Weird Science

The plant boxer - rapid movements of a barberry stamens

The fol­lo­wing article was ori­gi­nally publi­shed in jour­nal for tea­chers and lec­tu­rers Bio­lo­gia w Szkole (5/2020):

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Ples M., Roślinny bok­ser? Szyb­kie ruchy pręci­ków ber­be­rysu (eng. The plant boxer - rapid move­ments of a bar­berry sta­mens), Bio­lo­gia w Szkole, 3 (2020), Forum Media Pol­ska Sp. z o.o., str. 81-85

Move­ments in nature

I have always won­de­red why the vast majo­rity of peo­ple - not just lay­men - con­si­der plants to be more pri­mi­tive than ani­mals. It is the lat­ter (with few and rela­ti­vely recen­tly disco­ve­red excep­tions) that are not equ­ip­ped with a won­der­ful mecha­nism that allows direct dra­wing of energy from easily ava­i­la­ble sun­li­ght. The belief that plants are more pri­mi­tive than ani­mals cer­ta­inly results from their signi­fi­cant dif­fe­rence from our­se­lves. As humans, we belong to Ani­ma­lia, and it is easier for us to under­stand - or at least we usu­ally think so - other mem­bers of this king­dom. A plant orga­nism seems less advan­ced only because it does not defend itself aga­inst mani­pu­la­tion, while every ani­mal dri­ven by a self-pre­se­rva­tion instinct will try to pro­tect itself as much as pos­si­ble. This of course is not true, because plants also have defense mecha­ni­sms appro­priate to their needs [1][2]. Howe­ver, often they are more dif­fi­cult for us to obse­rve (and less obvious than sim­ple escape of an ani­mal) due to dif­fe­rent evo­lu­tio­nary stra­te­gies deve­lo­ped by these gro­ups of orga­ni­sms.

One of signi­fi­cant dif­fe­ren­ces between orga­ni­sms belon­ging to king­doms of Ani­ma­lia and Plan­tae is the ina­bi­lity of plants to move in terms of loco­mo­tion, i.e. auto­no­mous move­ment of the entire orga­nism. Never­the­less, plant orga­ni­sms are per­fec­tly capa­ble of whole range of other kinds of move­ments, fun­da­men­tally dif­fe­rent in their mecha­nism to ani­mal moti­lity based pri­ma­rily on use of musc­les.

Move­ments in the world of plants - if we take into acco­unt living struc­tu­res, because there also are motion mecha­ni­sms based on use of dead tis­sues, e.g. hygro­sco­pic move­ments of bracts (modi­fied lea­ves for­ming invo­lu­crum) in repre­sen­ta­ti­ves of the genus Xero­ch­ry­sum, as well as ele­ments of spruce Picea sp. cones [3] - are mainly cau­sed by cell growth (growth move­ments) or chan­ges in pres­sure inside them (tur­gor move­ments).

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Move­ment of Xero­ch­ry­sum bract
ani­ma­tion: sup­ple­men­tary mate­rial by author
Ilustracja
Picea cone (stro­bi­lus)
ani­ma­tion: sup­ple­men­tary mate­rial by author

The most fre­qu­en­tly cited divi­sion of plant move­ments inc­lu­des:

Tro­pi­sms are reac­tions of an orga­nism - usu­ally of a plant - in form of growth or tur­ning move­ment in response to an envi­ron­men­tal sti­mu­lus. In tro­pi­sms, this respon­ses depend on direc­tion of the sti­mu­lus. They are cau­sed by une­ven distri­bu­tion of spe­ci­fic phy­to­hor­mo­nes (auxins) within the tis­sues. Tro­pism can be posi­tive (+) when the organ is direc­ted to the site with the stron­ger sti­mu­lus, or nega­tive (-) in the case of oppo­site reac­tion. Depen­ding on the type of sti­mu­lus cau­sing spe­ci­fic tro­pism, we can say about pho­to­tro­pism, geo­tro­pism, hydro­tro­pism, ther­mo­tro­pism and others.

Taxes (sin­gu­lar taxis) are move­ments of an orga­nism in response to many dif­fe­rent kinds of sti­muli e.g. light or pre­sence of food. In this case the whole orga­nism is motile and demon­stra­tes gui­ded move­ment towards (+) or away (-) from the sti­mu­lus source. These move­ments are used to seek for the best envi­ron­men­tal con­di­tions, e.g. tem­pe­ra­ture (ther­mo­ta­xis), con­cen­tra­tion of spe­ci­fic che­mi­cal com­po­unds (che­mo­ta­xis), light inten­sity (pho­to­ta­xis) and so on.

