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When caterpillars or other insects chew a plant, it can release airborne chemicals, including the ones that give cut grass its smell. Nearby plants that sense them can strengthen their own chemical defences before they are attacked.

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The effect was first reported in 1983. Ian Baldwin and Jack Schultz found that young poplar and sugar maple trees sharing air with damaged plants raised their levels of defensive compounds, such as tannins, within about two days, an idea soon nicknamed “talking trees”. It was met with scepticism for years, but many later studies confirmed that such airborne signals exist, although how strongly plants respond varies with species and conditions. In 2023 Masatsugu Toyota's team at Saitama University in Japan filmed the process as it happened. When thale cress, a small plant widely used in laboratories, was exposed to air from injured plants, calcium signals spread through its leaves almost at once; plant cells use such signals to raise the alarm. Two of the cut-grass compounds were enough to trigger them. The chemicals enter through stomata, the tiny pores in leaves.

Türkçe oku
Tırtıllar ya da başka böcekler bir bitkiyi kemirdiğinde bitki havaya bazı kimyasallar salabilir; biçilmiş çimene kokusunu veren maddeler de bunlardandır. Bu kimyasalları algılayan komşu bitkiler, henüz saldırıya uğramadan kendi kimyasal savunmalarını güçlendirebilir.

Bu olgu ilk kez 1983'te bildirildi. Ian Baldwin ve Jack Schultz, hasar görmüş bitkilerle aynı havayı paylaşan genç kavak ve şeker akçaağacı fidanlarının, yaklaşık iki gün içinde tanen gibi savunma maddelerini artırdığını buldu. Buluşa kısa sürede “konuşan ağaçlar” adı takıldı. Bilim dünyası buna yıllarca kuşkuyla baktı; ama sonraki pek çok çalışma, havadan taşınan bu sinyallerin gerçek olduğunu doğruladı. Bitkilerin ne kadar güçlü tepki verdiği ise türe ve koşullara göre değişiyor. 2023'te Japonya'daki Saitama Üniversitesi'nden Masatsugu Toyota'nın ekibi süreci anbean görüntüledi. Araştırmacılar yaralı bitkilerden gelen havayı, laboratuvarlarda sık kullanılan küçük bir bitki olan Arabidopsis'e yönelttiler ve yapraklarda neredeyse anında kalsiyum sinyallerinin yayıldığını gördüler; bitki hücreleri alarm vermek için bu sinyalleri kullanır. Biçilmiş çimen kokusunu veren maddelerden ikisi bu tepkiyi başlatmaya yetti. Kimyasallar yapraklara, stoma denen minik gözeneklerden giriyordu.

Sources and further reading

Background reading: Plant communication
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