A multi-approach for understanding the root growth under hydric deficiency

Plants, as sessile organisms, should be adapted to a wide range of changes in the surrounding environment, so they have several mechanisms focused on minimizing the impact of these changes. The limited success of classical breeding programs in increasing tolerance to environmental stress factors has spurred efforts to understand the physiological mechanisms and the genetic regulation of abiotic stress. In this context, we focus our work on elucidating new components involved in plant abiotic stress tolerance. Build on our study several experimental strategies to explain the role of root systems in drought tolerance. Studying the root at different levels, including cells, tissue, and organs, could give a big picture of how the root responds to drought conditions and which responses could be associated with tolerance mechanisms.Agencia Nacional de Investigación e InnovaciónUniversidad de la República. Comisión Sectorial de Investigación Científic

Phenotyping Systems for Evaluating Saline Stress Response in Lotus

La tolerancia al estrés salino es un carácter complejo determinado por la sumatoria de los efectos de numerosos genes, cuya identificación es necesaria para la definición de estrategias de mejoramiento. En este sentido, el uso de plantas modelo genotipadas y la disponibilidad de métodos de fenotipado masivo son útiles para asistir a los programas de mejoramiento. Lotus japonicus (Regel) K. Larsen es un modelo de leguminosa con nodulación determinada, que puede ser utilizada en la identificación de determinantes genéticos en programas de mejoramiento de Lotus y otras leguminosas forrajeras. En este trabajo, para establecer un sistema de cultivo adecuado para el fenotipado masivo, se compararon cuatro sistemas experimentales para evaluar respuestas a estrés salino: placas, pouch, hidroponía y macetas. Los resultados obtenidos permitieron elegir el sistema de hidroponía como el más adecuado para evaluar el estrés salino, dado que se pudieron establecer diferencias en las respuestas fisiológicas basadas en parámetros de crecimiento y desarrollo en los genotipos Lotus japonicus Gifu y Lotus burttii. Además, el sistema de hidroponía permitió discriminar respuestas en una población de líneas recombinantes puras (RILs), producto del cruzamiento de Lotus japonicus Gifu x Lotus burttii. Contar con un sistema de cultivo que permita realizar de manera precisa el fenotipado masivo de plantas, es necesario para identificar regiones del genoma implicadas en las respuestas a estrés salino.Salt stress tolerance is a complex trait which is determined by the additive effects of several genes whose identification is necessary to define improvement strategies. In this sense, the use of model plants genotyped and the availability of massive phenotyping methods are useful to assist breeding programs. Lotus japonicus (Regel) K. Larsen has been adopted as a determined nodulating legume model, which can be used for identification of the genetic determinants in the breeding program of Lotus and other forage legumes. In this work, in order to establish a growth system suitable for massive phenotyping, we compared four experimental systems for evaluating saline stress responses: plates, pouch, hydroponic and pots. Results allow to choose the hydroponic system as the most suitable for evaluating saline stress, since it is able to establish differences in responses based on physiological parameters of growth and development in Lotus japonicus (Gifu) and Lotus burttii genotypes. Moreover, the hydroponic system allowed to discriminate the responses in a population of recombinant inbreed lines (RILs) originated by the crossing of Lotus japonicus Gifu x Lotus burttii. Having a culture system that allows precise and massive phenotyping is necessary for detecting genomic regions involved in the responses to saline stress.Fil: Quero, Gastón Eduardo. Universidad de la República; UruguayFil: Borsani, Omar. Universidad de la República; UruguayFil: Gutiérrez, Lucía. Universidad de la República; UruguayFil: Melchiorre, Mariana Noemi. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Instituto de Fisiología y Recursos Geneticos Vegetales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Monza, Jorge. Universidad de la República; UruguayFil: Lascano, Hernan Ramiro. Instituto Nacional de Tecnología Agropecuaria. Centro de Investigaciones Agropecuarias. Instituto de Fisiología y Recursos Geneticos Vegetales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin

Proline does not quench singlet oxygen: Evidence to reconsider its protective role in plants

Plants are commonly subjected to several environmental stresses that lead to an overproduction of reactive oxygen species (ROS). As plants accumulate proline in response to stress conditions, some authors have proposed that proline could act as a non-enzymatic antioxidant against ROS. One type of ROS aimed to be quenched by proline is singlet oxygen (1O2), molecular oxygen in its lowest energy electronically excited state, constitutively generated in oxygenic, photosynthetic organisms. In this study we clearly prove that proline cannot quench 1O2 in aqueous buffer, giving rise to a rethinking about the antioxidant role of proline against 1O2.This research has financial support from ANII and PEDECIBA(Uruguay), the Spanish Ministry of Economy and Competitiveness and the Research Council of Norway.Peer reviewe

Identification of Two Loci in Tomato Reveals Distinct

Salt stress is one of the most serious environmental factors limiting the productivity of crop plants. To understand the molecular basis for salt responses, we used mutagenesis to identify plant genes required for salt tolerance in tomato. As a result, three tomato salt-hypersensitive ( tss ) mutants were isolated. These mutants defined two loci and were caused by single recessive nuclear mutations.This work was supported by a grant from the Universidad de Málaga and Junta de Andalucía (Grant No. AGR-168).Peer reviewe

