Enjeux et amélioration de la réduction de l'acidité dans les fruits mûrs du palmier à huile, Elaeis guineensis Jacq. (synthèse bibliographique)

Introduction. L'acidification de l'huile de palme détermine la qualité et la stabilité de cette importante denrée alimentaire. Cette synthèse analyse les causes de l'acidification de l'huile et son impact sur la qualité et la stabilité de l'huile. Les enjeux liés à la réduction de l'acidification de l'huile et les approches utilisées sont aussi analysés, en particulier la réduction par l'amélioration génétique. Littérature. L'acidification est principalement due à l'action de la lipase endogène du mésocarpe, mais peut aussi être causée par des lipases microbiennes ou une hydrolyse autocatalytique. Plusieurs facteurs, notamment le matériel végétal, les conditions de récolte et de traitement post-récolte des régimes, d'extraction et de conservation de l'huile impactent de manière significative l'acidification de l'huile. L'acidification réduit la qualité et la valeur marchande de l'huile et engendre une baisse de productivité. Des fonds génétiques à faible acidité ont été identifiés. La variabilité de ce caractère rend possible la sélection variétale. Un gène impliqué dans l'acidification de l'huile est identifié, mais l'action d'autres gènes ou facteurs génétiques est soupçonnée. Conclusions. Ces recherches ont permis la récente commercialisation des premiers palmiers avec une huile faiblement acide. Ceci améliorera la qualité de l'huile tout en augmentant le rendement et en facilitant la gestion des opérations de récolte et de post-récolte, en particulier pour les petits producteurs. Il est nécessaire de continuer la recherche de tous les facteurs génétiques impliqués au niveau du genre Elaeis. La validation des ressources génomiques permettrait la sélection assistée par marqueurs de variétés à faible acidité de l'huile

Effect of Atg4B on LC3B processing.

<p><b><i>A,</i></b> MEFwt and MEFatg7KO cells were treated with 50 µM of CQ for 2 hours. LC3B expression patterns were then analyzed in 15% of SDS-PAGE by immunoblotting with LC3B antibody. <b><i>B,</i></b> Adenoviral vector expressing GFP-LC3B was used to infect MEFatg7KO cells in series double diluted doses for 24 hours (D1 = 20MOI). Ad-GFP-LC3B (20MOI) infected wild-type MEF cells were used as control or treated with 50 µM of CQ for 2 hours.GFP-LC3B expression patterns were analyzed by 15% of SDS-PAGE. <b><i>C,</i></b> Ad-GFP-LC3B infected MEFwt and MEFatg7KO cells were treated with 50 µM of CQ for 2 hours and images were recorded by fluorescence microscopy. <b><i>D,</i></b> HEK293 cells were transfected with Atg4B siRNA and Control siRNA for 48 h. 15 µg of total cell lysates were analyzed by immunoblotting with Atg4B, LC3B, and β-actin antibodies. Image J software was used to quantify band density using β-actin as loading control. <b><i>E,</i></b> Diagram of LC3 species migration patterns in 15% of SDS-polyacrylamide gel. The diagram summarizes LC3 species (pro-LC3, LC3-I and LC3-II) band patterns from human, mouse and rat origins. Refer to the result section for description in details.</p

Time evolutions of A) GSH, B) N₂O₃, C) FeL_nNO, and D) ONOO⁻ predicted by Model II.

<p>N₂O₃ and FeL_nNO increase to high concentrations by a switch-like mechanism induced by a decrease in GSH concentration due to conversion of GSH to GSNO and subsequently to GSSG. [ONOO⁻] does not follow a similar switch-like increase in its concentration. Solid curve is for [GSH]₀ = 10⁴ µM, dotted curve for [GSH]₀ = 10³ µM, and dashed curve with diamonds for [GSH]₀ = 10² µM. The response is thus sharper and earlier in the presence of lower initial concentrations of GSH.</p

Time evolution of [casp3] predicted by a bistable model in response to different strengths of apoptotic stimuli, A) in a cell subjected to a weak EC apoptotic signal (reflected by the low concentration [caps8]₀); B) in a cell that is subjected to a stronger EC pro-apoptotic signal.

