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Commentary

Evolution of floral form: electrostatic forces, pollination, and adaptive compromise

Do floral size and shape affect the electrostatic properties offlowers? Do electrostatic properties affect the delivery of pollento, and capture from, pollinators? The first detailed analysisof how variation in floral form may affect electrostatically‘assisted’ pollination is provided by Vaknin

et al

. (2001) in thisissue (see pp. 301–306). They used an experimental approachto study this question by examining the electrostatic pollinationof model flowers of different sizes and shapes. This studynot only illustrates a new way to analyse floral form andfunction experimentally, but also demonstrates the potentialimportance of a largely unrecognized selective force thatmay significantly influence the evolution of floral form.

A cornerstone of the evidence that Darwin mustered tosupport his new hypothesis of natural selection in 1859 wasthe adaptive interpretation of variation in form of the flowersof orchids (Darwin, 1859, 1862) and other angiosperm species(Darwin, 1877). Since Darwin’s time the adaptive analysis offloral form has been an active area of evolutionary research(Waser, 1983; Wilson & Thomson, 1996). Indeed, floral studysystems are arguably more amenable to adaptive analysisthan most other comparative systems because many featuresof floral form are directly and obviously related to floralfunction, and because floral function is closely connected toreproductive fitness. For example, flower colour interactsdirectly with animal colour perception, and floral fragrancewith animal olfaction, to attract pollinators, while flowersize and shape interact with animal size and behaviour toachieve pollen deposition and pickup (Wilson & Thomson,1996; Chittka

et al.

, 2001; Cresswell, 2001).

‘The process of adaptive compromise in flowers may

be more complex than we previously realised’

Electrostatic pollination

The first suggestions that electrostatic forces may be involvedin the pickup and deposition of pollen by pollinators were

theoretical discussions by Hardin (1976), Corbet

et al

. (1982),Erikson & Buchmann (1983), and by Buchmann & Hurley(1978) in connection with flowers that release pollen tobuzzing bees (‘buzz pollination’). Inductive charging causesmovement of charge through plant tissues when a bodyof opposite charge approaches a structure, such as the flower.Thus it can be expected that as a pollinator approaches a flower,the flower (and its pollen) develop an opposite (generallynegative) charge to that of the animal (and its pollen),potentially causing animal-borne pollen to be attracted to floralstructures and vice versa. This process may significantly enhancedeposition of pollen on pollinators and on stigmas.

Empirical evidence for the effects of electrostatic forceson pollination has been obtained only relatively recently(Gan-Mor

et al.

, 1995). Furthermore, up until now we havehad no empirical evidence that such processes influence theevolution of floral form. The experiments by Vaknin

et al

.(2001), using apple pollen and metal models of apple flowersof varying size and shape, provide the first empirical evidencesupporting the idea that the size and shape of flowers influencetheir electrostatic properties and, thereby, potentially the rateof arrival of pollinator-borne pollen on their stigmas. Thus,these new data show that floral electrostatic properties mightsometimes influence the evolution of floral form.

Adaptive compromise in floral evolution

One of the first to point out that the parts of a flower mayplay roles in multiple functions was Sprengel (1793). Henoted that structures, such as petals and petal appendages,may be involved in protecting floral nectar from dilution byrain water, in addition to attracting pollinators. Darwin(1859, 1862) drew on Sprengel’s observations, not only inhis adaptive interpretation of floral design, but as anexample of how organs with multiple functions must reflectthe net effect of multiple, often conflicting, selectivepressures. Organisms respond to the sum of combinedselective pressure generated by the different effects ofvariation in floral form on seed production. The net effectof opposing selective forces is usually declining fitness atboth extremes, with highest fitness at some intermediatevalue (e.g. fitness trade-offs leading to stabilizing selection;Fig. 1). A phenotype produced by such opposing selectiveforces can be said to reflect evolutionary or adaptive‘compromise’ (Armbruster, 1996; Brody, 1997).

