Effects of Environmental Change on Wood Production and Wood Structure in Picea sitchensis Seedlings

Changes in environment that would be expected to reduce substrateavailability, decrease the rate of xylem increment, tracheiddiameter and wall thickness, in seedlings of Picea sitchensis.But after reaching a minimum about 10 days to 3 weeks afterenvironmental change, xylem increment, tracheid wall thickness,and in some instances tracheid diameter, increase again up toabout 4 to 6 weeks after transfer. This recovery parallels arecovery in net assimilation rate, and is associated with anincrease in photosynthetic efficiency. Although the light intensity and temperature treatments imposedwere more drastic than those that would normally be expectedin the field, they had remarkably little net effect on tracheiddimensions. On the other hand change in photoperiod producedgreater changes in tracheid dimensions, photoperiodic effectsbeing superimposed on effects of change in substrate availability.It is suggested that adaptation to reduced substrate will bufferthe plant against climatic fluctuations during the growing season,while the photoperiodic response will ensure preparation forwinter dormancy. It is concluded that the major seasonal changes in tracheiddimensions are unlikely to be caused by variation in substrateavailability. Changes in light intensity and temperature haveminor effects on wood production and structure through effectson substrate availability, but the major seasonal trends aremore likely to be associated with changes in growth regulationproduction.     

Adaptations to Environmental Change in Picea sitchensis Seedling-changes in Photosynthesis, Growth and Substrate Availability

Effects of a change in night temperature with or without reductionin the duration of photosyntheticallyuseful light were studiedon assimilation and growth of Picea sitchensis seedlings. An increase in night temperature resulted in a rapid, but temporary,increase in photosynthesis while lowering the night temperaturedecreased photosynthetic rate. For the lowest night temperaturetreatments, reduction in light quantity resulted in increasedphotosynthetic efficiency while for the highest night temperaturetreatment, reduction in light quantity apparently checked thefinal decline in photosynthetic rate noted above. These changestended to minimize treatment effects on absolute growth andnet assimilation rates. The results are discussed in relationto the hypothesis or photosynthetic control by substrate level. Short-term redistribution of ¹⁴C labelled assimilate was examinedin control plants and those in the most and least adverse environments.In the most unfavourable environment, total ^l4C transport andincorporation into turnover materials increased while labellingof reserves and new growth decreased. Paradoxically, labellingpatterns for plants in the most favourable environment weresimilar although total ¹⁴C transport was much reduced. It issuggested that this indicates a substrate excess resulting fromoverloading of transport and utilization systems. Growth pattern was markedly affected in the case of developingbranch initials and established branches only. The possibilitythat the observed changes represent adaptive responses is discussed.     

Light Intensity and Substrate Availability in Relation to Tracheid Development in Picea sitchensis

Assimilation and growth of Picea sitchensis seedlings maintainedat three light intensities were examined in relation to previously-reporteddata on tracheid development in this species. Increases in photosynthetic efficiency with decreased lightlevel failed to compensate completely for reduced total amountsof incident radiation as judged from assimilate distributionpattern and growth rate. Incorporation of assimilate into reservesand new growth declined with decreased light level, while theextent of turnover materials generally increased. Most treatment differences in relative dry weight distributionappeared to result from a combination of differences in growthrate and changes in growth pattern. The proportion of dry weightin branches and roots increased with increased light intensitywhile that in stems and the hypocotyl decreased At the two highest light levels tested, both absolute stem growthrate and total wall accumulation appeared to be independentof substrate availability. This situation contrasts with thatobserved in older material and it is suggested that the initialindependence reflects the temporary existence of a high ratioof functional foliage to stem and cambial material during thefirst year of growth. Since tracheid diameter showed a consistent, positive relationshipwith assimilate status, it is suggested that substrate levelcan exert an important modifying influence on cell expansion.     

A Comparison of Root- and Shoot-wood Development in Conifer Seedlings

Tracheid diameter, wall thickness, and wall area per tracheidincreased towards the root tip in first-year seedlings of Piceasitchensis and Pinus sylvestris; this is shown to be associatedwith differences in duration of the expansion and wall thickeningphases of tracheid development. Transfer to short days producesa similar response throughout the plant, tracheid diameter andwall thickness decreasing shortly after transfer, due to a declinein rate of development. These data are discussed in relationto growth-regulator gradients likely to exist between root andshoot. It is pointed out that though effects of growth regulatorson tracheid dimensions are well documented, it has yet to beestablished whether this is due to their regulation of the rateor of the duration of development.     

