Grapevine leaves, like all other plants, have the remarkable ability to adapt to their environment, particularly when it comes to light exposure. Researchers have now gained deeper insight into the anatomy of grapevine leaves and how they respond to varying light conditions. This knowledge could be useful for vineyard management and optimizing grape production.
The study, conducted by Guillaume Théroux-Rancourt and colleagues, focused on the leaves of two grapevine cultivars (Vitis vinifera L.), Cabernet Sauvignon and Blaufränkisch. The researchers grew these cultivars under high and low light conditions and then analyzed their leaf structures using microcomputed tomography (micro-CT) and measured their gas exchange.
The botanists found that leaves grown under high light conditions were thicker and less porous than those grown under low light. The researchers discovered that these traits could nearly explain the differences in the mesophyll surface area available for diffusion per leaf area (Sm,LA), which is a key feature that links leaf structure to its function. This is particularly important for photosynthesis, the process by which plants convert light energy into chemical energy to fuel their growth.
To better understand the relationship between leaf structure and function, the researchers introduced a new concept called a “stomatal vaporshed.” This term describes the intercellular airspace unit most closely connected to a single stoma, a microscopic opening on the leaf surface that allows for gas exchange. By analyzing the stomata-to-diffusive-surface pathway, the researchers were able to investigate how different leaf structures impact the efficiency of photosynthesis. In their article Théroux-Rancourt and colleagues write:
Our analysis of airspace traits provides a basis for the commonly used dimensional abstraction when moving from an inherently 3D leaf structure to a 1D resistance model. After entering the stomatal pore, the CO2 flux needs to spread out over an ever increasing intracellular air volume, before dissolving into apoplastic water and diffusing towards the chloroplasts. Pickard (1981) described this using a model with concentric hemispherical domains (the stomatal cavity, the porous mesophyll) that roughly maps onto our stomatal vaporshed. The vaporshed thus becomes a useful unit for numerical models analyzing CO2 diffusion in a realistic leaf structure (Ho et al. 2016).Théroux-Rancourt et al. 2023
The study found that sun leaves have a larger Sm,LA, which is beneficial for photosynthesis under high light conditions. In addition, the researchers found that the shape of the mesophyll cells, which are responsible for photosynthesis, changed in response to light conditions. In sun leaves, these cells were more elongated and cylindrical, while in shade leaves, they were more funnel-like in shape.
Shading in vineyards happens due to multiple causes: natural shade due to training systems, shoot positioning, or dense canopies (leaves shading leaves), but also through the use of protection nets (e.g. against hail or birds) or shading nets against excessive heat stress. Depending on the growth conditions or genotypes under consideration, different strategies may exist to maintain whole-plant carbon balance under contrasting light availability.Théroux-Rancourt et al. 2023
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Guillaume Théroux-Rancourt, José Carlos Herrera, Klara Voggeneder, Federica De Berardinis, Natascha Luijken, Laura Nocker, Tadeja Savi, Susanne Scheffknecht, Moritz Schneck, Danny Tholen, Analyzing anatomy over three dimensions unpacks the differences in mesophyll diffusive area between sun and shade Vitis vinifera leaves, AoB PLANTS, Volume 15, Issue 2, February 2023, plad001, https://doi.org/10.1093/aobpla/plad001