Effects of SAG12-ipt expression on cytokinin production,growth and senescence of creeping bentgrass (<Emphasis Type="Italic">Agrostis stolonifera</Emphasis> L.) under heat stress

The study was conducted to determine the effects of expression of a transgene encoding adenine isopentenyl transferase (ipt), which controls cytokinin synthesis, on growth and leaf senescence of creeping bentgrass (Agrostis stolonifera L.), subjected to heat stress. Creeping bentgrass (cv. Penncross) was transformed with ipt ligated to a senescence-activated promoter (SAG12). Eight SAG12-ipt transgenic lines exhibiting desirable turf quality and a transgenic control line (transformed with the empty vector) were evaluated for morphological and physiological changes under normal growth temperature (20°C) and after 14 days of heat stress (35°C) in growth chambers. Six of the SAG12-ipt lines developed more tillers than the control line during establishment under normal growth temperature of 20°C. Following 14 days of heat stress, four of the SAG12-ipt lines had increased 65–83% of roots and for all six SAG12-ipt lines root elongation continued, whereas root production ceased and total root length decreased for the control line. Root isopentenyl adenine (iPA) content increased 2.5–3.5 times in five of the SAG12-ipt lines, whereas in the control line iPA decreased 20% after 14 days at 35°C. Total zeatin riboside (ZR) content was maintained at the original level or increased in five of the SAG12-ipt lines, whereas in the control line ZR decreased under heat stress. Our results suggest expression of SAG12-ipt in creeping bentgrass stimulated tiller formation and root production, and delayed leaf senescence under heat stress, suggesting a role for cytokinins in regulating cool-season grass tolerance to heat stress.     

Whole-plant carbon relations and root respiration associated with root tolerance to high soil temperature for Agrostis grasses

Plant tolerance to high soil temperature may be related to the adjustment in carbon production and utilization. The objective of this study was to determine changes in whole-plant carbon balance and root respiration rate in relation to root tolerance to high soil temperature for two Agrostis grass species varying in heat tolerance. Plant tolerance to high soil temperature was compared between Agrostis scabra, a thermal grass species adapted to chronic high-temperature soils in the geothermal areas in Yellowstone National Park, and creeping bentgrass (Agrostis stolonifera), a cultivated grass species adapted to cool climatic regions. Plant roots were exposed to low soil temperature (20 °C) or high soil temperature (37 °C) for 17 days in water baths placed in a controlled-environment growth chamber. Root biomass and cell membrane stability were determined to evaluate root thermotolerance of both species. Canopy photosynthetic rate (Pn), whole-plant respiration rate, root respiration rate, and total non-structural carbohydrate (TNC) content were measured to assess changes in carbon production and utilization in response to high soil temperature. Root biomass and cell membrane stability declined with increasing soil temperature, but the decline was much less for A. scabra than A. stolonifera, suggesting that roots of A. scabra were more tolerant to heat stress. Canopy Pn decreased and whole-plant respiration rate increased for A. stolonifera, but canopy Pn and respiration rate were unchanged for A. scabra in response to increasing soil temperature. After 17 days of high soil temperature treatment, A. stolonifera exhibited carbon deficit at the whole-plant level, whereas A. scabra maintained positive carbon gain. Root respiration of plants previously grown at 20 °C increased after a short-term treatment (24 h) at 37 °C, but the increase was significantly lower for A. scabra than for A. stolonifera. TNC content in roots did not show response to short-term (24 h) changes in temperature and did not exhibit species variations. Leaves of A. scabra, however, maintained TNC content under both low and high temperature regimes. Our results suggest that root thermotolerance of cool-season grasses could be related to the maintenance of positive whole-plant carbon balance, and down-regulation of whole-plant and root respiration rates in response to increasing soil temperature.     