<p>Caspase-3 is activated at 60 minutes; C) in a cell that is subjected to a stronger EC pro-apoptotic signal than one in panel B. Caspase-3 is activated at 30 minutes. Panels A and B illustrate two opposite effects induced by different initial concentrations of caspase-8. The threshold concentration of [caps8]₀ required for the switch from anti-apoptotic to pro-apoptotic response is calculated to be 8.35×10⁻⁵ µM. Panels B and C illustrate the shift in the onset time of apoptosis depending on [casp8]₀. D) Dependence of apoptotic response time on the initial caspase-8 concentration. The ordinate is the onset time of caspase-3 activation, and the abscissa is the initial concentration of caspase-8 in excess of the threshold concentration required for the initiation of apoptosis (evidenced by increase in [casp3], see panels B–C). The onset time of caspase-3 activation exhibits a logarithmic decrease with Δ[casp8]₀ ([casp8]₀–8.35×10⁻⁵ µM).</p

Analysis of different group amino acid replacement of Glycine 120 of human LC3B and LC3B truncates effect on their mobility in SDS-polyacrylamide gel.

<p><b><i>A,</i></b> plasmids expressing Flag-LC3B, Flag-LC3B^G120A, Flag-LC3B^G120 or Flag-LC3^A120 was expressed in HEK293 cells for 24 hours. Cells were treated with 50 µM of CQ for two hours and harvested and lysed. Total cell lysates (10 µg) was used for immunoblotting by Flag antibody. <b><i>B,</i></b> G120 point mutant plasmids were expressed in HEK293 cells for 24 hours. Immunoblotting was conducted to compare the band’s mobility with Flag-LC3B, Flag-LC3B^G120A or Flag-LC3B^G120A as indicated. <b><i>C,</i></b> Flag-LC3B^G120D and Flag-LC3B^G120E were expressed in HEK293 cells for 24 hours. Cells were then treated with 50 µM of CQ for 2 hours. Expression patters of Flag-LC3B^G120D and Flag-LC3B^G120E were compared with endogenous LC3B by immunoblotting with LC3B antibody (upper panels). Adenoviral vector expressing GFP-LC3B, GFP-LC3B^G120D or GFP-LC3B^G120E was used to infect A549 cells for 24 hours. Cells were then treated with 50 µM of CQ for 2 hours. Images were recorded using fluorescence microscopy. Scale bar: 25 micron. <b><i>D,</i></b> Truncates of LC3B (see Fig. 1) were expressed in HEK293 for 24hours. Cells were treated with 50 µM of CQ for two hours before harvesting. Total cell lysates were used for Wb assay to compare the mobility with Flag-LC3B-I and Flag-LC3B-II. Flag antibody was used to detect the recombinant proteins.</p

Reactions bridging between Models I to II (*)

<p>(^*) The parameters used in the present study are k_18NO = 1 µM⁻¹s⁻¹ (varying the value between 0.01 µM⁻¹s⁻¹ and 100 µM⁻¹s⁻¹ does not affect the results), k_19NO = 10 µM⁻¹s⁻¹<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002249#pone.0002249-Wink2" target="_blank">[<i>78</i>]</a>, k_20NO = k_21NO = k_22NO = 66 µM⁻¹s⁻¹ (the same value as k_11NO).</p

Reactions in Model II

a<p>Same as k_11NO</p

(A) Mitochondria-dependent apoptotic pathways in Model I.

