Variations in mental performance under moderate cold stress

Effects of moderate cold stress on reasoning ability, associative learning and critical flicker frequncy of Indian subjects were studied by exposing them to 25C,. 20C, 15C and 10C for three hours. A second set of experiments was also conducted to confirm the conclusions of the first by using the same temperatures and duration of exposure. However, not only the sample used in the second case was larger and different but also the mental functions tested were numerical ability, running memory and mental alertness. It has been concluded that there is a significant impairment of simple cognitive functions at 15C which is 10C lower than their most comfortable temperature of 25C.     

Combined effect of virus infection and water stress on water flow and water economy in grapevines

Water limitation is one of the major threats affecting grapevine production. Thus, improving water‐use efficiency (WUE) is crucial for a sustainable viticulture industry in Mediterranean regions. Under field conditions, water stress (WS) is often combined with viral infections as those are present in major grape‐growing areas worldwide. Grapevine leafroll‐associated virus 3 (GLRaV‐3) is one of the most important viruses affecting grapevines. Indeed, the optimization of water use in a real context of virus infection is an important topic that needs to be understood. In this work, we have focused our attention on determining the interaction of biotic and abiotic stresses on WUE and hydraulic conductance (K_h) parameters in two white grapevine cultivars (Malvasia de Banyalbufar and Giró Ros). Under well‐watered (WW) conditions, virus infection provokes a strong reduction (P < 0.001) in K_petiole in both cultivars; however, K_leaf was only reduced in Malvasia de Banyalbufar. Moreover, the presence of virus also reduced whole‐plant hydraulic conductance (K_hplant) in 2013 and 2014 for Malvasia de Banyalbufar and in 2014 for Giró Ros. Thus, the effect of virus infection on water flow might explain the imposed stomatal limitation. Under WS conditions, the virus effect on K_plant was negligible, because of the bigger effect of WS than virus infection. Whole‐plant WUE (WUE_WP) was not affected by the presence of virus neither under WW nor under WS conditions, indicating that plants may adjust their physiology to counteract the virus infection by maintaining a tight stomatal control and by sustaining a balanced carbon change.     

A global analysis of plant recovery performance from water stress

Plant post‐drought recovery performance is essential to predict shifts in ecosystem dynamics and production during frequent climate change‐driven drought events. Yet, it is not clear how post‐drought recovery is related to evolutionary and geographic variations in plants. In this study, we generated a global data set of post‐drought recovery performance in 140 plant species from published studies. We quantified the plant post‐drought recovery performance by calculating a recovery index for multiple plant physiological and hydraulic parameters, including leaf water potential, net photosynthetic rate, leaf hydraulic conductance and shoot biomass. The magnitude of recovery among four plant functional types (deciduous angiosperms, evergreen angiosperms, gymnosperms, and crops), two plant growth forms (shrubs and trees), two water management strategies (isohydric and anisohydric), four xylem porosity types (diffuse, ring, semi‐ring and tracheid), and four major biomes (dry sclerophyll forest, boreal forest, temperate forest and tropical/subtropical forest) were compared. We found the inability to completely recover immediately after severe water stress is ubiquitous across all plant functional types and growth forms, while the rate and magnitude of post‐drought recovery varied greatly across different plant taxonomic categories and geographic ranges. In general, plant hydraulic architecture, leaf anatomy and physiology affect plants’ propensity towards recovery, and reflect evolutionary consequences of plant adaptation to their habitat. Due to the essential role of plant functional traits in regulating carbon storage in each biome, a better understanding plant post‐drought recovery performance could improve our predictions on ecosystem productivity in a rapidly changing climate.     

Wool cortisol is a better indicator of stress than blood cortisol in ewes exposed to heat stress and water restriction

