In situ germination of two tropical recalcitrant seeds and changes in activity of ROS-scavenging enzymes

Tropical recalcitrant-seeded species, which disperse seeds at different seasons, provide evidence of the role of oxidative metabolism in seed bank dynamics. Our results indicate that CAT may regulate field germination. Oxidative metabolism during viability loss in recalcitrant seeds has been previously documented, but little is known about the role of ROS-scavenging enzymes in soil seed bank dynamics, especially in recalcitrant seeds. To address this, recalcitrant-seeded species were studied, Swartzia langsdorffii and Persea wildenovii. Diaspores were kept on the soil after natural dispersion, to simulate the seed bank, and were assessed for seed water content, viability, germination and changes in catalase (CAT), superoxide dismutase (SOD) and peroxidase (PRX) activity throughout the field experiment. These parameters were tested for correlations with climatic data. S. langsdorffii start to germinate after one month in soil, with an increase after two months, when CAT activity decreased and SOD activity increased. SOD was negatively correlated with CAT, and CAT was negatively correlated with germination. However, SOD and CAT were positively correlated for P. wildenovii, whose seeds did not germinate even after four months in the soil and with high activity of ROS-scavenging enzymes throughout the period in the soil. Seeds of these species remained viable during the period in the soil with no or little changes in seed water content. ROS-scavenging enzymes respond to environmental factors, adjusting their activity to maintain seed viability. P. wildenovii seeds did not germinate in the soil due to the timing of dispersal being at the end of rainy season, when additional water supply is limited; ROS-scavenging enzymes probably play a role in seed protection during this dry period. Relationship between CAT regulation and soil seed bank dynamics is discussed.