Germination, alpha-, beta-amylase and total dehydrogenase activities of Amaranthus caudatus seeds under water stress in the presence of ethephon or gibberellin A3

Amaranthus caudatus L. seed germination was studied under different levels of water deficit induced by PEG 6000 in laboratory conditions. PEG at osmotic potentials -0.2 to -0.3 MPa at 24°C in darkness delayed germination and reduced final germination percentage. PEG solutions at osmotic potential lower than -0.3 MPa almost totally blocked seed germination. Ethephon was much more effective than GA3 in reversing PEG-caused inhibition of A. caudatus seed germination. PEG decreased α-amylase activity after 14 h incubation. It decreased β-amylase activity after 14 and 20 h, and caused an increase in total dehydrogenase activity only after 20 h of incubation. Unlike GA3, ethephon increased α-amylase activity in seeds after 12 and 14 h of incubation under water deficit. After 20 h of incubation there was no difference in α-amylase activity in any of the treatments. Neither ethephon nor GA3 affected the activity of β-amylase and dehydrogenase.