Photosynthetic pigments,morphology and leaf gas exchange during ex vitro acclimatization of micropropagated CAM Doritaenopsis plantlets under relative humidity and air temperature

The effect of relative humidity (RH) and temperature on CO₂ assimilation (An), stomatal conductance (Sc), transpiration rate (Tr), chlorophyll content, fresh and dry weight, leaf length, leaf area, leaf width, formation of new root and survival rate have been assayed in Doritaenopsis in growth chamber after 1 month of acclimatization. Reduced growth was observed at below and above 25 °C whereas it was increased with increasing humidity. Relative water content (RWC) was decreased at 50% and 70% humidity after second day of transfer and recovered completely with the progression of acclimatization. RWC also reduced at high temperature but recovered slowly and a gradual decrease of RWC was observed at 15 °C. A visual symptom of severe leaf tip burn was observed at 50–70% humidity and at 35 °C during acclimatization. At 15 °C and 50% humidity sudden decrease of photosynthetic efficiency (F_v/F_m) was observed, which could not recover in temperature treated plantlets during acclimatization period. Chlorophyll content increased with increasing humidity and at 15 and 35 °C chlorophyll content was decreased compared to 25 °C. Chlorophyll a/b ratio was unchanged while total chlorophyll/carotenoids ratio was increased from low to high temperature. Exposure of plantlets to high temperature led to a noticeable decrease in An, Sc and Tr, and at 15 °C they were more decreased whereas significant differences were not observed in the parameters tested under humidity after 25 days of acclimatization. During daytime at 15 °C, increase in An, Sc and Tr indicates the plantlets adaptability in the new environment. The peroxidase activity remained unaffected in all humidity stress whereas low temperature increased the peroxidase activity compared to high temperature. These finding suggests that photosynthetic properties was greatly affected by air temperature conditions with a reduction of An, Sc and Tr at 15 and 35 °C compared to humidity stress that played a greater role in limiting photosynthesis.     

Low temperature induced floral abortion in chickpea: relationship to abscisic acid and cryoprotectants in reproductive organs

Cold stress (temperature <8 °C) during reproductive growth of chickpea is detrimental to flowering and pod set. Cold-sensitive genotypes either delay their flowering or abort their flowers produced during intermittent warm spells upon exposure to cold stress. To find out the mechanism of floral abortion in chickpea, a cold-sensitive genotype (PBG1) was grown under controlled (28 °C/12 °C) and cold-stressed conditions (12–15 °C/4–6 °C). Pod set was 95% in controlled conditions versus 20% under cold stress. The relative leaf water content (RLWC) of stressed plants was decreased by 26% over controls. The retained and aborted flowers harvested from the plants growing under cold stress along with flowers from control plants were examined for functioning of gametes, endogenous levels of ABA, sucrose, glucose, fructose, trehalose and proline in whole flowers, and their male (pollen, anthers) as well as female (stigma–style, ovary) parts. Flowers from stressed plants showed a decrease in functioning of gametes in comparison to those from control plants. The pollen germination (in vivo and in vitro) and viability did not differ significantly between the retained and aborted flowers of the stressed plants but stigma receptivity and ovary viability were significantly lower in aborted flowers. The ABA content in aborted flowers was 23% higher than in retained flowers. The content of sucrose, glucose and fructose in aborted flowers was 40, 25 and 23% lower, respectively, and the content of trehalose and proline was 50 and 73% lower, respectively, than in flowers on the plant. Male parts of aborted flowers contained 7–12% greater concentration of ABA and solutes than those retained on the mother plant but the female parts of the former, especially ovary contained 25% more ABA and 23–26% lower solute levels. Since the male parts of aborted flowers were relatively little affected by cold stress, the events in female parts appeared to be primarily responsible for floral abortion in chickpea. Reciprocal pollination between plants growing in controlled and stressed conditions indicated greater impairment of female parts than male parts under cold stress. Proline (5 mM) application to stressed plants improved the floral retention and pod set by 33%.     

Effect of high temperature on active oxygen species,senescence and photosynthetic properties in cucumber leaves

To gain a physiological understanding of the effects of high temperatures on cucumber (Cucumis sativus L.), we subjected seedlings to heat treatment at daytime temperatures of 28 °C, 32 °C, and 36 °C for 7 h a day for 30 days. The amount of active oxygen species, indicators of senescence, and photosynthetic properties in the second and third leaves were determined at the start of temperature treatment and on the 15th and 30th days of treatment. The amount of active oxygen species superoxide in leaves was greatest in the high temperature zones on the 15th day of treatment, and the amount of hydrogen peroxide was greatest in the high temperature zones on both the 15th and 30th days of treatment. The reduction in the amount of protein and the increase in the amount of malondialdehyde, both indicators of senescence, were greatest in the high temperature zones on both the 15th and 30th days of treatment, and the amount of chlorophyll was lowest in the 36 °C zone on the 15th day, and lower in the high temperature zones on the 30th day. It is clear from these results that a large amount of active oxygen species is generated and accumulated in the leaves at high temperatures, and senescence is significantly accelerated. The photosynthetic properties of stomatal conductance, sub-stomatal CO₂ concentration, and transpiration rate were at the same level on both the 15th and 30th days of treatment in all three temperature treatment zones. No significant difference was seen in the net photosynthesis rate between the 28 °C and 32 °C zones, was lower in the 36 °C zone than the 32 °C zone on the 15th day, and lowest in the 36 °C zone on the 30th day. CO₂ intake and water absorption are only mildly affected by high temperatures, and the reduction in net photosynthesis rate due to the 36 °C high temperature stress suggests that the large amount of active oxygen species induces inhibition of photosynthesis and damage to the mechanism of photosynthesis.     

