Plasmodesmatal pores in the torus of bordered pit membranes affect cavitation resistance of conifer xylem

摘要: The pit membrane in bordered pits of conifer tracheids is characterized by a porous margo and central thickening (torus), which traditionally considered to function as an impermeable safety valve against air-seeding. However, electron microscopy based on 33 species, including five families 19 genera, reveals that pores occur the torus 13 species studied. have plasmodesmatal origin with average diameter 51 nm grouped arrangement. Evidence for embolism spreading via tori supported pore sizes, correspond relatively well pressure inducing cavitation. Predictions earlier correlations between structure cavitation resistance were only weakly punctured tori. Moreover, are significantly less resistant than non-punctured Nevertheless, absolute diameters must be treated caution theoretical measured air-seeding pressures weak. Because most appear not traverse but limited one pad, complete would trigger Embolism through leaky universal across gymnosperms unlikely represent mechanism.