Biomechanics of isolated tomato (Solanum lycopersicum L.) fruit cuticles: the role of the cutin matrix and polysaccharides

Abstract

The mechanical characteristics of the cuticular membrane (CM), a complex composite biopolymer basically composed of a cutin matrix, waxes, and hydrolysable polysaccharides, have been described previously. The biomechanical behaviour and quantitative contribution of cutin and polysaccharides have been investigated here using as experimental material mature green and red ripe tomato fruits. Treatment of isolated CM with anhydrous hydrogen fluoride in pyridine allowed the selective elimination of polysaccharides attached to or incrusted into the cutin matrix. Cutin samples showed a drastic decrease in elastic modulus and stiffness (up to 92%) compared with CM, which clearly indicates that polysaccharides incorporated into the cutin matrix are responsible for the elastic modulus, stiffness, and the linear elastic behaviour of the whole cuticle. Reciprocally, the viscoelastic behaviour of CM (low elastic modulus and high strain values) can be assigned to the cutin. These results applied both to mature green and red ripe CM. Cutin elastic modulus, independently of the degree of temperature and hydration, was always significantly higher for the ripe than for the green samples while strain was lower; the amount of phenolics in the cutin network are the main candidates to explain the increased rigidity from mature green to red ripe cutin. The polysaccharide families isolated from CM were pectin, hemicellulose, and cellulose, the main polymers associated with the plant cell wall. The three types of polysaccharides were present in similar amounts in CM from mature green and red ripe tomatoes. Physical techniques such as X-ray diffraction and Raman spectroscopy indicated that the polysaccharide fibres were mainly randomly oriented. A tomato fruit CM scenario at the supramolecular level that could explain the observed CM biomechanical properties is presented and discussed.

Analyses of Tomato Fruit Brightness Mutants Uncover Both Cutin-Deficient and Cutin-Abundant Mutants and a New Hypomorphic Allele of GDSL Lipase

“…fruit growth, visual aspect, cracking, water loss, resistance to pathogens, and postharvest shelf-life) are highly dependent on fruit cuticle (Bargel and Neinhuis, 2005;Saladié et al, 2007;Matas et al, 2009;Domínguez et al, 2011;Parsons et al, 2012). An increasing number of studies highlight the possibilities offered by tomato for analyzing cuticle architecture, mechanical properties, and permeability (López-Casado et al, 2007;Saladié et al, 2007;MintzOron et al, 2008;Buda et al, 2009;Isaacson et al, 2009;Wang et al, 2011) and for discovering genes contributing to cuticle synthesis and regulation (Hovav et al, 2007;Mintz-Oron et al, 2008;Girard et al, 2012;Nadakuduti et al, 2012;Yeats et al, 2012b;Shi et al, 2013). Nevertheless, to further our understanding of the relationships between cuticle composition and architecture and cuticle properties and performance in plants, new tomato cuticle mutants are highly needed (Domínguez et al, 2011).…”

Localization of polysaccharides in isolated and intact cuticles of eucalypt, poplar and pear leaves by enzyme-gold labelling

“…Cellulose, hemicelluloses and pectins have been grossly isolated from tomato fruit cuticles, and they have been observed to play an important role on cuticle rheological properties [9]. The presence and characteristics of polysaccharides in leaf and fruit isolated cuticles examined as intact tissues or after cutin depolymerisation, have been analysed by different spectroscopic methods [e.g., [9][10][11].…”

“…The presence and characteristics of polysaccharides in leaf and fruit isolated cuticles examined as intact tissues or after cutin depolymerisation, have been analysed by different spectroscopic methods [e.g., [9][10][11]. Although it was found that cellulose fibres are mainly randomly oriented in cuticles of mature and ripe tomato fruits and Agave Americana young leaves [9,10], the position and distinction between groups of polysaccharides cannot be ascertained by such analytical techniques.…”

“…The presence and characteristics of polysaccharides in leaf and fruit isolated cuticles examined as intact tissues or after cutin depolymerisation, have been analysed by different spectroscopic methods [e.g., [9][10][11]. Although it was found that cellulose fibres are mainly randomly oriented in cuticles of mature and ripe tomato fruits and Agave Americana young leaves [9,10], the position and distinction between groups of polysaccharides cannot be ascertained by such analytical techniques. On the other hand, stains like osmium tetroxideuranyl acetate-lead citrate combination [12], calcofluor white [9], ruthenium red [13], periodic acid-thiosemicarbazide-silver proteinate tests [12,14] or chlor-zinc-iodine [15] have been used for detecting polysaccharides in cross-sections of isolated leaf and fruit cuticles by electron, optical and fluorescence microscopy.…”

“…Although it was found that cellulose fibres are mainly randomly oriented in cuticles of mature and ripe tomato fruits and Agave Americana young leaves [9,10], the position and distinction between groups of polysaccharides cannot be ascertained by such analytical techniques. On the other hand, stains like osmium tetroxideuranyl acetate-lead citrate combination [12], calcofluor white [9], ruthenium red [13], periodic acid-thiosemicarbazide-silver proteinate tests [12,14] or chlor-zinc-iodine [15] have been used for detecting polysaccharides in cross-sections of isolated leaf and fruit cuticles by electron, optical and fluorescence microscopy. Nevertheless, the lack of specificity of the dyes, the potential degree of impregnation of polysaccharides with chiefly lipidic cuticular components, and the restrictions to observe stained tissues at higher magnifications by optical and fluorescence microscopy, pose an obstacle for elucidating the nature and location of polysaccharides in the cuticle.…”