Water-deficit tolerance in citrus is mediated by the down regulation of PIP gene expression in the roots

Plant and Soil (Impact Factor: 2.95). 10/2011; 347(1):91-104. DOI: 10.1007/s11104-011-0826-7


Water deficit (WD) is a growing problem in agriculture. In citrus crops, genetically-determined rootstock characteristics
are important factors influencing plant responses to WD. Aquaporins are involved in regulating the water supply to the plant
by mediating water flow through the cell membranes. Recent studies support a direct role for aquaporins in plant water relations
and demonstrate their involvement in WD tolerance. This study investigates the relationship between photosynthetic and water-balance
parameters with aquaporin expression levels and hydraulic conductance of roots (Kr) in conditions of moderate WD in citrus
rootstocks. The plant materials used were the rootstocks Poncirus trifoliata (L.) Raf. (PT), Cleopatra mandarin (Citrus reshni Hort ex Tan.) (CM) and 030115 (a hybrid of the two former rootstocks), all grafted with the citrus variety ‘Valencia Late’
(C. sinensis (L.) Osb). Plants were irrigated with two differents irrigation doses (normal irrigation and moderate WD) during 70days
and leaf water potential (ψs), net CO2 assimilation (ACO2), transpiration, stomatal conductance (gs) and substomatal CO2 concentration (Ci) were measured periodically under both irrigation conditions. Kr and PIP1 and PIP2 gene expression levels
in fine roots of control plants and plants subjected to WD on day 43 of the experiment were determined. Under WD conditions,
the hybrid 030115 drastically reduced aquaporin expression and Kr, accompanied by a loss of plant vigour but without reducing
the net CO2 assimilation (ACO2). PT maintained the same aquaporin expression level and similar Kr under WD as under normal irrigation conditions, but suffered
a sharp reduction in ACO2. CM, which has lower Kr and aquaporin expression than PT under both normal irrigation conditions and WD, responded better
to water stress conditions than PT. Low aquaporin levels, or down-regulated aquaporin expression, accompanied by decreased
plant vigour led to decreased plasma membrane permeability, thereby facilitating water retention in the cells under water
stress conditions. This may induce water stress tolerance in citrus rootstocks.

KeywordsCitrus rootstocks–Aquaporins–Root hydraulic conductance–Photosynthesis–Transpiration–Water stress

