Adaptation of cucurbit species to changes in substrate temperature: Root growth,antioxidants, and peroxidation

To investigate their response to changes in substrate temperatures, the roots from six species of cucurbit plants were exposed to 14°C, 24°C, or 34°C, while their aerial portions were maintained at natural ambient temperatures (23°C to 33°C). These species could be classified into three groups based on their stress response: Group A,Cucurbita ficifolia and C.maxima, heatsensitive but cold-tolerant; Group B,Cucumis sativus and C.melo, heat- and cold-sensitive; and Group C,Luffa cylindrica andBenincasa hispida, heat-tolerant but cold-sensitive. The highest growth rates and lowest contents of malondialdehyde (MDA) for plants in Groups A, B, and C were achieved at temperatures of 14°C, 24°C, and 24°C to 34°C, respectively. Superoxide dismutase (SOD) activity was lowest in the roots exposed to optimal growth temperatures while activities of catalase (CAT), ascorbate peroxidase (APX), and guaiacol peroxidase (G-POD) operated coordinately in a complicated manner to prevent the accumulation of reactive oxygen species (ROS) in the root cells. Moreover, all plants, regardless of species, responded to unfavorable temperatures by increasing their synthesis of ascorbate and glutathione as well as by reducing the redox ratio of those two important antioxidants.     

Cd induced changes in proline level and peroxidase activity in roots of rice seedlings

The effects of Cd on changes in proline level and peroxidase activity in roots of rice seedlings were investigated. CdCl₂ was effective in inhibiting root growth and in accumulating proline in roots. The inhibition of root growth by Cd is reversible. The reduction of root growth induced by Cd is closely associated with accumulation of proline in roots. External application of proline markedly inhibited root growth of rice seedlings in the absence of Cd. Ionically bound, but not soluble, peroxidase activity in roots was increased by CdCl₂. Proline treatment also resulted in an increase in ionically bound peroxidase activity in roots. The relationship between growth inhibition of roots induced by Cd and changes of proline level and peroxidase activity is discussed.Abbreviations POX peroxidase     

NaCl induced changes in ionically bound peroxidase activity in roots of rice seedlings

The changes in ionically bound peroxidase activity in roots of NaCl-stressed rice seedlings and their correlation with root growth were investigated. Increasing concentrations of NaCl from 50 to 150 mM progressively decreases root growth. The reduction of root growth by NaCl is closely correlated with the increase in ionically bound peroxidase activity. Since proline and ammonium accumulations are associated with root growth inhibition caused by NaCl, we determined the effects of proline or NH4Cl on root growth and ionically bound peroxidase activity in roots. External application of proline or NH4Cl markedly inhibited root growth and increased ionically bound peroxidase activity in roots of rice seedlings in the absence of NaCl. An increase in ionically bound peroxidase activity in roots preceded inhibition of root growth caused by NaCl, NH4Cl or proline. Mannitol inhibited root growth, but decreased rather than increased ionically bound peroxidase activity at the concentration iso-osmotic with NaCl. The inhibition of root growth and the increase in ionically bound peroxidase activity in roots by NaClis reversible and is associated with ionic rather than osmotic component. This revised version was published online in June 2006 with corrections to the Cover Date.     

Homeoviscous and functional adaptations of mitochondrial membranes to growth temperature in soybean seedlings

The present study investigated whether the cold‐sensitive character of soybean is reflected at the level of mitochondrial membranes. When exposed to an increase of temperature (from 25 to 35 °C), mitochondrial membranes were characterized by a higher phosphatidylcholine : phosphatidylethanolamine ratio and a lower content in 18 : 3 fatty acid. After a reduction of temperature (from 25 to 18 °C) the opposite changes were found. Lipid lateral diffusion and local microviscosity appeared to be comparable in mitochondria from plantlets grown at 25 or 35 °C when assayed at the respective growth temperatures. Some functional aspects (cytochrome c oxidase activity or membrane conductance) tended to this behaviour whereas others (respiration rate or maximum membrane potential) did not. On the other hand, membranes from plants grown at 18 °C were more rigid. Moreover, as illustrated by cytochrome c oxidase activity or respiration rate, functional measurements suggested that these membranes were less active at this temperature. Thus the dynamic characteristics and functional properties measured in mitochondrial membranes were in favour of an adaptive trend at 35 °C, but not at 18 °C despite changes in lipid composition, in accordance with the cold‐sensitive character of the plant.     

