Clonal Plants Use Smart Connections to Boost Resistance Against Hungry Insects

New research shows how clonal plants can restructure their leaves in response to simulated insect damage. An article by Xuxu Chai and colleagues describes how clonal plants like Buffalo Grass, Bouteloua dactyloides, spread via underground stems called stolons that connect multiple rooted stems called ramets. These stolon connections allow the plant to share resources and signals between ramets.

Plants often respond to herbivory by thickening their leaves and increasing the density of veins, which provides more structural support. They can also transmit “herbivory signals” through their vascular system to alert undamaged leaves and induce systemic defences. Chai and colleagues investigated if ramets of Buffalo Grass acted like individual plants or if they were exchanging information between ramets through the stolons.

To investigate how clonal integration influences these responses, researchers subjected ramet pairs of Buffalo Grass to different levels of leaf removal, either severing or leaving intact the stolon connection between them. There were six treatments in total, with the ‘daughter’ ramet suffering 0%, 40% or 80% defoliation, while the ‘mother’ ramet was unmolested. Those three conditions were repeated with and without the stolon connection between the ramets to produce the six experiments.

Leaving the ramets connected by the stolon had a clear effect. While the ramets are clones, ‘mother’ and ‘daughter’ we not alike, write Chai and colleagues.

Without simulated herbivory, clonal integration strengthened the vascular system of mother ramets by increasing vein density and reducing leaf number, leaf thickness, midrib diameter and adaxial/abaxial epidermal cell size… In contrast, clonal integration had negative effects on leaf venation of unstressed daughter ramets, and most leaf anatomical traits were negatively affected by clonal integration too, except from bundle sheath cell number.

Chai et al. 2023

Removing 40% of leaves from a ‘daughter’ ramet led to an increase in vein density and thickness of the cuticle on both sides of the leaf, a decrease in leaf width and cell size. However, removing 80% of leaves had a much smaller effect on the daughter ramets. Instead, the ramets would attempt to grow new leaves rather than alter the structure of what they had left.

The story for the connected ‘mother’ ramet is slightly different. Remotely defoliating one ramet at 40% led the connected, undamaged ramet to increase leaf width and cell size and decrease vein density. When the remote ramet suffered 80% defoliation, the ‘mother’ ramet took a different tack. It reduced the leaf mechanical construction cost and produced fewer leaves but increased leaf width.

In natural grassland and lawn ecosystems, insect and herbivore may exert constant biotic herbivory stress on plant growth, which may cause defoliation and stolon/rhizome severance. Our study showed that induced defence signals can be transmitted from defoliated younger ramets of B. dactyloides to older ramets; clonal integration may regulate leaf microstructure of interconnected ramets according to the degree of herbivory stress. However, because insect herbivory is a rather uncertain and complex event, leaf microstructural response could also be related to resource reserves and resource uptake efficiency; signal and resource transmission between B. dactyloides ramets may therefore be more complicated than shown in our experiment. We propose that the function of stolons is far more than translocation of resources, but also coordinating the microstructure of different clonal parts, especially the leaf vascular system of interconnected ramets, for better performance of the whole genet.

Chai et al. 2023

Clonal integration helps younger ramets adjust their leaf structure based on the degree of herbivory, especially by changing vein density. This allows the plant as a whole to optimize growth and defence in the face of damage. The findings reveal a sophisticated mechanism by which clonal plants perceive and respond to threats.

READ THE ARTICLE

Chai, X., Sun, X., Cui, X., Johnson, P.G. and Fu, Z. (2023) “Clonal integration systemically regulates leaf microstructure of Bouteloua dactyloides interconnected ramets to better adapt to different levels of simulated insect herbivory,” AoB PLANTS, 15(2), plac062. Available at: https://doi.org/10.1093/aobpla/plac062