Expression of a Petunia inflata pectin methyl esterase in Solanum tuberosum L-enhances stem elongation and modifies cation distribution

Transgenic potato (Solanum tuberosum L.) plants were constructed with a Pet unia inflata-derived cDNA encoding a pectin methyl esterase (PME; EC 3.1.1. 11) in sense orientation under the control of the cauliflower mosaic virus 35S promoter. The PME activity was elevated in leaves and tubers of the tra nsgenic lines but slightly reduced in apical segments of stems from mature plants. Stem segments from the base of juvenile PME-overexpressing plants d id not differ in PME activity from the control, whereas in apical parts PME was less active than in the wild-type. During the early stages of developm ent stems of these trangenic plants elongated more rapidly than those of th e wild-type. Further evidence that overexpression of a plant-derived PME ha s an impact on plant development is based on modifications of tuber yield, which was reduced in the transgenic lines. Cell walls from transgenic tuber s showed significant differences in their cation-binding properties in comp arison with the wildtype. In particular, cell walls displayed increased aff inity for sodium and calcium, while potassium binding was constant. Further more, the total ion content of transgenic potatoes was modified. Indication s of PME-mediated differences in the distribution of ions in transgenic pla nts were also obtained by monitoring relaxations of the membrane potential of roots subsequent to changes in the ionic composition of the bathing solu tion. However, no effects on the chemical structure of pectin from tuber ce ll walls could be detected.