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A. M. Rychter - One of the best experts on this subject based on the ideXlab platform.
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Assimilate distribution in bean plants (Phaseolus vulgaris L.) during Phosphate limitation
Acta Societatis Botanicorum Poloniae, 2014Co-Authors: Iwona Ciereszko, Irena Miłosek, A. M. RychterAbstract:The influence of Phosphate Deficiency on the increased "C-assimilate transport from shoot to root of bean plants ( Phaseolus vulgaris L.) was studied. The roots of plants were cultured in split configurations (a half of the root system was exposed to a short-term or long-term culture in Phosphate-deficient nutrient medium, while the other half - in complete nutrient medium) to establish the conditions of translocation enhancement. It was found that both short term Pi stress applied to a part of root and longer localized Phosphate Deficiency is not sufficient to increase assimilate transport from the shoot to the root. Low concentration of Pi in tissues of the whole plant as a signal for changes in assimilate distribution and sugar accumulation in the roots is discussed.
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Pyruvate accumulation during Phosphate Deficiency stress of bean roots
Plant Physiology and Biochemistry, 2002Co-Authors: I. M. Juszczuk, A. M. RychterAbstract:Culture of bean plants (Phaseolus vulgaris L. cv., Zlota Saxa) for 16 d on Phosphate-deficient nutrient medium resulted in an over twofold increase of pyruvate concentration in the root tissues. In a variety of plant tissues, the marked decline in cellular concentrations of adenylates and inorganic Phosphate (Pi) influences the activity of pyruvate producing enzymes, which are dependent on the availability of ADP. In bean roots after 16 d of Phosphate starvation pyruvate producing enzymes: phosphoenolpyruvate phosphatase (EC 3.1.3.2) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) had higher activities compared to those of control plants. The observed decrease of alanine and ethanol concentration and also alcohol dehydrogenase (EC 1.1.1.1) activity in Phosphate-deficient roots may be the effect of the restrictions in pyruvate utilizing pathways. The increased activity of mitochondrial NAD-malic enzyme (EC 1.1.1.40) as well as the lower consumption of pyruvate during respiration of Phosphate-deficient roots indicate that pyruvate concentration in mitochondria may be elevated. It is proposed that pyruvate accumulation in Phosphate-deficient roots and alternative oxidase participation in respiration are important aspects of plant metabolic adaptations to Pi limitation, and may play a role in reducing oxidative stress induced by Phosphate Deficiency.
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Free radical production in roots of Phaseolus vulgaris subjected to Phosphate Deficiency stress
Plant Physiology and Biochemistry, 2002Co-Authors: Eligio Malusà, I. M. Juszczuk, Enzo Laurenti, Rosa Pia Ferrari, A. M. RychterAbstract:Abstract We subjected bean plants ( Phaseolus vulgaris L. cv. ‘Zlota Saxa’) to Phosphate Deficiency stress and studied free radical production in whole root extracts. Starting from the 12th day of growth a carbon-centred free radical was detected, by means of electron spin resonance (ESR) after spin trapping with 5,5-dimethyl-L-pyrroline- N -oxide (DMPO), only in Phosphate-deficient plants. The simulated hyperfine coupling constants of this spectrum ( a N = 16.2 G; a H = 23.6 G) are consistent with an aliphatic or an aromatic carbon-centred radical; this species could derive from lipid peroxidation or phenol oxidation processes, respectively. Hydrogen peroxide production was also enhanced. Production of both H 2 O 2 and DMPO adduct were related to the length of growth on the Phosphate-deficient medium. Roots from Phosphate-deficient plants showed increased content of phenols and a redox state of ascorbate similar to the control. These results indicate that Phosphate starvation imposes a mild oxidative stress.
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Phosphate Deficiency induced oxidative stress in bean (Phaseolus vulgaris L.)