O-Benzylhydroxylamine: An Inhibitor of Phenylpropanoid Metabolism in Plants

O-Benzylhydroxylamine (OBHA) is a potent inhibitor of phenylalanineammonialyase (PAL, EC 4.3.1.5 [EC] ) and phenylpropanoid metabolismas evidenced by its effects on three plant species [soybean(Glycine max (L.) Merr.), buckwheat (Fagopyrum esculentum Moench.),and mung bean (Vigna radiata L.)]. When supplied to roots, OBHA(10^–5 M) did not significantly inhibit light- or dark-growthof soybean seedlings, but reduced (25%) soluble hydroxyphenoliccompound accumulation in light-grown axes. Higher concentrations(510^–5 M) of OBHA caused reductions (25%) in axis freshweight of light-grown seedlings (72 h), but did not lower axisweight of dark-grown seedlings. Anthocyanin accumulation inhypocotyls of intact mung bean seedlings was reduced by 25%after 3 days light growth after treatment with OBHA (10^–5M) via root feeding. Anthocyanin content of excised, etiolatedbuckwheat hypocotyls floated on solutions of OBHA (10^–5M) and incubated in the light for 24 h was reduced by 40%. L-Phenylalanineand t-cinnamic acid, intermediates of phenylpropanoid metabolism,were able to partially reverse this inhibition in buckwheat.Extractable PAL activity (specific activity basis) in soybeanaxes was substantially reduced (20% in dark, 40% in light) asearly as 24 h after root feeding with OBHA (10^–5 M). Reductionof PAL activity (specific activity or per axis basis) by OBHAcompared to control levels, continued throughout a time courseof 96 h. Kinetic studies on soybean PAL revealed a K_m of 1.1mM for L-phenylalanine and an apparent K_i of 3.5 µM forOBHA. (Received May 31, 1985; Accepted August 6, 1985)     

Acclimation of Tomato Leaves to Changes in Light Intensity; Effects on the Function of the Thylakoid Membrane

When young tomato plants grown in high light (400 µmolquanta m^–2s^–1 PAR) were transferred to low light(100 µmol quanta m^–2s^–1 PAR), non-cyclic electrontransport capacity was decreased and the rate of dark re-oxidationof Q^–, the first quinone electron acceptor of photosystemII, was decreased within 1–2 d. In contrast, the amountof coupling factor CF₁, assayed by its ATPase activity, decreasedmore gradually over several days. The total chlorophyll contentper unit leaf area remained relatively constant, although thechlorophyll a/chlorophyll b ratio declined. When young tomato plants grown in low light were transferredto high light, the ATPase activity of isolated thylakoids increasedmarkedly within 1 d of transfer. This increase occurred morerapidly than changes in chlorophyll content per leaf area. Inaddition, in vivo chlorophyll fluorescence induction curvesindicate that forward electron transfer from Q^– occurredmore readily. The functional implications of these changes arediscussed. Key words: Tomato, leaves, light intensity, thylakoid membrane     

Changes in some Calvin Cycle Enzymes of the Tomato during Acclimation to Irradiance

The activities of three Calvin cycle enzymes, RuBPc (E.C. 4.1.1.39 [EC] ),3PGA phosphokinase (E.C. 2.7.2.3 [EC] ) and NADP-G3P dehydrogenase(E.C. 1.2.1.13 [EC] ), and the cytoplasmic enzyme PEPc (E.C. 4.1.1.31 [EC] )together with soluble protein and chlorophyll were measuredin extracts from young tomato leaves during acclimation to achange in irradiance. Leaf area and fresh weight were also measuredto show changes due to growth during treatments. Soluble proteinhad doubled on a unit leaf area basis 7 d after transfer from100 µmol quanta m^–2s^–1 PAR (low light) to400 µmol quanta m^–2s^–1 PAR (high light). Duringthis period the protein/chlorophyll ratio rose from 4•6to 10, RuBPc activity almost doubled and PEPc almost trebled.Following the reverse transfer from high to low light, solubleprotein decreased by 30% after 7 d and the protein/chlorophyllratio fell from 12 to 5•6. There was no change in RuBPcactivity 3 d after transfer from high to low light while PEPcactivity decreased by over 30%. There was no decrease in theactivity of 3PGA phosphokinase or NADP-G3P dehydrogenase 1 dafter transfer to low light, but decreases were apparent after3 d. The extracted kinase and dehydrogenase when fully activatedwere able to phosphorylate and reduce 3PGA at more than 2•5-foldits calculated rate of synthesis in the leaf. The data are discussedin relation to changes in the CO₂ exchange of the leaf. Key words: Photosynthetic acclimation, irradiance, tomato leaf, RuBP carboxylase     