This study investigated the effect of water restriction on wool and blood cortisol concentrations and water consumption patterns in heat-stressed sheep. Nine Corriedale female sheep (average BW=43±6.5 kg) were individually fed diets based on maintenance requirement in metabolic crates. They were assigned to three treatments according to a Latin square design (3×3) for three periods with a 21-day duration for each period (nine sheep per treatment). Treatments included free access to water (FAW), 2 h water restriction (2hWR) and 3 h water restriction (3hWR) after feeding. Average temperature–humidity index in the experimental room was 27.9 throughout the experiment that defines heat stress conditions. Wool samples were taken at the end of each period on day 21. No differences were found in cortisol concentration in each fragment (dried, washed and residual extract) of wool (P<0.05). Total wool cortisol concentration was higher in the 3hWR group than the other treatments (P<0.05). Blood cortisol was not different among the treatments (P>0.05) and resulted in higher variable data compared with wool cortisol. Blood neutrophils and neutrophil/lymphocyte ratio suppressed in FAW and 3hWR groups compared with the 2hWR group (P<0.05). The duration of water consumption recorded after feeding in the 3hWR group was higher than in the 2hWR group when recorded in the afternoon (P<0.01). Water consumption rate was higher in the 3hWR group than in the 2hWR group (P<0.01). However, total water consumed was lower in the 3hWR group compared with other treatments (P>0.05). It can be concluded that wool cortisol provides more precise and accurate data than blood cortisol during heat stress conditions. Water restriction for 3 h after feeding can act as a stressor and is critical for sheep during heat stress as the consumption of water decreases with restriction.     

Trait means predict performance under water limitation better than plasticity for seedlings of Poaceae species on the eastern Tibetan Plateau

Water availability may be altered by changes in precipitation under global climate change in alpine areas. Trait means and plasticity are important for plants in response to a changing environment. In an examination of alpine plant responses to changed water availability, and for determination of how trait means and plasticity predict the performance (e.g., biomass) of these species, seeds of ten Poaceae species from the eastern Tibetan Plateau were sown and grown in a manipulated environment during a growing season in which rainfall was removed and other climate conditions remained unchanged. Growth and leaf traits of these species were measured. We found significant effects of moderate water stress on the seedling biomass of these species; however, the responses of these species to changed water condition were strongly dependent on species identity. For example, the biomass of some species significantly decreased under moderate drought, whereas that of others were either significantly increased or unaffected. This pattern was also observed for growth and leaf traits. Overall, the alpine Poaceae species showed low plasticity of traits in response to water availability relative to reports from other areas . Notably, the results show that trait means were better correlated with the productivity than with the plasticity of traits; thus, we argue that the trait means were better predictors of performance than plasticity for alpine Poaceae species. Poaceae species in alpine areas are important for forage production and for water catchment health worldwide, and these species may face water shortage because of current and future climate change. Understanding the response of alpine Poaceae species to water availability would facilitate our ability to predict the impacts of climate change on the alpine vegetation.     

Study of the ionome and uptake fluxes in cherry tomato plants under moderate water stress conditions

Nutritional imbalance under water-deficit conditions depresses plant growth by affecting nutrient uptake, transport, and distribution. The present work analyses the variations in the foliar concentrations of macro- and micronutrients as well as the transport of these nutrients in five cherry tomato cultivars under well-watered and moderately water-stressed conditions with the aim of establishing whether the ionome of the plants is related to the degree of sensitivity or tolerance to this type of stress. The results show a general reduction in growth together with a lower concentrations and uptake both of macro- as well as micronutrients in all the cultivars studied, except for cv. Zarina, which showed better growth and increased in concentrations and uptake nitrogen, phosphorus, magnesium, potassium, and chloride with respect to control plants. In conclusion, in this work, our results suggest that a better understanding of the role of the mineral elements in plant resistance to drought could improve fertilization in arid and semi-arid regions in order to increase the tolerance of plants grown under these conditions.     

Physiological performance of two contrasting rice varieties under water stress

Two rice varieties PR-115 and Super-7 were imposed to water stress and different physiological traits were monitored to evaluate the performance of these varieties under drought. Under water stress condition although the relative water content, osmotic potential, chlorophyll content, photosynthesis rate, carbon discrimination and biomass decreased in both the varieties however, the reduction was more pronounced in Super-7 variety. Oryzanol a trans-ester of ferulic acid functions as antioxidant and it increased along with total phenolic and anthocyanin content in both the varieties under drought stress. However, gallic acid, 4 hydroxy benzoic acid, syringic acid and chlorogenic acid showed differential pattern in both of the varieties under water limiting conditions. Under drought, grain yield was penalized by 17 and 54% in PR-115 and Super-7 varieties, respectively in comparison to watered plants. Super-7 variety showed pronounced electrolyte leakage and MDA enhancement under water stress condition. High non photochemical quenching and reduction in Y(NO) and Y(II) indicated balanced energy management in tolerant PR-115 variety. The studies showed that PR-115 is a drought tolerant variety while Super-7 is drought sensitive in nature.     

