Abstract
Soluble sugars such as sucrose, glucose and fructose in plant host cells not only play the role as donors of carbon skeletons, but they may also induce metabolic signals influencing the expression of defense genes. These metabolites function in a complex network with many bioactive molecules, which independently or in dialogue, induce successive defense mechanisms. The aim of this study was to determine the involvement of sucrose and monosaccharides as signaling molecules in the regulation of the levels of phytohormones and hydrogen peroxide participating in the defense responses of Lupinus luteus L. to a hemibiotrophic fungus Fusarium oxysporum Schlecht f. sp. lupini. A positive correlation between the level of sugars and postinfection accumulation of salicylic acid and its glucoside, as well as abscisic acid, was noted. The stimulatory effect of sugars on the production of ethylene was also reported. The protective role of soluble sugars in embryo axes of yellow lupine was seen in the limited development of infection and fusariosis. These results provide evidence for the enhanced generation of signaling molecules both by sugar alone as well as during the crosstalk between sugars and infection caused by F. oxysporum. However, a considerable postinfection increase in the level of these signaling molecules under the influence of sugars was recorded. The duration of the postinfection generation of these molecules in yellow lupine was also variable.
Highlights
Soluble sugars such as sucrose, glucose and fructose in plant host cells play the role of donors of carbon skeletons and respiratory substrates, but they may induce metabolic signals influencing the expression of many genes, including defense genes [1,2,3,4,5,6]
Signaling molecules are compounds involved in the regulation of numerous genes, including defense genes triggering a specific metabolic effect
At various times after infection, these signaling molecules can be transiently accumulated and signal transduction induced by these molecules to the cell nucleus causes transcription activation of defense genes [15,16,17]
Summary
Soluble sugars such as sucrose, glucose and fructose in plant host cells play the role of donors of carbon skeletons and respiratory substrates, but they may induce metabolic signals influencing the expression of many genes, including defense genes [1,2,3,4,5,6]. Identification of a pathogen by a plant occurs through transmembrane pattern recognition receptors (PRRs) or via intracellular proteins of the nucleotide-binding domain (NBD), leucine-rich repeat (NLR) superfamily occurring inside the plant cell [13,14] Activation of these receptors induces defense reactions, which are highly coordinated with sequence alterations at the cellular level, including the synthesis of signaling molecules such as phytohormones, i.e., salicylic acid (SA), abscisic acid (ABA), jasmonic acid (JA), ethylene (ET) and free radicals arising from hydrogen peroxide (H2O2) and nitric oxide (NO). The aim of this study was to examine whether the level of saccharides, i.e., sucrose, glucose and fructose, in the embryo axes of yellow lupine It was important to demonstrate the correlation between the level of these saccharides and disease symptom development in yellow lupine embryo axes caused by F. oxysporum f. Progressing necrosis on the entire surface of the embryo axes, some of the axes without turgor none Significant loss of turgor, axes strongly overgrown with mycelium, necrosis and brown discoloration of whole axes, dieback whole axes, lividity tissues
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