AUTHOR=Jahan Eisrat , Sharwood Robert Edward , Tissue David T. 

TITLE=Effects of leaf age during drought and recovery on photosynthesis, mesophyll conductance and leaf anatomy in wheat leaves

JOURNAL=Frontiers in Plant Science

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2023.1091418

DOI=10.3389/fpls.2023.1091418

ISSN=1664-462X

ABSTRACT=<p>Summary statement: Mesophyll conductance (<italic>g</italic><sub>m</sub>) was negatively correlated with wheat leaf age but was positively correlated with the surface area of chloroplasts exposed to intercellular airspaces (<italic>S</italic><sub>c</sub>). The rate of decline in photosynthetic rate and <italic>g</italic><sub>m</sub> as leaves aged was slower for water-stressed than well-watered plants. Upon rewatering, the degree of recovery from water-stress depended on the age of the leaves, with the strongest recovery for mature leaves, rather than young or old leaves. Diffusion of CO<sub>2</sub> from the intercellular airspaces to the site of Rubisco within C<sub>3</sub> plant chloroplasts (<italic>g<sub>m</sub></italic>) governs photosynthetic CO<sub>2</sub> assimilation (<italic>A</italic>). However, variation in <italic>g</italic><sub>m</sub> in response to environmental stress during leaf development remains poorly understood. Age-dependent changes in leaf ultrastructure and potential impacts on <italic>g</italic><sub>m</sub>, <italic>A</italic>, and stomatal conductance to CO<sub>2</sub> (<italic>g</italic><sub>sc</sub>) were investigated for wheat (<italic>Triticum aestivum</italic> L.) in well-watered and water-stressed plants, and after recovery by re-watering of droughted plants. Significant reductions in <italic>A</italic> and <italic>g</italic><sub>m</sub> were found as leaves aged. The oldest plants (15 days and 22 days) in water-stressed conditions showed higher A and gm compared to irrigated plants. The rate of decline in <italic>A</italic> and <italic>g</italic><sub>m</sub> as leaves aged was slower for water-stressed compared to well-watered plants. When droughted plants were rewatered, the degree of recovery depended on the age of the leaves, but only for <italic>g</italic><sub>m</sub>. The surface area of chloroplasts exposed to intercellular airspaces (<italic>S</italic><sub>c</sub>) and the size of individual chloroplasts declined as leaves aged, resulting in a positive correlation between <italic>g</italic><sub>m</sub> and <italic>S</italic><sub>c</sub>. Leaf age significantly affected cell wall thickness (<italic>t</italic><sub>cw</sub>), which was higher in old leaves compared to mature/young leaves. Greater knowledge of leaf anatomical traits associated with <italic>g</italic><sub>m</sub> partially explained changes in physiology with leaf age and plant water status, which in turn should create more possibilities for improving photosynthesis using breeding/biotechnological strategies.</p>