Events Associated with Early Age-Related Decline in Adventitious Rooting Competence of Eucalyptus globulus Labill

Abstract

The development of adventitious roots is affected by several factors, including the age of the cutting donor plant, which negatively affects rooting capacity. Eucalyptus globulus quickly loses rooting capacity of cuttings as the donor plant ages, although the molecular and biochemical mechanisms behind this process are still unclear. To better understand the bases of rooting competence loss in E. globulus, the time required for a significant decline in rhizogenic ability without exogenous auxin was determined in microcuttings derived from donor plants of different ages after sowing. Tip cuttings of donor plants were severed before and after loss of rooting competence of microcuttings to test the hypothesis that auxin and carbohydrate homeostasis regulate rooting competence decline. There were no significant changes in concentration of carbohydrates, flavonoids, or proteins before and after the loss of rooting capacity. Peroxidase (EC 1.11.1.7) total activity increased with loss of rooting competence. Auxin concentration showed the opposite pattern. In good agreement, TAA1, a key gene in auxin biosynthesis, had lower expression after loss of rooting capacity. The same applied to the auxin receptor gene TIR1, suggesting reduced auxin sensitivity. On the other hand, genes associated with auxin response repression (TPL, IAA12) or with the action of cytokinins, the rhizogenesis inhibitor-related ARR1, showed higher expression in plants with lower rooting competence. Taken together, data suggest that age negatively affects E. globulus rooting by a combination of factors. Decreased endogenous auxin concentration, possibly caused by less biosynthesis, lower auxin sensitivity, higher expression of genes inhibiting auxin action, as well as of genes related to the action of cytokinins, appear to play roles in this process.

γ-Aminobutyric Acid Participates in the Adult-Phase Adventitious Rooting Recalcitrance

“…These indicated that the inhibitory effect of GABA on AR formation is conserved between AR-recalcitrant and easy-toroot species, and also between woody perennial and annual herbaceous plants. However, the findings might not be sufficient to completely explain the adult-phase-specific rooting recalcitrance because of several adult-phase soft-wood cuttings are difficult-to-root or rooted very poorly regardless of auxin application (Diaz-Sala et al 2010;Xiao et al 2014;Aumond et al 2017;Xu et al 2017). GABA application did not mimic this serious AR recalcitrance in both Mx-J and tobacco.…”

Genome-Wide Prediction of Complex Traits in Two Outcrossing Plant Species Through Deep Learning and Bayesian Regularized Neural Network

“…In this study, genomic prediction models based on DL and BRNN were investigated to predict complex traits in two economically important plant species: Eucalyptus globulus Labill. and Zea mays L. E. globulus is one of the most widely planted hardwood tree species in temperate regions of the world, mostly used as raw material for pulp and paper industry due to its highquality cellulose pulp, low lignin, and lipid content (Aumond et al, 2017). This species is also used for the production of essential oils in the pharmaceutical industry (Shao et al, 2020).…”

Cellular dynamics during maturation‐related decline of adventitious root formation in forest tree species

“…Rooting recalcitrance in difficult‐to‐root species of Eucapylptus has also been associated with relatively lower cambium‐auxin content and higher specific expression of rooting inhibitory genes, as compared to easy‐to‐root species (De Almeida et al ). The modification of auxin concentration and sensitivity during early age‐related decline in rooting competence of Eucalyptus globulus young seedlings has been described (Aumond Jr. et al ). Additionally, donor plants from this species treated with specific light quality yielded microcuttings showing higher rooting capacity than nontreated controls (Ruedell et al ).…”