Plant material and growth conditions
In vitro plantlets of Solanum tuberosum cv. White Lady
and their TPS1 transgenic progeny, T1 and T2 [17], were
propagated from nodal cuttings. Plantlets were maintained
for six weeks in 30-ml test tubes on RM medium
[40] at 24°C under 90 μE m−2 s
−1 and a 16 h light / 8 hdark photoperiod. The plantlets from in vitro culture
were transferred to 3,000 ml pots containing A260 sterile
soil (Stender, Germany) and grown in a greenhouse
at 20–28°C under long day conditions and 70% soil
water content. Four weeks after planting into soil, the
plants were divided into two groups. Three plants per
line were continuously irrigated to maintain 70% soil
moisture content, while three plants per line were
exposed to a uniformly ramped drought stress by withholding
irrigation.