduce import by buds, whereas application of 1.0per cent IAA both diverted labelled assimilates to upper internodesand reduced bud import. Radioactivity from [¹⁴C] IAA appliedto the upper leaves or to the ear base was recovered from budsin very small amounts; larger amounts were recovered from budsfollowing the application of labelled IAA to an elongating internode,especially from the bud at the base of the treated internode.It is suggested that tiller bud suppression may be influencedby the movement of inhibitory levels of auxin into buds fromnearby elongating stem internodes, whose activity in turn maybe controlled by the developing inflorescence and upper leaves.     

Characterization of oxidative enzyme changes in buffalograsses challenged by Blissus occiduus

This research investigated the role of oxidative enzymes in the defense response of buffalograss, Buchlo? dactyloides (Nuttall) Engelmann, to Blissus occiduus Barber. Changes in catalase and peroxidase activity were observed in both resistant and susceptible buffalograsses in response to chinch bug feeding. Susceptible plants were shown to have a lower level of catalase activity compared with their respective control plants. By contrast, catalase activities of resistant plants were similar between infested and control buffalograsses throughout the study. Resistant plants had higher levels of peroxidase activity compared with their control plants, whereas peroxidase activities for control and infested susceptible plants remained at similar levels or were slightly lower for infested plants. These findings suggest that chinch bug feeding leads to a loss in catalase activity in susceptible buffalograsses. In contrast, resistant buffalograsses may be able to tolerate chinch bug feeding by increasing their peroxidase activity. Polyphenol oxidase activities were similar between control and infested plants for the buffalograsses evaluated. Among the enzymes examined, no differences in isozyme profiles for peroxidase and polyphenol oxidase were detected between control and infested 378, NE91-118, Cody, and Tatanka plants. Gels stained for catalase identified differences in the isozyme profiles of infested and uninfested 378 plants; however, infested and control NE91-118, Tatanka, and Cody plants has similar isozyme profiles. No differences in protein profiles were observed between chinch buginfested 378, NE91-118, Cody, and Tatanka plants and their respective uninfested controls.     

Effect of Cry3Bb1-expressing transgenic corn on plant-to-plant movement by western corn rootworm larvae (Coleoptera: Chrysomelidae)

Dispersal of larvae of the western corn rootworm, Diabrotica virgifera virgifera LeConte, in specific combinations of transgenic corn expressing the Cry3Bb1 protein and nontransgenic, isoline corn was evaluated in a 2-yr field study. In total, 1,500 viable western corn rootworm eggs were infested in each subplot. Each year, plant damage and larval recovery were evaluated among four pedigree combinations (straight transgenic; straight nontransgenic corn; nontransgenic corn with a transgenic central, infested plant; and transgenic corn with a nontransgenic central, infested plant) on six sample dates between egg hatch and pupation. For each subplot, the infested plant, three successive plants down the row (P1, P2, and P3), the closest plant in the adjacent row of the plot, and a control plant were sampled. The number of western corn rootworm larvae recovered from transgenic rootworm-resistant plants adjacent to infested nontransgenic plants was low and not statistically significant in either 2001 or 2002. In 2001, significantly fewer larvae were recovered from transgenic rootworm-resistant plants than from nontransgenic plants when both were adjacent to infested, nontransgenic plants. In 2002, significantly more neonate western corn rootworm larvae were recovered from nontransgenic plants adjacent to infested, transgenic rootworm-resistant plants than nontransgenic plants adjacent to infested, nontransgenic plants on the second sample date. Together, these data imply that both neonate and later instar western corn rootworm larvae prefer nontransgenic roots to transgenic rootworm-resistant roots when a choice is possible. However, when damage to the infested, nontransgenic plant was high, western corn rootworm larvae apparently moved to neighboring transgenic rootworm-resistant plants and caused statistically significant, although only marginally economic, damage on the last sample date in 2001. Implications of these data toward resistance management plan are discussed.     

Influence of indole-3-acetic acid,kinetin and abscisic acid on the estrogens content of beans

No influence of IAA on the endogenous estrogen content in bean plants was stated. At the same time kinetin was found to increase and abscisic acid to decrease the amounts of estrogens.     

The influence of epiphytic bacteriae on auxin metabolism

Summary Plants are settled by epiphytic bacteriae able to convert tryptophan to IAA. This bacterial activity is abolished by chloramphenicol and streptomycin but not by penicillin. Tryptophan conversion to IAA by plant parts or enzyme preparations is far more intensive in non-sterile conditions than in sterile ones. This is true for all investigated objects: Helianthus annuus, Phaseolus vulgaris, Pisum sativum, Triticum vulgare, Zea mays, Enteromorpha compressa, Fucus vesiculosus, Furcellaria fastigiata. From pea plants, 58 strains of IAA producing bacteriae were isolated and partly identified.While non-sterile plants (Pisum, Zea) contain considerable amounts of IAA (extraction, thin layer chromatography, biotest), hardly any traceable auxin can be extracted of sterile plants. But sterile plants re-infected with mixtures or single strains of suitable bacteriae again contain considerable amounts of extractable IAA.

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Zusammenfassung Pflanzen sind von epiphytischen Bakterien besiedelt, die Tryptophan zu IES umsetzen können. Diese bakterielle Aktivität wird unterbunden durch Chloramphenicol und Streptomycin, aber nicht durch Penicillin. Der Tryptophanumsatz zu IES durch Pflanzenteile oder Enzympräparate ist unter unsterilen Bedingungen weit intensiver als unter sterilen. Das trifft für alle untersuchten Objekte zu: Helianthus annuus, Phaseolus vulgaris, Pisum sativum, Triticum vulgare, Zea mays, Enteromorpha compressa, Fucus vesiculosus, Furcellaria fastigiata. Von Erbsenpflanzen konnten 58 Stämme IES-produzierender Bakterien isoliert und zum Teil identifiziert werden.Während unsterile Pflanzen (Pisum, Zea) beträchtliche IES-Mengen enthalten (Extraktion, Dünnschichtchromatographie, Biotest), kann aus sterilen Pflanzen kaum nachweisbares Auxin extrahiert werden. Aber sterile, mit Mischungen oder einzelnen Stämmen geeigneter Bakterien re-infizierte Pflanzen enthalten wieder beträchtliche Menge extrahierbarer IES.