Sprengel’s (1793) observations suggest to an evolution-ist (he himself was not, of course, since his work precededthat of both Lamarck and Darwin) that selection forattraction of pollinators and protection of nectar may be in

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conflict with one another. Similarly, selection generated by theneed to attract pollinators and by the need to hide or protectflowers from flower-eating or seed-eating herbivores may oftenbe in conflict (Armbruster, 1997; Brody, 1997). More subtleadaptive compromise may result from selection for longerstyles that promote pollen-tube competition, thereby allowingfemale mate choice (Lankinen & Skogsmyr, 2001), vs selectionfor short or intermediate style length generated by the need tofit the size and shape of the principal pollinators (Armbruster,1996, Fig. 2). To this list we can now add the observation byVaknin

et al

. (2001), that selection for longer, more exertedstyles is potentially generated by the electrostatic enhancementof pollen arrival on the stigma, while the fit of flowers withpollinators may generally select for short or intermediatestyle lengths (Cresswell, 2001; Figs. 1, 2). Vaknin

et al

. (2001)also show that selection generated by electrostatic enhancementof pollination may favour wider, more-open corollas, whileselection generated by pollinators and nonpollinating floralvisitors (e.g. nectar thieves) may favour other corolla charac-teristics. Thus the process of adaptive compromise in flowersmay be more complex than we previously realized.

Analysis of complex evolution through study of floral form

The relatively direct relationship between floral form andfunction has allowed the discipline of floral biology toattempt analyses of more complex and subtle functionaland evolutionary processes than can usually be addressedwith empirical systems. These include studies of pollenarrival and departure dynamics involving pollinators(Harder & Thomson, 1989) or electrostatic properties(Vaknin

et al.

, 2001). They also include challenging issuesin evolution, such as the roles of drift, constraint, and

adaptive compromise in floral evolution (Armbruster, 1996;Wilson & Thomson, 1996; Chittka

et al.

, 2001). Recentstudies of floral form and function are showing that theevolutionary process is more complicated and idiosyncraticthan simple adaptive models suggest (Gould & Lewontin,1979). For example, integrated comparative studies of flowercolour in relation to sensory abilities of pollinating insectssuggest that diversification in flower colour may have beeninfluenced by genetic constraints, chance events, exaptation(preadaptation), and indirect selection manifested throughfloral-vegetative pleiotropy (Chitka

et al.

, 2001). And, asalluded to already, we can now suspect that the length andshape of angiosperms styles may sometimes reflect adaptivecompromise to selection generated by pollinator morphologyand behaviour, mate choice in plants, and the electrostaticforces influencing pollination (Fig. 2). These new insightsdemonstrate that experimental study of the relationshipbetween floral form and function remains a fruitful avenue forcomparative and functional analyses of the evolutionary process.

Summary

Darwin utilized the form and function of flowers as a primeexample of the workings of natural selection. Today, theevolution of floral form remains an exciting area of research.New investigations into the effects of floral shape and sizeon the electrostatic properties of flowers and electrostatically‘assisted’ pollination complement previous and ongoingstudies of the effect of floral form on plant mate choice,attraction of animals, and the placement of pollen on, andcapture of pollen from, pollinators.

W. Scott Armbruster

Department of Botany, Norwegian University of Scienceand Technology, N-7491 Trondheim, Norway; and

Institute of Arctic Biology, University of Alaska,Fairbanks, Alaska, 99775 USA

(email [email protected])

Fig. 1 The expected influence of electrostatic forces and fit with pollinators on pollen arrival rates for styles of different lengths. This scenario shows conflicting selective pressures favouring an intermediate style length. This adaptive compromise would result in styles shorter than are optimal electrostatically, but longer than are optimal for matching pollinator size and behaviour.

Fig. 2 Three conflicting selective pressures may influence style length. Electrostatic enhancement of pollination and improvement of offspring fitness through mate choice may select for longer styles, while enhanced pollination through optimal fit with the pollinator selects for styles of intermediate length.

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References

Armbruster WS. 1996.

Evolution of floral morphology and function: an integrated approach to adaptation, constraint, and compromise in

Dalechampia

(Euphorbiaceae). In: Lloyd DG, Barrett SCH, eds.

Floral biology

. New York, USA: Chapman & Hall, 241–272.

Armbruster WS. 1997.

Exaptations link the evolution of plant-herbivore and plant–pollinator interactions: a phylogenetic inquiry.

Ecology

78

: 1661–1674.

Brody AK. 1997.

Effects of pollinators, herbivores, and seed predators on flowering phenology.

Ecology

78

: 1624–1631.

Buchmann SL, Hurley JP. 1978.

