Physiological Changes and PP2A-C Expression Modulated by Waterlogging Conditions Are Organ-Specific in Tomato Seedlings

Waterlogging stress leads to a reduction in the oxygen level around the root system (hypoxia). It can be caused by poor air exchange in flooded or compacted soil or in a non-aerated medium. Such stress causes numerous morphological, physiological and biochemical changes. The present study aimed to specify hypoxia-influenced modifications of catalytic subunits of PP2A (PP2A-C) parallel to physiological processes in tomato cultivated in hydroponics. The analysis included ROS detection, photosynthetic apparatus efficiency, expression of the PP2A-C subunit protein level, PP2A-like activity, nitrogen metabolism and soluble sugars. Analyses were carried out separately for leaves and roots. In leaves, there was a decrease (52%) in total PP2A-C in response to hypoxia in the root system, but no significant changes in PP2A-related activity were found. In roots, there was a more than six-fold increase in total PP2A-C in response to hypoxia and this was accompanied by a doubling of PP2A-related activity. The applied stress increased nitrate reductase activity and the levels of free amino acids. The decrease in photosynthesis intensity was noticed in the case of stressed plants. These results show that the level of PP2A-C and physiological processes are differentially modulated by waterlogging conditions in an organ-dependent way.