Changes in phytohormones and oxidative stress markers in buried seeds of Vellozia alata

Little information is still available on the mechanisms underlying seed persistence in the soil in several species, and most particularly in vegetation of the rupestrian fields of the Espinhaço Range in Brazil, where ca. 90% of their species are endemic and are of interest for conservation biology. Here we aimed at examining the putative physiological and biochemical changes seeds of one of this species (Vellozia alata L.B.Sm., Velloziaceae) may experience after burial under natural conditions. Endogenous concentrations of phytohormones and oxidative stress markers were measured in seeds buried in the soil for 12 months. Buried seeds experienced a significant loss of germination capacity, which decreased from 58 to 29% during the first 6 months. This was associated with a decline in gibberellins (by 65%), abscisic acid (by 98%), cytokinins (up to 75%) and jasmonic acid (by 97%) during the first 3 months, while salicylic acid increased at 6 months of burial. Malondialdehyde and tocopherol levels also decreased dramatically to non-detectable values during this period, while all tocotrienol homologues decreased by 30%. By contrast, germination capacity remained constant around 30% between 6 and 12 months of burial. During this period, concentrations of all phytohormones examined remained unaltered, except for salicylic acid, whose levels returned to initial values. Tocotrienols decreased significantly, particularly between 9 and 12 months of burial, while the extent of lipid peroxidation remained constant. It is concluded that in V. alata, (i) seed burial causes dramatic changes in phytohormones and in the extent of lipid peroxidation, while the potential for germination decreases; (ii) after 6 months of burial, seed germination capacity remains constant, at least until one year, which is associated with absence of oxidative damage.