A new paper by Krauski and Pavlovic et al. (KPe) caught my eye, partly because it is an interesting topic and partly because it triggered a lot of alerts as it cites a lot of Annals of Botany papers.
The role of electrical and jasmonate signalling in the recognition of captured prey in the carnivorous sundew plant Drosera capensis is important because once a sundrew has a meal it has to coordinate reactions to digest it. This is what KPe investigate. In particular they look at two signals, electrical and jasmonates. Electrical signals in carnivorous plants are well known, but you might be surprised by jasmonate signalling as this is a chemical signal the plant uses in defence when it’s under attack. KPe point to recent work on jasmonates as signals in Venus Fly Traps and wondered if they could experiment to see if the signals are also important in Sundews.
The connection between carnivory and plant defence won’t be news to regular Annals readers as Andrej Pavlovič and Michaela Saganová looked into this last year with A novel insight into the cost–benefit model for the evolution of botanical carnivory (free access). Pavlovič et al. also proposed that jasmonates might be important to sundews in 2013 in Feeding on prey increases photosynthetic efficiency in the carnivorous sundew Drosera capensis (free access). So how did they test it?
They set up three experiments using Drosera capensis. The first was using polystryene balls on the leaves as mechanical stimulation. The next was live prey, dropping fruit flies, unlucky Drosophila melanogaster onto the leaves. They also ran a third test, piercing the petiole, the stalk that attaches the leaf to the stem, twenty times. Their idea was that if carnivory signalling evolved from plant defence, then the reaction between the mechanical stimulation and the damage should be similar.
This seems to be what KPe found. Damage to the petiole created electrical and jasnomate signals that spread through the plant, and led to the plant expressing some enzymes, like it would with mechanical stimulation.
But not as much as with live prey. What was the difference? It was the jasmonates in the feeding leaf.
The thing a live victim has that a polystyrene ball doesn’t is taste. KPe point to a paper from Annals this year, Slow food: insect prey and chitin induce phytohormone accumulation and gene expression in carnivorous Nepenthes plants (free access after Feb 2017), that shows Nepenthes, pitcher plants, respond to the chemical signal of chitin. Chitin is an important component of insect exoskeletons, so the chemical signal or the taste is a trigger for the pitcher to start producing enzymes to digest the insect. In a similar way it’s the chemical signal from chitin that pulls jasmonates to the part of the leaf where the insect is trapped, and triggers the digestive enzymes.
That triggers a boom in photosynthesis in the leaf. It turns out what limits the growth of Drosera capensis is the lack of phosphorus (free access). If it can grab more from a visitor then it can push those nutrients into growing much more.
All this is possible because sundews have taken a plant defence signalling system and reused it to go on the offensive.
* Not actually flesh, but chitin, the stuff around it.
** Not actually salivate, but produce digestive enzymes.