Drought and abscisic acid effects on aquaporin content translate into changes in hydraulic conductivity and leaf growth rate: a trans-scale approach.
ABSTRACT The effects of abscisic acid (ABA) on aquaporin content, root hydraulic conductivity (Lpr), whole plant hydraulic conductance, and leaf growth are controversial. We addressed these effects via a combination of experiments at different scales of plant organization and tested their consistency via a model. We analyzed under moderate water deficit a series of transformed maize (Zea mays) lines, one sense and three antisense, affected in NCED (for 9-cis-epoxycarotenoid dioxygenase) gene expression and that differed in the concentration of ABA in the xylem sap. In roots, the mRNA expression of most aquaporin PIP (for plasma membrane intrinsic protein) genes was increased in sense plants and decreased in antisense plants. The same pattern was observed for the protein contents of four PIPs. This resulted in more than 6-fold differences between lines in Lpr under both hydrostatic and osmotic gradients of water potential. This effect was probably due to differences in aquaporin activity, because it was nearly abolished by a hydrogen peroxide treatment, which blocks the water channel activity of aquaporins. The hydraulic conductance of intact whole plants was affected in the same way when measured either in steady-state conditions or via the rate of recovery of leaf water potential after rewatering. The recoveries of leaf water potential and elongation upon rehydration differed between lines and were accounted for by the experimentally measured Lpr in a model of water transfer. Overall, these results suggest that ABA has long-lasting effects on plant hydraulic properties via aquaporin activity, which contributes to the maintenance of a favorable plant water status.
- SourceAvailable from: R J Neil Emery[show abstract] [hide abstract]
ABSTRACT: Experiments were undertaken to test how aquaporins (AQPs) facilitate the uptake of water by roots of Pisum sativum. Changes in PsPIP2-1 gene expression and root hydraulic conductivity (Lpr) were measured in response to the time of day as well as treatment of the roots with a compound that reduced Lpr [i.e. mercuric chloride (HgCl2)] and one that was intended to increase Lpr [abscisic acid (ABA)]. There was a diurnal rhythm in PsPIP2-1 expression in lateral roots that was strongly correlated with diurnal changes in Lpr. Taproots also displayed a rhythm in PsPIP2-1 expression, but this was offset from that of Lpr. This suggested that changes in Lpr were mediated by changes in PsPIP2-1 mRNA transcript abundance. Reduction of Lpr by HgCl2 treatment was accompanied by an increase in PsPIP2-1 expression, implying that PsPIP2-1 expression may have increased to compensate for AQPs blocked by mercury. ABA usually increased Lpr, but changes in PsPIP2-1 were variable and the direction of the response was strongly dependent on the dose of ABA that was applied. Overall, the coincident rhythms in Lpr and PIP2 expression and response to AQP blockage are consistent with the hypothesis that Lpr changes are mediated, at least in part, by changes in PsPIP2-1 expression. Inconsistencies with ABA data may have been due to more complex interactions of ABA with AQP channels.Journal of Experimental Botany 02/2007; 58(6):1291-300. · 5.24 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Major intrinsic proteins (MIPs) are a family of channel proteins that are mainly represented by aquaporins in plants. These are divided into TIPs (tonoplast intrinsic proteins) and PIPs (plasma membrane intrinsic proteins) according to their subcellular localization. Homologues to PIPs and TIPs were isolated from the desiccation-tolerant resurrection plant Craterostigma plantagineum by two approaches: firstly, a cDNA library constructed from RNA of dehydrated C. plantagineum leaves was screened with an Arabidopsis thaliana Ath-PIP1b cDNA probe and, secondly, a cDNA library was screened differentially to isolate early drought-induced transcripts. According to sequence homologies the isolated cDNA clones were grouped as follows: Cp-PIPa, Cp-PIPb, Cp-PIPc and Cp-TIP. Cp-PIPa, Cp-PIPc and Cp-TIP transcript accumulation was regulated by dehydration and abscisic acid (ABA). Within the Cp-PIPa group transcripts were regulated either by drought only or by drought and ABA, indicating that ABA-dependent and -independent signal transduction pathways lead to Cp-PIPa expression. Comparison of Cp-PIPa expression in detached leaves and in whole plants suggested the involvement of a signal transmitted in the whole plant in response to drought. Cp-PIPb transcript levels were constitutive in all organs tested. Antibodies raised against a Cp-PIPA protein recognized a polypeptide with an apparent molecular mass of 28 kDa. Using these antibodies it was shown that both Cp-PIPA and Cp-PIPB proteins were localized to the plasma membrane. The role of different members of the MIP group in the dehydration response is discussed.Plant Molecular Biology 01/1999; 38(6):1089-99. · 3.52 Impact Factor
- [show abstract] [hide abstract]
ABSTRACT: Photosynthesis and biomass production of plants are controlled by the water status of the soil. Upon soil drying, plants can reduce water consumption by minimizing transpiration through stomata, the closable pores of the leaf. The phytohormone abscisic acid (ABA) mediates stomatal closure, and is the assigned signal for communicating water deficit from the root to the shoot. However, our study does not support ABA as the proposed long-distance signal. The shoot response to limited soil water supply is not affected by the capacity to generate ABA in the root; however, the response does require ABA biosynthesis and signalling in the shoot. Soil water stress elicits a hydraulic response in the shoot, which precedes ABA signalling and stomatal closure. Attenuation of the hydraulic response in various plants prevented long-distance signalling of water stress, consistent with root-to-shoot communication by a hydraulic signal.The Plant Journal 11/2007; 52(1):167-74. · 6.58 Impact Factor