Clorosis férrica: Caracterización del sistema de absorción de Fe en un patrón de cítricos

La clorosis férrica es uno de los estreses abióticos más importantes para las plantas, y como tal, resulta un problema agrícola muy extendido especialmente para aquellos cultivos que se desarrollan en terrenos alcalinos calizos, como es el caso de los cítricos en la Comunidad Valenciana. El objetivo del presente trabajo es caracterizar el sistema de absorción de hierro en un patrón de cítricos, y determinar su respuesta a nivel fisiológico, bioquímico y molecular en condiciones de ausencia de este elemento, dentro de la ¿Estrategia I¿ característica de las plantas dicotiledóneas. Para la consecución de estos objetivos se utilizó citrange Carrizo, considerado como un patrón de tolerancia moderada a la clorosis férrica. En éste, se evaluó el crecimiento vegetativo, el contenido de Fe en los distintos órganos y el estado del aparato fotosintético. Así mismo, se determinó la capacidad de reducción y acidificación de las raíces, mediante el análisis de las actividades de los principales enzimas involucrados, como son la Quelato Reductasa Férrica (FC-R), la Protón-ATPasa (H+-ATPasa) y la Fosfoenol Piruvato Carboxilasa (PEPCasa). También se identificaron en el genoma de los cítricos, secuencias homólogas a los genes FRO1, FRO2, HA1, HA2, PEPC1, IRT1 e IRT2 de Arabidopsis thaliana, que codifican para los enzimas FC-R, H+-ATPasa y PEPCasa, así como para los principales transportadores de hierro. Posteriormente, se diseñaron los oligonucleóticos correspondientes que permitieron analizar su expresión génica mediante RT-PCR. Finalmente, se determinó la tasa de absorción de hierro por la raíz y su transporte en la planta mediante la técnica de dilución isotópica. Los resultados del trabajo mostraron que la ausencia de Fe aumenta la expresión de los genes FRO2, HA1 y PEPC1 de cítricos que codifican para los enzimas FC-R, H+-ATPasa y PEPCasa, respectivamente; así como la del gen del transportador férrico IRT1. Este hecho se confirmó por la inducción de las correspondientes actividades enzimáticas, así como con el aumento de la absorción de 57Fe. De acuerdo con la información obtenida se concluye que la capacidad de absorción de hierro en cítricos aumentó en ausencia de Fe en el medio, debido a la activación de los componentes del sistema de absorción de este elemento. Además, se aprecia que todas las respuestas a la deficiencia de Fe de las raíces están metabólicamente inter-correlacionadas unas con otras y colaboran en la absorción de este elemento por la planta, solubilizando el Fe mediante la acidificación de la rizosfera, reduciendo el ion Fe3+ a Fe2+ absorbible por la planta, y activando los transportadores de hierro de la membrana plasmática de la raíz.Martínez Cuenca, MR. (2011). Clorosis férrica: Caracterización del sistema de absorción de Fe en un patrón de cítricos. http://hdl.handle.net/10251/16200Archivo delegad

RESPUESTAS DEL SISTEMA DE ABSORCIÓN DE HIERRO EN LAS RAÍCES DE LOS CÍTRICOS ANTE DIFERENTES CONDICIONES CLOROSANTES DEL MEDIO

La clorosis férrica es uno de los estreses abióticos más importantes para las plantas, y como tal, resulta un problema agrícola muy extendido especialmente para aquellos cultivos que se desarrollan en terrenos calizos, como es el caso de los cítricos en la comunidad Valenciana. El objetivo der este trabajo fue caracterizar el sistema de absorción de hierro en los cítricos y su respuesta ante distintas situaciones clorosantes que comprometen la disponibilidad del elemtento, provocanto la deficiencia de Fe en la planta. Los componentes del sistema de absorción del Fe -acidificación del medio, reducción del Fe(III), transporte a través de la membrana y alteración de la síntesis de ácidos orgánicos-, se analizaron a nivel fisiológico, bioquímico y molecular, en condiciones de ausencia de Fe externo, presencia de bicarbonato (HCO3) y de otros micronutrientes como zinc (Zn) y manganeso (Mn). Para la consecución de estos objetivos se utilizaron diversos genotipos de cítricos con diferente tolerancia a la clorosis férrica y se simularon diferentes condiciones clorosantes en el medio de cultivo, ya fuera eliminando el Fe o adicionando iones HCO3-, Zn2+ o Mn2+. En los distintos experimentos se evaluó, según cada caso, el crecimiento vegetativo de las plantas, el contenido de Fe total en los distintos órganos y en el apoplasto de la raíz, así como el estado del aparato fotosintético de las hojas tras la inducción de la clorosis. Así mismo, se determinó la capacidad de reducción y acidificación de las raíces, mediante el análisis de las actividades de los principales enzimas involucrados, como son la Quelato Férrico Reductasa (FC-R), la Protón-ATPasa (H+-ATPasa), la Fosfoenol Piruvato Carboxilasa (PEPCasa) y otros enzimas que intervienen en la biosíntesis de ácidos orgánicos, como la malato deshidrogenasa (MDH), la piruvato kinasa (PK), el enzima málico (ME), la citrato sintasa (CS), la aconitasa (ACO) y la fumarasa (FUM). Adicionalmente, se identificaron en el genoma de los cíMartínez Cuenca, M-R. (2012). RESPUESTAS DEL SISTEMA DE ABSORCIÓN DE HIERRO EN LAS RAÍCES DE LOS CÍTRICOS ANTE DIFERENTES CONDICIONES CLOROSANTES DEL MEDIO [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/17979Palanci