Metabolite Responses to Exogenous Application of Nitrogen,Cytokinin, and Ethylene Inhibitors in Relation to Heat-Induced Senescence in Creeping Bentgrass

The exogenous application of ethylene inhibitors, cyotkinins, or nitrogen has previously been shown to suppress heat-induced senescence and improve heat tolerance in cool -season grasses. The objectives of this study were to examine metabolic profiles altered by exogenous treatment of creeping bentgrass with an ethylene inhibitor, cytokinin or nitrogen under heat stress and to determine metabolic pathways regulated by those compounds in association with their effectiveness for improving heat tolerance. Creeping bentgrass (Agostis stolonifera) plants (cv. Penncross) were foliar sprayed with 18 mM carbonyldiamide (N source), 25μM aminoethoxyvinylglycine (AVG, ethylene inhibitor), 25μM zeatin riboside (ZR, cytokinin), or a water control, and then exposed to 20/15°C (day/night) or 35/30°C (heat stress) in growth chambers. All three exogenous treatments suppressed leaf senescence, as manifested by increased turf quality and chlorophyll content, and reduced electrolyte leakage under heat stress. Polar metabolite profiling identified increases in the content of certain organic acids (i.e. citric and malic acid), sugar alcohols, disaccharides (sucrose), and decreased accumulations of monosaccharides (i.e. glucose and fructose) with exogenous treatment of N, AVG, or ZR at the previously mentioned concentrations when compared to the untreated control under heat stress. Nitrogen stimulated amino acid accumulation whereas AVG and ZR reduced amino acid accumulation compared to the untreated control under heat stress. These results revealed that the alleviation of heat-induced leaf senescence by N, AVG, and ZR could be due to changes in the accumulation of metabolites involved in osmoregulation, antioxidant metabolism, carbon and nitrogen metabolism, as well as stress signaling molecules.     

Salt stress response in tomato beyond the salinity tolerance threshold

Crop salt tolerance is generally assessed as the relative yield response to increasing root zone salinity, expressed as soil (EC_e) or irrigation water (EC_w) electrical conductivity. Alternatively, the dynamic process of salt accumulation into the shoot relative to the shoot biomass has also been considered as a tolerance index. These relationships are graphically represented by two intersecting linear regions, which identify (1) a specific threshold tolerance, at which yield begins to decrease, and (2) a declining region, which defines the yield reduction rate. Although the salinity threshold is intuitively a critical parameter for establishing plant salt tolerance, we focused our interest on physiological modifications that may occur in the plant at salinity higher than the so-called tolerance threshold. For this purpose, we exposed hydroponically grown tomato plants to eight different salinity levels (EC = 2.5 (non-salinized control); 4.2; 6.0; 7.8; 9.6; 11.4; 13.2; 15.0 dS m⁻¹). Based on biomass production, water relations, leaf ions accumulation, leaf and root abscisic acid and stomatal conductance measurements, we were able to identify a specific EC value (approximately 9.6 dS m⁻¹) at which a sharp increase of the shoot and root ABA levels coincided with (1) a decreased sensitivity of stomatal response to ABA; (2) a different partitioning of Na⁺ ions between young and mature leaves; (3) a remarkable increase of the root-to-shoot ratio. The specificity and functional significance of this response in salt stress adaptation is discussed.     

Germination characteristics of the grass weed Digitaria nuda (Schumach.)

