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The present study evaluated, using a well-controlled dehydration protocol, the effects of 24 h fluid deprivation (FD) on selected mood and physiological parameters. In the present cross-over study, twenty healthy women (age 25 ( se 0·78) years) participated in two randomised sessions: FD-induced dehydration v . a fully hydrated control condition. In the FD period, the last water intake was between 18.00 and 19.00 hours and no beverages were allowed until 18.00 hours on the next day (23–24 h). Water intake was only permitted at fixed periods during the control condition. Physiological parameters in the urine, blood and saliva (osmolality) as well as mood and sensations (headache and thirst) were compared across the experimental conditions. Safety was monitored throughout the study. The FD protocol was effective as indicated by a significant reduction in urine output. No clinical abnormalities of biological parameters or vital signs were observed, although heart rate was increased by FD. Increased urine specific gravity, darker urine colour and increased thirst were early markers of dehydration. Interestingly, dehydration also induced a significant increase in saliva osmolality at the end of the 24 h FD period but plasma osmolality remained unchanged. The significant effects of FD on mood included decreased alertness and increased sleepiness, fatigue and confusion. The most consistent effects of mild dehydration on mood are on sleep/wake parameters. Urine specific gravity appears to be the best physiological measure of hydration status in subjects with a normal level of activity; saliva osmolality is another reliable and non-invasive method for assessing hydration status.

Studies have examined adding protein to carbohydrate–electrolyte rehydration drinks, but the effects of protein in isolation remain unknown. Ten subjects completed two trials in which they were dehydrated (~2 % of pre-exercise body mass) by intermittent cycling in the heat. Subjects then rehydrated (150 % total mass loss) over 1 h with mineral water (W) or mineral water plus 20 g L⁻¹whey protein isolate (WP) and remained in the laboratory for a further 4 h. Blood and urine samples were provided pre-exercise, post-exercise, post-rehydration and every hour thereafter. From blood samples, serum osmolality, change in plasma volume and plasma albumin content was determined, whilst the volume and osmolality of urine samples were determined. There was no difference between trials for total urine volume [W: 1,234 (358) mL; WP: 1,306 (268) mL; P = 0.409], drink retention [W: 40 (14) %; WP: 37 (14) %; P = 0.322] or net fluid balance [W: −605 (318) mL; WP: −660 (274) mL; P = 0.792] 4-h post-rehydration. Plasma volume was greater 3 and 4 h post-drinking during WP, and plasma albumin content relative to pre-exercise was increased 1–4 h post-drinking in WP only. These results suggest that addition of 20 g L⁻¹whey protein isolate neither enhances nor inhibits post-exercise rehydration, when a volume equivalent to 150 % of sweat losses is ingested in 1 h. As post-exercise nutritional requirements are multifactorial (rehydration, glycogen resynthesis, myofibrillar/mitochondrial protein synthesis), these data demonstrate that when post-exercise protein intake might benefit recovery or adaptation, this can be achieved without compromising rehydration.

A need exists to identify dehydrated individuals under stressful settings beyond the laboratory. A predictive index based on changes in saliva osmolality has been proposed, and its efficacy and sensitivity was appraised across mass (water) losses from 1 to 7%. Twelve euhydrated males [serum osmolality: 286.1 mOsm kg −1  H 2 O (SD 4.3)] completed three exercise- and heat-induced dehydration trials (35.6°C, 56% relative humidity): 7% dehydration (6.15 h), 3% dehydration (with 60% fluid replacement: 2.37 h), repeat 7% dehydration (5.27 h). Expectorated saliva osmolality, measured at baseline and at each 1% mass change, was used to predict instantaneous hydration state relative to mass losses of 3 and 6%. Saliva osmolality increased linearly with dehydration, although its basal osmolality and its rate of change varied among and within subjects across trials. Receiver operating characteristic curves indicated a good predictive power for saliva osmolality when used with two, single-threshold cutoffs to differentiate between hydrated and dehydrated individuals (area under curve: 3% cutoff = 0.868, 6% cutoff = 0.831). However, when analysed using a double-threshold detection technique (3 and 6%), as might be used in a field-based monitor, <50% of the osmolality data could correctly identify individuals who exceeded 3% dehydration. Indeed, within the 3–6% dehydration range, its sensitivity was 64%, while beyond 6% dehydration, this fell to 42%. Therefore, while expectorated saliva osmolality tracked mass losses within individuals, its large intra- and inter-individual variability limited its predictive power and sensitivity, rendering its utility questionable within a universal dehydration monitor.