A biophysical model for buzz pollination in angiosperms.

Journal of Theoretical Biology

72

: 639–657.

Chittka L, Spaethe J, Schmidt A, Hickelsberger A. 2001.

Adaptation, constraint, and chance in the evolution of flower color and pollinator color vision. In: Chittka L, Thomson JD, eds.

Cognitive ecology of pollination

. Cambridge, UK: Cambridge University Press, 106–126.

Corbet SA, Beament L, Eisikowitch D. 1982.

Are electrostatic forces involved in pollen transfer?

Plant, Cell & Environment

5

: 125–129.

Cresswell JE. 2001.

Manipulation of female architecture in flowers reveals a narrow optimum for pollen deposition.

Ecology

81

: 3244–3249.

Darwin C. 1859.

On the origin of species by means of natural selection

. London, UK: Murray.

Darwin C. 1862.

On the various contrivances by which British and foreign orchids are fertilized by insects, and on the good effects of intercrossing


Darwin C. 1877.

The different forms of flowers on plants of the same species


Erikson EH, Buchmann SL. 1983.

Electrostatics and pollination. In:

Jones CE, Little RJ

, eds.

Handbook of experimental pollination biology

. New York, UK: Van Nostrand Reinhold, 173–184.

Gan-Mor S, Schwartz Y, Bechar A, Eisikowitch D, Manor G. 1995.

Relevance of electrostatic forces in natural and artificial pollination.

Canadian Journal of Agricultural Engineering

37

: 189–194.

Gould SJ, Lewontin R. 1979.

The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme.

Proceedings of the Royal Society, Series B

205

: 581–598.

Harder LD, Thomson JD. 1989.

Evolutionary options for maximizing pollen dispersal of animal-pollinated plants.

American Naturalist

133

: 325–334.

Hardin GB. 1976.

Better charge, better pollination.

Agricultural Research

25

: 15.

Lankinen A, Skogsmyr I. 2001.

Evolution of pistil length as a choice mechanism for pollen quality.

Oikos

92

: 81–90.

Sprengel CK. 1793.

Das Entdeckte Geheimniss der Natur Im Bau und in der Befruchtung der Blumen

(Reprinted 1972). New York, USA: Weldon & Wesley.

Vaknin Y, Gan-Mor S, Bechar A, Ronen B, Eisikowitch D. 2001.

Are flowers morphologically adapted to take advantage of electrostatic forces in pollination?

New Phytologist

152

: 301–306.

Waser NM. 1983.

The adaptive nature of floral traits: ideas and evidence. In: Real LA, ed.

Pollination biology

. New York, USA: Academic Press, 241–285.

Wilson P, Thomson JD. 1996.

How do flowers diverge? In: Lloyd DG, Barrett SCH, eds.

Floral biology

. New York, USA: Chapman & Hall, 88–111.

Key words:

floral form, electrostatic forces, pollination, adaptive com-promise, selective pressure, style length.

2001152000000

Commentary

Multiple trophic levels in UV-B assessments – completing the ecosystem

By the mid 1980s, concerns about ozone depletion bychlorofluorocarbons (CFCs) and ensuing increases inultraviolet-B radiation (UV-B) reaching the earth’s surfaceprompted urgent research to examine the effects of UV-Bon plant processes. Although international agreements havenow slowed the production of CFCs, whether stratosphericozone and UV-B levels will revert to the preozone-depletionlevels of the 1970s by the end even of this century remainsuncertain because of noncompliance and the positive feed-back that greenhouse gases may have on ozone depletion(Madronich

et al.

, 1998; Shindell

et al.

, 1998). However,our ability to predict the impacts of changing UV-B levelson organisms and ecosystem processes is limited because fewfield studies have examined effects across multiple trophiclevels. In this issue, Searles

et al

. (2001b) (see pp. 213–221)examine how solar UV-B influences plants and microbes atthe southern extremity of South America, the Tierra delFuego archipelago – an area that is experiencing enhancedsolar UV-B levels during spring and summer due to theAntarctic ozone hole. Counterintuitively – since UV-B isdeemed detrimental to most organisms – they found thatsome microbes, in particular testate amoebae, occur in highernumbers in a

Sphagnum

peatland under near-ambient UV-Bthan under reduced UV-B levels. Less surprisingly, thesefindings reemphasize that what we know about UV-B effectson plants cannot easily be extrapolated to predict how UV-Bwill affect other trophic levels in a system.

