Essences in Metabolic Engineering of Lignan Biosynthesis
Dihydridiconiferyl alcohol and lariciresinol, known as phytotoxic lignans, acting on the germination of Lactuca sativa have been tested for lettuce seedling development. It has been evidenced that sucrose grown plants respond to such lignans differently from those grown without sucrose. Dihydridiconiferyl alcohol, which is more active than lariciresinol, reduced chlorophyll and carotenoid synthesis in sucrose grown plants. It also caused a greater decrease of photosystem efficiency, lowering of Yield and non-photochemical quenching in treated plants in respect to those in controls. Both lignans affected carbon and nitrogen metabolism, reducing, in particular, glucose-6-phosphate dehydrogenase (G6PDH) and glutamate synthase (GOGAT) activities in sucrose grown plants. The decrease of G6PDH (-80%) and GOGAT (-65%) activities was correlated to an increase of soluble sugars (up to + 100%) and glutamine (+70%), respectively. This is the first time an allelochemical affecting GOGAT activity has been reported.