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Temperature-dependent xyloglucan physicochemical changes are associated with XTH-mediated reserve mobilization in
Adriana Grandis1, Miguel José Minhoto2, Paulo Henrique Netto de Alcântara2
1Laboratório de Fisiologia Ecológica de Plantas, Lafieco, Departamento de Botânica, Instituto de Biociências, Universidade de São Paulo, São Paulo, Brazil.
Background And Aims:
Development of Hymenaea courbaril seedlings requires mobilization of xyloglucan (XyG), mediated by four enzymes whose coordinated action reduces cotyledon biomass. Xyloglucan endotransglycosylase/hydrolase (XTH) can display both xyloglucan endotransglucosylase (XET) and xyloglucan endohydrolase (XEH) activities. In Hymenaea-XTH activity is oligosaccharide-dependent, suggesting XET-like behavior. XyGs react with iodine to form a blue-colored, temperature-sensitive complex. Here, this interaction was used to study the biochemical and biophysical properties of XyGs and the Hymenaea-XTH interaction in vitro and in planta across a range of temperatures.
Methods:
We reacted XyGs from different sources with iodine and analyzed the resulting complexes across temperature cycles. Hymenaea-XTH was partially purified and assayed with various XyGs. We measured XTH transglycosylation and hydrolysis of XyG oligosaccharides at different temperatures. In planta, Hymenaea seedlings were subjected to four temperature regimes to assess responses in cotyledon reserve depletion and seedling growth.
Key Results:
XyGs from different sources exhibit varying physicochemical properties at physiological temperatures. Hymenaea-XTH showed maximal XyG-degrading activity near 35 °C, coinciding with the temperature transition associated with changes in XyG interactions, but only when oligosaccharides were added. Modeled potential XEH activity (XDA), estimated from enzyme-polysaccharide properties and leaf surface temperature, suggested that temperature modulates the Hymenaea-XTH and XyG interaction during seedling development. A constant 35 °C accelerated cotyledon reserve depletion, whereas alternating 20/35 °C regimes maintained coupling between reserve mobilization and biomass accumulation.
Conclusions:
Temperature-dependent changes in the XyG-iodine interaction were linked to maximal XyG-degrading activity in the Hymenaea-XTH-enriched preparation at 35 °C. These results support a proposed model in which daily warming may favor XyG modification by increasing putative polymer accessibility and enzyme activity. Under temperature treatments, a constant 35 °C accelerated cotyledon reserve depletion, whereas alternating 20/35 °C regimes better preserved the coupling between reserve depletion and biomass accumulation.