<p>The dotted box includes the interactions considered in the model. Solid arrows indicate chemical reactions or upregulation; those terminated by a bar indicate inhibition or downregulation; and dashed arrows indicate subcellular translocation. The components of the model are procaspase-8 (pro8), procaspase-3 (pro3), procaspase-9 (pro9), caspase-8 (casp8), caspase-9 (casp9), caspase-3 (casp3), IAP (inhibitor of apoptosis), cytochrome <i>c</i> (cyt <i>c</i>), Apaf-1, the heptameric apoptosome complex (apop), the mitochondrial permeability transition pore complex (PTPC), p53, Bcl-2, Bax, Bid, truncated Bid (tBid). The reader is referred to our previous work <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002249#pone.0002249-Bagci1" target="_blank">[28]</a> for more details. Three compounds (N₂O₃, FeL_nNO and ONOO⁻) not included in the original Model I <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002249#pone.0002249-Bagci1" target="_blank">[28]</a> are highlighted. These compounds establish the connection with the nitric oxide pathways delineated in panel B. (B) Nitric oxide (NO)-related reactions in Model II. The following compounds are included: ONOO⁻ (peroxynitrite), GPX (glutathione peroxidase), O₂⁻ (superoxide), GSH (glutathione), GSNO (nitrosoglutathione), GSSG (glutathione disulfide), C<i>c</i>OX (cytochrome <i>c</i> oxidase), SOD (superoxide dismutase), FeL_n (non-heme iron compounds), FeL_nNO (non-heme iron nitrosyl compounds), NADPH (reduced form of nicotinamide adenine dinucleotide phosphate), NADP+ (oxidized form of nicotinamide adenine dinucleotide phosphate). FeL_nNO, ONOO⁻ and N₂O₃, highlighted in both panels A and B, bridge between Models I to II. Model III integrates both sets of reactions/pathways through these compounds. GSH modulates their concentrations by reacting with them. GSH is converted by these reactions to GSNO, which is then converted to GSSG and finally back to GSH. Those compounds and interactions are shown in blue. See <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002249#pone-0002249-t001" target="_blank">Table 1</a> for the complete list of reactions and rate constants.</p

Time evolutions of [GSH] and [casp3] predicted by Model III in the presence of N₂O₃ effects.

<p>Here, in order to visualize the effect of N₂O₃ exclusively, the reaction <i>(xxii)</i> in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002249#pone-0002249-t004" target="_blank">Table 4</a> is included in the model while those involving FeL_nNO and ONOO⁻ (reactions (<i>xx, xxiii-xxv</i>) are not, assuming FeL_n concentration and rate of formation of superoxide to be zero. The solid curves depict the time evolution of [casp3], and dotted curves refer to [GSH]. The three rows of panels are the counterparts of those in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002249#pone-0002249-g002" target="_blank">Figure 2</a> A–C, with the different columns referring to different initial concentrations of GSH: A–C) [GSH]₀ = 10³ µM; D–F) [GSH]₀ = 10² µM; G–I) [GSH]₀ = 0 µM.</p

The faster migration is conserved in pro-LC3B of rodent species but not in human LC3C.

<p><b><i>A,</i></b> Compare pro-human LC3B with pro-mouse LC3B, pro-rat LC3B and their cleaved and lipidated forms’ band patterns by 15% of SDS-polyacrylamide gel. Indicated expression plasmids were expressed in HEK293 cells. <b><i>B,</i></b> compare pro-rat LC3B with pro-rat LC3 and cleaved forms by 15% of SDS-polyacrylamide gel. Correspondent expression plasmids were expressed in HEK293 cells. Note: human LC3B-I band is close to RatLC3B-I/RatLC3-I as indicated by arrows. <b><i>C,</i></b> pro-LC3A and its cleaved form comparison by 15% of SDS-polyacrylamide gel. Indicated expression plasmids were expressed in HEK293 cells. <b><i>D,</i></b> compare pro-human LC3B and LC3C species by 15% of SDS-polyacrylamide gel. Indicated expression plasmids were expressed in HEK293 cells for 24 h. HEK293 cells transient expressing Human LC3C were treated with 50 µM of CQ for 2 h to induce accumulation of human LC3B-II and LC3C-II. Total cell lysates were separated by a 15% of SDS-polyacrylamide gel. Protein transferred membrane was cut between human LC3B group and human LC3C group and immunoblotting by LC3B and LC3C antibody, respectively. The immunoblotting membrane was re-aligned before developing with chemiluminescent substrate in order to compare human LC3B species and human LC3C species in Wb.</p