Browsing by Subject "Abscisic acid"

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Abscisic acid and proline are not equivalent markers for heat, drought and combined stress in grapevines
(2021) Lehr, P.P.; Hernández‐Montes, E.; Ludwig‐Müller, J.; Keller, M.; Zörb, C.
Background and Aims: Viticulture will be particularly affected by increasing drought and heat waves in the future. It is of interest to find traits that indicate stress before symptoms become apparent. We investigated whether the commonly used traits, proline and abscisic acid (ABA) biosynthesis, are suitable markers for heat, drought or combined stress and whether gene expression of key enzymes of ABA biosynthesis is regulated in grapevine leaves under these stress conditions. Methods and Results: Plant growth and gas exchange were measured to evaluate plant reactions to increased temperature and water deficit. Proline and ABA concentration in leaf material was measured, respectively, photometrically and with GC/MS. Gene expression analysis of NCED1, NCED2 and P5CS was done by real-time quantitative reverse transcription-polymerase chain reaction. Drought stress had a stronger effect on growth, gas exchange, proline, and ABA biosynthesis than heat stress. An interaction between heat and drought stress was observed for gas exchange and for proline biosynthesis. Conclusions: Proline concentration and gene expression of P5CS are good markers for combined stress. The concentration of ABA is a suitable marker for drought stress and might be a suitable marker for combined stress. Gene expression of NCED1 in leaves was a good marker for drought stress and might be a suitable marker for combined stress, whereas NCED2 was not suitable. Significance of the Study: These results provide insight into the response of grapevines to heat, drought and combined stress and show the suitability of ABA and proline as stress markers.
Constant hydraulic supply and ABA dynamics facilitate the trade-offs in water and carbon
(2023) Abdalla, Mohanned; Schweiger, Andreas H.; Berauer, Bernd J.; McAdam, Scott A. M.; Ahmed, Mutez Ali
Carbon-water trade-offs in plants are adjusted through stomatal regulation. Stomatal opening enables carbon uptake and plant growth, whereas plants circumvent drought by closing stomata. The specific effects of leaf position and age on stomatal behavior remain largely unknown, especially under edaphic and atmospheric drought. Here, we compared stomatal conductance (gs) across the canopy of tomato during soil drying. We measured gas exchange, foliage ABA level and soil-plant hydraulics under increasing vapor pressure deficit (VPD). Our results indicate a strong effect of canopy position on stomatal behavior, especially under hydrated soil conditions and relatively low VPD. In wet soil (soil water potential > -50 kPa), upper canopy leaves had the highest gs (0.727 ± 0.154 mol m-2 s-1) and assimilation rate (A; 23.4 ± 3.9 µmol m-2 s-1) compared to the leaves at a medium height of the canopy (gs: 0.159 ± 0.060 mol m2 s-1; A: 15.9 ± 3.8 µmol m-2 s-1). Under increasing VPD (from 1.8 to 2.6 kPa), gs, A and transpiration were initially impacted by leaf position rather than leaf age. However, under high VPD (2.6 kPa), age effect outweighed position effect. The soil-leaf hydraulic conductance was similar in all leaves. Foliage ABA levels increased with rising VPD in mature leaves at medium height (217.56 ± 85 ng g-1 FW) compared to upper canopy leaves (85.36 ± 34 ng g-1 FW). Under soil drought (< -50 kPa), stomata closed in all leaves resulting in no differences in gs across the canopy. We conclude that constant hydraulic supply and ABA dynamics facilitate preferential stomatal behavior and carbon-water trade-offs across the canopy. These findings are fundamental in understanding variations within the canopy, which helps in engineering future crops, especially in the face of climate change.
Regulation of ammonium transport in Arabidopsis thaliana
(2022) Ganz, Pascal; Ludewig, Uwe
The overarching question of this thesis deals with how plants ensure the selective uptake of ammonium while maintaining ion and pH homeostasis. A key component of this is ammonium transporters (AMTs) with high affinity towards their substrate, which are at the same time part of a multilayered protection system against uncontrolled ammonium influx. Conserved protein sequences inside the transporter were analyzed as well as the regulatory system based on post-translational modification of the transporter.
Transporters mediating ammonium uptake in plants and their regulation by the abiotic stress signaling pathway
(2023) Porras Murillo, Romano; Ludewig, Uwe
Nitrogen nutrition refers to the uptake, assimilation, and utilization of ammonium, nitrate, and organic nitrogen sources. Ammonium is energetically a more cost-effective nitrogen source than nitrate but can be toxic for plants, and its use by plants is regulated at different levels. Ammonium transporters (AMTs) take up ammonium and are localized primarily in plant roots, working as trimers in the plasma membrane. Under high external ammonium concentrations, phosphorylation in AMTs C-termini shuts down transport to avoid toxicity. This phosphorylation is performed by CIPK23, a kinase shown to be inhibited by Clade A PP2Cs. This study aimed to characterize AMTs from wheat and analyze their transcriptional response to ammonium. Another aim was to determine the role of clade A PP2Cs and PYR/PYL receptor proteins for abscisic acid in ammonium nutrition. Chapter I describes the physiological responses of winter wheat to different nitrogen sources and ammonium concentrations. The plants mainly used root morphological responses to adapt to differences in the nitrogen source. High external concentrations of ammonium reduced plant growth, while these conditions induced the expression of TaAMT1;1 and TaAMT1;2. In Chapter II, we studied the capacity of TaAMT2s to transport ammonium and their transcriptional responsiveness to ammonium nutrition. From the six TaAMT2s, only TaAMT2;1 could transport ammonium in a yeast complementation line. Besides, its expression in roots is lower under ammonium than under nitrate. The expression pattern among the remaining TaAMT2s (TaAMT2;2-TaAMT2;6) is similar, with higher expression under ammonium, in both roots and leaves, compared to nitrate. Chapter III focused on the role of the PP2C phosphatase ABI1 (ABA-insensitive 1) in ammonium nutrition and the effect of external ammonium concentrations on ABA concentrations. Ammonium increased ABA concentrations in roots by activating ABA-GE, meaning ammonium toxicity could be sensed as abiotic stress through ABA. Without ammonium, ABI1 dephosphorylates AMTs and inhibits CIPK23; with ammonium, ABA-PYR/PYL complex-mediated inhibition of ABI1 releases CIPK23 to phosphorylate AMTs and avoids ammonium toxicity. Finally, in Chapter IV, we studied the role of AIP1 and its ammonium-dependent regulator, PYL8, in nitrogen nutrition. We described the function of AIP1, which was redundant to ABI1 in AMT regulation. Based on ammonium-dependent root architecture changes, and higher auxin accumulation in pyl8-1 root tips compared to the wild type, we suggest that PYL8 is involved in root-phenotype modulation in an ammonium-dependent manner.