Daylength Effects on Growth, Tracheid Development, and Photosynthesis in Seedlings of Picea sitchensis and Pinus sylvestris

Effects of change in daylength on tracheid expansion and tracheidwall thickening are considered in relation to shoot and rootgrowth, assimilation rate, and starch content, in seedlingsof Picea sitchensis and Pinus sylvestris grown in controlledenviroments. Rates of wall thickening decreased in the first tracheids tobegin wall thickening after decrease in daylength. A sharp decreasein starch-grain size at the same time supports previous suggestionsthat wall thickness is related to available substrate; however,rates of assimilation were found to be far greater in shortdays than in long, suggesting that a surplus of carbohydratemay be produced in long days. It is pointed out that if availablesubstrate does limit wall thickening it is likely to determineto al accumulation of wall material; wall material per tracheidwould follow logistically from this depending on the numberof tracheids around the xylem, and wall thickness would dependalso on the radial tracheid diameter. Unexpectedly, rate of shoot growth accelerated after transferto short days before its final cessation with terminal-bud formation.Root growth declined in short days, but later increased againafter terminal bud formation. Rate of root growth did not appearto be associated with tracheid development in the shoot.     

Xenopus oocyte plasma membrane sheets for FRET analysis

Plasma membrane sheets from Xenopus oocytes have been isolated for use in fluorescence resonance energy transfer (FRET) measurements. This system has the following advantages: 1) fluorescent recordings from a large surface area to maximize the signal-to-noise ratio, 2) reduction in background fluorescence from proteins retained in intracellular compartments, and 3) access to the cytoplasmic surface of the plasma membrane for rapid solution changes. To demonstrate the utility of this approach, we have examined a previously published FRET-based Ca²⁺ sensor, namely, the Cameleon-PM. This construct targets to the plasma membrane and, upon various Ca²⁺ additions to the cytoplasmic face of the membrane, shows ratiometric FRET changes. From the ratiometric changes recorded, an apparent Ca²⁺ affinity of 1.65 µM was determined. Thus preparation of Xenopus oocyte plasma membrane sheets and FRET measurements demonstrates all three of the advantages outlined above. fluorescence resonance energy transfer     

Effects of temperature and light on the population dynamics of the Asterionella-Rhizophydium association

Growth parameters of the diatom Astenonella formosa Hass, andits fungal parasite Rhizophydium planktoniacum Canter emend,were measured at five temperatures and six light intensitieswith a 15?9 h light:dark cycle, using laboratory cultures ofboth organisms. With the parameter values obtained, thresholdhost densities were calculated in order to estimate the effectsof light and temperature on survival and epidemic developmentof the parasite The uninfected host reached light-saturatedgrowth rates between 0.917 day^–1 at 21?C and 0 285 day¹at 2?C. Under light limitation the optimum growth temperaturefor Asterionella decreased because of a reduced growth efficiencyGrowth inhibition at high irradiances was only observed at 2?CThe parasite reached the highest zoospore production at 2?Cand saturating irradiances: 30 2 zoospores per sporangium. Thisvalue was consistently reduced by lower irradiances and highertemperatures to only 2.2 zoospores at the opposite light andtemperature extremes Low light conditions depressed also theinfectivity of the zoospores At very low irradiances, they becamecompletely uninfective The light dependence of zoospore productionand infectivity was restricted to light intensities that limitedthe growth rate of the host. The development time of the sporangiaand the mfecti ve lifetime of the zoospores were not affectedby light but only by temperature, and ranged from 19.0 and 121 days respectively at 2?C to 1.9 and 2 1 days at 21?C- Theseeffects result in optimal conditions for the development ofa Rhizophydium epidemic at 11?C and a moderate light limitationof Astenonella At temperature above 7?C, the possibilities forepidemic development are only slightly affected by light andtemperature, except for very low irradiance levels, when thezoospores of the parasite become uninfective. However, below5?C the development of an epidemic is only possible at limitinglight levels. Conditions for survival of the parasite at lowhost densities are optimal at low temperatures and high irradiancelevels     

Abscisic Acid Metabolism and Stomatal Physiology in Betula lutea Following Alteration in Photoperiod

Birch seedlings ceased extension growth when transferred fromlong days (LD) to short days (SD). The cessation of growth underSD was associated with enhanced rates of photosynthesis, probablydue to a lowered diffusive resistance to gas exchange. Endogenouslevels of ABA were lowered under SD but the degradation of 2-¹⁴C(±)ABAwas not disturbed. It is concluded that the photoperiodic controlof extension growth in Betula lutea is not mediated by ABA,although hormonal changes following transfer to SD may findsome expression in an altered stomatal physiology.     

