title: Intrusive trichome bases in the leaves of silverleaf nightshade (Solanum elaeagnifolium; Solanaceae) do not facilitate fluorescent tracer uptake.
abstract: OBJECTIVE
  Solanum elaeagnifolium (silverleaf nightshade), having originated in the Americas, is now a serious summer-growing, perennial weed in many countries, including Australia. Most surfaces of the plants have a dense covering of trichomes, giving them a silvery-white appearance, hence the common name. We aimed to identify structural and functional properties of its leaves, especially the trichomes, that may affect the uptake of foliar-applied tracer dyes.
  
  
  METHODS
  The structure of leaves of Solanum elaeagnifolium was examined by light and scanning electron microscopy. The potential for transport of materials between trichomes and veins was studied with symplastic (carboxyfluorescein diacetate) and apoplastic (lucifer yellow) tracer dyes.
  
  
  RESULTS
  Mature leaves had a dense covering of complex, stellate trichomes on both surfaces, particularly the abaxial. The basal cells of Solanum elaeagnifolium trichomes penetrated into the underlying palisade mesophyll layers. The innermost lobes of these basal cells sometimes contacted the bundle sheath of the veins, but were not observed to directly contact the xylem or phloem. We found that neither symplastic nor apoplastic dyes were transferred between the basal cells of the trichomes and the vascular tissues. The trichome layer repelled water-based tracer dyes, while one of four adjuvants tested facilitated entry of both symplastic and apoplastic dyes.
  
  
  CONCLUSIONS
  Our results did not support a transport function for the trichomes. The trichomes may protect the mesophytic leaves from invertebrate herbivory, while also probably decreasing radiation absorbed resulting in cooler leaves in this summer-growing species.
authors: Graham Centre for Agricultural Innovation (NSW Department of Primary Industries and Charles Sturt University), School of Agricultural & Wine Sciences, Locked Bag 588, Charles Sturt University, Wagga Wagga NSW 2678, Australia.
authors: Geoffrey E
authors: GE
authors: Burrows
authors: Rosemary G
authors: RG
authors: White
authors: John D I
authors: JD
authors: Harper
authors: Roger D
authors: RD
authors: Heady
authors: Rex A
authors: RA
authors: Stanton
authors: Xiaocheng
authors: X
authors: Zhu
authors: Hanwen
authors: H
authors: Wu
authors: Deirdre
authors: D
authors: Lemerle
mesh_terms: D001315:Australia; D001692:Biological Transport; D005456:Fluorescent Dyes; D052585:Phloem / Q000502:physiology*; D018515:Plant Leaves / Q000502:physiology*; D018526:Plant Transpiration; D057685:Plant Weeds; D032322:Solanum / Q000502:physiology*; D064201:Trichomes / Q000502:physiology*; D052584:Xylem / Q000502:physiology*
chemical_list: D005456:Fluorescent Dyes
keywords: Solanum elaeagnifolium; adjuvant; amphistomatous; herbicide; isobilateral; silverleaf nightshade; stomatal density; tracer dyes; trichome; weed