Metabolic and Regulatory Responses in Citrus Rootstocks in Response to Adverse Environmental Conditions

Abstract

In response to adverse environmental conditions, plants modify their metabolism in order to adapt to the new conditions. To differentiate common responses to abiotic stress from specific adaptation to a certain stress condition, two citrus rootstocks (Carrizo citrange and Cleopatra mandarin) with a different ability to tolerate stress were subjected to soil flooding and drought, two water stress conditions. In response to these conditions, both genotypes showed altered root proline and phenylpropanoid levels, especially cinnamic acid that was a common feature to Carrizo and Cleopatra. This was correlated with alterations in the levels of phenylpropanoid derivatives likely involved in lignin biosynthesis. In the regulatory part, levels of both stress hormones ABA and JA decreased in response to soil flooding irrespective of the genotype relative flooding tolerance but, on the contrary, concentration of both metabolites increased in response to drought, showing JA a transient accumulation after a few days and ABA a progressive pattern of increase. These responses are probably associated to different regulatory processes under soil flooding and drought. In addition, alterations in IAA levels in citrus roots seemed to be associated to particular stress tolerance. Moreover, both genotypes exhibited a low degree of overlapping in the metabolites induced under similar stress conditions, indicating a specific mechanism to cope with stress in plant species. Results also indicated a different metabolic basal status in both genotypes that could contribute to stress tolerance.

Depletion of abscisic acid levels in roots of flooded Carrizo citrange (Poncirus trifoliata L. Raf. × Citrus sinensis L. Osb.) plants is a stress-specific response associated to the differential expression of PYR/PYL/RCAR receptors

“…In this and previous works (Arbona and Gómez-Cadenas 2008;Argamasilla et al 2013), ABA depletion induced by soil waterlogging was proposed to be a specific signal to this environmental cue. In this work, some putative ABA receptors and some genes involved in ABAdependent signaling showed an upregulation in response to soil flooding (Figs.…”

“…Both environmental conditions limit the availability of capillary water that can be efficiently absorbed by plant roots (Yamaguchi and Sharp 2010). In citrus, drought causes a sharp and transient accumulation of JA followed by a progressive ABA buildup whereas soil waterlogging reduces root ABA and JA levels drastically (Arbona and Gómez-Cadenas 2008;Argamasilla et al 2013). …”

“…Analyses of ABA and catabolites were carried out by UPLC coupled to tandem mass spectrometry as described in Argamasilla et al (2013). Briefly, 0.2 g of powdered frozen root tissue was spiked with 50 ng of [ 2 H6]-ABA and 50 ng of [ 2 H3]-PA as internal standards before extraction in ultrapure water using a tissue homogenizer (Ultra-Turrax, Ika-Werke, Staufen, Germany).…”

“…In citrus, drought induces accumulation of ABA in roots and leaves, triggering several adaptive responses such as leaf abscission (De Ollas et al 2013). Soil waterlogging also induces ABA accumulation in leaves but, on the contrary, causes a severe reduction of the hormone levels in roots in clear contrast to water deficit (Arbona and Gómez-Cadenas 2008;Argamasilla et al 2013). …”

Plant strategies to deal with a combination of drought and high temperatures

“…For this reason, in the first chapter of this work, we aimed to study the physiological and molecular responses and the relative tolerance of two citrus genotypes (Carrizo citrange and Cleopatra mandarin) subjected to drought, heat or to a combination of both stress factors. These two citrus rootstocks, widely used in citriculture, have been previously reported to show different tolerance to abiotic stress conditions: whereas Cleopatra is more tolerant to drought and salinity, Carrizo is more tolerant to soil flooding (Argamasilla et al 2013). On the contrary, limited information of the responses of citrus plants to combined stress conditions is currently available.…”