‘Ecology has taught us that seemingly small changes inone process might ultimately have large effects at other

levels of organization’

Approaches in UV-B field studies

What have we learned since the 1980s from these researchefforts? Early work showed that UV-B exposure indoors,while providing useful information on mechanisms andshort-term responses, often exaggerates the effects of UV-Bon plants because of low visible and UV-A irradiance. Thisconcern was largely responsible for an emphasis on outdoor


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studies conducted under a background of sunlight. The twoapproaches employed in these outdoor UV-B studiesinvolve either reducing some of the ambient UV-B reachingplants through the use of UV-B absorbing filters (exclusionstudies), or supplementing ambient UV-B levels with UV-Blamps (lampbank studies). Regarding lampbank studies,when the levels of UV-B supplements are given at aconstant dose over the day, unrealistically high levels ofUV-B can be supplemented against low visible and UV-Airradiance, and UV-B effects may be exaggerated with theseso-called squarewave exposures. Modulated lampbank systems,which continuously measure solar UV-B and adjust lampoutput to compensate for low background irradiance, havelargely overcome this problem.

Response of plants to UV-B

A survey of recent studies employing filter exclusions ormodulated supplements found that, in the case of exclusionstudies, among those that examined biomass, one-halffound that production was compromised by ambientUV-B exposure (Day, 2001). Additionally, one-half of theexclusion studies detected reductions in the area of indi-vidual leaves and increases in the bulk concentration ofsoluble leaf UV-B absorbing or screening compounds(primarily phenolics). These reductions in individual leafarea usually carry over to the whole plant, and occur in theabsence of reductions in CO

2

assimilation rates per unit leaf(Allen

et al.

, 1998; but see Keiller & Holmes, 2001). Themechanisms responsible for UV-B induced leaf stunting andleaf area reductions remain unclear. In the case of modulatedlampbank studies, while all of the nine studies surveyeddetected at least one significant plant response, the mostconsistent response was an increase in concentrations ofsoluble leaf UV-B absorbing compounds; while the majorityof studies that examined this parameter found an increase,in some cases it was only detected in the epidermis or duringhigh levels of background solar UV-B. In no case didsupplemental UV-B reduce total biomass production

In summary, exposure to ambient UV-B (assessed in theseexclusion studies) does elicit responses in many plants, par-ticularly reductions in individual and whole-plant leaf areaand increases in UV-B absorbing compounds, and in somecases, it is responsible for impressive reductions (10–35%)in biomass production (Krizek

et al.

, 1997, 1998; Mazza

et al.

, 1999a; Day

et al.

, 2001; Xiong & Day, 2001). As Paul(2001) recently alluded to, these findings speak of currentUV-B levels as a significant factor in controlling some plantprocesses – however, how overall plant performance isinfluenced by the large natural variability in outdoor UV-Blevels, both spatially and temporally, remains unknown.

Regarding responses to supplemental UV-B, results frommodulated lampbank studies suggest that some plants areindeed responsive to supplemental UV-B; the majority of

these studies reported an increase in UV-B absorbing com-pound concentrations. Compared with exclusion studies,plant responses to UV-B supplements tended to be moresubtle and total biomass production was not impaired. Thegreater responsiveness of plants in exclusion studies was notnecessarily the result of greater absolute differences in bio-logically effective UV-B levels between treatments (Day,2001). Instead, plants may be more responsive to increasesin UV-B when added to relatively low, subambient levels ofUV-B (exclusion studies), than when added to relativelyhigh, ambient levels of UV-B (supplementation studies);targets and mechanisms may become saturated as UV-Bexceeds ambient levels, and at above-ambient supplementssome responses may be insignificant or difficult to detect.

UV-B absorbing phenolics

The majority of recent exclusion and modulated supplementstudies surveyed found that concentrations of soluble UV-Babsorbing compounds increased with UV-B level. Corro-borating this, in a recent meta-analysis of 103 outdoorlampbank studies (including both modulated and squarewavesupplements) Searles

et al

. (2001a) found that an increase inbulk UV-B absorbing compounds was the most consistentresponse to UV-B supplements. The implications of theseUV-B induced increases in concentrations are unclear. Whilethese compounds attenuate or screen UV-B, the protectionthat increases in bulk concentrations afford plants remainsdifficult to assess given their spatially heterogeneous compart-mentalization and the optically complex nature of leaves, alongwith our poor understanding of the identity and location ofUV-B targets (Day, 2001), although some progress in thisarena has been made (Barnes

et al.