Invasive species can handle higher leaf temperature under water stress than Mediterranean natives

Thermal tolerance of Photosystem II (PSII) highly influences plant distribution worldwide because it allows for photosynthesis during periods of high temperatures and water stress, which are common in most terrestrial ecosystems and particularly in dry and semi-arid ones. However, there is a lack of information about how this tolerance influences invasiveness of exotic species in ecosystems with seasonal drought. To address this question for Mediterranean-type ecosystems (MTE) of the Iberian Peninsula, we carried out an experiment with fifteen phylogenetically related species (8 invasive and 7 native, Pinus pinaster Ait., Pinus radiata D. Don, Schinus molle Linn., Elaeagnus angustifolia L., Eucalyptus globulus Labill., Acacia melanoxylon R. Br., Gleditsia triacanthos L., Pistacia terebinthus L., Rhamnus alaternus L., Anagyris foetida L., Colutea arborescens L., Oenothera biennis L., Epilobium hirsutum L., Achillea filipendulina Lam. and Achillea millefolium L). Seedlings were grown and maximal photochemical efficiency of PSII (Fv/Fm) was measured at two water availabilities (well-watered and with water stress). PSII thermal tolerance measurements were related to specific leaf area (SLA), which varied significantly across the study species, and to the mean potential evapotranspiration (PET) of the month with the lowest precipitation in the native areas of both groups and in the invaded area of the Iberian Peninsula. Additionally, PSII thermal tolerance measurements under water stress were phylogenetically explored. Invasive and native species neither differed in SLA nor in their thermal tolerance under well-watered conditions. For well-watered plants, SLA was significantly and positively related to PSII thermal tolerance when all species were explored together regardless of their invasive nature. However, this relationship did not persist under water stress and invasive species had higher plastic responses than Mediterranean natives resulting in higher leaf temperatures. Higher PSII thermal tolerance could explain invasiveness because it allows for longer periods of carbon acquisition under water stress. In fact, PSII thermal tolerance was positively related to the PET of the invaded and native areas of the Iberian Peninsula. PSII thermal tolerance was not related to PET at the native range of the invasive species, suggesting that successful invasive species were plastic enough to cope with novel dry conditions of the Iberian Peninsula. Moreover, our phylogenetic results indicate that future scenarios of increased aridity in MTE associated to climate change will filter invasion success by taxonomic identity. This study reveals the importance of studying ecophysiological traits to understand and better predict future biological invasions.     

Photoprotection processes under water stress and recovery in Mediterranean plants with different growth forms and leaf habits

The response of photoprotection mechanisms to a short-term water stress period followed by rewatering, to simulate common episodic water stress periods occurring in Mediterranean areas, was studied in 10 potted plants representative of different growth forms and leaf habits. During water stress and recovery, relative water content, stomatal conductance, leaf pigment composition, electron transport rates, maximum quantum efficiency of PSII photochemistry (F_v/F_m), thermal energy dissipation and photorespiration rates (P_r) were determined. All the species analyzed proved to be strongly resistant to photoinactivation of PSII under the imposed water stress conditions. The responses of the analyzed parameters did not differ largely among species, suggesting that Mediterranean plants have similar needs and capacity for photoprotection under episodic water stress periods regardless of their growth form and leaf habit. A general pattern of photoprotection emerged, consisting in maintenance or increase of P_r at mild stress and the increase of the thermal energy dissipation at more severe stress. Adjustments in pigment pool sizes were not an important short-term response to water stress. The increase of thermal energy dissipation because of water stress depended mostly on the de-epoxidation state of xanthophylls, although the slope and kinetics of such relationship strongly differed among species, suggesting species-dependent additional roles of de-epoxidated xanthophylls. Also, small decreases in F_v/F_m at predawn during water stress were strongly correlated with maintained de-epoxidation of the xanthophylls cycle, suggesting that a form of xanthophyll-dependent sustained photoprotection was developed during short-term water stress not only in evergreen but also in semideciduous and annual species.     

