Quality traits of conventional and transgenic lettuce (Lactuca sativa L.) at harvesting by NMR metabolic profiling.

Metabolism of genetically modified (GM) lettuce (Lactuca sativa L.) leaves wasinvestigated by comparing NMR metabolic profiles of three lines (T(3)B12, T(7)B7,and T(7)B14) overexpressing the E. coli asparagine synthetase A gene with thoseof the wild type (WT) at 24, 56, and 64 days after sowing (DAS). Statistical analyses based on hydro-soluble compound profiles significantly and maximally discriminated the WT from GM-lines at optimal harvest time (56 DAS). The T(7)B14 metabolic variations were opposite to those of both T(3)B12/T(7)B7 lines, suggesting that unexpected effects of transgenesis had occurred. Compared tocontrols, the T(3)B12/T(7)B7 plants shared the leaf mass increase, higher aminoacid (asparagine, glutamine, valine, and isoleucine) and protein levels, andlower nitrate contents, accompanied by a modest sink of organic acids (alpha-chetoglutarate, succinate, fumarate, and malate), sucrose, fructose, and inulins. Incongruously, the T(7)B14 butter heads were less leafy than the controls and showed lowered amino acid/protein contents and overstored inulin. To further investigate the metabolic discrepancies among the GM-lines, a set of key nitrogen and inulin genes was monitored. The T(3)B12/T(7)B7 lines sharedcomparable gene expression changes, including the induction of the endogenous asparagine synthetase1 and nitrate reductase1 that supported the targeted enhancement of nitrogen status. Transgene product malfunctioning and T-DNA rearrangements throughout generations were proposed to explain the decreased asparagine content and the complex expression pattern of N genes in T(7)B14leaves. In the latter, the inulin accumulation was associated with the up regulation of fructan biosynthesis genes and the intense repression of fructan hydrolases.