This study examined ornithine decarboxylase (ODC) activity and polyamine levels in Achlya ambisexualis, a water mold that responds to steroid hormones. Researchers measured ODC activity and intracellular putrescine and spermidine concentrations during two developmental processes: zoospore germination and hormone-induced sexual differentiation. During zoospore germination in enriched medium, ODC activity increased 5-7 fold within 8 hours, correlating with elevated putrescine and spermidine levels. When the hormone antheridiol was added to mycelium cultured in enriched media, ODC activity increased 5-2 fold transiently, peaking at 80 minutes. However, when mycelium was cultured in minimal medium, antheridiol treatment induced normal sexual differentiation (antheridial formation) without increasing ODC activity or polyamine accumulation. This finding contradicted the widely held notion that polyamine accumulation is essential for cellular differentiation and macromolecular synthesis, demonstrating that sexual morphogenesis in Achlya can occur independently of polyamine biosynthesis in certain growth conditions.

Key findings

• Ornithine decarboxylase activity increased 5-7 fold during zoospore germination, correlating with increases in putrescine and spermidine levels
• Antheridiol hormone induced a rapid, transient 5-2 fold increase in ODC activity in mycelium cultured in enriched media, with peak activity at 80 minutes
• Sexual differentiation occurred normally in minimal medium despite the absence of hormone-induced ODC activity or polyamine accumulation
• Polyamine synthesis is not essential for hormone-induced sexual differentiation in Achlya, challenging the established link between polyamines and cellular proliferation