Immunogold localization of pectins and glycoproteins in tissues of peach with reference to deep supercooling

Abstract

Abstract. Living xylem tissues and floral buds of several species of woody plants survive exposure to freezing temperatures by deep supercooling. A barrier to water loss and the growth of ice crystals into cells is considered necessary for deep supercooling to occur. Pectins, as a constituent of the cell wall, have been implicated in the formation of this barrier. The present study examined the distribution of pectin in xylem and floral bud tissues of peach (Prunus persica). Two monoclonal antibodies (JIM5 and JIM7) that recognize homogalacturonic sequences with varying degrees of esterification were utilized in conjunction with immunogold electron microscopy. Results indicate that highly esterified epitopes of pectin, recognized by JIM7, were the predominant types of pectin in peach and were uniformly distributed throughout the pit membrane and primary cell walls of xylem and floral bud tissues. In contrast, un-esterified epitopes of pectin, recognized by JIM5, were confined to the outer surface of the pit membrane in xylem tissues. In floral buds, these epitopes were localized in middle lamellae, along the outer margin of the cell wall lining empty intercellular spaces, and within filled intercellular spaces. JIM5 labeling was more pronounced in December samples than in July/August samples. Additionally, epitopes of an arabinogalactan protein, recognized by JIM14, were confined to the amorphous layer of the pit membrane. The role of pectins in freezing response is discussed in the context of present theory and it is suggested that pectins may influence both water movement and intrusive growth of ice crystals at freezing temperatures.

From the sap's perspective: The nature of vessel surfaces in angiosperm xylem

“…Images of vessel-parenchyma pits are inconclusive for pectins, because pit membranes cannot be distinguished from protective layers at that resolution (Fig. 2H-K), but some of the pectin signal likely originates from the vessel-parenchyma pit membrane itself, as shown previously for peach and poplar (Wisniewski and Davis, 1995;Arend et al, 2008).…”

The Role of Xylem Parenchyma in the Storage and Utilization of Nonstructural Carbohydrates

“…This so-called amorphous or protective layer may enlarge the actual area available for the exchange of substances (Barnett et al 1993 ); however, other functions such as providing a buffer against xylem pressure oscillations were also proposed (Van Bel and Van der Schoot 1988 ). Both the pit membrane and the amorphous layer are rich in pectins (Wisniewski and Davis 1995 ;Plavcová and Hacke 2011 ). The amorphous layer contains also arabinogalactan-rich glycoproteins (AGPs) (Wisniewski and Davis 1995 ).…”

“…Both the pit membrane and the amorphous layer are rich in pectins (Wisniewski and Davis 1995 ;Plavcová and Hacke 2011 ). The amorphous layer contains also arabinogalactan-rich glycoproteins (AGPs) (Wisniewski and Davis 1995 ). These extracellular proteins prevent a tight alignment of pectin molecules (Lamport et al 2006 ) and hence may increase the porosity and permeability of the amorphous layer.…”

Xylem Surfactants Introduce a New Element to the Cohesion-Tension Theory

“…5). Conduit-facing pit membrane surfaces of such cells often feature a coating of electron-dense material under TEM, the so-called black cap (Schaffer and Wisniewski, 1989;Wisniewski et al, 1991;Wisniewski and Davis, 1995;Rioux et al, 1998), and this cap may be the origin of the black nanoparticles elsewhere in the conduits. Further research will be required to test this hypothesis.…”