     

Electric and structural studies of hormone interaction with chloroplast envelope membranes isolated from vegetative and generative rape

The electric and structural properties of envelope membranes of chloroplasts obtained from vegetative and generative plants of rape and the effect of hormone (IAA, GA(3) and zearalenone) treatment were determined by zeta potential and small-angle X-ray scattering (SAXS) methods. Chloroplasts were isolated from leaves cut off from the vegetative (before cooling) and generative apical parts of plants. The lipid composition of chloroplast envelope membranes were analyzed by chromatographic techniques. Envelopes from generative plants contained higher levels of digalactosyldiacylglycerol (DGDG) and smaller amounts of phospholipids (PLs) in comparison to those obtained from vegetative ones. Moreover, envelopes of generative plants were characterized by higher fractions of unsaturated fatty acids. The zeta potential changes caused by hormone treatment were higher for chloroplasts isolated from vegetative plants in comparison to chloroplasts isolated from generative ones. An especially strong effect was observed for chloroplasts treated with IAA. The thickness of bilayers of untreated chloroplasts from vegetative plants were larger by 0.4 nm when comparing to the thickness of layers obtained from generative ones. The effect of hormones (GA(3) and zearalenone) was detected only for vegetative chloroplasts. Both applied methods indicated differences in the properties of untreated and hormone-treated chloroplasts obtained from vegetative and generative plants.     

Morphology and Hormone Levels of Tobacco and Carrot Tissues Transformed by Agrobacterium tumefaciens I. Auxin and Cytokinin Contents of Cultured Tissues Transformed with Wild-Type and Mutant Ti Plasmids

Carrot and tobacco plants were transformed with Agrobacteriumtumefaciens harboring wild-type, aux^– or cyt^– Tiplasmids. In tobacco, these wild and mutant Ti plasmids inducedthe formation of non-morphogenic galls, galls with shoots, andgalls with roots, respectively. In carrot, however, transformationwith any of these plasmids resulted in only the formation ofamorphous tumors. Determination of IAA and cytokinin contentsshowed that in tobacco, significantly high amounts of cytokininsor IAA are present in the cells transformed with Ti plasmidspossessing cytokinin or IAA biosynthetic genes, respectively.In carrot, cytokinin contents were also high in the cells transformedwith Ti plasmids having cytokinin biosynthetic genes, whereasIAA contents of the cells were similar regardless of the plasmidsused for transformation. These results suggest that the mechanism regulating IAA metabolismmay be different in tobacco and carrot. (Received June 25, 1987; Accepted February 1, 1988)     

Shoots from MM. 106 apple rootstocks grown in a polythene tunnel do not contain a higher IAA concentration than shoots from field-grown plants

MM. 106 apple rootstock plants grown in a polythene tunnel show greater apical dominance and a higher propensity to root as cuttings than plants grown in the field. Experiments were conducted to test the hypothesis that the growth habit and rooting behaviour of polythene tunnel plants were caused by increased concentrations of idole-3yl-acetic acid. Cuttings taken from field-grown plants which had been sprayed with IAA showed increased rooting. In shoots of both field-grown and polythene tunnel-grown plants endogenous IAA levels were highest in the upper shoot region and declined progressively with distance from the apex. Plants grown in the polythene tunnel, however, did not contain significantly higher IAA levels than field plants. The analytical data do not support the hypothesis that the growth and rooting behaviour of plants grown in a polythene tunnel were caused by increased concentrations of IAA.Abbreviations IAA indol-3yl-acetic acid     

Effects of Russian wheat aphid infestation on barley plant response to drought stress

The influence of Russian wheat aphid ( Diuraphis noxia Mordvilko) infestation on the response of barley ( Hordeum vulgare L. ev Hazen) plants to drought stress was investigated. Fourteen-day-old plants were infested with eight apterous adult aphids, which were removed 7 days later with systemic insecticide. Leaves previously infested with aphids had lower relative water content, reduced stomatal conductance, more negative water potential, lower levels of chlorophyll and higher levels of amino-N, proline and glycinebetaine than corresponding leaves from uninfested plants. When water was withheld for a period of 7 days after aphids were removed, the relative water content of previously infested plants dropped steadily from 0.89 to 0.60, while the relative water content of uninfested plants remained at about 0.94 for the first 4 days of the drought stress period followed by a steady drop to about 0.77 by the end of the drought stress period. Leaf water potentials dropped steadily during the drought stress period in both previously infested (-1.14 to -1.91 MPa) and unin-fested (-0.54 to -1.52 MPa) plants. Analysis of glycinebetaine and proline levels at the end of the drought stress period indicated that leaves of previously infested plants accumulated lower levels of these solutes than leaves from uninfested plants. Upon alleviation of drought stress, plants previously infested with aphids showed little increase in dry weight while younger leaves and tillers from uninfested plants showed large increases. It is concluded that Russian wheat aphids cause drought-stress symptoms in leaves of infested plants even in the presence of ample root moisture. The observations of low levels of glycinebetaine and proline present in leaves after water was withheld from roots and lack of leaf growth upon alleviation of drought stress in previously-infested plants, suggest that aphid infestation limits the capacity of barley plants to adjust successfully to drought stress.