In vitro Culture Optimization of Pomelo Seeds (Citrus maxima (Burm.) Merr.): A South Sulawesi Orange

<b>Background and Objective:</b> Indonesia boasts a variety of delicious tropical fruits, including pomelo, mainly grown in Pangkep Regency, South Sulawesi Province. However, in this region, some challenges hinder such as inadequate care, aging trees and limited seed supply hinder productivity in this region. <i>In vitro</i> culture methods present a solution by rapidly producing high quality, disease-free pomelo seeds. This study aims to determine the optimal concentration of the BAP added to the culture medium to induce shoots from pomelo seeds. <b>Materials and Methods:</b> The seeds were planted on MS media with the addition of BAP hormone (0.5, 1, 1.5, 2 and 2.5 ppm) and 0 ppm as the control. The experimental units were arranged in a CRD and analyzed using SPSS 20.0 software, employing the Shapiro-Wilk normality test and Levene's Statistic for homogeneity. If the data met the normality and homogeneity assumptions, ANOVA was applied, followed by the DMRT for a parametric test. Otherwise, a non-parametric test namely the Kruskal-Wallis was conducted and differences were further analyzed using the Mann-Whitney test at a 5% significance level. <b>Results:</b> The application of the BAP accelerated shoot emergence, with the most rapid development occurring on the 10th day after planting (DAP), at a BAP concentration of 2.5 ppm for red pomelo. For white pomelo and sweet pomelo, shoots appeared on the 19th and 20th days, respectively at a 2 ppm BAP. Interestingly, root development was fastest between the 4th and 6th DAP in 0 ppm BAP (control). <b>Conclusion:</b> The addition of the BAP at a concentration of 1.5 ppm in the culture medium promotes faster shoot emergence and has a significant impact on the number of shoots in red pomelo.

Testing Explant Sources, Culture Media, and Light Conditions for the Improvement of Organogenesis in Pinus ponderosa (P. Lawson and C. Lawson)

Pinus. ponderosa (P. Lawson and C. Lawson) is a commercial tree and one of the most important forest species in North America. Ponderosa pine suffers hardship when going through vegetative propagation and, in some cases, 15-30 years are needed to achieve full reproductive capacity. Based on previous works on P. ponderosa regeneration through in vitro organogenesis and trying to improve the published protocols, our objective was to analyze the influence of different types of explants, basal culture media, cytokinins, auxins, and light treatments on the success of shoot multiplication and rooting phases. Whole zygotic embryos and 44 µΜ 6-benzyladenine showed the best results in terms of explants survival. For shoot organogenesis, whole zygotic embryos and half LP (LP medium, Quoirin and Lepoivre, 1977, modified by Aitken-Christie et al., 1988) macronutrients were selected. A significant positive interaction between whole zygotic embryos and half LP macronutrients was found for the percentage of explants forming shoots. Regarding the light treatments applied, a significantly higher percentage of shoots elongated enough to be rooted was detected in shoots growing under blue LED at a light intensity of 61.09 µmol m^-2 s^-1. However, the acclimatization percentage was higher in shoots previously cultivated under fluorescent light at a light intensity of 61.71 µmol m^-2 s^-1. Anatomical studies using light microscopy and scanning electron microscopy showed the light treatments promoted differences in anatomical aspects in in vitro shoots; needles of plantlets exposed to red and blue LEDs revealed less stomata compared with needles from plantlets exposed to fluorescent light.

TiO2 nanoparticle synthesis, characterization and application to shoot regeneration of water hyssop (Bacopa monnieri L. Pennel) in vitro

Water hyssop (Bacopa monnieri L. Pennel) is a medicinal aquatic herb used to treat diseases in South Asia. Various regeneration protocols have been developed or modified in vitro to ensure the availability of biomass and secondary metabolites of Bacopa. We applied hydrothermally treated titanium dioxide (TiO₂) nanoparticles (NPs) (TiO₂-NPs) at different concentrations. Three explants, distal portion of half leaf (DPHL), proximal portion of half leaf (PPHL) and full leaf (FL), were used to evaluate response to TiO₂. Regeneration from the three explants in vitro was similar except for shoot length. Application of TiO₂-NPs exerted significant, but variable, effects on all parameters except percentage of shoot formation, which was 100%. Interactive effects of explant and TiO₂-NPs exhibited significant, but variable, effects on fresh weight and percentage of callus formation. All explants produced more shoots using TiO₂-NPs compared to control treatments. DPHL explants with application of 8 mg/l TiO₂ produced more shoots than controls. Similarly, FL explant treated with 2 mg/l TiO₂-NPs produced more shoots/explant than controls. All concentrations of TiO₂-NPs produced significantly longer shoots compared to controls. Increased elongation of shoots justifies use of TiO₂-NPs for propagation of plants in vitro during acclimatization. Use of TiO₂-NPs for rapid elongation of shoots ultimately fosters survival of plants.

Cytokinin Signaling and De Novo Shoot Organogenesis

The ability to restore or replace injured tissues can be undoubtedly named among the most spectacular achievements of plant organisms. One of such regeneration pathways is organogenesis, the formation of individual organs from nonmeristematic tissue sections. The process can be triggered in vitro by incubation on medium supplemented with phytohormones. Cytokinins are a class of phytohormones demonstrating pleiotropic effects and a powerful network of molecular interactions. The present study reviews existing knowledge on the possible sequence of molecular and genetic events behind de novo shoot organogenesis initiated by cytokinins. Overall, the review aims to collect reactions encompassed by cytokinin primary responses, starting from phytohormone perception by the dedicated receptors, to transcriptional reprogramming of cell fate by the last module of multistep-phosphorelays. It also includes a brief reminder of other control mechanisms, such as epigenetic reprogramming.