Osmotic stress-induced somatic embryo maturation of coffee Coffea arabica L., shoot and root apical meristems development and robustness.

Somatic embryogenesis (SE) is the most important plant biotechnology process for plant regeneration, propagation, genetic transformation and genome editing of coffee, Coffea arabica L. Somatic embryo (SEs) conversion to plantlets is the principal bottleneck for basic and applied use of this process. In this study we focus on the maturation of SEs of C. arabica var. Typica. SEs conversion to plantlet up to 95.9% was achieved under osmotic stress, using 9 g/L gelrite, as compared with only 39.34% in non-osmotic stress. Mature SEs induced in osmotic stress developed shoot and root apical meristems, while untreated SEs were unable to do it. C. arabica regenerated plants from osmotic stress were robust, with higher leaf and root area and internode length. To understand a possible regulatory mechanism, gene expression of key genes of C. arabica, homologous to sequences in the Arabidopsis thaliana genome, were analyzed. A set of two component system and cytokinin signaling-related coding genes (AHK1, AHK3, AHP4 and ARR1) which interact with WUSCHEL and WOX5 homedomains and morphogenic genes, BABY-BOOM, LEC1, FUS3 and AGL15, underwent significant changes during maturation of SEs of C. arabica var. Typica. This protocol is currently being applied in genetic transformation with high rate of success.

Effect of salicylic acid on the attenuation of aluminum toxicity in Coffea arabica L. suspension cells: A possible protein phosphorylation signaling pathway.

The protective effect of salicylic acid (SA) on aluminum (Al) toxicity was studied in suspension cells of Coffea arabica L. The results showed that SA does not produce any effect on cell growth and that the growth inhibition produced by aluminum is restored during simultaneous treatment of the cells with Al and SA. In addition, the cells exposed to both compounds, Al and SA, showed evident morphological signals of recovery from the toxic state produced in the presence of Al. The cells treated with SA showed a lower accumulation of Al, which was linked to restoration from Al toxicity because the concentration of Al(3+) outside the cells, measured as the Al(3+)-morin complex, was not modified by the presence of SA. Additionally, the inhibition of phospholipase C by Al treatment was restored during the exposure of the cells to SA and Al. The involvement of protein phosphorylation in the protective effect of SA on Al-toxicity was suggested because staurosporine, a protein kinase inhibitor, reverted the stimulatory effect of the combination of Al and SA on protein kinase activity. These results suggest that SA attenuates aluminum toxicity by affecting a signaling pathway linked to protein phosphorylation.

Mechanism and control of Solanum lycocarpum seed germination.

BACKGROUND AND AIMS: Solanaceae seed morphology and physiology have been widely studied but mainly in domesticated crops. The present study aimed to compare the seed morphology and the physiology of germination of Solanum lycocarpum, an important species native to the Brazilian Cerrado, with two species with endospermic seeds, tomato and coffee. METHODS: Morphological parameters of fruits and seeds were determined by microscopy. Germination was monitored for 40 d under different temperature regimes. Endosperm digestion and resistance, with endo-beta-mannanase activity and required force to puncture the endosperm cap as respective markers, were measured during germination in water and in abscisic acid. KEY RESULTS: Fruits of S. lycocarpum contain dormant seeds before natural dispersion. The best germination condition found was a 12-h alternating light/dark and high/low (20/30 degrees C) temperature cycle, which seemed to target properties of the endosperm cap. The endosperm cap contains 7-8 layers of elongated polygonal cells and is predestined to facilitate radicle protrusion. The force required to puncture the endosperm cap decreased in two stages during germination and showed a significant negative correlation with endo-beta-mannanase activity. As a result of the thick endosperm cap, the puncture force was significantly higher in S. lycocarpum than in tomato and coffee. Endo-beta-mannanase activity was detected in the endosperm cap prior to radicle protrusion. Abscisic acid inhibited germination, increase of embryo weight during imbibition, the second stage of weakening of the endosperm cap and of endo-beta-mannanase activity in the endosperm cap. CONCLUSIONS: The germination mechanism of S. lycocarpum bears resemblance to that of tomato and coffee seeds. However, quantitative differences were observed in embryo pressure potential, endo-beta-mannanase activity and endosperm cap resistance that were related to germination rates across the three species.

Efficient digestion and structural characteristics of cell walls of coffee beans.

Screening of effective food-processing cellulase for digestion of cell walls of coffee beans was carried out, and the cellulase from Trichoderma sp. was selected. The digestion of the cell walls of green and roasted coffee beans was carried out by sequential procedures of alkali boiling (0.1 M Na2CO3 buffer, pH 10, and 0.1 M NaOH), cellulase digestion, autoclaving with 0.1 M NaOH, and cellulase redigestion. The total digestion yields were >95 and >96%, respectively. The cell walls became thin, and the final residues of the cell walls were easily broken into small pieces. The neutral sugar analysis of the digestion or the extract and the residues and the microscopy observations with staining with toluidine blue O, Yariv reagent, and calcofluor for the residue in each step were investigated. Four structures, the galactomannan-cellulose (center part), the membrane of the arabinogalactan protein, the cellulose-rich galactomannan layer, and the arabinogalactan protein-rich layers (outer part), were found in the cell walls.