Some athletes ingest pickle juice (PJ) or mustard to treat exercise-associated muscle cramps (EAMCs). Clinicians warn against this because they are concerned it will exacerbate exercise-induced hypertonicity or cause hyperkalemia. Few researchers have examined plasma responses after PJ or mustard ingestion in dehydrated, exercised individuals. To determine if ingesting PJ, mustard, or deionized water (DIW) while hypohydrated affects plasma sodium (Na(+)) concentration ([Na(+)]p), plasma potassium (K(+)) concentration ([K(+)]p), plasma osmolality (OSMp), or percentage changes in plasma volume or Na(+) content. Crossover study. Laboratory. A total of 9 physically active, nonacclimated individuals (age = 25 ± 2 years, height = 175.5 ± 9.0 cm, mass = 78.6 ± 13.8 kg). Participants exercised vigorously for 2 hours (temperature = 37°C ± 1°C, relative humidity = 24% ± 4%). After a 30-minute rest, a baseline blood sample was collected, and they ingested 1 mL/kg body mass of PJ or DIW. For the mustard trial, participants ingested a mass of mustard containing a similar amount of Na(+) as for the PJ trial. Postingestion blood samples were collected at 5, 15, 30, and 60 minutes. The dependent variables were [Na(+)]p, [K(+)]p, OSMp, and percentage change in plasma Na(+) content and plasma volume. Participants became 2.9% ± 0.6% hypohydrated and lost 96.8 ± 27.1 mmol (conventional unit = 96.8 ± 27.1 mEq) of Na(+), 8.4 ± 2 mmol (conventional unit = 8.4 ± 2 mEq) of K(+), and 2.03 ± 0.44 L of fluid due to exercise-induced sweating. They ingested approximately 79 mL of PJ or DIW or 135.24 ± 22.8 g of mustard. Despite ingesting approximately 1.5 g of Na(+) in the PJ and mustard trials, no changes occurred within 60 minutes postingestion for [Na(+)]p, [K(+)]p, OSMp, or percentage changes in plasma volume or Na(+) content (P > .05). Ingesting a small bolus of PJ or large mass of mustard after dehydration did not exacerbate exercise-induced hypertonicity or cause hyperkalemia. Consuming small volumes of PJ or mustard did not fully replenish electrolytes and fluid losses. Additional research on plasma responses pre-ingestion and postingestion to these treatments in individuals experiencing acute EAMCs is needed.