The effect of various pre-treatments and their interaction with temperature on cumulative percentage and the rate of germination were evaluated for Digitaria nuda. Stored and fresh seeds were pre-treated with either 0.02 M KNO₃, soaked in water for 24 h (priming), sterilized with 0.5% NaOCl or heat treated at 60 °C. Seeds were germinated at constant temperatures of 25 and 30 °C and fluctuating temperature regimes of 25/10 and 30/15 °C. The effect of pre-chilling on germination of stored and fresh seed was evaluated at 30/15 °C, and seed emergence in two soil types at different burial depths (0, 0.5, 1, 2, 3, 4, 5 and 6 cm) was also determined. The pre-treatment of stored seed with KNO₃ resulted in the highest germination percentage (100%), whereas the pre-treatment of fresh seed with water for 24 h gave the best germination (99%), at constant temperatures of 25 and 30 °C. Pre-chilling of seed increased germination by more than 30%. Emergence from clay loam soil was greater compared with the emergence from sandy loam soil. Total seedling emergence decreased exponentially with increasing burial depths with only 5% of seed germinating from a burial depth of 6 cm. Results from this study showed that germination requirements are species specific and knowledge of factors influencing germination and emergence of grass weed seed can assist in predicting flushes in emergence allowing producers to implement control practices more effectively.     

Germination response and viability of an endangered tropical conifer Widdringtonia whytei seeds to temperature and light

The tropical conifer Widdringtonia whytei Rendle is an endangered species endemic to Mulanje Mountain in Malawi. A study was conducted for the first time under controlled conditions in order to assess the effects of temperature and light on germination and viability of W. whytei seeds. Seeds incubated at a constant temperature of 20 °C attained the highest cumulative germination percentage (100%) followed by 87% germination under fluctuating temperatures of 15 °C night/25 °C day. No seed germination occurred at temperatures below 15 °C. Seeds that failed to germinate at temperatures below 15 °C showed the highest (> 90%) viability compared to the seeds incubated at 25 °C (60%). Across temperature regimes, germination was significantly higher under light (44.7%) than dark (35.6%) conditions. It is concluded that temperature is one of the critical factors for germination of W. whytei seed. The ability of W. whytei seeds to germinate both in light and darkness implies that the species would unlikely form a persistent soil seed bank, an attribute which is common in species that survive in habitats frequently disturbed by fires.     

The effect of heat stress on intestinal integrity and Salmonella invasion in broiler birds

The intestinal mucosa works as a barrier to protect the internal environment of the animal from bacteria and bacterial toxins found in the gut lumen. Heat stress may harm this function. Therefore, we designed the current experiment to investigate the effect of heat stress on intestinal integrity, physiological and immunological responses and Salmonella invasion in broiler chickens. At 26 days of age, 72 birds were randomly distributed into 3 treatments, with 8 replicates per treatment and 3 birds per replicate. The three treatments were control treatment; kept at thermoneutral environmental conditions (20 ± 2 °C), chronic heat stress treatment (exposed to 30 ± 2 °C; 24 h/day) and acute heat stress treatment (exposed to 35 ±2 °C from 09:00 to 13:00 and kept at 20 ± 1 °C from 13:00 to 09:00). The heat stress exposure was conducted for 10 successive days. Compared with the control treatment, birds subject to chronic and acute heat stress had reduced (P < 0.05) body weight and body gain and increased (P < 0.05) feed conversion ratio. However, feed intake and mortality rate were only increased (P < 0.05) in the acute heat stress treatment. Rectal temperature and Δ rectal temperature (°C/h) increased (P < 0.05) sharply during the first 2 days of exposure followed by gradual decreases until a plateau was achieved. Heat-stressed birds had increased (P < 0.05) serum concentrations of corticosterone, endotoxin lipopolysaccharide and the systemic inflammatory cytokine: TNF-α and IL-2, as well as a higher (P < 0.05) prevalence of Salmonella spp. in meat and livers, as compared with control treatment. It can be concluded that heat stress impaired intestinal integrity which resulted in increased intestinal permeability to endotoxin, translocation of intestinal pathogens (Salmonella spp.) and serum inflammatory cytokines. Therefore, avoiding thermal dysfunction of intestinal barrier is a significant factor in maintaining welfare, immune status and meat safety of broiler birds.     

