New Light for Crop Breeding by Cracking Major Determinants of Mesophyll Conductance

Mesophyll conductance describes the diffusion resistance between the CO2 concentration in the sub-stomatal conductance through mesophyll cell wall, cytosol, chloroplast membrane, until the fixation of CO2 by Rubisco in the stroma of chloroplasts. Previous studies have shown that improving mesophyll conductance, a golden bullet for crop breeders, can increase photosynthetic rates without increasing stomatal conductance, i.e. without losing more water and hence decreasing water use efficiency. Unfortunately, mesophyll conductance is determined by a complex array of interacting factors, including anatomical and biochemical factors. Furthermore, contrary to common expectation, mesophyll conductance is not constant under different light, CO2 and humidity. So far, there has been no effective method to quantitatively and mechanistically determine the relative importance of these different factors.

Recently, professor ZHU Xinguang and his colleagues at the Shanghai Institute of Plant Physiology and Ecology, Chinese Academy of Sciences, made some breakthrough in dissecting major determinants of mesophyll conductance.

They developed a highly mechanistic model of mesophyll conductance, which incorporates 3D anatomical structure of a leaf, leaf internal light environment predicted by a ray tracing algorithm based on leaf structure and optical properties, and metabolic processes in the mesophyll cell, which enables mechanistic dissection of mesophyll conductance. With this model, scientists found four factors in determining mesophyll conductance: leaf light heterogeneity, respiration and photorespiration, membrane permeability to bicarbonate, CO2 hydration reaction in cytosol and chloroplast stroma.

This model can be used to guide improvement of mesophyll conductance for plants with different leaf anatomy and biochemical properties. In addition, an analytical model of mesophyll conductance was also derived, which can be used to study its physiology, ecology and mechanism. Hopefully, this finding can bring new insight for plant biologists and breeders on tackling how to improve crop photosynthetic light and water use efficiencies.

The study was published online in Plant, Cell & Environment on July 25, 2017, with a title “Components of Mesophyll Resistance and Their Environmental Responses: A Theoretical Modeling Analysis”. This work is funded by Chinese Academy of Sciences strategic leading project, China National Science Foundation, Ministry of Science and Technology of China, and Bill and Melinda Gates Foundation.

Article website:
http://onlinelibrary.wiley.com/doi/10.1111/pce.13040/full

Caption: the cross session of rice leaf;
Left bottom panel shows a 3D reconstruction of rice leaf;
The blue object is a vacuole and surrounding green session represents a chloroplast layer and red dots represents mitochondria.
The bottom right represents the CO2 reaction and diffusion processes inside a mesophyll cell.

Author contact:
ZHU Xinguang, Professor and principal investigator
Institute of Plant Physiology and Ecology (SIPPE)
Chinese Academy of Sciences (CAS)
300 Fenglin Road, Shanghai 200032, China
Phone: (86) 21-54924163
Email: zhuxinguang@picb.ac.cn