**4. Materials and Methods**

#### *4.1. Plant Material and Treatments*

*P. patens* was provided by the Biotechnology Department of the Universidad Politécnica (Madrid, Spain) and cultured as described previously [58]. *P. patens* gametophores were maintained in solid medium under standard conditions in a growth chamber at 25 ◦C with a 16 h photoperiod. For stress treatments, *P. patens* gametophores were grown in liquid medium on a rotator shaker (130 rpm) and then transferred into medium supplemented with 5 mM H2O2 (with or without 10 mM ascorbic acid), 250 mM NaCl, 250 mM mannitol, 10 μM abscisic acid (ABA) and 1 mM salicylic acid (SA), respectively [59–62].