Infection of the diatom Asterionella by a chytrid. I. Effects of light on reproduction and infectivity of the parasite

The influence of hight limitation of the diatom Asterionellaformosa Hass, on the growth-determining parameters of its fungalparasiteRhizophydium planktonicum Canter emend, was measured,using laboratory cultures of both organisms. The experimentswere earned out at 6°C under a 15:9 h light-dark cycle.At saturating light conditions, the mean zoospore productionof the parasite was 23.4 zoospores sporangium^–1, and themean development time of the sporangia was 7 9 days. Light limitationof the host caused a substantial decrease of the zoospore production,while the development time was only slightly reduced. The improvedzoospore production at high light intensities was mainly theresult of incorporation of photosynthetic products generatedby the host after infection. Under limiting light conditions,Asterionella cells were less susceptible to infection withfungal zoospores. No infection at all occurred below 2 µEm^–2 s^–1, a light intensity that still supportedsome algal growth The maximum infection rate indicated thatchemotactic attraction of the parasite's zoospores by extracellularproducts of the host is involved. The infective lifetime ofthe zoospores of the parasite did not depend on light conditions,and was estimated at 8 days. The measured zoospore productionrates, both under limiting and saturating light conditions,enable the parasite to exceed the specific growth rate of thehost, and thus become epidemic, at sufficiently high host densities.     

Effects of Blue Light Pretreatments on Internode Extension Growth in Mustard Seedlings after the Transition to Darkness: Analysis of the Interaction with Phytochrome

The effects of blue light (B) pretreatments on internode extensiongrowth and their possible interaction with phytochrome mediatedresponses were examined in Sinapis alba seedlings grown for11 d under 280 µmol m^–2 s^–1 of continuousblue-deficient light from low pressure sodium lamps (SOX). SupplementaryB (16 µmol m^–2 s^–1) caused no detectable inhibitionof the first internode growth rate under continuous SOX, butgrowth rate was inhibited after transfer to darkness. This effect,and the growth promotion caused by far-red bend-of-day' lightpulses were additive. The addition of B at 16 µmol m^–2s^–1 during 11 d, or only during the first 9 or 10 d orthe latest 0.75, 1 or 2 d of the SOX pretreatment caused approximatelythe same extent of inhibition after the transition to darkness.A single hour of supplementary B before darkness caused morethan 50% of the maximum inhibition. However, 24 h of lower fluencerates of B (4 or 7 µmol m^–2 s^–1) were ineffective.Covering the internode during the supplementary B period didnot prevent the response to B after the transition to darkness.Far-red light given simultaneously with B (instead of the SOXbackground) reduced the inhibitory effect of B. Above a given threshold fluence rate, B perceived mainly inthe leaves inhibits extension growth in subsequent darkness,provided that high phytochrome photo-equilibria are presentduring the irradiation with B. Once triggered, this effect doesnot interact significantly with the ‘end-of-day’phytochrome effect. Key words: Blue light, extension growth, phytochrome     

The Growth and Survival of Severely-shaded Tillers in Lolium perenne L.

The effect of shading a single tiller to below its compensationpoint for a period of 5 weeks in vegetative plants of Loliumperenne L. cv. S23, was studied in two different experimentseach employing two light regimes, one of which was common toboth experiments. In the first experiment tillers in the axils of the first leafwere shaded three weeks from appearance at both 40 and 70 Wm^–2. None of the shaded tillers died and they continuedto produce new leaves and increase in dry weight but at a reducedrate. In the second experiment, tillers with one emerged leafin any leaf axil position were shaded at 70 W m^–2 andin a treatment in which light was reduced to 13 W m^–2after initial growth at 70 W m^–2. As in the first experimentall shaded tillers survived at 70 W m^–2 but in the 70 13 W m^–2 transfer regime all shaded tillers died. In the second experiment shaded tillers in both light regimeswere supplied with ¹⁴C-assimilate by translocation from theremainder of the plant but in the 70 13 W m^–2 the initialsupport was withdrawn within 5 weeks of shading. The results are discussed in terms of the physiological relationshipsbetween the tillers of the grass plant. Lolium perenne L., growth of tillers, survival of tillers, effect of light     