Plant Nutrition, 2001Co-Authors: I. M. Juszczuk, M. Malusa, A. M. RychterAbstract:Prolonged Phosphate starvation of bean plants (Phaseolus vulgaris L.) and severe decrease of inorganic Phosphate concentration in root tissues resulted in increased lipid peroxidation. Concentration of hydrogen peroxide was higher in Phosphate deficient (−P) roots and in isolated mitochondria. Phosphate Deficiency increased the ratio of reduced to total ubiquinone and pyruvate concentration in the roots. Phosphate Deficiency did not affect ascorbate peroxidase and superoxide dismutase activities. The activities of catalase and peroxidases, however, were higher in extracts and isolated mitochondria of Phosphate deficient roots.
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Oxidative stress during Phosphate Deficiency in roots of bean plants (Phaseolus vulgaris L.)
Journal of Plant Physiology, 2001Co-Authors: I. M. Juszczuk, Eligio Malusà, A. M. RychterAbstract:Summary The oxidative stress symptoms were studied during Phosphate Deficiency. Prolonged Phosphate starvation of bean plants (Phaseolus vulgaris L.) and severe decrease of inorganic Phosphate concentration resulted in increased lipid peroxidation and hydrogen peroxide concentration in root tissues. The ratio of reduced to total ubiquinone was also higher in whole roots and isolated mitochondria from the roots of Phosphate-deficient plants. No effect of Phosphate Deficiency on ascorbate peroxidase and superoxide dismutase activities was detected. However, the activities of catalase and total peroxidase were higher in extracts of Phosphate-deficient roots compared to control roots. These results indicate that Phosphate starvation is an abiotic stress that imposes an oxidative stress in bean root cells. The role of alternative oxidase in stabilizing the reduction level of ubiquinone, and thus preventing active oxygen species formation, is discussed.
D W Lawlor - One of the best experts on this subject based on the ideXlab platform.
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dependence of photosynthesis of sunflower and maize leaves on Phosphate supply ribulose 1 5 bisPhosphate carboxylase oxygenase activity and ribulose 1 5 bisPhosphate pool size
Plant Physiology, 1992Co-Authors: James Jacob, D W LawlorAbstract:Sunflower (Helianthus annuus L. cv Asmer) and maize (Zea mays L. cv Eta) plants were grown under controlled environmental conditions with a nutrient solution containing 0, 0.5, or 10 millimolar inorganic Phosphate. Phosphate-deficient leaves had lower photosynthetic rates at ambient and saturating CO(2) and much smaller carboxylation efficiencies than those of plants grown with ample Phosphate. In addition, Phosphate-deficient leaves contained smaller quantities of total soluble proteins and ribulose-1,5-bisPhosphate carboxylase/oxygenase (Rubisco) per unit area, although the relative proportions of these components remained unchanged. The specific activity of Rubisco (estimated in the crude extracts of leaves) was significantly reduced by Phosphate Deficiency in sunflower but not in maize. Thus, there was a strong dependence of carboxylation efficiency and CO(2)-saturated photosynthetic rate on Rubisco activity only in sunflower. Phosphate Deficiency decreased the 3-phosphoglycerate and ribulose-1,5-bisPhosphate (RuBP) contents of the leaf in both species. The ratio of 3-phosphoglycerate to RuBP decreased in sunflower but increased in maize with Phosphate Deficiency. The calculated concentrations of RuBP and RuBP-binding sites in the chloroplast stroma decreased markedly with Phosphate Deficiency. The ratio of the stromal concentration of RuBP to that of RuBP-binding sites decreased in sunflower but was not affected in maize with Phosphate Deficiency. We suggest that a decrease in this ratio made the RuBP-binding sites more vulnerable to blockage or inactivation by tight-binding metabolites/inhibitors, causing a decrease in the initial specific activity of Rubisco in the crude extract from Phosphate-deficient sunflower leaves. However, the decrease in Rubisco specific activity was much less than the decrease in the RuBP content in the leaf and its concentration in the stroma. A large ratio of RuBP to RuBP-binding sites may have maintained the Rubisco-specific activity in Phosphate-deficient maize leaves. We conclude that the effect of Phosphate Deficiency is more on RuBP regeneration than on Rubisco activity in both sunflower and maize.