Nastic move­ments are non-direc­tio­nal respon­ses to sti­mu­la­tion. The move­ment can result from chan­ges in tur­gor (more often) or take form of spe­ci­fic tis­sue growth. Decre­ase in tur­gor pres­sure cau­ses shrin­kage while incre­a­sing results in swel­ling of cells and thus whole tis­sues. Direc­tion of nastic move­ments is inde­pen­dent from sti­mu­lus's posi­tion in space. Taking into acco­unt the type of sti­mu­lus it is pos­si­ble to distin­gu­ish, among others, che­mo­na­sty, ther­mo­na­sty, sei­smo­na­sty and pho­to­na­sty [4].

Move­ment of plants is usu­ally imper­cep­ti­ble to naked eye and its effects can only be noti­ced after a long time span. Howe­ver, if we want to obse­rve the phe­no­me­non of plant move­ment, we can use the tech­ni­que of time-lapse pho­to­gra­phy but it is quite a labo­rious pro­cess.

There are plants move­ment of which can be obse­rved without use of spe­cia­li­zed devi­ces. Exam­ples inc­lude some car­ni­vo­rous plants, such as sun­dews Dro­sera or the Venus Fly­trap Dio­naea musci­pula, trap­ping struc­ture of which (for­med by the ter­mi­nal ele­ment of each of the lea­ves) usu­ally clo­ses in seconds.

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An ant cau­ght by the leaf of Dro­sera capen­sis
ani­ma­tion: sup­ple­men­tary mate­rial by author

The repre­sen­ta­tive of excep­tio­nally active non-car­ni­vo­rous plants is the Mimosa pudica also known as touch-me-not plant [5]. It exhi­bits very distinct sei­smo­na­stic move­ments: lea­flets of its com­po­und lea­ves (Photo 1A) fold inward and droop within seconds after even a gen­tle touch (Photo 1B).

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Photo 1 – Sei­smo­na­sty of Mimosa pudica; A – Lea­flets in nor­mal posi­tion (the arrow shows point of sti­mu­la­ting), B – Lea­flets fol­ded after being tou­ched
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Move­ment of Mimosa lea­flets
ani­ma­tion: sup­ple­men­tary mate­rial by author

It may seem that plants sho­wing fast move­ments are repre­sen­ta­ti­ves only of exo­tic spe­cies. Howe­ver, as It turns out, among spe­cies that occur natu­rally in Poland, you can also find those whose move­ments can be easily obse­rved with the naked eye.

Bar­berry

I want to tell you, my Dear Rea­der, about a native to Poland plant which is the bar­berry Ber­be­ris vul­ga­ris, also known here as kwa­śnica (from polish "kwa­śny" - "sour"). Said plant is a deci­du­ous shrub belon­ging to the Ber­be­ri­da­ceae family.

This spe­cies of bar­berry was once com­mon thro­u­ghout Poland - simi­larly to the entire con­ti­nen­tal part of Europe, and also (as natu­ra­li­sed) on the Scan­di­na­vian Penin­sula and the Bri­tish Isles. It grew on balks, slo­pes, thic­kets and on the edges of fore­sts. Howe­ver, far­mers have noti­ced that pre­sence of bar­berry can be harm­ful to local crops, because this shrub is an inter­me­diate host of Puc­ci­nia gra­mi­nis - fun­gus cau­sing a dan­ge­rous cereal dise­ase cal­led stem rust [6]. It was the rea­son why this plant was almost com­ple­tely era­di­ca­ted in nature. The­re­fore, if we find bar­berry some­where, we sho­uld obse­rve this plant, but not damage or harm it in any way.

Rela­ted spe­cies are cur­ren­tly often used as orna­men­tal plants, for exam­ple Thun­berg's bar­berry Ber­be­ris thun­ber­gii from Japan (Photo 2).

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Photo 2 – Thun­berg's bar­berry

Bar­berry has dimor­phic sho­ots: long sho­ots which form the struc­ture of the plant, and short sho­ots up to 2mm long. The lea­ves on long sho­ots aren't pho­to­syn­the­ti­cally active, deve­lo­ped into one to three or more spi­nes. The bud in the axil of each thorn-leaf then deve­lops a short shoot with seve­ral nor­mal, pho­to­syn­the­tic lea­ves. Leaf blade is undi­vi­ded (lat. folia inte­grum) and ser­ra­ted. My Thun­berg's bar­berry is of the 'Atro­pur­pu­rea' cul­ti­var, one of the most com­mon. Its lea­ves are pur­ple-red rather than green. This plant has a cha­rac­te­ri­stic, domed shape.

