Drought Stress Response on Some Key Enzymes of Cowpea (<Emphasis Type="Italic">Vigna unguiculata</Emphasis> L. Walp.) Nodule Metabolism

A greenhouse experiment was carried out aiming to evaluate the response to drought stress of cowpea nodule enzymatic activities during different plant developmental stages leading to biological N₂ fixation. Stress was applied by controlling soil’s water-potential through a porous cup. Cowpea plants cv IPA 205 were grown in pots with yellow latosol soil under three different matric potential (ψ_m) treatments. Even with high evaporative demand and limited soil water availability, cowpea could not induce an extremely low leaf water potential (ψ_w). Sap ureides concentration in cowpea declined during the drought stress period. There was a decline in enzyme activity in the metabolic pathways concerned with N₂ fixation: NADH-dependent glutamate synthase (EC 1.4.1.14), glutamine synthetase (EC 6.3.1.2) and phosphoenolpyruvate carboxylase (EC 4.1.1.31). In contrast, an increase in glutamate dehydrogenase (EC 1.4.1.4) was observed as the ψ_m declined. Metabolism associated with N₂ assimilation was impaired every time that the ψ_w was reduced below −0.73 MPa as had happened in the stressed treatments. The stress applied by the porous cup was gradual and the plant recovered its turgor, avoiding permanent deleterious alterations in the cellular metabolism, even from a limited cowpea-growth ψ_m.     

Alleviation of water stress effects in cowpea by Bradyrhizobium spp. inoculation

Experiments were carried out to investigate the effects of different degrees of water stress on cowpea in the presence and absence of Bradyrhizobium spp. inoculation and to evaluate physiological responses to stress. The soil used was Yellow Latosol, pH 6.3 and the crop used was cowpea (Vigna unguiculata (L.) Walp.) cv. ‘IPA 204’. Stress was applied continuously by the control of matric potential (ψ _m ) through a porous cup. The lowered soil ψ _m had a direct effect on the N2 fixation, but the strains Bradyrhizobium introduced by inoculation in the cowpea plants were superior to the indigenous strain demonstrating the importance of inoculation in the stressed plants. At the more negative ψ _m plants inoculated with the strains EI 6 formed associations of greater symbiotic efficiency which helped the cowpea plants to withstand drought stress better than the strain BR 2001 and the uninoculated control. The leghaemoglobin concentration was not inhibited in the drought-stressed plants at ψ _m -70 kPa when inoculated with the strain EI 6, which confered a differential degree of drought resistance in plants. The ψ _w declined in the stressed plants reaching values of -1.0 MPa which was sufficient to cause disturbance in nodulation and biomass production. This revised version was published online in June 2006 with corrections to the Cover Date.     

Thermocouple psychrometer for measurements of water potential in plant tissues by isopiestic method

The paper describes a thermocouple psychrometer for measurements of water potential (ψ_w) and its components—osmotic potential (ψ_{s + m}) and turgor pressure (ψ_p)—in biological objects. The isopiestic method applied in this work does not require preliminary scarification of plant material for eliminating cuticular resistance to diffusion of water vapors. The device is reliable and simple in operation owing to an original design of replaceable plungers carrying the thermocouples. A modified construction of the lid for a thermocouple chamber and the application of a cryoholder excluded the necessity of removing the sample from the chamber after ψ_w measurements prior to its freezing in liquid nitrogen and subsequent thawing for determination of ψ_{s +m}. This feature improves the accuracy of determining ψ_p, which is calculated as ψ_w − ψ_{s + m}. The device can operate with minimal quantities of plant material and allows determination of all three components (ψ_w, ψ_{s + m}, ψ_p) for the same sample.     