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Dependence of photosynthesis of sunflower and maize leaves on Phosphate supply, ribulose-1,5-bisPhosphate carboxylase/oxygenase activity, and ribulose-1,5-bisPhosphate pool size
Plant physiology, 1992Co-Authors: James Jacob, D W LawlorAbstract:Sunflower (Helianthus annuus L. cv Asmer) and maize (Zea mays L. cv Eta) plants were grown under controlled environmental conditions with a nutrient solution containing 0, 0.5, or 10 millimolar inorganic Phosphate. Phosphate-deficient leaves had lower photosynthetic rates at ambient and saturating CO(2) and much smaller carboxylation efficiencies than those of plants grown with ample Phosphate. In addition, Phosphate-deficient leaves contained smaller quantities of total soluble proteins and ribulose-1,5-bisPhosphate carboxylase/oxygenase (Rubisco) per unit area, although the relative proportions of these components remained unchanged. The specific activity of Rubisco (estimated in the crude extracts of leaves) was significantly reduced by Phosphate Deficiency in sunflower but not in maize. Thus, there was a strong dependence of carboxylation efficiency and CO(2)-saturated photosynthetic rate on Rubisco activity only in sunflower. Phosphate Deficiency decreased the 3-phosphoglycerate and ribulose-1,5-bisPhosphate (RuBP) contents of the leaf in both species. The ratio of 3-phosphoglycerate to RuBP decreased in sunflower but increased in maize with Phosphate Deficiency. The calculated concentrations of RuBP and RuBP-binding sites in the chloroplast stroma decreased markedly with Phosphate Deficiency. The ratio of the stromal concentration of RuBP to that of RuBP-binding sites decreased in sunflower but was not affected in maize with Phosphate Deficiency. We suggest that a decrease in this ratio made the RuBP-binding sites more vulnerable to blockage or inactivation by tight-binding metabolites/inhibitors, causing a decrease in the initial specific activity of Rubisco in the crude extract from Phosphate-deficient sunflower leaves. However, the decrease in Rubisco specific activity was much less than the decrease in the RuBP content in the leaf and its concentration in the stroma. A large ratio of RuBP to RuBP-binding sites may have maintained the Rubisco-specific activity in Phosphate-deficient maize leaves. We conclude that the effect of Phosphate Deficiency is more on RuBP regeneration than on Rubisco activity in both sunflower and maize.
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Stomatal and Mesophyll Limitations of Photosynthesis in Phosphate Deficient Sunflower, Maize and Wheat Plants
Journal of Experimental Botany, 1991Co-Authors: J Jacob, D W LawlorAbstract:The effects of Phosphate Deficiency on the composition and photosynthetic C02 assimilation rates of fully expanded leaves of sunflower, maize and wheat plants are described. The regulation of photosynthesis by stomatal and mesophyll characteristics of leaves of different Phosphate status is analysed and related to structure. Phosphate deficient leaves had small concentrations of inorganic Phosphate, Pi, in the tissue water. Rate of photosynthesis in leaves and stomatal conductance were smaller in plants grown with inadequate Phosphate when measured under any given light intensity or C02 partial pressure. Despite the decrease in stomatal conductance (and without evidence of patchy stomatal closure), the relative stomatal limitation of photosynthesis was similar in the plants grown with deficient or abundant Phosphate. However, the mesophyll capacity for photosynthesis was greatly limited by Phosphate Deficiency. Leaves deficient in Phosphate had larger numbers of small size cells per unit leaf area than leaves with adequate Phosphate. The total soluble protein content of leaves decreased with Phosphate Deficiency in all three species; however, the leaf chlorophyll content was decreased only in sunflower and maize and not in wheat. These results suggest that stomatal conductance did not restrict the C02 diffusion rate, rather the metabolism of the mesophyll was the limiting factor. This is shown by poor carboxylation efficiency and decreased apparent quantum yield for C02 assimilation, both of which contributed to the increase in relative mesophyll limitation of photosynthesis in Phosphate deficient plants.
Iwona Ciereszko - One of the best experts on this subject based on the ideXlab platform.