A salt-sensitive Dunaliella mutant I. Growth and osmoregulatory responses to increases in salt concentration

Dunaliella is a genus of green unicellular algae distributedin all the oceans and saline bodies of water throughout theworld and distinguished by unusual tolerance to salt. Sincethe cells of this genus do not possess a rigid cell-wall, theyrespond to changes in salt concentration by rapid alterationsin cell volume and then return to their original volume as aresult of adjustments in the amounts of intracellular ions andglycerol, this latter being the major organic osmoticum. Thepaper describes the behaviour of a mutant of D. parva 19/9 withreduced capabilities of growth above 0.5 kmol m^–3 NaCl.The mutant is unusual in that its abilities to synthesize glyceroland pump out Na⁺ and Cl^– do not appear to be impaired;volume changes in the hyperosmotic range also appear to be roughlythe same as in D. parva. The average cell volume of mutant cellsis reduced (206µm³ as opposed to 255 µm³ in D. parva)and their rate of change of cell volume after an increase insalt concentration is lower; it took about 10 min for mutantcells in the light to reach a new cell volume whereas D. parvacells reached their new volume in less than 1 min. Both factorsmay be dependent on components of the cytoskeleton. The mutantthrows light on adaptations necessary to allow Dunaliella cellsto grow at high salt concentrations and demonstrates that halotoleranceincludes, but is not equivalent to, osmoregulation. Key words: Dunaliella, salt tolerance, mutant     

Circadian Rhythms of Potassium and Sodium Contents in the Growing Front of Neurospora crassa

The temporal changes of potassium (K⁺) and sodium (Na⁺) contentsin the growing front of Neurospora crassa (al-2, bd strain)grown on solid medium showed circadian rhythms which persistedfor at least 45 h in the dark. The K⁺ content reached a maximumat about 10 and 30 h after the transfer from light to darkness,while the Na⁺ content was at a minimum at these times. Boththe rhythms were set off by the light to dark transition andwere not observed in constant light. The phase of the circadianrhythm of conidiation of this strain was delayed by 5 h by exposureto 50 min of white light (photon fluence rate 20.7 W/m²) 7 hafter the light to dark transition. The same exposure significantlychanged the ratio of K⁺ to Na⁺ content in the growing frontmeasured 8 h after the exposure. ³ Present address: Pesticides Research Laboratory, TakarazukaResearch Center, Sumitomo Chemical Co., Ltd., 2-1, 4-chome,Takatsukasa Takarazuka, Hyogo 665, Japan. (Received June 26, 1984; Accepted January 11, 1985)     

The Regulation of Proton/Amino Acid Symport in Riccia fluitans L. by Cytosolic pH and Proton Pump Activity

In the aquatic liverwort Riccia fluitans the regulation of theplasma membrane H⁺/amino acid symport has been investigated.Cytosolic pH (pH_c), membrane potential (E_m) and membrane conductancehave been measured and related to transport data, (i) The releaseof [¹⁴C]amino acids is strongly stimulated by cytosolic acidification,induced by the external addition of acetic acid, a decreasein external K⁺, and in the change from light to dark. On average,a decrease in pHc of 0.5 to 0.6 units corresponded with a 4-foldstimulation in amino acid efflux. (ii) External pH changes havefar less effect on substrate transport than the cytosolic pHshifts of the same order. (iii) The inwardly directed positivecurrent, induced by amino acids, is severely inhibited by cytosolicacidification. (iv) Fusicoccin (FC) stimulates amino acid uptakewithout considerable change in proton motive force. (v) Whenthe proton motive force is kept constant, the uptake of aminoacids into Riccia thalli is much lower than when the pump isdeactivated. It is suggested that both the proton pump activityand cytosolic pH are the dominant factors in the regulationof the H⁺/amino acid symport across the plasma membrane of Ricciafluitans, and it is concluded that the proton motive force isnot a reliable quantity to predict and interpret transport kinetics. Key words: Amino acid, cytosolic pH, pH-sensitive electrode, proton motive force, regulation, Riccia fluitans     

Responses to Saturation Deficit in a Stand of Groundnut (Arachis hypogaea L.). 2. Growth and Development

