Plant chemicals are more important in carnivory than previously thought

Carnivorous plants have long fascinated people. Unique adaptations have enabled these plants to attract, capture and digest prey, which is useful in low-nutrient environments. One of the most well-known traits of sundews are the sticky hairs on curling leaves, but there is also a lot going on in the less visible, chemical world.

Dr Christopher Hatcher from Loughborough University and colleagues are the first to track the changes in all chemical compounds in Cape sundew leaves before and after capturing some prey. The researchers found that out of over 3,250 compounds, around 2,380 changed in response to feeding. Some chemicals had 30-fold changes up until 72 hours after capturing the prey. This study, which was part of Chris Hatcher’s PhD thesis, suggests that secondary plant metabolites might be more important than previously thought.

Hatcher and colleagues grew hundreds of Cape sundews in the greenhouses of Loughborough University. The researchers collected leaf and root samples from sundews before and then seven times after feeding, up to 72 hours post-feeding. The experiments started at 5.15 am each day. The botanists created the food from fruit fly powder mixed in with a bit of water that they pipetted onto the sundew leaves. 

Biochemical analysis was carried out by Ultra-High-Performance Liquid Chromatography-Mass Spectrometry (UHPLC-MS). 

Out of 3,257 identified compounds, over 2,380 peaked at least one time after feeding. Most of the compound rapidly increased for the first 45 minutes post-feeding. Afterwards, some compounds still increased slowly whilst others started to decline. 

“We have profiled, for the first time, the whole-leaf metabolome response to the addition of animal substrate to a carnivorous plant trap,” Hatcher and colleagues wrote. 

Over 20 compounds had 10-fold increases, and 12 had over 30-fold increases compared to the pre-feeding leaf and root samples. Eleven of these compounds were new to this group of carnivorous plants (Nepenthales). 

“Defence related jasmonates such as isoleucine increased by 3000% within 24 hrs of simulated prey capture and was sustained above this level for the full 72-hr experiment,” the researchers explained.

“Furthermore, we measured 36-fold increases in the floral scent and flavour phenylacetaldehyde in response to prey capture.”

The complete list of plant chemical compounds identified in this study can be found online. Whilst chemistry might bring up some stressful exams in high school, combing through these compounds tells an exciting story to scientists. 

“Not only does it appear that there is a strong biochemical basis in response to prey capture, there also appears to be a large diversity of compounds – larger than previously considered – that are important for carnivory in plants. Secondary metabolites may be much more important for plant carnivory than previously thought.”