Physiological and Endogenous Hormonal Responses During In Vitro Culture of Citral-Rich Camphora officinarum

Bud-bearing stem segments of citral-rich Camphora officinarum were used to optimize in vitro shoot proliferation and adventitious root induction by screening basal media and plant growth regulator types and concentrations. Physiological and endogenous hormonal responses were compared between the two culture stages. At each stage, plantlets cultured on the selected medium and a control medium without plant growth regulators were sampled on days 0, 7, 14, 21, and 28. Soluble sugar, soluble protein, and total phenolic contents; superoxide dismutase (SOD) and peroxidase (POD) levels; and zeatin riboside (ZR), gibberellic acid (GA₃), indole-3-acetic acid (IAA), and abscisic acid (ABA) contents were determined. These parameters were also compared among medium formulations. Murashige and Skoog (MS) medium supplemented with 2.00 mg/L 6-benzyladenine (6-BA), 0.20 mg/L 1-naphthaleneacetic acid (NAA), and 0.05 mg/L kinetin (KT) yielded a proliferation coefficient of 8.16. Within the concentration ranges tested, 6-BA had a greater effect on proliferation than KT or NAA. Half-strength MS medium (1/2MS) was suitable for rooting, and 0.50 mg/L indole-3-butyric acid (IBA) produced a rooting rate of 92.22%. Under the selected culture conditions, soluble sugar content generally increased during shoot proliferation, soluble protein content peaked on day 14, and SOD and POD levels peaked on day 21. During rooting, soluble sugar content declined after day 7, whereas soluble protein content and SOD levels reached high values on day 14. During the middle and later culture periods, treated plantlets generally had higher IAA and lower ABA contents than the controls at both stages. Comparisons among formulations showed that the treatment favorable for proliferation had relatively high soluble sugar and ZR contents, whereas the treatment favorable for rooting had relatively low contents of both. This study identified suitable proliferation and rooting conditions for the genotype represented by the single donor tree examined and revealed differences in sugar dynamics and endogenous hormonal responses between the two culture stages. The selected growth regulator concentrations were suitable within the tested ranges for this genotype. Their applicability to other C. officinarum genotypes requires further validation.