Photosynthetic electron transport and proton flux under moderate heat stress

Moderate heat stress has been reported to increase PSI cyclic electron flow (CEF). We subjected leaves of Arabidopsis (Arabidopsis thaliana) mutants disrupted in the regulation of one or the other pathway of CEF flow—crr2 (chlororespiratory reduction, deficient in regulation of chloroplast NAD(P)H dehydrogenase-dependent CEF) and pgr5 (proton gradient regulation, proposed to have reduced efficiency of antimycin-A-sensitive-CEF regulation) to moderate heat stress. Light-adapted leaves were switched from 23 to 40°C in 2 min. Gas exchange, chlorophyll fluorescence, the electrochromic shift (ECS), and P700 were measured. Photosynthesis of crr2 and pgr5 was more sensitive to heat and had less ability to recover than the genetic background gl. The proton conductance in light was increased by heat and it was twice as much in pgr5, which had much smaller light-induced proton motive force. We confirmed that P700 becomes more reduced at high temperature and show that, in contrast, the proportion of PSII open centers (with Q _A oxidized) increases. The two mutants had much slower P700⁺ reduction rate during and after heat than gl. The proportion of light absorbed by PSI versus PSII was increased in gl and crr2 during and after heat treatment, but not in pgr5. We propose that heat alters the redox balance away from PSII and toward PSI and that the regulation of CEF helps photosynthesis tolerate heat stress.     

Photosynthetic performance and water relations in young pubescent oak (Quercus pubescens) trees during drought stress and recovery

The capability to withstand and to recover from severe summer droughts is becoming an important issue for tree species in central Europe, as dry periods are predicted to occur more frequently over the coming decades. Changes in leaf gas exchange, chlorophyll a fluorescence and leaf compounds related to photoprotection were analysed in young Quercus pubescens trees under field conditions during two summers (2004 and 2005) of progressive drought and subsequent rewatering. Photochemistry was reversibly down-regulated and dissipation of excess energy was enhanced during the stress phase, while contents of leaf pigments and antioxidants were almost unaltered. Plant water status was restored immediately after rewatering. Net photosynthesis (P(n)) measured at ambient CO2 recovered from inhibition by drought within 4 wk. P(n) measured at elevated CO2--to overcome stomatal limitations--was restored after a few days. A network of photoprotective mechanisms acted in preserving the potential functionality of the photosynthetic apparatus during severe drought, leading to a rapid recovery of photosynthetic activity after rewatering. Thus, Q. pubescens seems to be capable of withstanding and surviving extreme drought events.     

Near isohydric grapevine cultivar displays higher photosynthetic efficiency and photorespiration rates under drought stress as compared with near anisohydric grapevine cultivar

Drought stress is known to limit photosynthesis rates and to inflict photo‐oxidative damage in grapevines. Grapevines, which are considered drought‐tolerant plants, are characterized by diverse hydraulic and photosynthetic behaviors, depending on the cultivar. This research compared the photosynthesis and the photorespiration of Cabernet Sauvignon (Cs) (isohydric) and Shiraz (anisohydric) in an attempt to acquire a wider perspective on the iso/anisohydric phenomenon and its implications. Shiraz and Cs were subjected to terminal drought in the greenhouse. Soil water content (θ), leaf water potential (Ψ_l) and stomata conductance (g_s) were measured to determine the cultivars' hydraulic behavior. Gas exchange and fluorometry measurements were taken at 21 and 2% O₂ to acquire photosynthesis and photorespiration characteristics. Cs was found to behave in a near isohydric manner whereas Shiraz behaved in a near anisohydric manner. Compared to Shiraz, the reduced stomata conductance values of Cs were accompanied by higher water use efficiency and photorespiration rates, as well as photosystem II photochemical potential (F_v/F_m). As compared with Shiraz, Cs compensated for lower stomata conductance by higher photosynthesis and photorespiration. These two processes contributed to higher electron flow rates that might have a role in photoinhibition avoidance, which was observed in the stability of F_v/F_m under drought stress.     