Influence of Rootstock on Citrus Tree Growth: Effects on Photosynthesis and Carbohydrate Distribution, Plant Size, Yield, Fruit Quality, and Dwarfing Genotypes

Citrus species are the most widely produced fruit crops in the world, and Spain is one of the leading citrus producers that supply the fresh market. Rootstocks greatly influence variety behaviour as it ensures tolerance to abiotic stress conditions, as well as the provision of minerals and water for the total plant, and consequently impact crop yield and fruit quality. So, rootstock choice is one of the most important decisions a grower makes when establishing commercial citrus orchards. In this chapter, we attempted to provide an overview of the response in terms of plant growth, fruit quality and yield parameters of several citrus cultivar trees grafted onto different commercial rootstocks, plus new hybrids and some dwarfing genotypes, to reduce costs in some cultural practices. In particular, we considered the rootstock influence on scion photosynthetic capacity linked to carbohydrate distribution for plant vegetative and reproductive development

Screening of ‘King’ Mandarin Hybrids as Tolerant Citrus Rootstocks to Flooding Stress

This work compares the tolerance to long-term anoxia conditions (35 days) of five new citrus ‘King’ mandarin (Citrus nobilis L. Lour) Poncirus trifoliata ((L.) Raf.) hybrids (named 0501XX) and Carrizo citrange (CC, Citrus sinensis (L.) Osb. Poncirus trifoliata (L.) Raf.), the widely used citrus rootstock in Spain. Growth parameters, chlorophyll concentration, gas exchange and fluorescence parameters, water relations in leaves, abscisic acid (ABA) concentration, and PIP1 and PIP2 gene expressions were assessed. With a waterlogging treatment, the root system biomass of most hybrids went down, and the chlorophyll a and b concentrations substantially dropped. The net CO2 assimilation rates (An) and stomatal conductance (gs) lowered significantly due to flooding, and the transpiration rate (E) closely paralleled the changes in gs. The leaf water and osmotic potentials significantly increased in most 0501 hybrids. As a trend, flooding stress lowered the ABA concentration in roots from most hybrids, but increased in the leaves of CC, 05019 and 050110. Under the control treatment (Ct) conditions, most 0501 hybrids showed higher PIP1 and PIP2 expressions than the control rootstock CC, but were impaired due to the flooding conditions in 05019 and 050110. From this study, we conclude that 0501 genotypes develop some adaptive responses in plants against flooding stress such as (1) stomata closure to prevent water loss likely mediated by ABA levels, and (2) enhanced water and osmotic potentials and the downregulation of those genes regulating aquaporin channels to maintain water relations in plants. Although these traits seemed especially relevant in hybrids 050110 and 050125, further experiments must be done to determine their behavior under field conditions, particularly their influence on commercial varieties and their suitability as flooding-tolerant hybrids for replacing CC, one of the main genotypes that is widely used as a citrus rootstock in Spain, under these condition

Seasonal Fe Uptake of Young Citrus Trees and Its Contribution to the Development of New Organs