Changes in the water status and rheological characteristics of pea seedling axillary buds during their transitions growth-dormancy-growth in apical dominance

The technique of isopiestic thermocouple psychrometry was used for the analysis of bud transition from dormancy to growth and back in 8-18-day-old pea (Pisum sativum L.) seedlings. We monitored changes in the water (ψ_w) and osmotic (ψ_{s + m}) potentials and also turgor pressure (ψ_p) in dormant buds and threshold turgor (Y) in growing buds, the latter being one of the cell-wall rheological characteristics. Seedling decapitation resulted in a decrease of Y in the bud, which coincided with the start of its outgrowth. The replacement of terminal shoot with exogenous auxin (IAA or NAA) retarded bud outgrowth and maintained the high level of Y, which argues for the auxin control of this parameter. When growth of the first axillary bud was inhibited by the second one, positioned higher and remained on the plant, the beginning of Y increase preceded visible correlative growth suppression; this makes this rheological index an early marker of bud transition from growth to dormancy. The effects of the terminal shoot part and auxin application on the bud osmotic status differed substantially. In fact, bud transition to dormancy in the presence of the terminal shoot, the main or developing from the second axillary bud, was accompanied by the rise in ψ_{s + m}, whereas, in the case of the replacement of the second bud with exogenous auxin, the first bud growth suppression occurred with the decrease in ψ_{s + m}. The low value of the bud ψ_{s + m} is a factor for creating a considerable gradient of the water potential between the stem and bud supporting water transport to the bud, which was much more active than in plants with a terminal shoot. It seems likely that this is the reason for the absence of complete growth suppression observed by us and other researchers even after application of high auxin concentrations. Immediately after seedling decapitation, ψ_{s + m} in the buds reduced; however, this was not the result of trophic metabolite redistribution due to the loss of their active sink because ψ_{s + m} reduced also in experiments with complete isolation of the bud releasing from dormancy in the chamber at 100% humidity. Auxin application to the cut surface of decapitated seedlings did not affect the ψ_{s + m} decrease. Like decapitation, cotyledon removal resulted in the increase in the bud turgor pressure. However, in this case, water stress did not change the bud osmotic status. Thus, the induction of osmotica accumulation in the bud after the removal of the terminal shoot is evidently related to neither trophic, nor auxin, nor hydraulic signal. The data obtained allowed us to conclude that both components of the bud water potential—ψ_{s + m} and Y—play an important role in the control of bud growth at apical dominance. Auxin produced in the shoot apex is involved in the control of Y, whereas the nature of the signal controlling the ψ_{s + m} level is unclear.     

Distinctive effects of cadmium on glucosinolate profiles in Cd hyperaccumulator Thlaspi praecox and non-hyperaccumulator Thlaspi arvense

We investigated the hypothesis that continuous water application allows favorable and steady water content and hydraulic conductivity in the root zone, thus enabling higher water potential in the soil–root interface (ψ_root). Elevated ψ_root increases transpiration (T) and prevents yield loss due to stomatal closure or to low root osmotic potential that develops in response to low ψ_root. We assume further, that the advantage of continuous water application is more pronounced for young plants, where water uptake per root length and competition on resources in the root system is higher. We investigated this hypothesis by examining the average water content of the root zone and T as a function of time for sunflowers grown under varied irrigation frequencies experimentally and in a modeled simulations, and by solving for the necessary effective root length and ψ_root for each case. High frequency water application was shown to positively affect root water uptake efficiency and yield, especially when plants were young. Irrigation frequency affected growth through the water content in the bulk soil (θ_soil) which in turn affects ψ_root. A low θ_soil and coupled low hydraulic conductivity decreased T and yield. Moreover, a decreased θ_soil caused low ψ_root, inefficient allocation of energy and carbohydrates and eventual yield loss. It was likely that these phenomena were more pronounced with young plants due to higher water uptake per root length.     

Can water responses in Stipa tenacissima L. during the summer season be promoted by non-rainfall water gains in soil?

This article reports on quantified soil water gains and their possible effects on summer water relationships in a semiarid Stipa tenacissima L. grasslands located in SE Spain. We believe that the net soil water gains detected using minilysimeters could be from soil water vapour adsorption (WVA). Our study of high water-stress showed stomatal conductance (21.8–43.1 mmol H₂O m⁻² s⁻¹) in S. tenacissima leaves unusual for the summer season, and the evapotranspiration from S. tenacissima grassland, estimated by a multi-source sparse evapotranspiration model, closely corresponding to total WVA. This highlights the importance of summer soil WVA to stomatal conductance and vital transpiration in S. tenacissima. This study measured pre-dawn leaf water potential (ψ) response to sporadic light rainfall, finding that a light summer rainfall (1.59 mm day⁻¹) was sufficient to vary ψ in S. tenacissima from −3.8 (close to the turgour loss point) to −2.7 MPa. We hypothesize that soil WVA can supply vegetation with water vital to its survival in seasons with a severe water deficit, giving rise to a close relationship between soil water dynamics and plant water response.     