Stands of groundnut were grown in four glasshouses with themaximum saturation deficit (D) of the air limited to 1.0, 2.0,2.5 or 3.0 kPa. The soil was near field capacity when plantsemerged and no water was applied thereafter. In a fifth glasshouse,a stand was grown at low D on soil irrigated to field capacityevery few days. Developmental processes such as timing of flowering, peggingand pod formation were unaffected by D, but the numbers of branches,flowers and pegs were reduced in the drier treatments. Measurementsduring the first 30 d showed that in the drier treatments leafgrowth was reduced, and the partitioning of dry matter intoroots was enhanced. In the unirrigated stands, dry matter production in shoots wasreduced by 40 per cent as the maximum D increased from 1.0 to3.0 kPa. Growth was affected through reductions both in leafarea (and therefore light interception) and in the productivityper unit of light intercepted. These responses to D and soilwater were linked to changes in bulk water potential of leaves. Productivity per unit of water transpired (q) decreased withincreasing D. The product of q and the mean daytime value ofthe difference in vapour pressure between leaf and air was moreconservative than q, and ranged from 3.1 to 5.6 g kPa kg^–1. Groundnut, Arachis hypogaea L., saturation deficit, growth, development, light interception, water use efficiency     

The Role of Benzyladenine in the Differentiation of Tracheary Elements in Jerusalem Artichoke Tuber Explants Cultured in vitro

The role of benzyladenine (BA) in the differentiation of trachearyelements in Jerusalem artichoke (Helianthus tuberosus L.) tuberexplants was studied. For maximum differentiation of trachearyelements (25–30% of the cell population), treatment withoptimal concentrations of benzyladenine (5.0 mg dm^–3)in the presence of -naphthaleneacetic acid |NAA| (1.0 mg dm^–3)for the first 6 d was as effective as its continued presenceduring the entire 14 d period of study. A majority of the differentiatedtracheary element appeared between the 10th and 14th days ofculture. It was further observed that concentrations of activecytokinins in the tissue were considerably reduced within 2d after transfer from the BA-containing medium to a BA-freemedium. This was shown in three different ways: (1) monitoringthe amount of ethanol-soluble radioactivity at various timesafter transfer from |14C|-BA containing medium to BA-free medium;(2) bioassay of various cytokinin fractions from tissue extractseparated by thin layer chromatography; (3) indirect assay oftissue cytokinin activity through its interaction with abscisicacid for the promotion of auxin-induced cell division in thistissue. Both gibberellic acid (5.0 mg dm^–3) and abscisic acid(2–0 mg dm^–3) effectively inhibited the differentiationof tracheary elements even if provided after 6 d of pre-incubationin a high tracheid inducing medium. However, the appearanceof differentiated cells for the first 2 d after transfer wasnot significantly affected. A hypothetical scheme for the role of benzyladenine in the differentiationof tracheary elements in this tissue is discussed. It is suggestedthat during one or more critical cell divisions in the presenceof optimal levels of benzyladenine, a proportion of cells areinduced or committed for later differentiation into trachearyelements. The high concentrations of benzyladenine requiredduring induction are not needed during the intervening celldivisions, nor for the actual differentiation of the trachearyelements. Key words: Tracheary element differentiation, Jerusalem artichoke (Heliantlus tuberosus), Benzyladenine, Gibberellic acid, Abscisic acid     

Endosulfan-enhanced crest induction in Daphnia longicephala: evidence for cholinergic innervation of kairomone receptors

Daphnia iongicephala were reared from early embryogenesis inthe presence or absence of crest-inducing kairomones releasedby Anisops gratus (Notonectidae) and from birth in one of fiveconcentrations of the organochiorine pesticide, endosulfan (0,0.1, 1.0, 10 or 100 g 1^–1 The morphologyof the daphnidswas measured 3 days after birth and on production of the firstbrood of eggs. The reproductive parameters, first brood size,age at first reproduction, mean egg volume and total egg volume,were also measured. Endosulfan significantly induced crest developmentin 3-day-old daphnids at 0.1, 1.0 and 10 g ^1– in thepresence and absence of Anisops kairomone, although crest sizein the absence of kairomone was only marginally greater thancontrols. A concentration of 10 pg 1^–1 endosulfan significantlyenhanced crest growth of kairomone-exposed daphnids at maturity.The Anisops kairomone alone induced a large crest in D.iongicephola,reduced first brood size, mean egg volume and total egg volume,and increased age at maturity. The coefficient of variationof mean egg volume was significantly reduced by Anisops kairomone.It is hypothesized that endosulfan enhances crest developmentbyinhibition of .