Carbon mineralization of Chinese fir (Cunninghamia lanceolata) soils under different temperature and humidity conditions

Burned and unburned mineral soils (0–10 cm) from a 40-year-old Chinese fir (Cunninghamia lanceolata) forest in Nanping, Fujian, China were incubated for 90 days at different temperatures (25 °C and 35 °C) and humidity [25%, 50%, and 75% of water holding capacity (WHC)] conditions. Carbon (C) mineralization of all soils was determined using CO₂ respiration method. The results showed that CO₂ evolution rates of the burned and control soils exhibited similar temporal patterns, and similar responses to temperature and moisture. CO₂ evolution rates for all soil samples decreased with incubation time. At different humidity conditions, average rate of C mineralization and cumulative mineralized C from burned and control soils were significantly higher at 35 °C than at 25 °C. This implied that C mineralization was less sensitive to soil moisture than to temperature. In both soils at 25 °C or 35 °C, the amount of soil evolved CO₂ over the 90 days incubation increased with increasing moisture content from 25% to 75% WHC. A temperature coefficient (Q₁₀) varied with soil moisture contents. The maximum values recorded for Q₁₀ were 1.7 in control soil and 1.6 in burned soil both at 25% WHC. However, there were no significant differences in Q₁₀ values between the control and burned soils over all moisture ranges (P > 0.05). The data of cumulative C–CO₂ released from control and burned soils were fitted to two different kinetic models. The two simultaneous reactions model described mineralization better than the first-order exponential model, which reflected the heterogeneity of substrate quality. Based on these results, it is possible to conclude that temperature and moisture are important in the controls of C mineralization, and the combined effects of these variables need to be considered to understand and predict the response of CO₂ release in subtropical ecosystems to climate change.     

Environmental indicators for estimating the potential soil respiration rate in alpine zone

Soil respiration is the main form of carbon flux from soil to atmosphere in the global carbon cycle. The effect of temperature on soil respiration rate is important in evaluating the potential feedback of soil organic carbon to global warming. We incubated soils from the alpine meadow zone and upper rocky zone along an altitudinal gradient (4400–5500 m a.s.l.) on the Tibetan Plateau under various temperature and soil moisture conditions. We evaluated the potential effects of temperature and soil moisture on soil respiration and its variation across altitudes. Soil respiration rates increased as the temperature increased. At 60% of soil water content, they averaged 0.21–5.33 μmol g soil⁻¹ day⁻¹ in the alpine meadow zone and 0.11–0.50 μmol g soil⁻¹ day⁻¹ in the rocky zone over the experimental temperature range. Soil respiration rates in the rocky zone did not increase between 25 and 35 °C, probably because of heat stress. Rates of decomposition of organic matter were high in the rocky zone, where the CN ratio was smaller than in the middle altitudes. Soil respiration rates also increased with increasing soil water content from 10% to 80% at 15 °C, averaging 0.04–2.00 μmol g soil⁻¹ day⁻¹ in the alpine meadow zone and 0.03–0.35 μmol g soil⁻¹ day⁻¹ in the rocky zone. Maximum respiration rates were obtained in the middle part of the alpine slope in any case of experimental temperature and soil moisture. The change patterns in soil respiration rate along altitude showed similar change pattern in soil carbon content. Although the altitude is a variable including various environmental factors, it might be used as a surrogate parameter of soil carbon content in alpine zone. Results suggest that temperature, soil moisture and altitude are used as appropriate environmental indicators for estimating the spatial distribution of potential soil respiration in alpine zone.     

Response to heat stress of populations of two Sphagnum species from alpine bogs at different altitudes

Sphagnum mosses are a fundamental component of bog vegetation in northern regions, where these plants play a major role in controlling important ecosystem processes. As heat waves are expected to become increasingly intense and frequent, especially in cold territories, it is important to improve our knowledge of heat resistance in Sphagnum species. We investigated the response to heat stress of S. fuscum and S. magellanicum. Three populations of the two species collected at different altitudes (1090 m, 1870 m and 2100 m) were grown at three daytime temperature levels: 25 °C (AT); 36 °C (MT); 43 °C (HT). The HT treatment decreased concentrations of chlorophyll and nitrogen in the plant tissues, which resulted in lower net CO₂ exchange rates and quantum yield of PS_II. The plants recovered significantly within six days, probably because temperature in the living tissue did not reach lethal thresholds because of the high water content in the plant tissues. Contrary to our main hypothesis, that S. magellanicum had greater resistance to high temperatures because of its more southern distribution, the two species showed much the same response patterns to heat stress. Supporting our second hypothesis, populations of both species originating from the highest site suffered somewhat stronger, although still reversible, damage when grown at HT. Heat stress brought about by heat waves will unlikely have differential effects on these two Sphagnum species. We also conclude that heat waves are unlikely to exert irreversible damage to the Sphagnum layer in bog ecosystems if high temperatures are not coupled with drought.     