Download full-text


Available from: Frederic Aparicio, Mar 28, 2014
    • "Citrus rootstocks have differential capacities for supplying shoot tissues with water and carbon, improving resistance to biotic and abiotic stresses and affecting plant water status and photosynthesis (Barry et al., 2004; Romero et al., 2006; Rodríguez-Gamir et al., 2010; Machado et al., 2013). Water relations have been well studied in citrus trees, showing that rootstocks alter the physiological performance under water deficit through variations in plant hydraulic conductance, leaf water potential and stomatal conductance (Romero et al., 2006; Magalhães Filho et al., 2008; Rodríguez-Gamir et al., 2011). However, the importance of rootstock as source of carbohydrates is poorly reported. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Valencia orange scions grafted on Rangpur lime or Swingle citrumelo were grown under water deficit to evaluate how those rootstocks modulate the non-structural carbohydrate (NSC) availability and the drought tolerance of citrus trees. Additionally, the importance of young mature leaves as possible sources of carbon in citrus trees was studied. Herein, young mature leaves are those ones fully expanded and developed during water deficit. After 30 days under water limiting conditions, plant growth, leaf water status, photosynthetic rate and carbohydrate availability in old mature and young mature leaves, branches and roots were evaluated. Water deficit reduced the leaf water potential and caused diffusive limitation of photosynthesis in both rootstocks. Drought-induced decrease in total NSC content occurred only in plants grafted on Swingle. While plant growth on Swingle citrumelo was severely reduced by water deficit, plants grafted on Rangpur did not exhibited impairment of dry matter accumulation. The lower sensitivity of plant growth on Rangpur lime was associated with the enhanced root growth, the maintenance of the total carbohydrate pool and to a large shift in the carbohydrate partitioning, with the roots accumulating carbohydrates under water deficit. Regarding the young mature leaves, they exhibited higher photosynthetic rates than the old mature leaves after 30 days of treatment, regardless of the water conditions. As possible sources of carbohydrates, young mature leaves have equal importance as compared to branches under well-watered conditions.
    No preview · Article · May 2014 · Environmental and Experimental Botany
  • [Show abstract] [Hide abstract]
    ABSTRACT: A comparative proteomics study using isobaric tags for relative and absolute quantitation (iTRAQ) was performed on a mesophytic tomato (Solanum lycopersicum) cultivar and a dehydration-resistant wild species (Solanum chilense) to identify proteins that play key roles in tolerance to water deficit stress. In tomato 'Walter' LA3465, 130 proteins were identified, of which 104 (80%) were repressed and 26 (20%) were induced. In S. chilense LA1958, a total of 170 proteins were identified with 106 (62%) repressed and 64 (38%) induced. According to their putative molecular functions, the differentially expressed proteins belong to the following subgroups: stress proteins, gene expression, nascent protein processing, protein folding, protein degradation, carbohydrate metabolism, amino acid and nucleotide metabolism, lipid metabolism, signal transduction, and cell cycle regulation. Based on changes in protein abundance induced by the dehydration treatment, cellular metabolic activities and protein biosynthesis were suppressed by the stress. In S. chilense, dehydration treatment led to elevated accumulation of proteins involved in post-transcriptional gene regulation and fidelity in protein translation including prefoldin, which promotes protein folding without the use of adenosine-5#-triphosphate (ATP), several hydrophilic proteins, and calmodulin in the calcium signal transduction pathway. Those protein changes were not found in the susceptible tomato, 'Walter'. Within each functional protein group, proteins showing opposite changes (dehydration induced vs. repressed) in the two species were identified and roles of those proteins in conferring tolerance to water deficit stress are discussed. Information provided in this report will be useful for selection of proteins or genes in analyzing or improving dehydration tolerance in tomato cultivars.
    No preview · Article · Mar 2013 · Journal of the American Society for Horticultural Science. American Society for Horticultural Science
  • [Show abstract] [Hide abstract]
    ABSTRACT: Soil and water salinity substantially constrain crop and biomass production. Research over the last two plus decades, facilitated by advances in molecular genetics and biotechnology, and with genetic model systems, has identified genes involved in salt acclimation or adaptation and linked these to critical mechanisms and processes. A case in point is present understanding of critical transport determinants that facilitate intra- and intercellular Na+ homeostasis of plants in saline environments predominated by NaCl. Pumps in the plasma membrane (H+-ATPase), and the tonoplast (H+-ATPase) and H+ pyrophosphatases (AVP1) generate proton electrochemical gradients necessary to energize Na+ efflux to the apoplast and influx into vacuoles, respectively. The plasma membrane Na+/H+ antiporter SOS1 is responsible for apoplastic efflux, and NHX type Na+/H+ antiporters for vacuolar and endosomal compartmentalization. Ca2+ext reduces passive intracellular Na+ influx cells by decreasing Na+ transport through high affinity K+ uptake systems and what are presumed to be nonselective cation channels, and activating, through the SOS signal pathway, the SOS1 plasma membrane Na+/H+ antiporter. Moreover, there is greater understanding about how cellular transport systems functionally integrate to facilitate tissue and organismal Na+ homeostasis. Notable in this process are HKT1 Na+ transporters, which regulate Na+ loading into the root xylem, limiting flux to and accumulation in the shoot. This review will summarize ion transport systems that facilitate plant Na+ homeostasis. Halophyte and glycophyte salinity responses and transport determinant function are compared and contrasted. The potential of halophytes as genetic resources for unique alleles or loci of transport protein genes and transcriptional and post-transcriptional regulation of transport protein function are discussed in the context of crop salt tolerance.
    No preview · Article · Aug 2013 · Environmental and Experimental Botany
Show more