, 2000; Mazza

et al.

, 2000).The vast number of these phenolic compounds, which probablydiffer in their roles, further complicates our understandingof the significance of this generalized response.

Many additional roles have been proposed for some ofthese compounds including as antioxidants (Bornman

et al.

,1997), constraints to cell and leaf expansion (Liu & McClure,1995), deterrents against herbivores and pathogens, and allelo-pathic compounds (Klein & Blum, 1990). These diverse func-tions suggest that UV-B induced changes in plant phenolicchemistry could have a wide range of effects on the exposedplant, adjacent plants and other trophic levels.

Compared with effects of UV-B on plants, effects on ter-restrial herbivores, consumers and decomposers have receivedless attention, especially in an ecological context, and aframework for predicting the influence of UV-B on theseother trophic levels, as well as what feedbacks these might inturn have on plant performance, has yet to emerge. How-ever, it is likely that the effects of alterations in the UV-Benvironment of a system will take several years to manifestthemselves, in part because of the time required for feed-backs between trophic levels to develop. The handful of


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longer-term UV-B studies reported have found that plantresponses to higher UV-B levels tend to increase or be cumu-lative over successive years (Sullivan & Teramura, 1992;Johanson

et al.

, 1995; Björn

et al.

, 1998; Phoenix

et al.

, 2000;Day

et al.

, 2001). Along with the need to examine UV-Beffects over several years at several trophic levels is the need toincorporate other climatic factors into experimental designs,since UV-B sometimes has strong interactions with otherclimate change factors such as CO

2

(Beerling

et al.

, 2001) orwarming/precipitation (Kiesecker

et al.

, 2001).

Response of other trophic levels to UV-B

Work to date has found both negative and positive UV-Beffects on organisms at other trophic levels, and these appearto depend on a complex array of biotic and abiotic factors.For example, exposure of leaf litter to enhanced UV-B caneither accelerate, slow or have no noticeable effect on littermicrobial respiration, litter mass loss rates or chemistry(Gehrke

et al.

, 1995; Newsham

et al.

, 1997, 1999, 2001;Rozema

et al.

, 1997). Contrasting effects of UV-B have alsobeen found when the indirect effect of different plant UV-Bexposure has been assessed on subsequent litter decom-position. Some studies have also focused on the influence ofUV-B on insect herbivory. Exposure of field plants to UV-Boften reduces insect herbivory, abundance and performance(Ballaré

et al.

, 1996; Rousseaux

et al.

, 1998; Mazza

et al.

, 1999b),although the causes for this are largely unknown. This mayinvolve both indirect effects of plant UV-B exposure on leafphysiochemical properties, as well as direct effects of UV-Bon insects. Mazza

et al

. (1999b) found that thrips perceiveand avoid UV-B, and this effect was detectable in responseto small changes in the level of outdoor UV-B supplements.Hence, failure to detect reductions in plant growth underUV-B supplements might in some cases be partly attribut-able to the insect deterrent afforded by supplemental UV-B.

Relatively few studies have examined the influence ofUV-B on multiple trophic levels. In this issue, Searles

et al

.(2001b) (pp. 213–221) examine how 3 yr of solar UV-Bexposure influenced plants and microbes in Tierra delFuego. They show that testate amoebae in a

Sphagnum

peatland occur in higher numbers under near-ambient thanreduced UV-B levels. As already mentioned, greater numbersof amoebae under higher UV-B levels is counterintuitive,based on our current understanding of UV-B as generallydetrimental to organisms, but highlights our lack of under-standing of UV-B effects across multiple trophic levels.Such findings are not uncommon; researchers examiningmultiple trophic levels in aquatic systems have sometimesfound complex, counterintuitive results: algae can increasein abundance in response to solar UV-B because they areless sensitive than their consumers to UV-B (Bothwell

et al.

,1994), and bacteria can increase in abundance due to photo-chemical changes in dissolved organic matter which render

it more easily consumed (Herndl

et al.