Plant water status and genotype affect fruit respiration in grapevines

An understanding of fruit gas exchange is necessary to determine the carbon balance in grapevines, but little attention has been paid to the relationships among fruit respiration, plant water status and genetic variability. The effect of plant water status and genotype on cluster respiration was studied over two seasons (2013 and 2014) under field conditions using a whole cluster respiration chamber. Whole cluster CO₂ fluxes were measured in growing grapevines at hard-green, veraison and ripening stages under irrigated and non-irrigated conditions, and under light and dark conditions in two grapevine varieties, Tempranillo and Grenache. A direct relationship between cluster CO₂ efflux and plant water status was found at hard-green stage. Genotype influenced the fruit CO₂ efflux that resulted in higher carbon losses in Tempranillo than in Grenache. Fruit respiration rates decreased from the first berry developmental stages to ripening stage. The integration of fruit respiration rates under light and dark conditions showed the magnitude of fruit carbon losses and gains as well as interesting variety and environmental conditions effects on those processes.     

Photosynthetic behaviour of Arabidopsis plants with a Cap Binding Protein 20 mutation under water stress

Under non-stressed conditions the net photosynthetic rate (P _N) of the mutant plants cbp20 of Arabidopsis was similar to that of the wild type (WT). In response to water deprivation, however, P _N started to decrease later in the mutants and remained substantially higher. Thermoluminescence measurements showed that the lipid peroxidation induced by severe water stress was also less pronounced in the mutant than in the WT. Both soil gravimetric and plant water potential data showed that cbp20 mutants lose water more slowly than the WT plants. The drought-induced decline in F_v/F_m, the quantum efficiency of photosystem 2, and photochemical quenching parameters also started later in the cbp20 mutants than in the WT plants. Thus the restricted gas exchange in the cbp20 mutants does not impair the photosynthetic performance of the plant; however, under drought improved water retention provides significant protection for the photosynthetic apparatus.     

Birth weight in an African-American population living under moderate ecologic stress

The African-American population of McNary, Arizona, resides at an altitude of 2200 m. The lengthy winters are typically quite cold; the monthly mean temperature from November to April is 1.8 degrees C. Data from 318 singleton full-term births of African-American babies from 1949 to 1972 show a mean weight of 3095 g (s.d. = 427 g). At birth 1.9% of the babies weighed at least 4 kg; 9.7% weighed less than 2.5 kg. These data suggest that altitude may have influenced birth weight in this sample. Significant patterns in birth weight exist for sex, parity, mother's age, and severity of the winter preceding the year of birth. The birth weight of female babies born following warm winters is significantly lighter than those born during years following cold winters. There are relatively fewer high-birth-weight babies, in comparison to other African-American populations. Birth weight is also significantly lighter than three other African-American samples, even though African-American mothers of McNary had full-term professional care. Birth weight of African-American babies born in McNary is consistent with the overwhelming African ancestry of the African-American population of McNary. Sex differences in birth weight of babies born following cold winters can be ascribed to gender-related hereditary or physiologic factors at the level of the fetus. Maternal inactivity during particularly cold winters may be a contributing factor.     

Hybridoma cell behaviour in continuous culture under hyperosmotic stress

In this paper, we propose an alternative strategy to the ones proposed before (Oh et al., 1993; Øyaas et al., 1994a) to get real increases of global final antibody titer and production at hyperosmotic stress, by reducing the detrimental effect of such a stress on cell growth, and conserving the stimulating effect on antibody production. It consists of cultivating the cells in continuous culture and increasing the osmolality stepwise. In this way, the cells could progressively adapt to the higher osmolality at each step and antibody titers could be nearly doubled at 370 and 400 mOsm kg-1, compared to the standard osmolality of 335 mOsm kg-1. Surprisingly, the stimulation of antibody production was not confirmed for higher osmolalities, 425 and 450 mOsm kg- 1, despite the minor negative effect on cell growth. Intracellular IgG analysis by flow cytometry revealed at these osmolalities a significant population of non-producing cells. However, even when taking into account this non-producing population, a stimulating effect on antibody production could not be shown at these highest osmolalities. It seems to us that osmolality has a significant effect on the appearance of these non-producing cells, since they were not observed in continuous cultures at standard osmolality, of comparable duration and at an even higher dilution rate. The appearance of the non-producing cells coincides furthermore with modifications of the synthesised antibody, as shown by electrophoretic techniques. It is however not really clear if these two observations reflect actually the same phenomenon. Hyperosmolality affects the cell behaviour in continuous culture in multiple ways, independently of the growth rate, counting all at least partially for the observed stimulation of antibody production: acceleration of the amino acid, and in particular the glutamine metabolism, increase of the cell volume, increase of the intracellular pH and accumulation of cells in the G1 cell cycle phase.