Carnivory, more than meets the eye…

There can be no plant-aware person who has not heard of carnivorous plants, and the view that the carnivorous (plant) lifestyle is all about such botanics supplementing their nitrogen (N) uptake from the digested bodies of the animals captured by various contrivances fashioned from modified leaves. That seems reasonable; nitrogen is a macronutrient essential for plant life, and is often in short supply in the environment, i.e. it’s a limiting nutrient. And N is even more deficient in habitats such as acid bogs that certain carnivorous plants occupy. So, any mechanism that can help a plant secure more N from the environment is to be welcomed. But, it seems that this nitrivory/nitriphagy isn’t just about diet, as Lukas Fasbender et al. have discovered.

Examining the iconic insectivorous plant, the Venus fly-trap (Dionaea muscipula), they show that the amino acid glutamine, added to the plant’s traps as a proxy for the N-containing amino acids normally obtained from digested prey, has at least two fates in the body of the plant. As expected, glutamine was incorporated into the plant’s own N-containing cellular components. In addition, and rather unexpected, was the finding that the amino acid was also used as a substrate for Dionaea’s respiration, hence energy – ATP (adenosine triphosphate – production. So, the ‘two for the price of one’ principle is embodied in nitrogenous compound construction and energy production. Eminently, and elegantly, energetically, economically efficient plants! (Presumably this is what actually happens in the plant with proper – i.e. non-proxy – prey-derived amino acids…)

[Ed. – what this work (and such reviews as Mark Chase et al’s ‘Murderous plants: Victorian Gothic, Darwin and modern insights into vegetable carnivory’) highlights is how straitjacketed and blurred is the traditional view of organisms as either autotrophs – such as photosynthetic organisms – or heterotrophs – e.g. animals, and fungi. When it comes to energy sources, multiple examples in nature suggest that most organisms should probably – and more properly – be regarded as mixotrophs. ‘Mixotrophy is an intermediate nutritional strategy, merging autotrophy and heterotrophy to acquire organic carbon and/or other elements, mainly N, P or Fe’, and is considered by Marc-André Selosse et al.. More insights specifically into the carnivorous plant lifestyle are likely to follow as the genome of the Australian pitcher plant (Cephalotus follicularis) is picked apart following its publication by Kenji Fukushima et al.]