Esther Casanova

Auxin: A major player in the shoot-to-root regulation of root Fe-stress physiological responses to Fe deficiency in cucumber plants

The aim of this study was to investigate the effects of IAA and ABA in the shoot-to-root regulation of the expression of the main Fe-stress physiological root responses in cucumber plants subjected to shoot Fe functional deficiency. Changes in the expression of the genes CsFRO1, CsIRT1, CsHA1 and CsHA2 (coding for Fe(III)-chelate reductase (FCR), the Fe(II) transporter and H+-ATPase, respectively) and in the enzyme activity of FCR and the acidification capacity were measured. We studied first the ability of exogenous applications of IAA and ABA to induce these Fe-stress root responses in plants grown in Fe-sufficient conditions. The results showed that IAA was able to activate these responses at the transcriptional and functional levels, whereas the results with ABA were less conclusive. Thereafter, we explored the role of IAA in plants with or without shoot Fe functional deficiency in the presence of two types of IAA inhibitors, affecting either IAA polar transport (TIBA) or IAA functionality (PCIB). The results showed that IAA is involved in the regulation at the transcriptional and functional levels of both Fe root acquisition (FCR, Fe(II) transport) and rhizosphere acidification (H+-ATPase), although through different, and probably complementary, mechanisms. These results suggest that IAA is involved in the shoot-to-root regulation of the expression of Fe-stress physiological root responses.

Antioxidant and Antifungal Activity of Verbena officinalis L. Leaves

The scavenging activity against DPPH (1,1-diphenil-2-picrylhydrazyl) radical and the antifungal effect against chloroform, ethyl acetate and 50% methanolic extracts of Verbena officinalis leaves were investigated. The activity of different fractions of 50% methanolic extract and some isolated compounds were also investigated. The results suggest that 50% methanolic extract and caffeoyl derivatives could potentially be considered as excellent and readily available sources of natural antifungal and antioxidant compounds.

Screening of Spanish Medicinal Plants for Antioxidant and Antifungal Activities

Abstract Dichloromethane, ethyl acetate, methanol, and aqueous extracts obtained from 16 Spanish medicinal plants were screened for their antioxidant and antifungal activities. The radical scavenging capacity was evaluated by the DPPH method using a rapid screening by TLC and a spectrophotometric assay. Polar extracts obtained from Jasonia glutinosa L. (Lamiaceae), Tanacetum parthenium (L.) Schultz (Lamiaceae), Equisetum telmateia Ehrh. (Equisetaceae), Verbena officinalis L. (Verbenaceae), and Lythrum salicaria L. (Lythraceae) showed high antioxidant properties. Among them, the methanol extract of Lythrum salicaria showed the strongest antiradical capacity with an IC50 value similar to the positive control ascorbic acid. On the contrary, the best antifungal properties against Rhizopus stolonifer were produced by ethyl acetate or dichloromethane extracts from Anthemis arvensis L. subsp. arvensis (Asteraceae), Tanacetum parthenium, Santolina chamaecyparissus L. subsp. squarrosa Nyman (Asteraceae), Anagallis arvensis L. (Primulaceae) and the methanol extract of Anagallis foemina Miller (Primulaceae). The dichloromethane extract of Anthemis arvensis subsp. arvensis was the best inhibitor of fungus growth.

Fine regulation of leaf iron use efficiency and iron root uptake under limited iron bioavailability.

Numerous studies have investigated the molecular and physiological-morphological mechanisms induced in plant roots in response to specific nutrient deficiencies. Both transcriptional and post-transcriptional mechanisms are involved that increase root uptake under nutrient deficiency. Root nutrient deficiency-stress root responses are mainly regulated by the nutrient status in the shoot. The signals involved in shoot to root cross-talk regulation processes for the activation of nutrient-deficiency induced root responses are not clearly elucidated. The physiological-molecular events in the leaf linked to the nutrient availability for metabolic use, are also poorly known. In this context, we focus our attention on iron plant nutrition. Some experimental evidence suggests the existence of a regulatory system concerned with the optimization of the metabolic use of iron, mainly under conditions of iron starvation. This system seems to be activated by the deficiency in iron-availability for metabolic processes in the leaf and regulates the activation of some iron-stress root responses. This regulation seems to be probably expressed by affecting the production and/or translocation of the activating signal sent from the shoot to the root under conditions of iron deficiency in the shoot.

Abscisic Acid Regulation of Root Hydraulic Conductivity and Aquaporin Gene Expression Is Crucial to the Plant Shoot Growth Enhancement Caused by Rhizosphere Humic Acids.

An ABA-dependent increase of root hydraulic conductivity and aquaporin expression mediates the plant shoot enhancement caused by dissolved sedimentary humic acids. The physiological and metabolic mechanisms behind the humic acid-mediated plant growth enhancement are discussed in detail. Experiments using cucumber (Cucumis sativus) plants show that the shoot growth enhancement caused by a structurally well-characterized humic acid with sedimentary origin is functionally associated with significant increases in abscisic acid (ABA) root concentration and root hydraulic conductivity. Complementary experiments involving a blocking agent of cell wall pores and water root transport (polyethylenglycol) show that increases in root hydraulic conductivity are essential in the shoot growth-promoting action of the model humic acid. Further experiments involving an inhibitor of ABA biosynthesis in root and shoot (fluridone) show that the humic acid-mediated enhancement of both root hydraulic conductivity and shoot growth depended on ABA signaling pathways. These experiments also show that a significant increase in the gene expression of the main root plasma membrane aquaporins is associated with the increase of root hydraulic conductivity caused by the model humic acid. Finally, experimental data suggest that all of these actions of model humic acid on root functionality, which are linked to its beneficial action on plant shoot growth, are likely related to the conformational structure of humic acid in solution and its interaction with the cell wall at the root surface.