Activity levels of six glycoside hydrolases in apple fruit callus cultures depend on the type and concentration of carbohydrates supplied and the presence of plant growth regulators

Abstract

Sucrose presence and concentration modulated in different ways and to different extents the activity of six plant glycoside hydrolases (PGHs) extracted from apple callus cultures, both in the water soluble fraction (WS-F) and in the NaCl-released fraction (NaCl-F). b-D-Glucosidase activity increased because of sucrose starvation and the addition of sucrose decreased both WS-F and NaCl-F b-D-glucosidase from calli grown in a Murashige and Skoog's basal medium with (MSH) or without (MS0) plant growth regulators (PGRs). WS-F and NaCl-F a-L-arabinofuranosidase, NaCl-F b-D-galactosidase and NaCl-F b-Dxylosidase activity reached a maximum when 0.045 M sucrose was added to the MS0 medium with an ensuing decline at higher sucrose concentrations. a-D-Galactosidase and a-D-xylosidase activity reached a maximum when 0.045 M sucrose was supplied and did not decline significantly in 0.09 M sucrose-supplied calli. When the effects of PGR presence or absence were analysed, NaCl-F b-Dglucosidase, a-D-galactosidase, b-D-galactosidase, a-D-xylosidase and b-D-xylosidase activities were found to be higher in MS0 than in MSH. To assess whether sugar effects were sucrose-specific, other sugars (glucose, fructose, galactose, maltose, lactose, raffinose, sorbitol and mannitol) were tested, with or without PGR supplementation. In general, sugar alcohols (mannitol, sorbitol) and some monosaccharides (fructose and glucose in particular) were better inducers of NaCl-F a-L-arabinofuranosidase, b-D-galactosidase and b-D-xylosidase activity than disaccharides (sucrose, maltose, and lactose) or the trisaccharide raffinose. This trend was not widespread to all PGHs assessed since sucrose-supplemented calli displayed higher NaCl-F a-D-galactosidase than those supplemented with glucose, galactose, sorbitol or mannitol. These results show that sugars supplied to callus tissue cultures as a carbon source can also modulate PGH activity. Modulation is different for each PGH, sugar-specific and, at least in the case of sucrose, concentration-dependent. Results also suggest the existence of regulatory interactions between PGRs and sugars as part of an intricate sensing and signalling network. Combination of PGR, sugar type and concentration should be taken into account to maximize each PGH activity for further enzyme studies.Keywords Malus 9 domestica Á a-L-Arabinofuranosidase Á a-and b-D-Galactosidase Á a-and b-D-Xylosidase Á b-D-Glucosidase Á Sugars

Morphological and proteomic analyses of sugar beet cultures and identifying putative markers for cell differentiation

“…Extracellular proteins participate in cell morphology, cell division, proliferation, plant defense reactions, responses to stress, and cell-to-cell adhesion (Iwata 1995;Tian et al 2009). The majority of extracellular proteins in Arabidopsis were enzymes involved in polysaccharide metabolism (glycoside hydrolase, glycosyl transferase, expansins), oxido-reductases (peroxidases, multicopper oxidases, germins), and cleaving proteins (subtilisins, aspartic acid, cysteine proteases) (Jamet et al 2008;Alayón-Luaces et al 2010). Some extracellular proteins interact with other proteins, while others may be involved in signalling; 13% of extracellular proteins still have no known function (Jamet et al 2008).…”