Effects of polyamines on the early development of cystocarps, spore release, survival, and germination rate of Gracilariopsis lemaneiformis

Three polyamines (PAs) (spermidine (Spd), spermine (Spm), and putrescine (Put)) were used as growth regulators to the marine macroalgae Gracilariopsis lemaneiformis and to female gametophyte and reproductive tissues (cystocarps were constructed), which led to early maturation of cystocarps and spore release. Laboratory cultivation revealed that exogenous PA application accelerated the development of cystocarps, and the mean sporeling growth rate was 20%–50%/d during the initial week of cultivation. The spore count (SC), survival rate (SR), and germination rate (GR) of G. lemaneiformis showed different responses to PA (10 −6 mol/L and 10 −3 mol/L) treatments under different temperatures (18, 26, and 34 °C), light intensities (30, 60, and 90 µmol photons/(m 2 ·s)), salinities (25, 30, and 35), and nutrient levels (25: 2.5, 50:5.0, and 75:7.5 µmol/L NH 4 Cl:K 2 HPO 4 ), and the optimal conditions were 26 °C, light intensity of 60 µmol/(m 2 ·s), salinity of 35, and nutrient level of 50: 5.0 µmol/L NH 4 Cl: K 2 HPO 4 . Under the optimum conditions, the SC per cystocarp increased by 82.38%, and the spore SR and GR increased by 33.07% and 46.44%, respectively. Each experiment lasted for 7 days, with the highest SC on Day 4 and plateauing on Day 7. The results indicate that PAs could promote the early maturation, spore release, survival, and germination of G. lemaneiformis under laboratory conditions.