Bar­berry tis­sues con­tain large amo­unts of an inte­re­sting che­mi­cal com­po­und cal­led ber­be­rine C20H18NO4+. This sub­stance shows strong bio­lo­gi­cal acti­vity: it has anti­bac­te­rial, anti­pro­to­zoal, anti­diarr­heal, anti-can­ce­ral, anti­dia­be­tic, anti­hy­per­ten­sive, anti­de­pres­sant, and anti-inflam­ma­tory pro­per­ties, while also­re­du­cing cho­le­ste­rol levels in our orga­nism. Howe­ver, it sho­uld be men­tio­ned that it has nume­rous side effects, e.g. rela­ted to rele­ase of bili­ru­bin C33H36N4O6 from its inso­lu­ble com­plex with albu­min in the blood [7]. Ber­be­rine also has inte­re­sting opti­cal pro­per­ties: its yel­low-green flu­o­re­scence under UV light is very strong [8].

From the point of view of topic of this article, the most inte­re­sting are the gene­ra­tive organs of plants of the Ber­be­ris genus, because it is them - or rather their spe­ci­fic ele­ments - that show an inte­re­sting adap­ta­tion rela­ted to move­ment.

The flo­wers of bar­berry are small, yel­low or yel­low-orange in color (Photo 3). They are arran­ged in umbels, and they do not smell stron­gly, tho­ugh ple­a­san­tly.

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Photo 3 – Flo­wers of bar­berry

Sta­mens and pistils mature simul­ta­ne­o­u­sly. Flo­wers, due to their small dimen­sions, are not the most deco­ra­tive ele­ments of bar­berry, altho­ugh it must be admit­ted that during the flo­we­ring period (in spring) the plant displays pecu­liar beauty - the con­trast between colors of lea­ves and flo­wers can be a source of really nice aesthe­tic impres­sions.

Bar­berry is pol­li­na­ted by insects.

The struc­ture of the flo­wer is shown in the flo­ral dia­gram (Figure 1) [9] [10].

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Figure 1 – Flo­ral dia­gram of bar­berry flo­wer

As you can see, both calyx and corolla con­tain two whorls of three ele­ments each: sepals sepala and petals petala. The andro­e­cium is simi­lar, con­si­sting of six sta­mens sta­mina. The gyno­e­cium con­si­sts of one pistil pistyl­lum which is made of a sin­gle car­pel car­pel­lae. At the base of the petals there are nec­ta­ries nec­ta­ria - struc­tu­res that secrete nec­tar thus attrac­ting insects which pol­li­nate the plant. The descri­bed ele­ments can be seen in Photo 4.

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Photo 4 – Bar­berry flo­wer, A – as in nature, B – petals cut­ted

Photo 4A shows natu­ral appe­a­rance of the flo­wers - we can easily see the beau­ti­fully colo­red sepals, petals and the stigma of the pistil. The petals, howe­ver, hide the sta­mens from our sight. Of course obse­rva­tions can be done even in such case, but it is easier to do it after pre­pa­ring the flo­wer by gen­tly cut­ting or tea­ring off the petals at their base with twe­e­zers (near nec­ta­ries), while not dama­ging the rema­i­ning ele­ments of the flo­wer (Photo 4B). This way the sta­mens are expo­sed. I admit that descri­bed ope­ra­tion requ­i­res a ste­ady hand and a good eye (or a magni­fy­ing glass), but after some tra­i­ning it is pos­si­ble to per­form said ope­ra­tion not only at the labo­ra­tory table on a flo­wer cut from the plant, but also out­side direc­tly on the living plant. Of course, when the flo­wer gets cut-off from the plant, obse­rva­tions must be done rela­ti­vely quic­kly so the tis­sues will not dehy­drate and die.

The result of exem­plary obse­rva­tions of bar­berry sta­men move­ments is pre­sen­ted in Photo 5. Ini­tially the sta­mens are evenly bent outwards and the ima­gi­nary line con­nec­ting the anthers the­cae forms a fairly regu­lar circle (Photo 5A). Howe­ver, it is eno­ugh to touch sta­men - even extre­mely deli­ca­tely - with a pre­pa­ra­tion nee­dle or other tool (Photo 5B) to be able to see an inte­re­sting phe­no­me­non. Right after con­tact, the whole sta­men makes a very quick move­ment (lasting only a frac­tion of a second) towards the pistill (Photo 5C). The photo shows effects for only two sta­mens before and after being tou­ched to make the com­pa­ri­son easier.

