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.
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ABSTRACT: Lowland rice (Nipponbare) and upland rice (Gaoshan 1) that are comparable under normal and moderate drought conditions showed dramatic differences in severe drought conditions, including natural-occurring long-term drought and simulated rapid water deficits. We focused on their root response and found that enhanced tolerance of upland rice to severe drought conditions was mainly due to the lower level of ABA in its roots than that in the lowland rice. We firstly excluded the effect of ABA biosynthesis and catabolism on root-accumulated ABA levels in both rice by monitoring the expressions of four OsNCED genes and two OsABA8ox genes. Next, we excluded the impact of the aerial parts on roots by suppressing leaf-biosynthesized ABA with fluridone and NDGA (nordihydroguaiaretic acid) and measuring ABA level in detached roots. Instead, we proved that upland rice had the ability to export considerably more root-sourced ABA than lowland rice under severe drought, which improved ABA-dependent drought adaptation. The investigation of apoplastic pH in root cell and root anatomy evidenced that ABA leakage in the root system of upland rice was related to high apoplastic pH and the absence of Casparian bands in the sclerenchyma layer. Finally, taking some genes as examples, we predicted that different ABA levels in rice roots stimulated distinct ABA perception and signaling cascades, which influenced its response to water stress. © The Author 2015. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For Permissions, please e-mail: email@example.com.Plant and Cell Physiology 03/2015; DOI:10.1093/pcp/pcv022 · 4.98 Impact Factor
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ABSTRACT: Individuals in northern populations of Lilium longiflorum in the Ryukyu Archipelago between Japan and Taiwan exhibit deep dormancy which is induced by high temperatures in the Summer, while plants of southern ecotypes and L. formosanum show no dormancy. In higher plants, 9-cis-epoxycarotenoid dioxygenase (NCED) is the critical enzyme for the regulation of abscisic acid (ABA) biosynthesis.The relationships between levels of expression of the LlNCED gene (GenBank Accession No. KC357734) and endogenous ABA levels were examined in 1-year-old seedlings of an L. formosanum population domesticated in Fukuoka (FFU) and in two L. longiflorum populations native to Pitouchiao (LPI), Taiwan, or Kikai Jima (LKI), Japan. The deduced amino acid sequences of the NCED proteins shared high identity with NCED proteins in other monocotyledons, and were closely related to enzymes in other members of the class Liliopsida. A high correlation was observed between levels of LlNCED gene expression and ABA concentration. Seedlings from LKI had the highest level of expression of LlNCED in August, while seedlings from FFU had the lowest level. Higher expression of the LlNCED gene in mid-Summer in the dormant population was related to higher endogenous concentrations of ABA. These results provide evidence that the induction of deep dormancy was initiated by the accumulation of ABA in dormant types of L. longiflorum, which was induced by high Summer temperatures.Journal of Horticultural Science and Biotechnology 01/2015; 90(2):121-126. · 0.51 Impact Factor
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ABSTRACT: While much recent science has focused on understanding and exploiting root traits as new opportunities for crop improvement, the use of rootstocks has enhanced productivity of woody perennial crops for centuries. Grafting of vegetable crops has developed very quickly in the last 50 years, mainly to induce shoot vigour and to overcome soil-borne diseases in solanaceous and cucurbitaceous crops. In most cases, such progress has largely been due to empirical interactions between farmers, gardeners, and botanists, with limited insights into the underlying physiological mechanisms. Only during the last 20 years has science realized the potential of this old activity and studied the physiological and molecular mechanisms involved in rootstock×scion interactions, thereby not only explaining old phenomena but also developing new tools for crop improvement. Rootstocks can contribute to food security by: (i) increasing the yield potential of elite varieties; (ii) closing the yield gap under suboptimal growing conditions; (iii) decreasing the amount of chemical (pesticides and fertilizers) contaminants in the soil; (iv) increasing the efficiency of use of natural (water and soil) resources; (v) generating new useful genotypic variability (via epigenetics); and (vi) creating new products with improved quality. The potential of grafting is as broad as the genetic variability able to cross a potential incompatibility barrier between the rootstock and the scion. Therefore, understanding the mechanisms underlying the phenotypic variability resulting from rootstock×scion×environment interactions will certainly contribute to developing and exploiting rootstocks for food security. © The Author 2015. Published by Oxford University Press on behalf of the Society for Experimental Biology. All rights reserved. For permissions, please email: firstname.lastname@example.org.Journal of Experimental Botany 03/2015; 66(8). DOI:10.1093/jxb/erv027 · 5.79 Impact Factor