Uliuliza swali: Je, mimea inawasilianaje?

If you’ve read this article you’ll already know that plants are not just standing there. In a great book by Daniel Chamowitz called What A Plant Knows: A Field Guide to the Senses, that author discusses the plant senses- sight, smell, touch, and hearing.

In the second chapter he discusses plant smell. As we know, smell is the ability to detect compounds in the air that carry various chemical signatures that the nerves in our nose can interpret. Plants don’t have a nervous system controlled by a brain, but they do have the ability to sense chemical compounds in the air and then react to that “smell”. The most obvious example of plant communication through smell happens when fruit ripens.

One of the environmental challenges that plants face is seed dispersion and as a result a lot of plants produce fruit that attracts animals to eat them. The seeds are usually well protected and travel through the animal’s digestive system without being harmed, emerging with a nice dose of fertilizer away from the parent tree. If a tree wants baboons to disperse its seeds, it wants to produce enough ripe fruit for the whole troop to spend some time in the tree, which means it wants the fruit to ripen at the same time. This ripening is induced by a chemical called ethylene which is produced by the ripening fruit. We can use this to our advantage when we have green fruit. If you want an avocado to ripen quickly- put it in a bag with a ripe banana. The avocado will sense the ethylene being produced by the banana and ripen quickly.

The next fascinating example of plants communicating using the sense of smell is in a defensive way. As already mentioned in the giraffe-acacia article, acacias produce a compound called methyl jasmonate which stimulates the production of tannins in the leaves which browsers don’t like. The methyl jasmonate is actually produced to speed up the reaction within the tree because it is quicker to send out a chemical warning into the air than to send it through the system of vessels in the plant. Because it is transported in the air, other trees can “eavesdrop” and react too to produce the defensive chemicals.

Unfortunately most of the controlled research on plant communication and smell has been done in the northern hemisphere in temperate climates, so we need to be careful with our statements and assumptions because they might not apply here. However we can apply the concepts here and hopefully we can start to look for evidence specific to African ecosystems. In a study on Lima beans, the scientists discovered that the plant reacted by producing different chemical compounds depending on what was attacking them. If the plant was being attacked by a bacteria it produced a compound called methyl salicate which stimulated a specific defense reaction. If it was a herbivore the plant produced methyl jasmonate (the same chemical acacias produce to warn each other). This is amazing in itself, but what is even more fascinating is that instead of just increasing tannin content of the leaves to deter the herbivore, the plant started to produce chemicals to attract a wasp that would attack the aphids and beetles that were eating the plant.

Another incredible discovery involves an underground communication between plants. Most plants have a mutual relationship with fungi in their root system. We call this fungi- mycorrhizal mycelia. These mycelia spread out through the soil and help provide the tree with nutrients and at the same time get their sugars from the tree. These networks of fungi are incredible and connect trees together. They’ve even been shown to take nutrients from healthy trees to help trees that are struggling. Of course, if they can do that, they can also transfer warning signals between species. This is all a relatively recent discovery so we still have an incredible amount to learn, let alone in African ecosystems.

One thing for sure, there are a lot of really amazing things happening that we can’t see or smell.

Here are a couple short video that shows these co-relationships. The Secret Social Life of Plants by Minute Earth and The Amazing Way Plants Defend Themselves by TedEd.

Here’s a very good article too.

(Sources at the bottom of the page)

Swahili version

Kama umesoma nakala hii tayari utafahamu kwamba mimea haikubali tu kukaa. Kwenye kitabu kizuri kilichoandikwa na Daniel Chamowitz kinachoitwa “What A Plant Knows: A Field Guide to the Senses”, mwandishi anaongea kuhusu hisia za mimea za kuona, kunusa, kugusa na kusikia.

Kwenye sura ya pili anaandika kuhusu hisia ya mimea ya kusikia harufu. Tunavyofahamu, hisia ya kunusa ni uwezo wa kusikia misombo kwenye hewa inayobeba chapa ya kemikali kinacho tafsirika na mishipa ya fahamu kwenye pua. Mimea haina mfumo wa fahamu inachoongozwa na ubongo, lakini ina uwezo wa kuhisi kemikali hewani na kuitikia. Mfano dhariri ya mimea kuwasiliana na kusikia harufu ni wakati matunda yanaiiva.