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Mechanisms of oat (Avena sativa L.) acclimation to Phosphate Deficiency
PeerJ, 2017Co-Authors: Ewa Żebrowska, Marta Milewska, Iwona CiereszkoAbstract:Background Deficiency of available forms of phosphorus is common in most soils and causes reduction of crop plants growth and yield. Recently, model plants responses to Phosphate (Pi) Deficiency have been intensively studied. However, acclimation mechanisms of cereals like oat (Avena sativa L.), to low Pi stress remains not fully understood. Oat plants have been usually cultured on poor soils, with a low nutrient content, but their responses to such conditions are not well known, therefore the main goal of the study was to investigate the mechanisms that enable oat plants to grow under low Pi conditions. Methods Four oat cultivars (A. sativa, cv. Arab, Krezus, Rajtar and Szakal) were grown for three weeks in a nutrient media with various P sources: inorganic-KH2PO4 (control), organic-phytate (PA) and with no Phosphate (-P). The effects of Pi Deficiency on the level of P, oat growth parameters, intensity of photosynthesis, plant productivity, root exudation ability, localization, activity and isoforms of acid phosphatases, enzymes involved in Pi mobilization, were estimated. In addition, the effect of mycorrhization on plant growth was also observed. Results All studied oat cultivars grown on Pi-deficient media had significantly decreased Pi content in the tissues. Pi Deficiency caused inhibition of shoot growth, but generally it did not affect root elongation; root diameter was decreased, root/shoot ratios increased, whereas PA plants showed a similar growth to control. Photosynthesis rate and productivity parameters decreased under low Pi nutrition, however, sugar content generally increased. Studied oat cultivars did not respond to low Pi via increased exudation of carboxylates from the roots, as pH changes in the growth media were not observed. Pi starvation significantly increased the activity of extracellular and intracellular acid phosphatases (APases) in comparison to the control plants. Three major APase isoforms were detected in oat tissues and the isoform pattern was similar in all studied conditions, usually with a higher level of one of the isoforms under Pi starvation. Generally no significant effects of mycorrhizal colonization on growth of oat cultivars were observed. Discussion We postulated that acid phosphatases played the most important role in oat cultivars acclimation to Pi Deficiency, especially extracellular enzymes involved in Pi acquisition from soil organic P esters. These APases are mainly located in the epidermis of young roots, and may be released to the rhizosphere. On the other hand, intracellular APases could be involved in fast Pi remobilization from internal sources. Our study showed that oat, in contrast to other plants, can use phytates as the sole source of P. The studied oat cultivars demonstrated similar acclimation mechanisms to Pi Deficiency, however, depending on stress level, they can use different pools of acid phosphatases.
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Assimilate distribution in bean plants (Phaseolus vulgaris L.) during Phosphate limitation
Acta Societatis Botanicorum Poloniae, 2014Co-Authors: Iwona Ciereszko, Irena Miłosek, A. M. RychterAbstract:The influence of Phosphate Deficiency on the increased "C-assimilate transport from shoot to root of bean plants ( Phaseolus vulgaris L.) was studied. The roots of plants were cultured in split configurations (a half of the root system was exposed to a short-term or long-term culture in Phosphate-deficient nutrient medium, while the other half - in complete nutrient medium) to establish the conditions of translocation enhancement. It was found that both short term Pi stress applied to a part of root and longer localized Phosphate Deficiency is not sufficient to increase assimilate transport from the shoot to the root. Low concentration of Pi in tissues of the whole plant as a signal for changes in assimilate distribution and sugar accumulation in the roots is discussed.
