Walls of allergenic pollen: Special reference to the endexine

Abstract

Allergic rhinitis is an increasing health problem and pollen allergens are amongst the main elicitors of hay fever symptoms. Allergenic pollen contains a set of differently allergenic proteins which are thought to play a role in the pollen germination and fertilisation process. They are released upon contact with the stigma or mucosa or upon pollen grain rupture. Although the determinants of allergenicity of these proteins are still largely undiscovered, accessibility and solubility are now thought to mainly influence allergenic potency. Pollen of 61 allergenic plants was investigated with scanning and transmission electron microscopy. Most of the minor allergenic plants like species of the families Salicaceae, Fagaceae or Ulmaceae show the typical pollen wall organisation with intine, compact endexine and ektexine whereas in the majority of the major allergenic plants like species of Betulaceae and Poaceae the endexine is not detectable. Ambrosia artemisiifolia exhibits a laminated endexine. In addition, pollen of these major allergenic plants does not have electron-dense pollenkitt and starch is stored in a high proportion of the examined pollen. The question is raised whether pollen morphology and ultrastructure might contribute to the accessibility and therefore allergenicity of allergenic proteins.

The endexine: a frequently overlooked pollen wall layer and a simple method for detection

“…Used in a 1% aqueous solution of potassium permanganate, it particularly stains the endexine producing a distinct contrast. This has been confirmed for many species (Ulrich, 2006;Diethart et al, 2007). The application of different TEM staining techniques for one and the same sample is very important and highly recommended in order to avoid misinterpretations in the pollen wall architecture.…”

“…A morphological feature of the endexine is its increasing thickness closer to the aperture. According to Hesse et al (2009), the endexine may be compact, as in Oenothera (Takahashi & Skvarla, 1990), spongy, as in several Araceae (Weber et al, 1999) or lamellar as seen in Ambrosia (Diethart et al, 2007), Brasenia (Taylor & Osborn, 2006) and in many gymnosperm taxa (Kurmann, 1990(Kurmann, , 1994. The endexine has a distinct substructure including laterally oriented white line-centred lamellations (Rowley, 1988(Rowley, , 1995.…”

“…Gmel. and Utricularia alpina Jacq., there are angiosperm species with continuously lamellar endexines (Jérémie et al, 1990;Taylor & Osborn, 2006;Diethart et al, 2007).…”

Efectos de la disminución de temperatura sobre el desarrollo de la pared de la antera y el grano de polen en Oryza sativa L.

“…En el grano de polen maduro se observó que la pared carece de endexina y corresponde al tipo III de la clasificación de Walker & Doyle (1975). Esto concuerda con observaciones de granos de polen de otras especies de cereales, tales como Triticum aestivum L., Secale cereale L., Zea mays L. y Avena sativa L. (Diethart et al 2007).…”

Sporoderm development inSwida alba(Cornaceae), interpreted as a self-assembling colloidal system

“…Specific staining with potassium permanganate showed that endexine contains phospholipid-protein complexes (Diethart et al, 2007;Weber & Ulrich, 2010), a fact that emphasises the similarity of plasma membrane and initial endexine lamellae (lamellar micelles).…”