Author: SOLEDAD MARIA TERESA HERNANDEZ SOTOMAYOR
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 Al3+ outside the cells, measured as the
Al3+–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
An early response of plants to environmental signals or abiotic stress suggests that the phospholipid signaling pathway plays a pivotal role in these mechanisms. The phospholipid signaling cascade is one of the main systems of cellular transduction and is related to other signal transduction mechanisms. These other mechanisms include the generation of second messengers and their interactions with various proteins, such as ion channels. This phospholipid signaling cascade is activated by changes in the environment, such as phosphate starvation, water, metals, saline stres, and plant-pathogen interactions. One important factor that impacts agricultural crops is metal-induced stress. Because aluminum has been considered to be a major toxic factor for agriculture conducted in acidic soils, many researchers have focused on understanding the mechanisms of aluminum toxicity in plants. We have contributed the last fifteen years in this field by studying the effects of aluminum on phospholipid signaling in coffee, one of the Mexico's primary crops. We have focused our research on aluminum toxicity mechanisms in Coffea arabica suspension cells as a model for developing future contributions to the biotechnological transformation of coffee crops such that they can be made resistant to aluminum toxicity. We conclude that aluminum is able to not only generate a signal cascade in plants but also modulate other signal cascades generated by other types of stress in plants. The aim of this review is to discuss possible involvement of the phospholipid signaling pathway in the aluminum toxicity response of plant cells.
The phospholipidic signal transduction system involves generation of second messengers by hydrolysis or changes in phosphorylation state. Several studies have shown that the signaling pathway forms part of plant response to phytoregulators such as salicylic acid (SA) and methyl jasmonate (MJ), which have been widely used to stimulate secondary metabolite production in cell cultures. An evaluation was made of the effect of SA and MJ on phospholipidic signaling and capsaicinoid production in Capsicum chinense Jacq. suspension cells. Treatment with SA inhibited phospholipase C (PLC) (EC: 184.108.40.206) and phospholipase D (PLD) (EC: 220.127.116.11) activities in vitro, but increased lipid kinase activities in vitro at different SA concentrations. Treatment with MJ produced increases in PLC and PLD activities, while lipid kinase activities were variable and dose-dependent. The production of vanillin, a precursor of capsaicinoids, increased at specific SA or MJ doses. Preincubation with neomycin, a phospholipase inhibitor, before SA or MJ treatment inhibits increase in vanillin production which suggests that phospholipidic second messengers may participate in the observed increase in vanillin production.
The accumulation of reactive oxygen species (ROS) and concomitant oxidative stress have been considered deleterious consequences of aluminum toxicity. However, several lines of evidence suggest that ROS can function as important signaling molecules in the plant defense system for protection from abiotic stress and the acquisition of tolerance. The role of ROS-scavenging enzymes was assayed in two different coffee cell suspension lines. We treated L2 (Al-sensitive) and LAMt (Al-tolerant) Coffea arabica suspension cells with 100 μM AlCl3 and observed significant differences in catalase activity between the two cell lines. However, we did not observe any differences in superoxide dismutase or glutathione reductase activity in either cell line following Al treatment. ROS production was diminished in the LAMt cell line. Taken together, these results indicate that aluminum treatment may impair the oxidative stress response in L2 cells but not in LAMt cells. We suggest a possible role for Al-induced oxidative bursts in the signaling pathways that lead to Al resistance and protection from Al toxicity.
In the last three decades, interest has turned to in vitro cell culture in different areas of coffee research. In vitro techniques have been applied not only for coffee improvement through genetic transformation but also to study various aspects in coffee cells such as chemical (caffeine synthesis and the production of coffee aroma), physiological and more recently, biochemical aspects. The most important advances obtained to date on in vitro coffee techniques in fields like biochemistry, physiology, regeneration systems and genetic engineering, are presented and discussed.