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Phosphate Deficiency AFFECTS ACID PHOSPHATASE ACTIVITY AND GROWTH OF TWO WHEAT VARIETIES
Journal of Plant Nutrition, 2011Co-Authors: Iwona Ciereszko, Agnieszka Szczygła, Ewa ŻebrowskaAbstract:The effects of Phosphate Deficiency on the plant growth and acid phosphatase activity in two wheat cultivars (Triticum aestivum L. cv. ‘Bryza’ and ‘Opatka’) were studied. Pi content decreased significantly in the shoots and roots of all plants grown for one to three weeks in the nutrient medium without Phosphate (−P). Phosphate starvation affected growth of both wheat cultivars in a similar way: significantly decreased shoot and root mass, especially after three weeks growth on −P medium, even up to 8–11% of control. However the ratio of root/shoot fresh weight of −P plants increased (2–3 times more than control). The shoot height of −P wheat plants decreased to about 50–60% of the control after two to three weeks of culture; less affected by Pi Deficiency was root elongation—no significant changes were observed for both wheat cultivars during one to three weeks of culture. Phosphate Deficiency increased the activity of extracellular and intracellular acid phosphatases in comparison to Phosphate-sufficien...
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Sucrose metabolism in leaves and roots of bean (Phaseolus vulgaris L.) during Phosphate Deficiency
Journal of Plant Physiology, 2000Co-Authors: Iwona Ciereszko, Agnieszka BarbachowskaAbstract:Summary The influence of Phosphate Deficiency on the accumulation and metabolism of sugars in the source and sink leaves and roots of bean ( Phaseolus vulgaris L.) was studied after 16 days of plant culture. Glucose, sucrose and starch contents increased in all tissues of Phosphate-deficient plants as compared with control plants. Phosphate Deficiency increased activities of enzymes involved in sucrose synthesis in the leaves and root; sucrose Phosphate synthase (EC 2.4.1.14) activity increased about twice, while sucrose synthase (EC 2.4.1.13) activity increased about 3-fold in the mature leaves and 50% and 90% in the young leaves and roots, respectively. Phosphate Deficiency also increased the activities of enzymes hydrolyzing sucrose in the leaves and roots; neutral invertase (EC 3.2.1.26) activity increased twice in the source leaves and about 50% in sink leaves and roots. Acid invertases (EC 3.2.1.26) were divided into soluble and insoluble forms; insoluble invertases activities were several times lower than those of soluble invertases, both in the leaves and roots. Pi starvation increased mainly the activities of insoluble forms of acid invertases in all tissues in bean plants.
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Compartmentation and Fluxes of Sugars in Roots of Phaseolus Vulgaris Under Phosphate Deficiency
Biologia plantarum, 1999Co-Authors: Iwona Ciereszko, J.f. Farrar, A. M. RychterAbstract:The influence of Phosphate Deficiency on the sugar accumulation and sugar partitioning in the root cells of bean (Phaseolus vulgaris L.) was studied. Bean plants were cultured 17 - 19 d on a Phosphate-sufficient and Phosphate-deficient nutrient medium. Phosphate deficit in the growth medium resulted in increased sugar concentration for about 30 % in the apoplastic and cytoplasmic compartments as well as in the vacuoles of root cells. However, the distribution of sugars between apoplast and cytoplasm compartment and vacuole was not affected by decreased Phosphate concentration. About 20 % of sugars were found in the apoplast and cytoplasm, about 80 % in the vacuole. Low Phosphate concentration enhanced influx of exogenous 14C-sucrose into meristematic and elongation zones of root. The 14C-labelled sugar content in the root tips increased for about 60 % as compared to control plants. Phosphate Deficiency increased also 14C-glucose uptake and content in the root tips. However, the amount of 14CO2 liberated during respiration of P-deficient roots (after feeding with uniformly labelled 14C-glucose) was lower than 14CO2 respired by control plants, thus a large part of accumulated sugars seems to be metabolically inactive.