Stearns, RL, Casa, DJ, Lopez, RM, McDermott, BP, Ganio, MS, Decher, NR, Scruggs, IC, West, AE, Armstrong, LE, and Maresh, CM. Influence of hydration status on pacing during trail running in the heat. J Strength Cond Res 23(9)2533-2541, 2009-The purpose of this study was to determine the influence of hydration status on pacing of trail runners in the heat (wet bulb globe temperature = 26.2 ± 1.8°C). A randomized, crossover design was used and the participation occurred within a 2-week period. Seventeen competitive, well-trained distance runners (9 men, 8 women, age 27 ± 7 years, height 171 ± 9 cm, weight 64.2 ± 9.0 kg, body fat 14.6 ± 5.5%) completed the study. Subjects started maximum effort trials that were either hydrated (HYR) and dehydrated (DHR). Each trial subjects ran three 4-km loops with a 4-minute rest between loops. Significance was set at p ≤ 0.05. The DHR had a significantly greater body mass loss at the pre- and posttrial time points (−2.05 ± 1.25 and −4.3 ± 1.25%, respectively) vs. HYR (−0.79 ± 0.95 and −2.05 ± 1.09%, respectively). Subjects ran the 12 km faster (p < 0.001) in HYR (3,191 ± 366 seconds) vs. DHR (3,339 ± 450 seconds). Differences between fastest and slowest loops during HYR (54 ± 40 seconds) were significantly smaller than DHR (111 ± 93 seconds; p = 0.041). Additionally, loop times were slower for loop 1 (HYR 1,039 ± 116 seconds vs. DHR 1,071 ± 123 seconds; p = 0.028), loop 2 (HYR 1,066 ± 123 seconds vs. DHR 1,105 ± 148 seconds; p = 0.01) and loop 3 (HYR 1,081 ± 132 seconds vs. DHR 1,168 ± 189 seconds; p = 0.003) when dehydrated. Percent of the race completed by loop as calculated by finishing time was significantly different at loop 2 between HYR (33.6 ± 0.36%) and DHR (33.1 ± 0.35%, p = 0.002) and loop 3 (33.8 ± 0.75% vs. 34.9 ± 1.35%, respectively, p = 0.01). Total variation from the mean pace for the duration of the HYR compared to the DHR approached significance (p = 0.064). Average percent of variance approached significance between trials (p = 0.057). Differences between the fastest and slowest loops between trials demonstrated an increased ability for hydrated individuals to evenly pace themselves. While total variation from the mean pace was not significantly different, it could have practical applicability. These findings reveal that dehydration is associated with decreases in a runnersʼ ability to evenly pace themselves during a competitive situation.

Flavonoids are stress-inducible metabolites important for plant-microbe interactions. In contrast to their well-known function in initiating rhizobia nodulation in legumes, little is known about whether and how flavonoids may contribute to plant stress resistance through affecting non-nodulating bacteria. Here we show that flavonoids broadly contribute to the diversity of the Arabidopsis root microbiome and preferentially attract Aeromonadaceae , which included a cultivable Aeromonas sp. H1 that displayed flavonoid-induced chemotaxis with transcriptional enhancement of flagellum biogenesis and suppression of fumarate reduction for smooth swims. Strain H1 showed multiple plant-beneficial traits and enhanced plant dehydration resistance, which required flavonoids but not through a sudden “cry-for-help” upon stress. Strain H1 boosted dehydration-induced H 2 O 2 accumulation in guard cells and stomatal closure, concomitant with synergistic induction of jasmonic acid-related regulators of plant dehydration resistance. These findings revealed a key role of flavonoids, and the underlying mechanism, in mediating plant-microbiome interactions including the bacteria-enhanced plant dehydration resistance.

Four selected Amaranthus tricolor cultivars were grown under four irrigation regimes (25, 50, 80, and 100% field capacity) to evaluate the mechanisms of growth and physiological and biochemical responses against drought stress in randomized complete block design with three replications. Drought stress led to decrease in total biomass, specific leaf area, relative water content (RWC), photosynthetic pigments (chlorophyll a , chlorophyll b , chlorophyll ab ), and soluble protein and increase in MDA, H 2 O 2 , EL, proline, total carotenoid, ascorbic acid, polyphenols, flavonoids, and antioxidant activity. However, responses of these parameters were differential in respect to cultivars and the degree of drought stresses. No significant difference was observed in control and LDS for most of the traits. The cultivars VA14 and VA16 were identified as more tolerant to drought and could be used for further evaluations in future breeding programs and new cultivar release programs. Positively significant correlations among MDA, H 2 O 2 , compatible solutes, and non-enzymatic antioxidant (proline, TPC, TFC, and TAC) suggested that compatible solutes and non-enzymatic antioxidant played vital role in detoxifying of ROS in A. tricolor cultivar. The increased content of ascorbic acid indicated the crucial role of the ASC–GSH cycle for scavenging ROS in A. tricolor .

