Effect of Prolonged Water Deficiency of Various Intensities on Growth, Water Homeostasis and Physiological Activity of Pine Seedlings

Resumo

Plant growth is the physiological process that is generally the most affected by drought, and growth inhibition is one of the main contributors to ecosystem productivity loss under water stress. We investigated the relationship between water homeostasis and the growth of Scots pine (Pinus sylvestris L.) seedlings under different intensities of polyethylene glycol (PEG)-induced water deficit over a period of 21 days. In culture medium water potentials from –0.15 to –1.5 MPa, we observed dose-dependent deleterious effects on seedling roots, including root growth inhibition and the depression of root cell physiological activity. One characteristic feature of severe water stress (–1.0 MPa and lower) was a drastic increase in reactive oxygen species in root cells. In contrast to root growth, needle growth was sufficiently more resistant to the decrease in needle water content. The ability to maintain the growth of the aboveground part of the seedling in conditions of water deficiency was determined primarily by the well-developed ability for cell wall adjustment. It allowed the maintenance of the turgor pressure, despite a significant drop in tissue water content, mainly due to the decrease in the osmotic volume of needle cells. We conclude that seedling growth processes, especially shoot growth, are highly resistant to water deficit, which might underlie the high competitiveness of Scots pine seedlings under the conditions of the native habitat of this species.