Water potential and gas exchange did not reflect performance of Pinus radiata D. Don in an agroforestry system under conditions of soil-water deficit in a temperate environment

In order to understand how radiata pines respond to declining supply of soil-water in agroforestry systems, we monitored water potential in xylem (ψ _x ), osmotic potential (ψ) and relative water content (q) for fascicles at pre-dawn and at mid-day for 3-year-old trees that were raised from either seedlings (Seedling) or from tissue culture (TC3 and TC4), and grown either alone (Control) or over lucerne (Medicago sativa) pasture (Lucerne). Water relations at dawn were mostly similar for all the pines, except late in the season when ψ was lower, bulk turgor pressure (P), deduced as the difference between ψ _x and ψ, was higher, for TC3 than for the other two pines. At mid-day, Seedling often had higher ψ _x and ψ, but because of its poor osmotic adjustment (OA) had lower P, than either TC3 or TC4. The cell walls were more elastic in Seedling with modulus of elasticity (e) of 6.5 MPa compared with 8.1 MPa for both TC3 and TC4, while loss of turgor was estimated to occur at ψ _x of −1.45 MPa for Seedling, −1.38 MPa for TC3 and −1.35 MPa for TC4. All trees irrespective of their origin had higher ψ _x , P, CO₂ assimilation (A), and stomatal conductance (g _s ), but lower ψ, in Control than in Lucerne in which the soil profile was consistently drier. The trends in ψ _x , ψ, q and A did not reflect the known differences in dry weight of trees, P was in the order TC3 > TC4 > Seedling, consistent with previously reported tree weights. Both TC3 and TC4 had higher P, due to their larger OA, than Seedling, although the latter had higher A. Thus ψ _x and A that are routinely measured may not always adequately explain differences in growth amongst pines; it is advisable that ψ be determined to allow deductions of P be made when using water relations to analyse plant growth.     

Effects of water stress on gas exchange of field grown <Emphasis Type="Italic">Zea mays</Emphasis> L. in Southern Italy: an analysis at canopy and leaf level

Zea mays is cultivated in the Mediterranean regions where summer drought may lead to photoinhibition when irrigation is not available. In this work the response of maize to water stress was evaluated by gas exchange measurements at the canopy and leaf level. Leaf gas exchange was assessed before, during and after water stress, while canopy turbulent fluxes of mass and energy were performed on a continuous basis. In the early growth period, a linear increment of net ecosystem photosynthetic rate (P _NE) to incoming of photosynthetic photon flux density (PPFD) was found and net leaf photosynthetic rate (P _NL) showed the tendency to saturate under high irradiance. During water stress, the relationship between P _NE and PPFD became curvilinear and both P _NE and P _NL saturated in a range between 1,000 and 1,500 μmol (photons) m⁻² s⁻¹. Leaf water potential (ψ_l) dropped from −1.50 to −1.88 MPa during water stress, indicating that leaf and canopy gas exchanges were limited by stomatal conductance. With the restoration of irrigation, P _NE, P _NL and ψ_l showed a recovery, and P _NE and P _NL reached the highest values of whole study period. Leaf area index (LAI) reached a value of 3.0 m² m⁻². The relationship between P _NE and PPFD remained curvilinear and P _NE values were lower than those of a typical well-irrigated maize crop. The recovery in P _NE and P _NL after stress, and ψ_l values during stress indicate that the photosynthetic apparatus was not damaged while soil moisture stress after-effects resulted in a sub-optimal LAI values, which in turn depressed P _NE.     