, 1997). Searles

et al

.(2001b) also found that changes in amoebae abundancewas affected by UV-B treatments not only in upper layersof

Sphagnum

, but also in lower layers where UV-B levels arenegligible, suggesting that not only direct, but indirect effectsof UV-B were responsible. Such evidence of indirect effectsseems to reiterate the idea that UV-B effects need to bestudied at multiple trophic levels if we are to understand themechanisms responsible for alterations in the performanceand abundance of organisms.

Summary

While one can find ample examples in the literature thatambient and enhanced levels of UV-B do not have detectableeffects on various plant and litter parameters, this should notbe taken as a verdict that UV-B has no effect on other, asyet unstudied parameters in a system, or on any parametersin other systems. Furthermore, many plant species areresponsive to ambient UV-B, as well as supplemental UV-B,although total biomass production does not appear to be com-promised by the latter. Much of the UV-B research to datehas focused on plant performance, largely because of concernsabout ozone depletion effects on agricultural productivity.More research is now needed that focuses on UV-B effectsover multiple trophic levels, and over longer time frames, ifwe are to understand how UV-B levels influence plant per-formance, as well as how ecosystem processes feedback toprimary producers. While many of the UV-B effects detectedto date appear subtle, and some researchers may have concludedthat changing UV-B levels are of little consequence to plantperformance, ecology has taught us that seemingly smallchanges in one process might ultimately have large effects atother levels of organization, and have the potential to developfeedbacks that are initially difficult to envision. The work bySearles

et al

. (2001b) shows us that UV-B can have signifi-cant effects on other trophic levels, and that our existingUV-B paradigm is not robust enough to predict such effects.

Thomas A. Day

Department of Plant Biology and The PhotosynthesisCenter, LSE-218, PO Box 871601,

Arizona State University, Tempe, AZ 85287–1601, USA(tel +1 480 9658165; fax +1 480 9656899

email [email protected])

References

Allen DJ, Nogués S, Baker NR. 1998.

Ozone depletion and increased UV-B radiation: is there a real threat to photosynthesis.

Journal of Experimental Botany

49

: 1775–1788.

Ballaré CL, Scopel AL, Stapleton AE, Yanovsky MJ. 1996.

Solar ultraviolet-B radiation affects seedling emergence, DNA integrity,


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plant morphology, growth rate, and attractiveness to herbivore insects in

Datura ferox

.

Plant Physiology

112

: 161–170.

Barnes PW, Searles PS, Ballaré CL, Ryel RJ, Caldwell MM. 2000.

Non-invasive measurements of leaf epidermal transmittance of UV radiation using chlorophyll fluorescence: field and laboratory studies.

Physiologia Plantarum

109

: 274–283.Beerling DJ, Terry AC, Mitchell PL, Callaghan TV, Gwynn-Jones D,

Lee JA. 2001. Time to chill: effects of simulated global change on leaf ice nucleation temperatures of subarctic vegetation. American Journal of Botany 88: 628–633.

Björn LO, Callaghan TV, Gehrke C, Johanson U, Sonesson M, Gwynn-Jones D. 1998. The problem of ozone depletion in northern Europe. Ambio 27: 275–279.

Bornman JF, Reuber S, Cen YP, Weissenböck G. 1997. Ultraviolet radiation as a stress factor and the role of protective pigments. In: Lumsden P, ed. Plants and UV-B: responses to environmental change. New York, USA: Cambridge University Press, 157–168.

Bothwell ML, Sherbot DMJ, Pollock CM. 1994. Ecosystem response to solar ultraviolet-B radiation: influence of trophic-level interactions. Science 265: 97–100.

Day TA. 2001. Ultraviolet radiation and plant ecosystems. In: Cockell CS, Blaustein AR, eds. Ecosystems, evolution, and ultraviolet radiation. New York, USA: Springer-Verlag, 80–117.

Day TA, Ruhland CT, Xiong FS. 2001. Influence of solar ultraviolet-B radiation on Antarctic terrestrial plants: results from a 4-year study. Journal of Photochemistry and Photobiology B: Biology 62: 78–87.

Gehrke C, Johanson U, Callaghan TV, Chadwick D, Robinson CH. 1995. The impact of enhanced ultraviolet-B radiation on litter quality and decomposition processes in Vaccinium leaves from the Subarctic. Oikos 72: 213–222.

