Bundle sheath extensions affect leaf structural and physiological plasticity in response to irradiance
2019
Barbosa, Maria Antonia M. | Chitwood, Daniel H. | Azevedo, Aristéa A. | Araújo, Wagner L. | Ribeiro, Dimas M. | Peres, Lázaro E.P. | Martins, Samuel C.V. | Zsögön, Agustin
Coordination between structural and physiological traits is key to plants' responses to environmental fluctuations. In heterobaric leaves, bundle sheath extensions (BSEs) increase photosynthetic performance (light‐saturated rates of photosynthesis, Aₘₐₓ) and water transport capacity (leaf hydraulic conductance, Kₗₑₐf). However, it is not clear how BSEs affect these and other leaf developmental and physiological parameters in response to environmental conditions. The obscuravenosa (obv) mutation, found in many commercial tomato varieties, leads to absence of BSEs. We examined structural and physiological traits of tomato heterobaric and homobaric (obv) near‐isogenic lines grown at two different irradiance levels. Kₗₑₐf, minor vein density, and stomatal pore area index decreased with shading in heterobaric but not in homobaric leaves, which show similarly lower values in both conditions. Homobaric plants, on the other hand, showed increased Aₘₐₓ, leaf intercellular air spaces, and mesophyll surface area exposed to intercellular airspace (Sₘₑₛ) in comparison with heterobaric plants when both were grown in the shade. BSEs further affected carbon isotope discrimination, a proxy for long‐term water‐use efficiency. BSEs confer plasticity in traits related to leaf structure and function in response to irradiance levels and might act as a hub integrating leaf structure, photosynthetic function, and water supply and demand.
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