Genetic manipulation of polyamine metabolism in poplar II: effects on ethylene biosynthesis

Possible competition between polyamine and ethylene metabolisms was studied in two types of transgenic poplar (Populus nigra × maximowiczii) cells: (a) constitutively expressing a mouse ornithine decarboxylase (ODC, EC 4.1.1.17) cDNA under the control of double 35S cauliflower mosaic virus (CaMV) promoter (cell line 2E), and (b) constitutively expressing a Datura S-adenosylmethionine decarboxylase (SAMDC, EC 4.1.1.50) cDNA under the control of a single 35S CaMV promoter (line PS-18). The 2E cells contained significantly higher putrescine (Put) as well as spermidine (Spd) contents than the non-transgenic (NT) cells. The PS-18 cells contained three- to five-fold lower amounts of Put than the NT cells; their Spd content was either comparable to NT cells (at 3 d of culture) or it was higher than the NT cells (at 6 d of culture). The production of ethylene in the 2E cells was generally higher than in the NT cells throughout the 7-d culture period. Ethylene production in the PS-18 cells was comparable to NT cells. The cellular content of 1-aminocyclo-propane-1-carboxylic acid in the NT and 2E cells was quite similar, while it was slightly lower in the PS-18 cells. It is concluded that in poplar cells the cellular pool of S-adenosylmethionine is probably large enough to satisfy the demand for both polyamine and ethylene production and no competition between the two pathways is apparent.