Herndl GJ, Brugger A, Hager S, Kaiser E, Obernosterer I, Reitner B, Slezak D. 1997. Role of ultraviolet-B radiation on bacterioplankton and the availability of dissolved organic matter. Plant Ecology 128: 42–51.

Johanson U, Gehrke C, Björn LO, Callaghan TV. 1995. The effects of enhanced UV-B radiation on the growth of dwarf shrubs in a subarctic heathland. Functional Ecology 9: 713–719.

Keiller DR, Holmes MG. 2001. Effects of long-term exposure to elevated UV-B radiation on the photosynthetic performance of five broad-leaved tree species. Photosynthesis Research 67: 229–240.

Kiesecker JM, Blaustein AR, Belden LK. 2001. Complex cause of amphibian population declines. Nature 410: 681–684.

Klein K, Blum U. 1990. Inhibition of cucumber leaf expansion by ferulic acid in split-root experiments. Journal of Chemical Ecology 16: 455–463.

Krizek DT, Britz SJ, Mirecki RM. 1998. Inhibitory effects of ambient levels of solar UV-A and UV-B radiation on growth of cv. New Red Fire lettuce. Physiologia Plantarum 103: 1–7.

Krizek DT, Mirecki RM, Britz SJ. 1997. Inhibitory effects of ambient levels of solar UV-A and UV-B radiation on growth of cucumber. Physiologia Plantarum 100: 886–893.

Liu L, McClure JW. 1995. Effects of UV-B on activities of enzymes of secondary phenolic metabolism in barley primary leaves. Physiologia Plantarum 93: 734–739.

Madronich S, McKenzie RL, Björn LO, Caldwell MM. 1998. Changes in biologically active ultraviolet radiation reaching at the Earth’s surface. Journal of Photochemistry and Photobiology B: Biology 46: 5–19.

Mazza CA, Battista D, Zima AM, Szwarcberg-Bracchitta M, Giordano CV, Acevedo A, Scopel AL, Ballaré CL. 1999a. The effects of solar ultraviolet-B radiation on the growth and yield of barley are accompanied by increased DNA damage and antioxidant responses. Plant, Cell and Environment 22: 61–70.

Mazza CA, Boccalandro HE, Giordano CV, Battista D, Scopel AL, Ballaré CL. 2000. Functional significance and induction by solar radiation of ultraviolet-absorbing sunscreens in field-grown soybean crops. Plant Physiology 122: 117–125.

Mazza CA, Zavala J, Scopel AL, Ballaré CL. 1999b. Perception of solar UVB radiation by phytophagous insects: behavioral responses and ecosystem implications. Proceedings of the National Academy of Sciences of the United States of America 96: 980–985.

Newsham KK, Greenslade PD, Kennedy VH, McLeod AR. 1999. Elevated UV-B radiation incident on Quercus robur leaf canopies enhances decomposition of resulting leaf litter in soil. Global Change Biology 5: 403–409.

Newsham KK, McLeod AR, Roberts JD, Greenslade PD, Emmett BA. 1997. Direct effects of elevated UV-B radiation on the decomposition of Quercus robur leaf litter. Oikos 79: 592–602.

Newsham KK, Splatt P, Coward PA, Greenslade PD, McLeod AR, Anderson JM. 2001. Negligible influence of elevated UV-B radiation on leaf litter quality of Quercus robur. Soil Biology and Biochemistry 33: 659–665.

Paul N. 2001. Plant responses to UV-B: time to look beyond stratospheric ozone depletion? New Phytologist 150: 5–8.

Phoenix GK, Gwynn-Jones D, Lee JA, Callaghan TV. 2000. The impacts of UV-B radiation on the regeneration of a sub-arctic heath community. Plant Ecology 146: 67–75.

Rousseaux MC, Ballaré CL, Scopel AL, Searles PS, Caldwell MM. 1998. Solar ultraviolet-B radiation affects plant–insect interactions in a natural ecosystem of Tierra del Fuego (southern Argentina). Oecologia 116: 528–535.

Rozema J, Tosserams M, Nelissen HJM, van Heerwaarden L, Broekman RA, Flierman N. 1997. Stratospheric ozone reduction and ecosystem processes: enhanced UV-B radiation affects chemical quality and decomposition of leaves of the dune grassland species Calamagrostis epigeios. Plant Ecology 128: 284–294.