Effects of heat stress on some reproductive parameters of male cavie (Cavia porcellus) and mitigation strategies using guava (Psidium guajava) leaves essential oil

Climate changes, particularly the increase of temperature are among the main causes behind the decline of fertility in humans as well as animals. In this study, the effects of heat stress on some reproductive parameters of male cavies and mitigation strategies using guava leaves essential oil (GLEO) were studied. For this purpose, 40 male cavies aged 2.5–3 months and weighing between 348 and 446 g were divided into 4 groups of 10 animals each and subjected to the following temperatures: Ambient temperature (20–25 °C) for the control group, 35 °C for group 1, 45 °C for group 2 and 45 °C+100 µl GLEO/kg body weight, administered by gavage to animals for group 3. Exposure time of heat was 7 h per day for 60 days. Results reveal that the relative weights of testes, epididymis, vas deferens and seminal vesicles were hardly affected by the temperature levels considered (P>0.05). The mass and individual sperm motility was significantly lower (P<0.05) in cavies exposed to the temperature of 35 and 45 °C as compared with those which received GLEO and controls. The percentages of abnormal sperm and altered sperm DNA were higher in animals exposed to temperature of 35 and 45 °C as compared with the controls. The activity of superoxide dismutase significantly increased (P<0.05) in animals exposed to temperature of 45 °C and in those of 45 °C and orally treated with GLEO, compared with cavies exposed to temperature of 45 °C without receiving GLEO. The level of malondialdehyde was significantly increased (P<0.05) in animals exposed to temperature of 35 and 45 °C, whereas the level of nitric oxide was significantly lower (P<0.05) in exposed animals as compared with controls. It was concluded that the exposure of male cavies at 35 and 45 °C for 60 days induce heat stress that causes deterioration of sperm characteristics. These effects that can be mitigated by the administration of guava leaves essential oil.     

Thermal analysis for differentiating between oleaginous and non-oleaginous microorganisms

The potential of thermal analysis for differentiating between oleaginous and non-oleaginous microorganisms was investigated using thermogravimetry (TG) and differential thermal analysis (DTA). The model oleaginous microorganisms used in the present study were the fungi, Mortierella alpina IFO32281 and Mortierella alliacea YN-15, the unicellular alga, Aurantiochytrium sp. CB 15-5, and the yeast, Rhodosporidium toruloides DMKU3-TK 16. Escherichia coli JM109, Rhodococcus opacus B-4, and Saccharomyces cerevisiae were used as the control non-oleaginous microorganisms. In simultaneous TG and DTA, the furnace temperature was linearly increased from 30 to 280 °C, decreased to 30 °C, linearly increased from 30 to 360 °C, and then isothermally held at 360 °C for 30 min. This two-step linear temperature program was effective in resolving overlapping exothermic peaks in the DTA curves in the temperature range from 280 to 360 °C. Heat evolved from a microbial sample was estimated from the area under the exothermic peak between 280 and 360 °C using indium as a standard material. There was a linear relationship between the exothermic heat and total lipid content of the tested microorganisms. Exothermic heat per dry sample mass (kJ/g) in the temperature range from 280 to 360 °C is a promising measure for differentiating between oleaginous and non-oleaginous microorganisms.     

Ability of bacterium Bacillus subtilis to produce cytokinins and to influence the growth and endogenous hormone content of lettuce plants

Hormone production by micro-organisms selected as antagonists of pathogenic fungi and the effect of their introduction into soil on hormone content and growth of lettuce plants were studied. Hormones in bacterial cultural media and in plant extracts were immunopurified and assayed using specific antibodies to indolyl-3-acetic acid (IAA), abscisic acid (ABA), and different cytokinins (zeatin riboside (ZR), dihydrozeatinriboside (DHZR) and isopentenyladenosine (iPA)). ZR was shown to be the main cytokinin present in bacterial cultural media as a complex with a high molecular weight component. Inoculation of lettuce plants with bacteria increased the cytokinin content of both shoots and roots. Accumulation of zeatin and its riboside was greatest in roots shortly 2days after inoculation, when their content was 10 times higher than in control. Changes in the content of other hormones (ABA and IAA) were observed at the end of experiments only. Accumulation of cytokinins in inoculated lettuce plants was associated with an increase in plant shoot and root weight of approximately 30% over 8days.     

