Selenium nanoparticles promote adventitious rooting without callus formation at the base of passion fruit cuttings via hormonal homeostasis changes

Callus formation at the cutting base is an interesting and common phenomenon in cuttings; however, little is known of histology and hormonal dynamics during the adventitious root formation (AR) and callusing stages of cuttings, also the relationship between them, were the aims of this study. The results showed that all SeNPs selenium nanoparticles (SeNPs) concentrations (1.0; 3.0; 5.0; 7.0 and 9.0 mg/L) and control (-) which is AR stimulants-free showed an impact AR formation without callusing in passion fruit cuttings. Meanwhile, regardless of the callus accumulation induced by cortex cell proliferation at cutting base that promoted by 2.5 mg/L IBA-control (+), no ARs differentiated from callus but rather from vascular cambium cells. It implies callus formation is not an obligatory trigger/signal for AR formation. Interestingly, SeNPs regulate IAA, Kin, zeatin, GA3 and ABA levels that peak during the S1 phase (S1-induction root/callus founder cells) consequent an increase in GA3/IAA, GA3/CKs, GA3/ABA ratios and a decrease in CKs/ABA ratio causing early vascular differentiation and of cambial derivatives behavioral modification, when crosstalk further regulates responses during AR-forming cellular reprogramming. On the other hand, callus induced by IBA impeded AR formation and growth traits due to increased endogenous 2ip, IAA/CKs and decreased GA3/IAA ratio during S1. Furthermore, the sustained high maintenance IAA/CKs and IAA/ABA ratios during S1-S3 (S3-massive rooting phase) favor callusing. SeNPs derived-plantlets without accumulate callus exhibited higher survival rate and superior growth during acclimatization stage compared with those controls, emphasizing that callusing was detrimental to passion fruit cuttings.

Automated summary

This study aims to investigate the histology and hormonal dynamics during adventitious root formation and callusing stages of passion fruit cuttings, as well as their relationship. The results show that callus formation is not necessary for adventitious root formation and that selenium nanoparticles can regulate hormone levels, promoting early vascular differentiation and cellular reprogramming. However, callus induced by exogenous hormones inhibits adventitious root formation and growth traits.