Is polyphenol induction simply a result of altered carbon and nitrogen accumulation?

Abstract

C arbon translocation in plants isshaped by phyllotaxis and regulated by source/sink interactions that respond to the demands of growth and defense. We have studied this extensively in poplar saplings, and recently showed that unlike carbon import, nitrogen is not translocated to sink leaves in response to application of jasmonic acid. Here we report that this is also true for young trees in the field. We discuss the importance of transport processes in establishing local C:N ratios, and suggest that the JA-induced flow of C but not N to sink tissues, and their corresponding increases in C-based defenses, may simply reflect a plant adaptation to handle excess reduced carbon and energy.Local increases in sink strength are essential components of plant responses to grazing, mechanical wounding, infection, hormones and artificial elicitors in a wide range of plant species.1 These responses involve rapid increases in the local activities of cell wall invertase enzymes (CWI; EC 3.2.1.26), which boost phloem unloading and carbohydrate (CHO) transport to the elicited tissues.2-8 We have found that both insect grazing and exogenous jasmonate (JA) trigger increased sink strength, including a 3-fold increase in the import of 13 C-labeled CHOs from orthostichously linked source leaves to sink leaves in poplar saplings. 1,3,4 We recently found that unlike carbon import, nitrogen translocation was not increased by JA treatment in poplar saplings.

Flexible resource allocation during plant defense responses

“…15 N transport from roots also was not disrupted by steam girdling, indicating that the 15 N label was largely restricted to xylem and independent of source-to-sink phloem flow (Appel et al, 2012a). This was confirmed in larger, 4-year-old trees, using whole branches, longer transport distances, and multiple sampling intervals (Arnold et al, 2004; Appel et al, 2012b). JA treatment led to significantly lower rates of 15 N import at 24, 48, and 72 h. It is possible that nitrogen from sources other than roots might have reached the elicited leaves (e.g., stems; Welter, 1989; Fan et al, 2009); that nitrogen would not be labeled and hence would not be detected.…”

“…The strong connection between regulation of source/sink relations and pathogen success makes sink-regulating apoplastic invertases a key part of plant defense against microbes, too (Berger et al, 2007). It seems clear that long-distance transport of resources is a component of plant defense responses to insects and pathogens (Truernit and Sauer, 1995; Arnold and Schultz, 2002; Roitsch et al, 2003; Roitsch and González, 2004; Matyssek et al, 2005; Appel et al, 2012a, b). …”

Leaf-galling phylloxera on grapes reprograms host metabolism and morphology

“…Defense hormones (such as JA) may also enhance C translocation to natural plant sinks by increasing invertase activity as a means to increase defense compound synthesis and potentially compensate for herbivore-induced reductions in photosynthesis (26,27). We observed nearly universal up-regulation of transcripts encoding JA synthesis and up-regulation in vacuolar invertase transcripts (Fig.…”

Influence of Genotype, Environment, and Gypsy Moth Herbivory on Local and Systemic Chemical Defenses in Trembling Aspen (Populus tremuloides)

“…Here, we showed that induction responses differ spatially with respect to the location of the damage and depend on constitutive levels. Many factors can influence the concentrations and inducibility of phytochemicals, including plant tissue age (Koricheva and Shevtsova 2002), vascular architecture and physiology (Arnold and Schultz 2002;Arnold et al 2012;Jones et al 1993), and priming via volatile organic compounds emitted from neighboring damaged tissues (Frost et al 2007). More research is needed to examine the collective influence of these factors on the spatial patterns of carbon-and protein-based plant defense traits at the canopy scale.…”