As our interest is focused in obtaining a betler knowledge of the plant phosphate metabolism and its interactions with Al ion, we used an in vitro coffee cellline (Coffia arabica L.) tolerant to allllIlimun ion to purify a protein with phosphate hydrolysing activity with the airn to analyze whether the enzyrne can be contributing to the Al-tolerance in this coffee cellline. The protein was purified at least 138-fold; silver stain on a 10% SDS-PAGE detected a partially purified 30 kDa polypeptide which showed ability to hydrolyse phosphate either in native gels or soluble assays. The semipurified protein is able to hydrolyse sodiurn pyrophosphate (PPi-Na) and adenosine triphosphate (ATP) very efficiently, a1lhough P-serine (P-ser), P-Threonine (P-thr), P-Tyrosine (P-Tyr), Phytate, D-Myo-lnositol-lP (D-Myo Inos-lP) and lhe synlhetic p-nyliophenyl phosphate (P-NPP) could also be used as substrates. Enzyrnatic activity ofthe EDTA-inactivated enzyrne can be restored by Mg2+, as well as other divalent cations such as Fe2+, Co2+, Cu2+, Zn2+, Ca2+ and Mn2+. In contrast, Al3+ could only partially reactivate the phosphate hydrolysing activity, which suggests that it is not a cofactor for this enzyrne. Vv'hen Al3 + was added to the Mg2+ -enzyrne complex, it strongly inhibited the enzyrnatic activity either, exerting a negative effect over the enzyrne or the substrate. Between a munber of phosphohydrolase inhibitors, only KN03 was able to decrease the activity suggesting that this enzyme should be related with the V-ATPase protein family or with plant phosphatases.
In Cantharanthus roseus transformed roots, the application of methylglyoxal bis(guanylhydrazone) (MGBG), an inhibitor of S-adenosylmethionine decarboxylase (SAMDC; EC 18.104.22.168), inhibited the root growth in a dose-dependent manner with a DL50 of about 300 μm. Spermidine and spermine (Spm) levels and SAMDC and phospholipase C (PLC; EC 22.214.171.124) activities were reduced in the presence of the inhibitor. The inhibition was reversed by the addition of Spm. Radioactivity from [14C[Spm was detected in an immunoprecipitated fraction with an antibody anti-PLC-δ. To our knowledge, this is the first direct evidence that demonstrates an interaction of Spm with the signal transduction cascade phosphoinositide-Ca 2+.
Gea Guerriero Roberto Berni JOSE ARMANDO MUÑOZ SANCHEZ Fabio Apone Eslam Abdel_Salam Abdulhakim Qahtan Abdulrahman A. Alatar CLAUDIO CANTINI Giampiero Cai Jean-Francois Hausman Khawar Siddiqui SOLEDAD MARIA TERESA HERNANDEZ SOTOMAYOR Mohammed Faisal (2018)
Plants are sessile organisms and, in order to defend themselves against exogenous (a)biotic constraints, they synthesize an array of secondary metabolites which have important physiological and ecological effects. Plant secondary metabolites can be classified into four major classes: terpenoids, phenolic compounds, alkaloids and sulphur-containing compounds. These phytochemicals can be antimicrobial, act as attractants/repellents, or as deterrents against herbivores. The synthesis of such a rich variety of phytochemicals is also observed in undifferentiated plant cells under laboratory conditions and can be further induced with elicitors or by feeding precursors. In this review, we discuss the recent literature on the production of representatives of three plant secondary metabolite classes: artemisinin (a sesquiterpene), lignans (phenolic compounds) and caffeine (an alkaloid). Their respective production in well-known plants, i.e., Artemisia, Coffea arabica L., as well as neglected species, like the fibre-producing plant Urtica dioica L., will be surveyed. The production of artemisinin and caffeine in heterologous hosts will also be discussed. Additionally, metabolic engineering strategies to increase the bioactivity and stability of plant secondary metabolites will be surveyed, by focusing on glycosyltransferases (GTs). We end our review by proposing strategies to enhance the production of plant secondary metabolites in cell cultures by inducing cell wall modifications with chemicals/drugs, or with altered concentrations of the micronutrient boron and the quasi-essential element silicon.