Mimea inakutana na changamoto mmojawapo ya kimazingira ya kusambaza mbegu, na mimea mingi hutengeneza matunda ya kuvutia wanyama watakavyo kula. Mbegu huwa na maganda magumu, huweza kupita kwenye mfumo wa mmeng’enyo bila kuathirika, na kuoteshwa mbali na mti wakati mnyama akienda haja kubwa. Mti ukitaka nyani wasambaze mbegu zake, unahitaji kutengeneza matunda ya kutosha ili kikosi cha nyani ibaki kwenye mti kwa muda wakila matunda. Hivyo inahitaji matunda iive kwa wakati mmoja. Uivaji wa matunda husababishwa na kemikali kinachoitwa ethylene kinachotengenezwa na matunda yanayoiva. Sisi tunaweza kutumia mbinu huu kuivisha matunda mabichi. Ukitaka parachichi iive, iweke kwenye mfuko pamoja na ndizi iliyoiva. Parachichi itahisi harufu ya ethylene inachotengenezwa na ndizi na kuiva haraka zaidi. 

Mfano mwengine wa kusisimua mimea kuwasiliana kwa kutumia hisia ya kunusa ni kwenye kujitetea. Nilivyotamka kwenye nakala ya twiga na migunga, migunga hutengeneza kemikali inayoitwa methyl jasmonate inayochochochea majani kutengeneza ‘tannin’ kwa ajili ya walamajani ambayo hawaipendi. Methyl jasmonate inatengenezwa kwa ajili ya kuongeza mwendo wa mti kuitikia kwa sababu mwendo wa kusambaza kemikali kwa hewa ni haraka kuliko kusambaza kwenye mzunguko wa mishipa ya mti.  Kwa vile inasambazwa hewani, miti mingine inaweza kusikia na kuitikia pia kwa kutengeneza kemikali ya kujilinda.

Kwa bahati mbaya, utafiti mwingi kuhusu mimea kusikia harufu imefanyika kwenye Kizio cha Kaskazini kwenye hali ya hewa tofauti, na kwa vile inabidi tuwe waangalifu na matamshi na udhanifu wetu kwa sababu kuna uwezekano isitekelezwe hivyo hapa. Lakini tunaweza kuyatumia dhana hapa na kuanza kutafuta ushahidi wa kamili. Kwenye utafiti wa maharage aina ya Lima, watafiti waligundua kuwa mimea ilitengeneza kemikali tofauti kulingana na adui aliyekuwa anaishambulia. Kama adui ilikuwa bakteria, walitengeneza kemikali inachoitwa methyl salicate inachosababisha itiko la kujilinda kwa magonjwa.  Kama ni mlamajani mmea ulitengeneza methyl jasmonate (kemikali iliile inachotengenezwa na migunga).  Hii ni tendo la kushangaza yenyewe, lakini cha kushangaza zaidi, badala ya kutengeneza ‘tannin’ peke yake kwenye majani ya kuzuia walamajani hawa, mti ulianza kutengeneza kemikali ya kuvutia aina ya nyigu anayewashambulia hao vidukari na mbawakawa waliokuwa wanaushambulia mmea.

Magunduzi mengine ya ajabu yanahusu mawasiliano kwenye ardhi kati ya mimea. Baadhi ya mimea ina mawasiliano ya kutegemezana pamoja na aina za kuvu kwenye mfumo wa mizizi. Hizi kuvu zinaitwa mycorrhizal mycelia. Hii mycelia inatambaa kwenye ardhi na kusaidia kuipa mmea virutubisho na kupokea sukari na wanga kutoka kwa mmea. Mtandao huu ni wa ajabu na kuunganisha miti mingi pamoja. Unajulikana mara mwingine mtandao huu unapotoa virutibisho kwenye mimea yenye afya na kuyagawia mimea iliyo dhaifu. Kama mtandao unaweza kufanya hivi, pia unaweza kusambaza ishara za onyo kati ya spishi tofauti. Haya yote ni magunduzi mapya na baado tuna mengi ya kujifunza, haswa kwenye mazingira ya kiAfrika.

Hakika ni kwamba kuna vitu vingi vya ajabu vinatokea tusivyo na uwezo wa kuyaona na kuyasikia harufu.

Bonyeza kiungo kuona video fupi. The Secret Social Life of Plants by Minute Earth and The Amazing Way Plants Defend Themselves by TedEd.

Unaweza kusoma zaidi katika maandiko rejea haya.

Sources:

Cossins, D. 2013. Plant Talk. The Scientist.

Babikova, Z. Gilbert, L. et al. 2013. Underground signals carried through common mycelial networks warn neighbouring plants of aphid attack. Ecological Letters.

Chamowitz, D. What A Plant Knows: A Field Guide to the Senses (Chapter 2)