ABA- and ethylene-mediated responses in osmotically stressed tomato are regulated by the TSS2 and TOS1 loci

The study of mutants impaired in the sensitivity or synthesis of abscisic acid (ABA) has become a powerful tool to analyse the interactions occurring between the ABA and ethylene signalling pathways, with potential to change the traditional view of the role of ABA as just being involved in growth inhibition. The tss2 tomato mutant, which is hypersensitive to NaCl and osmotic stress, shows enhanced growth inhibition in the presence of exogenous ABA.This work was supported by a grant from the Ministerio de Ciencia y Tecnología (BIO2002-04541-C02-01). OB wants to thank CONICYT- Fondo Clemente Estable (No. 8285) for funding partially this study.Peer reviewe

Puesta a punto de un sistema de generación de gradiente osmótico

El meristemo radicular debe enfrentar uno de los ambientes más complejos en la tierra: el suelo, cuyas propiedades fisicoquímicas pueden variar dramáticamente en la escala de micras exponiendo a las raíces a distintos tipos de estrés como el osmótico. El estrés osmótico limita la habilidad de las células de absorber agua provocando un retraso o detención del crecimiento. El objetivo de este trabajo fue desarrollar un método que busca simular condiciones de retención de agua similares a las de un suelo en condición de déficit hídrico. Utilizando un gradientómetro establecimos un gradiente osmótico con concentraciones crecientes de manitol (0 a 400 mM) que genera potenciales osmóticos decrecientes (0 a -1.2 MPa) en placas de petri. En dichas placas, se ensayó el porcentaje de germinación de semillas de Col-0. Se observó una disminución del porcentaje de germinación significativa a partir de 250 mM de manitol; 53% con respecto a 0 mM de manitol. Además, este sistema nos permitió cuantificar el crecimiento de la raíz primaria de Arabidopsis en condiciones de disponibilidades decrecientes de agua. El fenotipado en este sistema, hasta donde sabemos, no ha sido muy utilizado y abre nuevas oportunidades para realizar estudios moleculares en condiciones que simulan mejor el crecimiento en suelos sometidos a déficit hídrico.ANI

Root growth adaptation under water deficit

Growth and development of the root system require the coordinated regulation of developmental programs and environmental signals; however, the knowledge about its interconnection is scarce. The balance between cell division, regulated cellular expansion, and differentiation in the root apical meristem directs primary root growth in Arabidopsis. Cellular expansion requires cell wall controlled relaxation, which ensures cell integrity during the expansion process. In field conditions, the root faces different kinds of stress, including osmotic stress. Mutations in the Arabidopsis Tetratrico-peptide Thioredoxin-Like 1 (TTL1) cause hypersensitivity to osmotic stress evidenced by root tip swelling, making it an attractive model to explore how root growth is regulated under osmotic stress conditions. We found that osmotic stress decelerates root growth by reducing first cell elongation in the elongation zone and second the number of cortical cells in the proximal meristem. Using atomic force microscopy, we measure the stiffness of epidermal cell walls in the root elongation zone of ttl1 mutants, and we found that the mean apparent elastic modulus was 448% higher for live Col-0 cell walls than for ttl1 (88.1 ± 2.8 vs. 16.08 ± 6.9 kPa) in plants grown in control conditions. Furthermore, cell walls of epidermal cells in the elongation zone increase their stiffness 87% and 84% for Col-0 and ttl1, respectively, in response to seven days of osmotic stress. These findings suggest that TTL1 may play a role in controlling cell expansion orientation during root growth, necessary for osmotic stress adaptation.Agencia Nacional de Investigación e Innovació

A Simple and Accurate Method Based on a Water-Consumption Model for Phenotyping Soybean Genotypes under Hydric Deficit Conditions

Drought limits crop productivity and reduces yield stability. Drought tolerance as a selection criterion in breeding programs requires the development of high-throughput, precise, and low-cost phenotyping strategies. We developed a mathematical model, based on biological approaches, for evaluating soybean plants’ response to drought under controlled growth conditions. The model describes the kinetics of water consumption of a plant pot substrate system (PPS) with low sampling requirements. The model generated two parameters, t0.5 (time necessary for the PPS to reach half of the maximum amount of evapotranspirable water) and Gw(t0.5) (stomatal conductance [Gw] at t0.5), which determined the water- consumption curve of each genotype. An analysis of the kinetics of water consumption in response to a progressive water deficit in a biparental and breeding population was performed as a preliminary test of the model. A correspondence analysis between the t0.5 and Gw(t0.5) parameters with the genetic structure of the populations shows a genetic association. The phenotyping methodology presented in this work and drought susceptibility in field conditions are discussed based on previous results. This work could be useful for improving the selection of soybean genotypes in relation to their performance under drought conditions