I. M. Juszczuk - One of the best experts on this subject based on the ideXlab platform.
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Pyruvate accumulation during Phosphate Deficiency stress of bean roots
Plant Physiology and Biochemistry, 2002Co-Authors: I. M. Juszczuk, A. M. RychterAbstract:Culture of bean plants (Phaseolus vulgaris L. cv., Zlota Saxa) for 16 d on Phosphate-deficient nutrient medium resulted in an over twofold increase of pyruvate concentration in the root tissues. In a variety of plant tissues, the marked decline in cellular concentrations of adenylates and inorganic Phosphate (Pi) influences the activity of pyruvate producing enzymes, which are dependent on the availability of ADP. In bean roots after 16 d of Phosphate starvation pyruvate producing enzymes: phosphoenolpyruvate phosphatase (EC 3.1.3.2) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) had higher activities compared to those of control plants. The observed decrease of alanine and ethanol concentration and also alcohol dehydrogenase (EC 1.1.1.1) activity in Phosphate-deficient roots may be the effect of the restrictions in pyruvate utilizing pathways. The increased activity of mitochondrial NAD-malic enzyme (EC 1.1.1.40) as well as the lower consumption of pyruvate during respiration of Phosphate-deficient roots indicate that pyruvate concentration in mitochondria may be elevated. It is proposed that pyruvate accumulation in Phosphate-deficient roots and alternative oxidase participation in respiration are important aspects of plant metabolic adaptations to Pi limitation, and may play a role in reducing oxidative stress induced by Phosphate Deficiency.
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Free radical production in roots of Phaseolus vulgaris subjected to Phosphate Deficiency stress
Plant Physiology and Biochemistry, 2002Co-Authors: Eligio Malusà, I. M. Juszczuk, Enzo Laurenti, Rosa Pia Ferrari, A. M. RychterAbstract:Abstract We subjected bean plants ( Phaseolus vulgaris L. cv. ‘Zlota Saxa’) to Phosphate Deficiency stress and studied free radical production in whole root extracts. Starting from the 12th day of growth a carbon-centred free radical was detected, by means of electron spin resonance (ESR) after spin trapping with 5,5-dimethyl-L-pyrroline- N -oxide (DMPO), only in Phosphate-deficient plants. The simulated hyperfine coupling constants of this spectrum ( a N = 16.2 G; a H = 23.6 G) are consistent with an aliphatic or an aromatic carbon-centred radical; this species could derive from lipid peroxidation or phenol oxidation processes, respectively. Hydrogen peroxide production was also enhanced. Production of both H 2 O 2 and DMPO adduct were related to the length of growth on the Phosphate-deficient medium. Roots from Phosphate-deficient plants showed increased content of phenols and a redox state of ascorbate similar to the control. These results indicate that Phosphate starvation imposes a mild oxidative stress.
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Phosphate Deficiency induced oxidative stress in bean (Phaseolus vulgaris L.)
Plant Nutrition, 2001Co-Authors: I. M. Juszczuk, M. Malusa, A. M. RychterAbstract:Prolonged Phosphate starvation of bean plants (Phaseolus vulgaris L.) and severe decrease of inorganic Phosphate concentration in root tissues resulted in increased lipid peroxidation. Concentration of hydrogen peroxide was higher in Phosphate deficient (−P) roots and in isolated mitochondria. Phosphate Deficiency increased the ratio of reduced to total ubiquinone and pyruvate concentration in the roots. Phosphate Deficiency did not affect ascorbate peroxidase and superoxide dismutase activities. The activities of catalase and peroxidases, however, were higher in extracts and isolated mitochondria of Phosphate deficient roots.
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Oxidative stress during Phosphate Deficiency in roots of bean plants (Phaseolus vulgaris L.)
Journal of Plant Physiology, 2001Co-Authors: I. M. Juszczuk, Eligio Malusà, A. M. RychterAbstract:Summary The oxidative stress symptoms were studied during Phosphate Deficiency. Prolonged Phosphate starvation of bean plants (Phaseolus vulgaris L.) and severe decrease of inorganic Phosphate concentration resulted in increased lipid peroxidation and hydrogen peroxide concentration in root tissues. The ratio of reduced to total ubiquinone was also higher in whole roots and isolated mitochondria from the roots of Phosphate-deficient plants. No effect of Phosphate Deficiency on ascorbate peroxidase and superoxide dismutase activities was detected. However, the activities of catalase and total peroxidase were higher in extracts of Phosphate-deficient roots compared to control roots. These results indicate that Phosphate starvation is an abiotic stress that imposes an oxidative stress in bean root cells. The role of alternative oxidase in stabilizing the reduction level of ubiquinone, and thus preventing active oxygen species formation, is discussed.