Properties of peat-based casing soils and their influence on the water relations and growth of the mushroom (Agaricus bisporus)

Different combinations of peat and chalk or lime sources with differing moisture contents were used to determine how specific physical and chemical properties of the casing soil relate to the growth and water relations of the mushroom. The peat types varied in terms of decomposition and extraction method; the lime addition varied in terms of rate and type (chalk or sugar beet lime). During the colonisation of the casing soil before fruiting, the extension growth rate of mushroom mycelium was most closely correlated (negatively) with the volumetric moisture content of the casing soil. Scanning electron microscopy showed that mycelium growing at a lower casing soil matric potential (Ψ_m) had a much finer and branched structure than mycelium growing at a higher Ψ_m. Across all the peat and lime source treatments, a relationship was found between the mean Ψ_m of the casing soil and mushroom yield, with an optimum Ψ_m of -7.9 to -9.4 kPa. Mushrooms are produced in ‘flushes’ at about 8-day intervals and during the development of each flush of mushrooms, there was a significant decrease in casing soil Ψ_m . This decrease (to below -40 kPa) was greatest in the second flush, which was the highest yielding. There were no relationships between mushroom yield and casing soil osmotic potential Ψ_π within the range -93 to -154 kPa or any of the other chemical properties and water and air holding characteristics of the casing soils which were determined. Across different casing soil treatments, mushroom dry matter content was negatively correlated with mushroom yield and positively correlated with mushroom tissue osmotic potential. This revised version was published online in June 2006 with corrections to the Cover Date.     

The interaction of temperature, water availability and fire cues regulates seed germination in a fire-prone landscape

Ambient temperature and water availability regulate seasonal timing of germination. In fire-prone landscapes, the role of fire-related cues in affecting the range of temperatures and water potentials (ψs) across which germination can occur is poorly known, especially in non-Mediterranean landscapes. We examined interactive effects of temperature (15 or 25°C), ψ (0 to −0.9 MPa), and fire-related cues (heat and smoke) on germination for seeds of three shrub species from fire-prone southeastern Australia. Incubation temperature affected germination of untreated seeds of Kunzea ambigua and Kunzea capitata (Myrtaceae) (reduction at 25°C), but germination was uniformly low in Epacris obtusifolia (Ericaceae). Decreasing ψ reduced germination across both incubation temperatures. Fire cues increased germination at both incubation temperatures and across ψs, although in Kunzea the increase was smaller and occurred over a narrower range of ψs at 25°C. Hydrotime analysis suggested that fire cues reduced the amount of water necessary for germination of Kunzea seeds. Post-fire germination of the three study species may occur during the warm season, although it is reduced and confined to wet periods for the two Kunzea species. Warm season germination of the study species is consistent with a trade-off between the increased risk of failure of a cohort of seedlings, and benefits of early establishment of a cohort that may survive in an environment with aseasonal rainfall.     

A comparison of sap flux and water relations of leaves of various isolated trees with special reference to foundation movement in clay soil

Diurnal variation in sap flux (S) through stems of six trees, two each of Ulmus procera SALISB., Melaleuca styphelioides SM. and Prunus cerasifera EHRH. ‘Nigra’ (referred to hereafter by their generic names), were estimated from measurements of heat pulse velocities. Leaf water potential (ψ), stomatal conductance (g _s ) and transpiration from leaves (T) of all replicate trees were measured at 1300–1500h, once during the summer. On two separate occasions measurements were made of S, ψ, (g _s ) and T for one each of Ulmus and Melaleuca trees to study diurnal variations in these parameters. A 12×12 m² area around each tree was kept covered to simulate the condition of trees growing on pavements adjacent to residential properties. Sap flux for these tree species was in the order Melaleuca>Ulmus>Prunus. It is suggested that the smaller canopy and sapwood area in Prunus compared to the other two species is responsible for lower water potential and lower transpiration rate than the other species. Detailed analysis of the diurnal variation in sap flux and water relation of leaves of Melaleuca and Ulmus indicated sap flux of Melaleuca to be greater than that of Ulmus at the same transpiration rate per unit leaf area although the sapwood area of the two species was marginally different. This may have been due either to the difference in canopy conductance or in leaf area between the two species. With the assumption that sap flux closely resembles the rate of soil water extraction for both species, results indicate that Melaleuca is likely to extract soil water at a higher rate than Ulmus and hence is capable of causing greater shrinkage and soil movement than Ulmus.     

