Wheat fructosylsucrose synthases induction mediated by sugars is related to the action of calcium-dependent protein kinases

MARTÍNEZ NOËL G; TOGNETTI J; PONTIS H

Rhode Island, USA

Congreso; ASPB; 2001

The initiation of fructan synthesis in cool temperate grasses is dependent on the activities of fructosylsucrose synthases (FSS), which include sucrose:sucrose-1-fructosyl transferase (1-SST) and sucrose:fructan-6-fructosyl transferase (6-SFT)]. Many sugars induce in vivo these enzymes in barley leaf blades. We have tested FSS induction in wheat, by using detached primary leaf blades immersed in different sugar solutions in the dark. There is a threshold sucrose concentration for the induction of FSS. The highest induction was obtained with sucrose. The inhibition of the sucrose effect by protein kinase inhibitors such as W7 and staurosporine indicates that Ca2+ or calmodulin-dependent protein kinases may be involved in the signaling occurring during fructan synthesis initiation. Additionally, genistein, a protein kinase inhibitor not related to calcium signaling, had no effect. Experiments with EDTA and EGTA also support the involvement of Ca2+ ions, while the strong inhibitory action found with the highly selective calcium chelating agent BAPTA (1,2,-bis(2-aminophenoxy)ethane-N,N,N´,N´-tetraacetic acid) upbears it. Moreover, the expression of 6-SFT mRNAs as seen in Northern blot assays closely corresponded to the activity inhibition pattern. Experiments with the addition of okadaic acid revealed the involvement of protein phosphatases in the FSS induction process as well. Further research is being undertaken in order to assess the role and timing of protein kinases and phosphatase actions. (Supported by grants of FIBA, CONICET, Univ.Nac. de Mar del Plata, and ANPCYT).