Cellular perspectives for improving mesophyll conductance

Abstract

Summary After entering the leaf, CO2 faces an intricate pathway to the site of photosynthetic fixation embedded within the chloroplasts. The efficiency of CO2 flux is hindered by a number of structural and biochemical barriers which, together, define the ease of flow of the gas within the leaf, termed mesophyll conductance. Previous authors have identified the key elements of this pathway, raising the prospect of engineering the system to improve CO2 flux and, thus, to increase leaf photosynthetic efficiency. In this review, we provide a perspective on the potential for improving the individual elements that contribute to this complex parameter. We lay particular emphasis on generation of the cellular architecture of the leaf which sets the initial boundaries of a number of mesophyll conductance parameters, incorporating an overview of the molecular transport processes which have been proposed as major facilitators of CO2 flux across structural boundaries along the pathway. The review highlights the research areas where future effort might be invested to increase our fundamental understanding of mesophyll conductance and leaf function and, consequently, to enable translation of these findings to improve the efficiency of crop photosynthesis.

Biomass Accumulation in the Fern Asplenium nidus avis (L) under Root Restriction

“…These responses would be interpreted as a mechanism for increasing photosynthetic surface and maximizing photosynthetic capacity, particularly if coupled with a decrease in SLA (higher frond thickness) in agreement with Liao et al [4]. hindered by a number of structural and biochemical barriers which, together, define the ease of flow of the gas within the leaf, termed mesophyll conductance, which increased as frond thickness increased as well [13]. If the mesophyll cell space is large enough to avoid excessive cell to cell contact, it is possible to increase mesophyll and chloroplast surface area exposed to intercellular airspace per unit leaf area and improve mesophyll conductance [14].…”

Maximum CO2diffusion inside leaves is limited by the scaling of cell size and genome size

“…Diffusion of CO2 inside the leaf is a major limitation to photosynthesis 3,4 and has been considered for several decades to be a prime target for selection to increase photosynthetic capacity 21,22 . Unlike other tissues, the mesophyll is defined by both its cells and their surrounding intercellular airspace, both of which determine the overall CO2 conductance of the tissue.…”

“…These two conductances are arranged roughly in series, with gliq acting as a greater limitation to CO2 uptake. While multiple factors, such as membrane permeability 4 , carbonic anhydrase 23 , and chloroplast positioning 24 can be actively controlled over short timescales to regulate gliq, once a leaf is fully expanded, the structural determinants of gias and gliq, which include the sizes and configurations of cells and airspace in the mesophyll, are thought to be relatively fixed 4,22 . Of the various mesophyll traits commonly measured, the three-dimensional (3D) surface area of the mesophyll (SAmes) is thought to be the most important structural determinant of gliq.…”

Fluorescence visualization of cellulose and pectin in the primary plant cell wall

“…Pavement cells form interlocking jigsaw puzzle shapes the emergence of which was shown to correlate with a subcellularly varying distribution of cellulose and pectin (Panteris & Galatis, 2005; Bidhendi et al ., 2019). The kidney‐shaped profile of guard cells is related to their morphogenesis and function — the turgor‐driven deformation that reversibly opens the stomatal pores controlling gas exchange (Cooke et al ., 1976; Bidhendi & Geitmann, 2018; Yi et al ., 2018; Lundgren & Fleming, 2019; Rui et al ., 2019). In all cell types featured in this paper, the correlation between morphogenesis, form and function can be understood only through the investigation of the architectural details of their respective cell walls.…”