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Regulation of alternative oxidase activity during Phosphate Deficiency in bean roots (Phaseolus vulgaris).
Physiologia plantarum, 2001Co-Authors: I. M. Juszczuk, Anneke M. Wagner, A. M. RychterAbstract:Cyanide-resistant respiration was studied in mitochondria isolated from the roots of bean plants (Phaseolus vulgaris L. cv. Zlota Saxa) grown hydroponically up to 16 days on a Phosphate-sufficient (+P, control) or Phosphate-deficient (-P) medium. Western blotting indicated that the alternative oxidase (AOX) was present only in its reduced (active) form, both in Phosphate-sufficient and Phosphate-deficient roots, but in the latter, the amount of AOX protein was greater. Addition of pyruvate to the isolation, washing and reaction media made mitochondria from +P roots cyanide-insensitive, similar to mitochondria from -P roots. The doubled activity of NAD-malic enzyme (NAD-ME) in -P compared with +P root mitochondria may suggest increased pyruvate production in -P mitochondria. Lower cytochrome c oxidase (COX) activity and no uncoupler effect on respiration indicated limited cytochrome chain activity in -P mitochondria. In -P mitochondria, the oxygen uptake decreased and the level of Q reduction increased from 60 to 80%. With no pyruvate present (AOX not fully activated), inhibition of the cytochrome pathway resulted in an increased level of the ratio of reduced ubiquinone (Qr) to total ubiquinone (Qt) (Qr/Qt) in +P mitochondria, but did not change Qr/Qt in -P mitochondria. When pyruvate was present, the kinetics for AOX were similar in mitochondria from -P and +P roots. It is suggested that AOX participation in -P respiration may provide an acclimation to Phosphate Deficiency. Stabilization of the ubiquinone reduction level by AOX might prevent the harmful effect of an increased formation of reactive oxygen species.
Ray A Bressan - One of the best experts on this subject based on the ideXlab platform.
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the arabidopsis sumo e3 ligase siz1 controls Phosphate Deficiency responses
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Kenji Miura, Ana Rus, Altanbadralt Sharkhuu, Shuji Yokoi, Athikkattuvalasu S Karthikeyan, Kashchandra G Raghothama, Dongwon Baek, Yoon Duck Koo, Jing Bo Jin, Ray A BressanAbstract:Plants sense Phosphate (Pi) Deficiency and initiate signaling that controls adaptive responses necessary for Pi acquisition. Herein, evidence establishes that AtSIZ1 is a plant small ubiquitin-like modifier (SUMO) E3 ligase and is a focal controller of Pi starvation-dependent responses. T-DNA insertional mutated alleles of AtSIZ1 (At5g60410) cause Arabidopsis to exhibit exaggerated prototypical Pi starvation responses, including cessation of primary root growth, extensive lateral root and root hair development, increase in root/shoot mass ratio, and greater anthocyanin accumulation, even though intracellular Pi levels in siz1 plants were similar to wild type. AtSIZ1 has SUMO E3 ligase activity in vitro, and immunoblot analysis revealed that the protein sumoylation profile is impaired in siz1 plants. AtSIZ1-GFP was localized to nuclear foci. Steadystate transcript abundances of Pi starvation-responsive genes AtPT2, AtPS2, and AtPS3 were moderate but clearly greater in siz1 seedlings than in wild type, where Pi is sufficient. Pi starvation induced the expression of these genes to the same extent in siz1 and wild-type seedlings. However, two other Pi starvation-responsive genes, AtIPS1 and AtRNS1, are induced more slowly in siz1 seedlings by Pi limitation. PHR1, a MYB transcriptional activator of AtIPS1 and AtRNS1, is an AtSIZ1 sumoylation target. These results indicate that AtSIZ1 is a SUMO E3 ligase and that sumoylation is a control mechanism that acts both negatively and positively on different Pi Deficiency responses.