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Photo 5 – Sej­smo­na­stic move­ments of bar­berry sta­mens; A - ini­tial state, stra­i­ght sta­mens, B - sta­mens just before being tou­ched with a nee­dle a, C - tou­ched sta­mens (mar­ked with a circle) bent to the pistil
Ilustracja
Move­ment of the sta­mens
ani­ma­tion: sup­ple­men­tary mate­rial by author

It is worth men­tio­ning that the descri­bed sei­smo­na­stic move­ment is not a sin­gle-time reac­tion. After some time, the sta­mens - if the flo­wer is not dried out - return to their ori­gi­nal posi­tions. Just after making the move­ment, as we have alre­ady seen, the sta­mens stick to the pistil (Photo 6A). After seve­ral minu­tes, sta­mens are stra­i­gh­te­ned and then they become able to per­form new cycle of move­ment (Photo 6B). Some ben­ding of the sepals can also be noti­ced here, but this is most likely cau­sed by their dry­ing out resul­ting from lights neces­sary to take the photo.

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Photo 6 – Return of the sta­mens to their ori­gi­nal posi­tion; A - just after sei­smo­na­stic move­ment (the sta­mens bent towards the pistil), B - after 1h (the sta­mens lar­gely retur­ned to their ori­gi­nal state)
Ilustracja
Rela­xa­tion of sta­mens
ani­ma­tion: sup­ple­men­tary mate­rial by author

The descri­bed obse­rva­tions are very inte­re­sting and, despite their small scale, truly spec­ta­cu­lar. Deco­ra­tive varie­ties of bar­berry are often found in our gar­dens, but also in city parks as small hed­ges, etc. This ensu­res high ava­i­la­bi­lity of mate­rial for rese­arch, which is inva­lu­a­ble from the point of view of any natu­ra­list.

Expla­na­tion

Move­ments of the sta­mens of bar­berry are undo­ub­te­dly cau­sed by a change in tur­gor in gro­ups of spe­ci­fic cells. Mecha­ni­cal con­tact ini­tia­tes the tran­s­port of cer­tain ions across the cell mem­brane. In the case of chan­ges in tur­gor of cells respon­si­ble for sei­smo­na­stic move­ments, the most impor­tant fac­tor seems to be the potas­sium cation K+. As a result of sti­mu­la­tion, they are inten­si­vely tran­s­por­ted out­side the cells, which also cau­ses out­flow of water from the pro­to­pla­sts. The tur­gor of these cells is lowe­red, cau­sing their dimen­sions to change. These chan­ges are rela­ti­vely small, but due to the large num­ber of cells, they add up in the form of obse­rved motion. The plant takes some time to rege­ne­rate by tran­s­por­ting water back into the cells.

Why has the plant deve­lo­ped such an inte­re­sting mecha­nism of descri­bed move­ment? I think that the answer to this que­stion will not be too dif­fi­cult for the Rea­der to find. This is, of course, an adap­ta­tion to pol­li­na­tion by insects. If we look at Photo 4A, we will easily notice that the insect, in order to get to the nec­tar pro­du­ced at the base of the petals, must pass thro­ugh a small win­dow for­med by conver­ging petals, and then pass in-between the pistil and the sta­mens. After being tou­ched they per­form move­ment loo­king as if they are hit­ting the insect, which became inspi­ra­tion for this article. In this way, much more pol­len is depo­si­ted on the sur­face of the pol­li­na­tor's body than if sta­mens rema­i­ned sta­tio­nary. On the other hand, pres­sing the insect aga­inst the pistil incre­a­ses the chance of trans­fer­ring the pol­len to the stigma of the plant. As you can see, sei­smo­na­stic move­ments can signi­fi­can­tly incre­ase the plant's chan­ces of pol­li­na­ting (and thus repro­du­cing), which is a impor­tant thing from the point of view of every living orga­nism.

Lite­ra­ture:

The author of the text and pho­tos is Marek Ples.

In rela­tion to article publi­shed in the jour­nal, minor edi­to­rial chan­ges were intro­du­ced in order to sup­ple­ment and adapt this text to pre­sent it on web­site.

Marek Ples

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