Indirect somatic embryogenesis of Theobroma cacao L. in liquid medium and improvement of embryo-to-plantlet conversion rate

Abstract

The establishment of cocoa embryogenic cell lines in liquid medium starting from high frequency somatic embryogenesis (HFSE) callus is described. The growth kinetics of the cultures during the multiplication and the expression steps conducted in 250 mL Erlenmeyer flasks were described for three genotypes selected for their agronomical traits (EET95, EET96, and EET103). The glucose and dissolved oxygen concentrations and the absorption of Murashige and Skoog medium macronutrients (nitrate, ammonium, potassium, sulfate, calcium, phosphorus, and magnesium) were monitored. The multiplication of the embryogenic calluses in a medium containing 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) at 1 mg L−1, initiated with an inoculation density of 20 g L−1 of callus, was achieved. The growth rate was characterized by two phases, with the second being concomitant with a depletion of phosphorus and magnesium, and a decrease in the embryogenic potential of the callus. The expression of the callus embryogenic capacity was conducted in an auxin-free medium. The embryo production starting from 1 and 5 g L−1 inoculation densities was compared. When placed in the optimal expression conditions in flasks, 1 g of callus produced 1000 to 1500 embryos within 5 to 7 wk. Finally, two paths for improving the plantlet regenerative capacities of cocoa SE produced in liquid medium were identified. Supplementing the expression medium with myo-inositol used as an osmotic agent at a concentration of 50 g L−1 increased the embryo-to-plantlet conversion rate from 13–16% to 40–48%. A 6-wk culture of the embryos on a maturation medium in Petri dishes optimized their subsequent development into plantlets.

Morpho-histological development of the somatic embryos of Typha domingensis

“…For example, embryogenic induction and proliferation have been stimulated in monocotyledons by exposure to the auxin 2,4-dichlorophenoxyacetic (2,4-D) ( Máthé et al, 2000 ; Rogers, 2003 ; Oh et al, 2008 ). Analogous to the development of zygotic embryos in nature ( Von Aderkas et al, 2015 ), the elimination of auxin exposure during periods of darkness has been frequently applied to obtain competent embryos ( Filonova, Bozhkov & Von Arnold, 2000 ; Guillou et al, 2018 ). Consequently, experimental studies aimed at quantifying the effect of light on SE maturation have been unable to resolve the possible discrepancies arising from its effects ( Devi, Sharma & Ahuja, 2014 ; Mikuła et al, 2015 ), because in some ferns, angiosperms, and gymnosperms, light exposure improves SE formation and maturation, both anatomically and biochemically ( Mikuła et al, 2015 ; Von Aderkas et al, 2015 ; Klubicová et al, 2017 ).…”

An innovative automated active compound screening system allows high-throughput optimization of somatic embryogenesis in Coffea arabica

“…The industrial application of SE in hardwoods remains limited to a few species, such as the hybrid yellow-poplar, cocoa, and coffee 8 . SE technology is still work-in-progress, mainly due to low biological efficiency and high genotypic effects resulting in high production costs 6,9 .…”

Cross Talk among Phytohormone Signal and Carbohydrate Metabolism Involving Regenerable Calli Induction under Osmotic Treatment

“…Except the function of seed dormancy regulation and stress responses, ABA is also reported to have function on root and shoot development [46,47]. Although there were some genes participating in ABA signaling, which were also reported to involve in the shoot regeneration process, there is still no clarity about the molecular function of endogenous ABA on the shoot organogenesis process [14,15]. However, some studies, including our previous works, found that ABA was highly accumulated in HRC, but not in NRC [5].…”

“…Previous studies had identified that added osmotic agents like sorbitol or mannitol in callus induction medium can stimulate HRC formation instead of NRC, thus promoting the shoot formation frequency [5,7,[9][10][11]. It is still unclear why appropriate osmotic stress during callus induction can promote shoot organogenesis frequency, but there were lots of studies indicating that osmotic stress can stimulate endogenous phytohormone abscisic acid (ABA) accumulation which is also proven to have the function of promoting somatic embryogenesis and shoot organogenesis when it used as an exogenous plant growth regulator in callus culture [11][12][13][14][15]. ABA is widely recognized as a negative plant hormone which mainly functions on stress responses and seed dormancy, but when it is treated in low concentration, ABA could become a positive regulator on root elongation [16].…”