Effect of explant age on phytochemicals and morphogenesis in begonia

In this study, different explant ages related to phytohormones and phytochemicals was analyzed, as well as their role in somatic embryogenesis, flower-like structure formation, adventitious shoots and roots formation were revealed. For that purpose, in vitro Begonia tuberosa petals of different ages were collected from flower buds after 5, 10, 15 and 20 days (P1, P2, P3 and P4, respectively) of surface sterilization with silver nanoparticles (AgNPs). The results showed that there exist synergistic and antagonistic relationships between the hormones Indole-3-acetic acid (IAA), Kinetin (KIN), trans-Zeatin (ZEA), melatonin (MEL), meta-Topolin (MT), gibberellin A3 (GA3), jasmonic acid (JA) and salicylic acid (SA) with morphogenesis programs. Accordingly, the P1 petals containing low levels of IAA, MEL, JA as well as high anthocyanin content and catalase (CAT), Ascorbate peroxidase (APX) activities regenerated the highest number of de novo flower-like structures. High levels of IAA, MEL, phenol, IAA/GA3, IAA/SA, IAA/JA and IAA/MEL ratios in P2 seem to be responsible for the highest frequency of somatic embryogenesis. Alternatively, the phytohormones GA3, SA, JA and MEL may have a synergistic effect in directing adventitious root regeneration of P3 explants. Low concentrations of GA3, MEL, JA, IAA/CKs, JA/ML, anthocyanins and phenolics were detected in the oldest petals (P4), which tended to have stronger shoot regeneration than younger explants. Interestingly, petal senescence did not change starch and sugar levels, but it also exhibited distinct correlations with regeneration programs. The present results suggest that phytohormone and phytochemical content in the explants are important determinants (biomarkers) of in vitro regeneration in begonia.