Post-translational processing of beta-d-xylanases and changes in extractability of arabinoxylans during wheat germination.
Endo-1,4-beta-d-xylanase (EC 3.2.1.8, beta-d-xylanase) activity, and arabinoxylan (AX) level and extractability were monitored for the first time simultaneously in wheat kernels (Triticum aestivum cv. Glasgow) up to 24 days post-imbibition (DPI), both in the absence and presence of added gibberellic acid (GA). Roughly three different stages (early, intermediate and late) can be discriminated. Addition of GA resulted in a faster increase of water extractable arabinoxylan (WEAX) level in the early stage (up to 3-4 DPI). This increase was not accompanied by the discernible presence of homologues of the barley X-I beta-d-xylanase as established by immunodetection. This suggests that other, yet unidentified beta-d-xylanases operate in this early time window. The intermediate stage (up to 13 DPI) was characterized by the presence of unprocessed 67 kDa X-I like beta-d-xylanase, which was much more abundant in the presence of GA. The occurrence of higher levels of the unprocessed enzyme was related with higher beta-d-xylanase activities and a further increase in WEAX level, pointing to in vivo activity of the unprocessed 67 kDa beta-d-xylanase. During the late stage (up to 24 DPI) gradual processing of the 67 kDa beta-d-xylanase occurred and was associated with a drastic increase in beta-d-xylanase activity. Up to 120-fold higher activity was recorded at 24 DPI, with approx. 85% thereof originating from the kernel remnants. The WEAX level decreased during the late stage, suggesting that the beta-d-xylanase is processed into more active forms to achieve extensive AX breakdown.
De Backer
Evelien
E
Laboratory of Food Chemistry and Biochemistry, and Leuven Food Science and Nutrition Research Centre (LFoRCe), Katholieke Universiteit Leuven, Kasteelpark Arenberg 20 bus 2463, B-3001 Leuven, Belgium.
Gebruers
Kurt
K
Van den Ende
Wim
W
Courtin
Christophe M
CM
Delcour
Jan A
JA
D043364:Endo-1,4-beta Xylanases / Q000378:metabolism*; D018525:Germination / Q000502:physiology*; D005875:Gibberellins / Q000378:metabolism; D001467:Hordeum; D010937:Plant Growth Regulators / Q000378:metabolism; D012639:Seeds / Q000254:growth & development* / Q000378:metabolism*; D012995:Solubility; D014908:Triticum / Q000254:growth & development* / Q000378:metabolism; D014990:Xylans / Q000378:metabolism*
D005875:Gibberellins; D010937:Plant Growth Regulators; D014990:Xylans; C085118:arabinoxylan; C007842:gibberellic acid; D043364:Endo-1,4-beta Xylanases