This work quantifies Fe uptake in young citrus trees, its partitioning among plant compartments, and the contribution of the Fe absorbed from fertilizer to the development of new tissues. A soil pot experiment was conducted using 4-year-old clementine trees (Citrus clementina Hort ex Tan), and a dose of 240 mg Fe was applied by labeled fertilizer (92% atom 57Fe excess). Plants were uprooted at five different phenologic states: end of flowering (May 15), end of fruit setting and fruit drop (July 1), two fruit growing moments (August 1 and October 15), and at complete fruit maturity (December 10). The Fe accumulated in the root system exceeded 90% of the total Fe content in the plant. All organs progressively enriched with 57Fe (8.5–15.5% and 7.4–9.9% for young and old organs, respectively). Reproductive ones reached the highest increase (111% between May and October). 57Fe enrichment from woody organs reflects an increasing gradient to sink organs. The root system accumulated 80% of the Fe absorbed from the fertilizer, but the young organs accumulated relatively more Fe uptake during flowering and fruit setting (15.6% and 13.8%, respectively) than old organs (around 9.8%). Although iron derived from fertilizer (Fedff) preferably supplied young organs (16.7–31.0%) against old ones (2.5–14.9%), it only represented between 13.8% and 21.4% of its content. The use efficiency of the applied Fe (FeUE) barely exceeded 15%. The lowest FeUE were found in young and old organs of the aerial part (1.1–1.8% and 0.7–1.2%, respectively). Since the pattern of the seasonal absorption of Fe is similar to the monthly distribution curve of the supplied Fe, it is recommended that the application of Fe chelates in calcareous soils should be performed in a similar way to that proposed in this curve

Gene Expression under Short-Term Low Temperatures: Preliminary Screening Method to Obtain Tolerant Citrus Rootstocks

Climate change and global warming are leading to a change in weather patterns toward hot and cold waves. Citrus fruits are a tropical or subtropical crop whose growth is altered by changes in weather patterns. Thus, in the present work, two experiments are evaluated to obtain a screening method to select citrus rootstocks that help us to select new low-temperature-tolerant plant materials. One cold experiment was carried out with the Poncirus trifoliata and Citrus macrophylla rootstocks at 4 °C for 4, 8, 24 and 56 h. A second experiment was performed at 4 °C for 5 days with subsequent acclimatization lasting 0, 5, 10 and 24 h. The expression of the cold response genes CAMTA1, CAMTA3, CAMTA5, CBF1, ICE1 and COR413 IM1 was quantified. The results showed that the best rootstock selection strategy was the second experiment, as a higher expression of the genes CAMTA3, CAMTA5, CBF1 and COR413 IM1 was seen in the tolerant genotype P. trifoliata. We quantified the gene expression of proline biosynthesis P5CS1, dOAT and the proline transporters PROT1 and PROT2; the concentration of the amino acid proline in leaves was also quantified. These results once again showed that the best experiment to differentiate between tolerant and sensitive rootstocks was the second experiment with acclimation time

Suitable rootstocks can alleviate the effects of heat stress on pepper plants

[EN] In this study, different pepper rootstocks are tested for their ability to overcome heat stress situations. This work aims to evaluate: (i) the physiological mechanisms that occur during long heat stress periods (7 days) under controlled conditions in a pepper variety grafted onto accessions; (ii) the heat stress behaviour of these grafted pepper plants under greenhouse conditions in terms of marketable yields. For this purpose, plants of Lamuyo-type sweet pepper `Herminio F1¿ (VA), grafted onto six accessions (VA/A25, VA/A31, VA/A34, VA/A52, VA/A57, VA/A6), and a self-grafted variety (VA/VA) were grown under controlled conditions in growth chambers (28/24 °C, day/night temperatures and 38/24 °C for control and heat stress, respectively) and under greenhouse conditions (38/24 °C). For the controlled conditions, relative growth rate, leaf area, electrolyte leakage, chlorophyll a fluorescence and heat shock proteins were determined. For the greenhouse conditions, fresh and dry weigh, electrolyte leakage and fruit yield were determined. Our results confirmed that grafting a pepper cultivar onto appropriate rootstocks such as A6, A25 and A57 can overcome the negative effects of heat stress conditions with a higher relative growth rate, leaf area and Fv/Fm, and lower electrolyte leakage under the controlled conditions, and with higher marketable yields under the greenhouse conditions.This work has been financed by the INIA (Spain) and the Spanish Ministry of Science, Innovation and Universities through Project RTA-2017-00030-C02 and the European Regional Development Fund (ERDF) . Ramon Gisbert-Mullor is a beneficiary of a doctoral fellowship (FPU-MEFP (Spain) ) . Yaiza Gara Padilla is a beneficiary of a doctoral fellowship (FPI-INIA (Spain) ) .Gisbert-Mullor, R.; Padilla, YG.; Martínez-Cuenca, M.; López Galarza, SV.; Calatayud, Á. (2021). Suitable rootstocks can alleviate the effects of heat stress on pepper plants. Scientia Horticulturae. 290:1-11. https://doi.org/10.1016/j.scienta.2021.11052911129