title: Plasticity in bundle sheath extensions of heterobaric leaves.
abstract: OBJECTIVE
  Leaf venation is linked to physiological performance, playing a critical role in ecosystem function. Despite the importance of leaf venation, associated bundle sheath extensions (BSEs) remain largely unstudied. Here, we quantify plasticity in the spacing of BSEs over irradiance and precipitation gradients. Because physiological function(s) of BSEs remain uncertain, we additionally explored a link between BSEs and water use efficiency (WUE).
  
  
  METHODS
  We sampled leaves of heterobaric trees along intracrown irradiance gradients in natural environments and growth chambers and correlated BSE spacing to incident irradiance. Additionally, we sampled leaves along a precipitation gradient and correlated BSE spacing to precipitation and bulk δ(13)C, a proxy for intrinsic WUE. BSE spacing was quantified using a novel semiautomatic method on fresh leaf tissue.
  
  
  RESULTS
  With increased irradiance or decreased precipitation, Liquidambar styraciflua decreased BSE spacing, while Acer saccharum showed little variation in BSE spacing. Two additional species, Quercus robur and Platanus occidentalis, decreased BSE spacing with increased irradiance in growth chambers. BSE spacing correlated with bulk δ(13)C, a proxy for WUE in L. styraciflua, Q. robur, and P. occidentalis leaves but not in leaves of A. saccharum.
  
  
  CONCLUSIONS
  We demonstrated that BSE spacing is plastic with respect to irradiance or precipitation and independent from veins, indicating BSE involvement in leaf adaptation to a microenvironment. Plasticity in BSE spacing was correlated with WUE only in some species, not supporting a function in water relations. We discuss a possible link between BSE plasticity and life history, particularly canopy position.
authors: Northwestern University, Program in Plant Biology and Conservation, 2205 Tech Drive, Evanston, IL 60208, USA. dlynch3@uic.edu
authors: Douglas J
authors: DJ
authors: Lynch
authors: Francesca A
authors: FA
authors: McInerney
authors: Lenny L R
authors: LL
authors: Kouwenberg
authors: Miquel A
authors: MA
authors: Gonzalez-Meler
mesh_terms: D031002:Acer / Q000502:physiology*; D000222:Adaptation, Physiological; D002247:Carbon Isotopes / Q000032:analysis; D008027:Light; D031317:Liquidambar / Q000502:physiology*; D018515:Plant Leaves / Q000737:chemistry; D058526:Plant Vascular Bundle / Q000502:physiology*; D011891:Rain
chemical_list: D002247:Carbon Isotopes