Searles PS, Flint SD, Caldwell MM. 2001a. A meta-analysis of plant field studies stimulating stratospheric ozone depletion. Oecologia 127: 1–10.

Searles PS, Kropp BR, Flint SD, Caldwell MM. 2001b. Influence of solar UV-B radiation on peatland microbial communities of southern Argentina. New Phytologist 152: 213–221.

Shindell DT, Rind D, Lonergan P. 1998. Increased polar stratospheric ozone losses and delayed eventual recovery owing to increasing greenhouse-gas concentrations. Nature 392: 589–592.

Sullivan JH, Teramura AH. 1992. The effects of ultraviolet-B radiation on loblolly pine. Trees 6: 115–120.

Xiong FS, Day TA. 2001. Effect of solar ultraviolet-B radiation during springtime ozone depletion on photosynthesis and biomass production of Antarctic vascular plants. Plant Physiology 125: 738–751.

Key words: amoebae, feedbacks, insects, leaf area, litter, ozone depletion, phenolics, trophic level, UV-B radiation.20011521000


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Books

Integrative plant anatomy

Integrative Plant Anatomy

By William C. Dickison. 544 pages. San Diego, CA, USA: Harcourt Academic Press, 2000. $69.95 h/b. ISBN 0 12 215170 4

These days, when molecular bio-logy, and functional genomics inparticular, seem to dominate thewhole of plant biology, and whentraditional botanical areas no longerform part of most plant sciencedegrees, any new book on plantanatomy is unlikely to be regardedas particularly topical. However,the stock in trade of molecularbiologists is mutants, whethernatural or induced, or novel geno-

types resulting from expression of transgenes. These oftendisplay modifications in developmental processes, whichresult in morphological and anatomical modifications to thebody of the plant. An understanding of plant anatomy andhow this integrates with physiology, development, ecology,genetics and systematics should therefore be highly pertinentand this book provides an up-to-date account of currentthinking in these areas.

The first four chapters cover the anatomical foundationof the primary and secondary plant body, providing an over-view of organization and structure; subsequent chapters dealwith specialized topics in some detail, including evolutionary,physiological and ecological plant anatomy and macro-morphology. The author gives numerous interesting examplesin which studies of applied plant anatomy have resulted ineconomic gains, such as in crop breeding, wood utilizationand animal nutrition. He also gives the anatomical basis ofcommercially valuable compounds that occur in herb, spiceand drug plants. The final chapters are used to illustrate theintegration of plant anatomy with a range of diverse areas suchas forensic science, archaeology, anthropology, climatology

and the arts. The text is easy to read because of the minimal useof technical terminology and there is also a short but valuableglossary to help where this is unavoidable. References forfurther reading at the end of each chapter have been restrictedto key recent works and to citations to classical textbooksand reviews, and information is provided on a number ofuseful websites dealing with plant anatomy.

This book does not cover the subject of plant anatomyexhaustively, concentrating on seed plants, particularly angio-sperms, and the emphasis of the work described naturallyreflects the author’s research interests in the anatomy ofwood. Unlike most books on plant anatomy, however, thisone succeeds in integrating structural biology with other areasof plant science and gives many amply illustrated examplesof ubiquitous structures as well as of common but oftenneglected specialized anatomical features. This emphasizesthe basic heterogeneity of plant organs at the cellular leveland reinforces the view that a realistic interpretation of plantfunction can only be achieved through a comprehensiveknowledge of the structure and organization of cells andtissues. To paraphrase Katherine Esau, the study of the develop-ment of form and organization requires the constant correla-tion between molecular, biochemical and structural changesin the experimental plant (Esau, 1960). There is thereforemuch to recommend this book, and it should be of interestboth to plant biology students requiring some awareness ofplant anatomy and to current molecular-based biologistsattempting to determine how modifications in gene activitytranslate into the higher order phenotypic characteristics ofplants.

Phillip Morris

Cell Biology Department, IGER, Plas Gogerddan,Aberystwyth SY23 3EB, UK

(tel +44 1970823112; fax +44 1970823242email [email protected])

Reference

Esau K. 1960. Anatomy of seed plants. New York, USA: John Wiley and Sons.

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Integrative plant anatomy

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