Photoperiod and plant growth regulator combinations influence growth and physiological responses in Pelargonium sidoides DC.

The aim of the present study was to evaluate the influence of photoperiod and meta-methoxytopolin riboside (MemTR)-auxin combinations on in vitro growth and physiological responses of Pelargonium sidoides DC. Shoot proliferation was highest under the conventional 16-h photoperiod. Based on the superiority of MemTR among other cytokinins from our previous study, it was selected for evaluating the cytokinin-auxin combination effect under long-day conditions. MemTR-auxin combinations had a significant effect on shoot proliferation compared to the control. The highest shoot proliferation rate (4.5 shoots/explant) was obtained on Murashige and Skoog medium supplemented with a combination of MemTR (1.0 μM) and α-naphthaleneacetic acid (NAA; 0.5 μM). Furthermore, combinations of MemTR and auxins had a synergistic effect on the concentration of photosynthetic pigments. On the other hand, photoperiod had no significant effect on the concentration of photosynthetic pigments. Formation of leaf glandular trichomes was influenced by photoperiod. Both 12- and 16-h photoperiods led to higher glandular trichome densities on the abaxial leaf surfaces of P. sidoides compared to plants grown under the 24-h photoperiod. MemTR-auxin combinations had a significant effect on the concentration of total phenolic compounds and flavonoids.