Abstract
Coordination between structural and physiological traits is key to plants’ responses to environmental fluctuations. This is especially relevant to leaf hydraulics, as plant face constant imbalances between water supply and demand. In heterobaric leaves, bundle sheath extensions (BSEs) increase water transport capacity, as measured by leaf hydraulic conductance (Kleaf). 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 (NILs) grown at two different irradiance levels. We found that Kleaf, minor vein density and stomatal pore area index decrease with shading in heterobaric but not in homobaric leaves, which show similarly lower values in both conditions. Whole plant dry mass, as well as fruit yield, were altered by irradiance but not by genotype. We propose that BSEs confer plasticity in traits related to leaf structure and function in response to irradiance levels and might act as a hub integrating water supply and demand. Similar plant growth and yield in both NILs suggests that other developmental pathways can compensate for the lack of BSEs. This is in line with the fact that obv is not a deleterious mutation, and probably confers some adaptive advantage, as it was selected during commercial tomato breeding.