Effects of polyamine type and concentration on growth and physiological traits of in vitro Dendrobium parishii plantlets

Abstract Dendrobium usually require more diversified nutritional support during long-term tissue culture; polyamines (putrescine, spermidine, and spermine), as a class of small-molecule aliphatic amines extensively involved in plant growth and development, morphogenesis, and stress responses, have demonstrated promising application prospects in tissue culture. We compared putrescine (Put), spermidine (Spd) and spermine (Spm), each at 0.3–0.8 mg L⁻¹, with paclobutrazol and an unsupplemented control (CK) in Dendrobium parishii tissue culture. Clump-level leaf number differed among treatments in a vessel-cluster-preserving permutation test (Holm-adjusted P = 0.024). Spd 0.8 had the greatest mean shoot number, whereas Put 0.8 had the maximum mean fresh weight and leaf number. The highest descriptive Fv/Fm means at 30 d occurred in Put 0.4 (0.768), Spd 0.4 (0.768) and Put 0.6 (0.766); at 120 d, they occurred in Spm 0.3 (0.755), Spd 0.8 (0.749) and Spm 0.6 (0.737). An exploratory index integrating six morphological traits with endpoint Fv/Fm ranked Spm 0.6, Spd 0.8 and Spm 0.3 closely (I = 0.696, 0.681 and 0.678). Biochemical responses were not uniformly aligned with this ranking: Spm 0.6 combined the lowest endpoint MDA with the highest H₂O₂, while CK had the highest CAT activity. These complementary developmental and physiological profiles indicate that, according to the culture objective, either a specific type of polyamine may be selected or combinations of different polyamines may be considered.