Effects of fungus inoculation and salt stress on physiology and biochemistry of in vitro grapevines: Emphasis on sugar composition changes by FT-IR analyses

The impacts of salt stress and inoculation in in vitro grapevine (Vitis vinifera L.) growth, nutrient accumulation, osmoregulation, photosynthesis and membrane integrity were evaluated. One month exposure to 100 mM NaCl as well as to inoculation with Phaeomoniella chlamydospora reduced relative growth rate (RGR) and induced senescence in grapevine plants, shown by: (1) decrease of Ψπ without osmoregulation, (2) decrease of chlorophyll content and fluorescence, (3) loss of membrane integrity and (4) nutritional disorders. To assess putative changes in structural and/or non-structural carbohydrates induced by these two stress conditions, alcohol insoluble residues from the roots, stems and leaves were also characterised by FT-IR and GC with respect to the sugar composition. The referred organs were distinguished based on: (1) higher proportion of uronic acid residues in leaves which diagnose the presence of pectic polysaccharides (wavenumbers 1100, 1150 and 1018 cm−1 in FT-IR spectra), (2) higher proportion of xylose and glucose on stems and FT-IR spectra diagnostic of xylose-rich polysaccharides (1041 cm−1) and cellulose (1060 cm−1), (3) higher proportion of glucose residues, xylose and arabinose on roots and a FT-IR spectra characteristic of xylose-rich polysaccharides (1041 cm−1). The main alterations induced by salt stress and inoculation were more visible in leaves, where the content of uronic acid decreased showing that changes in cell wall composition occurred, mostly at the pectic fraction. Besides, an accumulation of insoluble glucose was found, and FT-IR spectra showed that this glucose-based material was starch (maximum absorption at 998 cm−1), accumulated as a non-specific response to salt stress and P. chlamydospora inoculation.