Abscisic acid (ABA) plays a key role in plant acclimation to abiotic stress. Although recent studies suggested that ABA could also be important for plant acclimation to a combination of abiotic stresses, its role in this response is currently unknown. Here we studied the response of mutants impaired in ABA signalling (abi1-1) and biosynthesis (aba1-1) to a combination of water deficit and heat stress. Both mutants displayed reduced growth, biomass, and survival when subjected to stress combination. Focusing on abi1-1, we found that although its stomata had an impaired response to water deficit, remaining significantly more open than wild type, its stomatal aperture was surprisingly reduced when subjected to the stress combination. Stomatal closure during stress combination in abi1-1 was accompanied by higher levels of H₂O₂ in leaves, suggesting that H₂O₂ might play a role in this response. In contrast to the almost wild-type stomatal closure phenotype of abi1-1 during stress combination, the accumulation of ascorbate peroxidase 1 and multiprotein bridging factor 1c proteins, required for acclimation to a combination of water deficit and heat stress, was significantly reduced in abi1-1. Our findings reveal a key function for ABA in regulating the accumulation of essential proteins during a combination of water deficit and heat stress.

As a resource allocation strategy, plant growth and defense responses are generally mutually antagonistic. Brassinosteroid (BR) regulates many aspects of plant development and stress responses, however, genetic evidence of its integrated effects on plant growth and stress tolerance is lacking. We overexpressed the Arabidopsis BR biosynthetic gene AtDWF4 in the oilseed plant Brassica napus and scored growth and stress response phenotypes. The transgenic B. napus plants, in comparison to wild type, displayed increased seed yield leading to increased overall oil content per plant, higher root biomass and root length, significantly better tolerance to dehydration and heat stress and enhanced resistance to necrotrophic fungal pathogens Leptosphaeria maculans and Sclerotinia sclerotiorum. Transcriptome analysis supported the integrated effects of BR on growth and stress responses; in addition to BR responses associated with growth, a predominant plant defense signature, likely mediated by BES1/BZR1, was evident in the transgenic plants. These results establish that BR can interactively and simultaneously enhance abiotic and biotic stress tolerance and plant productivity. The ability to confer pleiotropic beneficial effects that are associated with different agronomic traits suggests that BR–related genes may be important targets for simultaneously increasing plant productivity and performance under stress conditions.

Drought is one of the most important environmental factor limiting the growth of woody and non woody plants. In the present paper, we aimed to explore the performance of Maclura pomifera under a prolonged drought period followed by re-watering. M. pomifera plants were exposed to four different watering regimes (100%, 75%, 50% and 30% of the field capacity (FC)) for three weeks and then rewatered. The exposure to drought affected physiological, morphological and biochemical traits of M. pomifera . Leaf area, relative water content and water potential of leaf decreased in parallel with increased water deficit. Malondialdehyde content increased along with the drought stress experiment. Soluble carbohydrates (sucrose, glucose and fructose) accumulated during drought stress, but decreased after 22 days of water deficit in severe stressed plants (30% FC). Proline and mannitol, two compatible osmolytes, were higher in drought stresses plants than in control plants. Additionally the activity of antioxidant enzymes (SOD, APX, DHAR and GR) resulted affected by drought stress. In the recovery period, the physiological parameters as well as the proline content recovered at control levels, whereas soluble sugars, mannitol and total activity of antioxidant enzymes remained slight higher than in control plants, presumably to allow plants a complete recovery after stress. Our results suggest that M. pomifera has a good adaptive response to drought stress, probably corresponded to decreasing oxidative injury by induction of the antioxidant system and accumulation of stable and protective osmolytes such as proline and mannitol at higher rates.