In situ separation of root hydraulic redistribution of soil water from liquid and vapor transport

Nocturnal increases in water potential (ψ) and water content (θ) in the upper soil profile are often attributed to root water efflux, a process termed hydraulic redistribution (HR). However, unsaturated liquid or vapor flux of water between soil layers independent of roots also contributes to the daily recovery in θ (Δθ), confounding efforts to determine the actual magnitude of HR. We estimated liquid (J _l) and vapor (J _v) soil water fluxes and their impacts on quantifying HR in a seasonally dry ponderosa pine (Pinus ponderosa) forest by applying existing datasets of ψ, θ and temperature (T) to soil water transport equations. As soil drying progressed, unsaturated hydraulic conductivity declined rapidly such that J _l was irrelevant (<2E−05 mm h⁻¹ at 0–60 cm depths) to total water flux by early August. Vapor flux was estimated to be the highest in upper soil (0–15 cm), driven by large T fluctuations, and confounded the role of HR, if any, in nocturnal θ dynamics. Within the 15–35 cm layer, J _v contributed up to 40% of hourly increases in nocturnal soil moisture. While both HR and net soil water flux between adjacent layers contribute to θ in the 15–65 cm soil layer, HR was the dominant process and accounted for at least 80% of the daily recovery in θ. The absolute magnitude of HR is not easily quantified, yet total diurnal fluctuations in upper soil water content can be quantified and modeled, and remain highly applicable for establishing the magnitude and temporal dynamics of total ecosystem water flux.     

Gas exchange in the salt marsh species <Emphasis Type="Italic">Atriplex portulacoides</Emphasis> L. and <Emphasis Type="Italic">Limoniastrum monopetalum</Emphasis> L. in Southern Portugal

Salt marshes are ecosystems subjected to a variety of environmental stresses like high salinity, water deficit, intense radiation or high temperatures. Field measurements were conduced in two halophyte species, Atriplex portulacoides L. and Limoniastrum monopetalum L., in the Reserva Natural do Sapal de Castro Marim, to compare their physiological response, i.e., water potential (ψ), net photosynthetic rate (A), stomatal conductance (gs) under natural conditions. Both species demonstrated marked variations in ψ throughout the year, with very low values in the summer, the period of higher salinity, drought and temperature. Deficit water potential (Δψ = ψ_midday − ψ_predawn) was lower in the summer than in other seasons in A. portulacoides but not in L. monopetalum. The highest values for A and gs in L. monopetalum were observed in autumn and for A. portulacoides in winter, presenting both lowest values in spring and summer. A_max was particularly high for L. monopetalum than for A. portulacoides in summer and autumn, despite gs_max was similar in both species. Diurnal pattern of A and gs were similar in both species, with higher values in the morning, decreasing throughout the day.     

Changes in spectral reflectance of a foliar lichen <Emphasis Type="Italic">Umbilicaria hirsuta</Emphasis> during desiccation

Water potential (ψ_w) and water saturation deficit (WSD), and several reflectance (R) indexes were assessed in an aerophytic lichen Umbilicaria hirsuta (Sw. ex Westr.) Hoffm. The water index (WI, R₉₀₀/_R970) and normalized difference vegetation index, NDVI [(R₉₀₀-R₆₈₀)/(R₉₀₀+R₆₈₀)] were strongly correlated both with the ψ_w and the WSD of lichen thalli. No significant changes during desiccation were found in structural independent pigment index, SIPI [(R₈₀₀-R₄₄₅)/(R₈₀₀-R₆₈₀)]. Sensitivity of the spectral detection of water status was rather small at high hydration level (WSD < 25 %, or ψ_w > −1 MPa), but this is not much limiting its value and potential use, because physiological processes in lichens are usually inhibited at much lower values of ψ_w than in leaves of vascular plants.     

Effects of Temperature and Water Potential on Germination, Radicle Elongation and Emergence of Mungbean

Controlled environment experiments were performed to determinethe effects of temperature and water potential on germination,radicle elongation and emergence of mungbean (Vigna radiata(L.) Wilczek cv. IPB-M79-17-79). The effects of a range of constant temperatures (15–45°C) and water potentials (0 to –2.2 MPa) on germinationand radicle elongation rates were studied using an osmoticumtechnique, in which seeds were held against a semi-permeablemembrane sac containing a polyethylene glycol solution. Linearrelationships were established between median germination time(Gt₅₀) and water potential at different temperatures, and betweenreciprocal Gt₅₀ (germination rate) and temperature at differentwater potentials. Germination occurred at potentials as lowas –2.2 MPa at favourable temperatures (30–40 °C),but was fastest at 40 °C when water was not limiting, withan estimated base temperature (T_b) of about 10 °C. Subsequentradicle elongation, however, was restricted to a slightly narrowertemperature range and was fastest at 35 °C. The conceptof thermal time was used to develop an equation to model thecombined effects of water potential and temperature on germination.Predictions made using this model were compared with the actualgermination obtained in a related series of experiments in columnsof soil. Some differences observed suggested the additionalimportance of the seed/soil/water contact zone in influencingseed germination in soil. Seedling emergence appeared to reflectfurther the radicle elongation results by occurring within anarrower range of temperatures and water potentials than germination.Emergence had an estimated T_b of 12.6 °C and was fastestat 35 °C. A soil matric potential of not less than about–0.5 MPa at sowing was required to obtain 50% or moreseedling emergence. Key words: Germination, temperature, water potential     