Combined effects of temperature and salinity on functional responses of haemocytes and survival in air of the clam Ruditapes philippinarum

The combined effects of temperature and salinity on both immune responses and survival in air of the clam, Ruditapes philippinarum, were evaluated for the first time. The animals were kept for 7 days at three differing temperature (5 °C, 15 °C, 30 °C) and salinity values (18 psu, 28 psu, 38 psu), and effects of the resulting 9 experimental conditions on total haemocyte count (THC), Neutral Red uptake (NRU), haemolymph protein concentration, and lysozyme activity in both haemocyte lysate (HL) and cell-free haemolymph (CFH) were evaluated. The survival-in-air test was also performed. Two-way ANOVA analysis revealed that temperature influenced significantly THC and NRU, whereas salinity and temperature/salinity interaction affected NRU only. Temperature and salinity did not influence significantly HL and CFH lysozyme activity, as well as haemolymph total protein content. Survival-in-air test is widely used to evaluate general stress conditions in clams. In the present study, temperature and salinity were shown to influence the resistance to air exposure of R. philippinarum. The highest LT₅₀ (air exposure time resulting in 50% mortality) value was recorded in clams kept at 18 psu and 15 °C, whereas the lowest value was observed in clams kept at 28 psu and 30 °C. Overall, results obtained demonstrated that temperature and salinity can affect some functional responses of haemocytes from R. philippinarum, and suggested a better physiological condition for animals kept at 15 °C temperature and 18 psu salinity.     

Hormone Signals from Roots to Shoots of Sunflower (Helianthus annuus L.). Moderate Soil Drying Increases Delivery of Abscisic Acid and Depresses Delivery of Cytokinins in Xylem Sap

We quantified abscisic acid and a cytokinin trans zeatin ribosideas potential positive or negative signals in root to shoot communicationin sunflower plants (Helianthus annuus L.) growing in dryingsoil. Delivery rates rather than concentration values were usedbecause the former are less subject to change as a result ofdifferences in sap flow through dilution. ABA concentrationand delivery rate increased under the mild drought stress. Incontrast, t-ZR concentration did not change under mild stressalthough delivery rates decreased significantly. With more severedrought stress, both delivery rates and concentration of t-ZRdecreased considerably while ABA concentration and deliverywere enhanced markedly. Root ABA contents mirrored those ofxylem ABA. Helianthus annuus ; soil drying; root signals; ABA; cytokinins; delivery rate; delivery rate     

Temperature-dependent physiological and biochemical responses of the marine medaka Oryzias melastigma with consideration of both low and high thermal extremes

This study aimed to investigate temperature effect on physiological and biochemical responses of the marine medaka Oryzias melastigma larvae. The fish were subjected to a stepwise temperature change at a rate of 1 °C/h increasing or decreasing from 25 °C (the control) to six target temperatures (12, 13, 15, 20, 28 and 32 °C) respectively, followed by a 7-day thermal acclimation at each target temperature. The fish were fed ad libitum during the experiment. The results showed that cumulative mortalities were significantly increased at low temperatures (12 and 13 °C) and at the highest temperature (32 °C). For the survivors, their growth profile closely followed the left-skewed ‘thermal performance curve’. Routine oxygen consumption rates of fish larvae were significantly elevated at 32 °C but suppressed at 13 and 15 °C (due to a high mortality, larvae from 12 °C were not examined). Levels of heat shock proteins and activities of malate dehydrogenase and lactate dehydrogenase were also measured in fish larvae exposed at 15, 25 and 32 °C. The activities of both enzymes were significantly increased at both 15 and 32 °C, where the fish larvae probably suffered from thermal discomfort and increased anaerobic components so as to compensate the mismatch of energy demand and supply at these thermal extremes. Coincidently, heat shock proteins were also up-regulated at both 15 and 32 °C, enabling cellular protection. Moreover, the critical thermal maxima and minima of fish larvae increased significantly with increasing acclimation temperature, implying that the fish could develop some degrees of thermal tolerance through temperature acclimation.