BACKGROUND AND AIMS: Since the proposal of the cohesion theory there has been a paradox that the lumenal surface of vessels is rich in hydrophobic lignin, while tension in the rising sap requires adhesion to a hydrophilic surface. This study sought to characterize the strength of that adhesion in maize (Zea mays), the wettability of the vessel surface, and to reconcile this with its histochemical and physical nature. METHODS: Wettability was assessed by emptying the maize root vessels of sap, perfusing them with either water or oil, and examining the adhesion (as revealed by contact angles) of the two liquids to vessel walls by cryo-scanning electron microscopy. The phobicity of the lumenal surface was also assessed histochemically with hydrophilic and hydrophobic probes. KEY RESULTS: Pit borders in the lumen-facing vessel wall surface were wetted by both sap/water and oil. The attraction for oil was weaker: water could replace oil but not vice versa. Pit apertures repelled oil and were strongly stained by hydrophilic probes. Pit chambers were probably hydrophilic. Oil never entered the pits. When vessels were emptied and cryo-fixed immediately, pit chambers facing away from the vessels were always sap-filled. Pit chambers facing vessel lumens were either sap- or gas-filled. Sap from adjoining tracheary elements entering empty vessels accumulated on the lumenal surface in hemispherical drops, which spread out with decreasing contact angles to fill the lumen. CONCLUSIONS: The vessel lumenal surface has a dual nature, namely a mosaic of hydrophilic and hydrophobic patches at the micrometre scale, with hydrophilic predominating. A key role is shown, for the first time, of overarching borders of pits in determining the dual nature of the surface. In gas-filled (embolized) vessels they are hydrophobic. When wetted by sap (vessels refilling or full) they are hydrophilic. A hypothesis is proposed to explain the switch between the two states.
BACKGROUND AND AIMS: Since the proposal of the cohesion theory there has been a paradox that the lumenal surface of vessels is rich in hydrophobic lignin, while tension in the rising sap requires adhesion to a hydrophilic surface. This study sought to characterize the strength of that adhesion in maize (Zea mays), the wettability of the vessel surface, and to reconcile this with its histochemical and physical nature. METHODS: Wettability was assessed by emptying the maize root vessels of sap, perfusing them with either water or oil, and examining the adhesion (as revealed by contact angles) of the two liquids to vessel walls by cryo-scanning electron microscopy. The phobicity of the lumenal surface was also assessed histochemically with hydrophilic and hydrophobic probes. KEY RESULTS: Pit borders in the lumen-facing vessel wall surface were wetted by both sap/water and oil. The attraction for oil was weaker: water could replace oil but not vice versa. Pit apertures repelled oil and were strongly stained by hydrophilic probes. Pit chambers were probably hydrophilic. Oil never entered the pits. When vessels were emptied and cryo-fixed immediately, pit chambers facing away from the vessels were always sap-filled. Pit chambers facing vessel lumens were either sap- or gas-filled. Sap from adjoining tracheary elements entering empty vessels accumulated on the lumenal surface in hemispherical drops, which spread out with decreasing contact angles to fill the lumen. CONCLUSIONS: The vessel lumenal surface has a dual nature, namely a mosaic of hydrophilic and hydrophobic patches at the micrometre scale, with hydrophilic predominating. A key role is shown, for the first time, of overarching borders of pits in determining the dual nature of the surface. In gas-filled (embolized) vessels they are hydrophobic. When wetted by sap (vessels refilling or full) they are hydrophilic. A hypothesis is proposed to explain the switch between the two states.
Authors: H J Wagner; H Schneider; S Mimietz; N Wistuba; M Rokitta; G Krohne; A Haase; U Zimmermann Journal: New Phytol Date: 2000-11 Impact factor: 10.151
Authors: Michael W Shane; Margaret E McCully; Martin J Canny; John S Pate; Cheng Huang; Hai Ngo; Hans Lambers Journal: New Phytol Date: 2010-01-18 Impact factor: 10.151
Authors: H Jochen Schenk; Susana Espino; David M Romo; Neda Nima; Aissa Y T Do; Joseph M Michaud; Brigitte Papahadjopoulos-Sternberg; Jinlong Yang; Yi Y Zuo; Kathy Steppe; Steven Jansen Journal: Plant Physiol Date: 2016-12-07 Impact factor: 8.340
Authors: Luciano Pereira; Denisele N A Flores-Borges; Paulo R L Bittencourt; Juliana L S Mayer; Eduardo Kiyota; Pedro Araújo; Steven Jansen; Raul O Freitas; Rafael S Oliveira; Paulo Mazzafera Journal: Plant Physiol Date: 2018-06-05 Impact factor: 8.340
Authors: Vivien Rolland; Dana M Bergstrom; Thomas Lenné; Gary Bryant; Hua Chen; Joe Wolfe; N Michele Holbrook; Daniel E Stanton; Marilyn C Ball Journal: Plant Physiol Date: 2015-06-19 Impact factor: 8.340