Predawn disequilibrium between plant and soil water potentials in two cold-desert shrubs

Classical water relations theory predicts that predawn plant water potential should be in equilibrium with soil water potential (soil Ψ_w) around roots, and many interpretations of plant water status in natural populations are based on this expectation. We examined this expectation for two salt-tolerant, cold-desert shrub species in glasshouse experiments where frequent watering assured homogeneity in soil Ψ_w and soil-root hydraulic continuity and where NaCl controlled soil Ψ_w. Plant water potentials were measured with a pressure chamber (xylem Ψ_p) and thermocouple psychrometers (leaf Ψ_w). Soil Ψ_w was measured with in situ thermocouple psychrometers. Predawn leaf Ψ_w and xylem Ψ_p were significantly more negative than soil Ψ_w, for many treatments, indicating large predawn soil-plant Ψ_w disequilibria: up to 1.2 MPa for Chrysothamnus nauseosus (0 and 100 mm NaCl) and 1.8 MPa for Sarcobatus vermiculatus (0, 100, 300, and 600 mm NaCl). Significant nighttime canopy water loss was one mechanism contributing to predawn disequilibrium, assessed by comparison of xylem Ψ_p for bagged (to minimize transpiration) and unbagged canopies, and by gas exchange measurements. However, nighttime transpiration accounted for only part of the predawn disequilibrium. Other mechanisms that could act with nighttime transpiration to generate large predawn disequilibria are described and include a model of how leaf apoplastic solutes could contribute to the phenomenon. This study is among the first to conclusively document such large departures from the expectation of predawn soil-plant equilibrium for C₃ shrubs, and provides a general framework for considering relative contributions of nighttime transpiration and other plant-related mechanisms to predawn disequilibrium. Received: 12 November 1998 / Accepted: 5 May 1999     

Evaluation of physiological screening tests for breeding drought resistant triticale (x <Emphasis Type="Italic">Triticosecale</Emphasis> wittmack)

Effects of soil drought on crop yield of 4 strains and 7 cultivars of spring triticale was investigated under field condition. The Drought Susceptibility Index (DSI) was evaluated in a two year experiment by the determination of grain loss in conditions of two soil moisture levels (drought-D and irrigated-IR). In the experiment response to drought was evaluated by different screening tests (leaf gaseous exchange, leaf water potential, chlorophyll content and fluorescence, leaf injury by drought and by simulated drought and heat temperature and water loss by excited leaf. The DSI values and the results of screening tests showed the genetic variation in the degree of drought tolerance. The values of DSI enabled the ranking of the tested triticale genotypes with respect to their drought tolerance and allow to divide them into three groups of drought susceptibility. Large differences among studied forms were observed also in changes of leaf water potential, fluorescence and leaf injury. For plants in vegetative stage of growth the tested breeding forms were easily separated into groups of different drought tolerance. Changes of ψ, Fv/Fm and LI as a screening tests were the most suitable techniques for estimation of degree of drought tolerance for triticale. Laboratory screening tests (leaf injury by simulated drought (LI_DS) and high temperature (LI_HT) and water loss (WL) of excited leaf conducted for nonstressed plants in most cases were significantly correlated with DSI. The statistically significant correlation between leaf water potential (ψ) was observed only with leaf fluorescence (Fv/Fm). Changes of Fv/Fm were significantly correlated with ψ, LI and LI_HT for 50 °C. Index of leaf injury (LI) by soil drought were significantly correlated with Fv/Fm, LI_DS (−1.0, −1.5 MPa), LI_HT (45 and 50°C) and water loss (WL). The correlation coefficient between the tests LI_DS and LI_HT were most of the considered cases statistically significant which indicate that the mechanism of membranes injury resulted from simulated drought or high temperature were similar in triticale. Water loss (WL) of excited leaves was the most suitable test for screening drought tolerance in triticale population. Changes of gaseous exchange parameters were not useful as screening test in this research.     

Protective Effects of the Synthetic Cannabinoids CP55,940 and JWH-015 on Rat Brain Mitochondria upon Paraquat Exposure

The effects of cannabinoids in mitochondria after acute oxidative stress insult are not fully established. We investigated the ability of CP55,940 and JWH-015 to scavenge reactive oxygen species and their effect on mitochondria permeability transition (MPT) in either a mitochondria-free superoxide anion generation system, intact rat brain mitochondria or in sub-mitochondrial particles (SMP) treated with paraquat (PQ). Oxygen consumption, mitochondrial membrane potential (Δψ_m) and MPT were determined as parameters of mitochondrial function. It is found that both cannabinoids effectively attenuate mitochondrial damage against PQ-induced oxidative stress by scavenging anion superoxide radical (O₂ ^∙−) and hydrogen peroxide (H₂O₂), maintaining Δψ_m and by avoiding Ca²⁺-induced mitochondrial swelling. Understanding the mechanistic action of cannabinoids on mitochondria might provide new insights into more effective therapeutic approaches for oxidative stress related disorders.     

Mitochondrial dysfunction in platelets and hippocampi of senescence-accelerated mice

Senescence-accelerated mice (SAM) strains are useful models to understand the mechanisms of age-dependent degeneration. In this study, measurements of the mitochondrial membrane potential (Δψ_m) of platelets and the Adenosine 5^′-triphosphate (ATP) content of hippocampi and platelets were made, and platelet mitochondria were observed in SAMP8 (faster aging mice) and SAMR1 (aging resistant control mice) at 2, 6 and 9 months of age. In addition, an Aβ-induced (Amyloid beta-protein) damage model of platelets was established. After the addition of Aβ, the Δψ_m of platelets of SAMP8 at 1and 6 months of age were measured. We found that platelet Δψ_m, and hippocampal and platelet ATP content of SAMP8 mice decreased at a relatively early age compared with SAMR1. The platelets of 6 month-old SAMP8 showed a tolerance to Aβ-induced damages. These results suggest that mitochondrial dysfunction might be one of the mechanisms leading to age-associated degeneration in SAMP mice at an early age and the platelets could serve as a biomarker for detection of mitochondrial function and age related disease.     

Several QTLs involved in osmotic-adjustment trait variation in barley (Hordeum vulgare L.)

 Osmotic adjustment (OA) was previously demonstrated to be an important adaptive mechanism of drought tolerance in cereals. In order to determine which genomic regions are involved in OA variation, 187 barley (Hordeum vulgare L.) recombinant inbred lines (RILs) derived from a cross between Tadmor (drought tolerant) and Er/Apm (susceptible) were studied in a growth chamber for their OA capacity (through correlated traits and by calculation), at an early growth stage and under two water treatments (soil moisture of 14% and 100% of field capacity). The continuous distribution of the traits and their broad-sense line heritabilities, ranging from 0.04 to 0.44, indicated that OA and related traits should have a polygenic nature. A subset of 167 RILs were also genotyped using 78 RFLP, 32 RAPD and three morphological markers and a linkage map was constructed. Despite strong environmental effects acting on the traits, interval mapping and single-marker ANOVA allowed the detection of three QTLs for relative water content (RWC), four QTLs for osmotic potential (ψ_π), two QTLs of osmotic potential at full turgor (ψ_π100) and one QTL for osmotic adjustment at a soil moisture of 14% field capacity. For the irrigated treatment, only two QTLs were detected: one for RWC and one for ψ_π100. Two chromosomal regions were involved in several OA-related trait variations and could be considered as regions controlling OA; these were present on chromosome 1 (7H) and chromosome 6 (6H), whereas other regions were specific for one trait. No major QTL was found. However, the genomic region involved in OA-related traits on chromosome 1 (7H) in barley seemed to be conserved for OA variation among cereals. Epistatic effects, with or without additive effects, acted on the traits. Received: 15 July 1997 / Accepted: 29 October 1997