Differential temperature dependencies of antioxidative enzymes in two contrasting species: Fagus sylvatica and Coleus blumei

In order to characterise the sensitivity of antioxidative systems to temperature-induced oxidative stress, two species (Coleus blumei and Fagus sylvatica, L.) representative of environments with contrasting temperature characteristics have been exposed to low or high temperatures of 10 or 35 °C, respectively. Beech leaves were harvested in light and darkness. Coleus leaves were separated into green and white leaf tissue. The thermal dependencies of the activities of protective enzymes and chlorophyll fluorescence over a temperature range from 10 to 35 °C were determined. Ascorbate peroxidase activities were activated at low temperatures in vitro and, thereby, may provide an instantaneous protection against H₂O₂ accumulation which is faster than de novo synthesis. Monodehydroascorbate radical reductase was apparently not involved in short-term acclimation to low or high temperature. After short-term acclimation to low temperature, glutathione reductase and glutathione were more diminished in Coleus than in beech. Both species contained higher concentrations of ascorbate and glutathione at high temperatures than at low temperatures whereas glutathione reductase activity increased. Ascorbate peroxidase activity from Coleus leaves, though detectable under standard assay conditions (25 °C), failed at 35 °C in vitro. The results suggest that the higher temperature susceptibility of Coleus than that of beech was associated with a differential loss in glutathione reductase/glutathione at low temperature and an inhibition of ascorbate peroxidase at high temperature. Since the thermal dependencies of antioxidative enzymes were significantly affected by the preceding environmental conditions, the relative enzymatic activities determined under standard assay conditions may not be representative of enzymatic activities in foliage exposed to varying environmental temperatures.     

Root membrane thermostability of red maple cultivars

Nine red maple cultivars originating in different USDA hardiness zones were grown in containers in 1995 and 1996 prior to laboratory procedures to determine root cell membrane thermostability.Electrolyte leakage from excised root tissue exposed for 30 min to temperatures ranging from 20 to 63°C, was used to assess cellular injury of unsuberized, current season, fine roots.Electrolyte leakage was an effective means for measuring cell membrane thermostability in root tissue. The critical killing temperatures of root tissue of cultivars evaluated ranged from 52.0±0.8°C to 53.3±0.5°C, indicating minimal differences in root membrane thermostability.Critical temperatures for cultivars selected from the northern part of the native range did not differ from cultivars originating elsewhere.     

Effects of nitrogen supply and high temperature on the growth and physiology of the chickpea

Chickpeas were grown with or without nitrate nitrogen feeding, or nodulated with Rhizobium leguminosarum. High [40°C day, 25°C night (HT)] and moderate [25°C day, 177°C night (LT)] temperature regimes were employed during growth. Growth rates, photosynthetic capacity and enzymes of carbon and nitrogen metabolism were monitored to assess the acclimatory capacity of the chickpea. Initial growth rates were stimulated by high temperatures, particularly in nitrate-fed and nodulated plants. Older HT plants had fewer laterals, smaller leaves, and fewer flowers were produced than in LT plants. There was some indication of an acclimation of photosynthesis to high temperatures and this was independent of nitrogen supply. Rubisco activity was increased by high growth temperatures. However, HT plants also had higher transpiration rates and lower water use efficiency than LT plants both in respective growth conditions and when compared in a common condition. High temperatures reduced shoot nitrate reductase activity but had little effect on root activity, which was the same if not greater than activity in LT roots. The amino acid, asparagine, was found at high concentrations in all treatments. Concentrations were maintained throughout growth in HT plants but declined with age in LT plants.     

Arbuscular mycorrhiza colonization and development at suboptimal root zone temperature

Temperature has a strong influence on the activity of living organisms. This study, involving two indoor experiments, evaluated the effects of root zone temperature (10, 15 and 23°C) on the formation and development of arbuscular mycorrhizae (AM). In the first trial, greenhouse-grown sorghum [Sorghum bicolor (L.) Moench] was either colonized by Glomus intraradices Schenck & Smith or left non-mycorrhizal. Root length, root and shoot weight and root colonization were measured after 5, 10 and 15 weeks of plant growth. Although suboptimal root zone temperatures reduced growth in both mycorrhizal and non-mycorrhizal plants, mycorrhizal plants were larger than non-mycorrhizal plants after 15 weeks at 15 and 23°C. At suboptimal root zone temperatures, mycorrhizal inoculation sometimes slightly reduced root development. AM colonization was more affected than root growth at suboptimal root zone temperatures. Colonization was markedly reduced at 15°C compared with 23°C, and almost completely inhibited at 10°C. The second experiment was conducted in vitro using transformed carrot (Daucus carota L.) roots supporting G. intraradices. Mycelium length and spore number were measured weekly for 15 weeks. Spore metabolic activity (iodonitrotetrazolium reduction), root length and percentage root colonization were measured after 15 weeks. G. intraradices sporulation was reduced at temperatures below 23°C, while spore metabolic activity was significantly reduced only at 10°C. Root length and in particular percentage colonization were decreased at suboptimal temperatures. A negative interaction between AM hyphal growth and root growth resulting in reduced probability of contact at suboptimal root zone temperatures is proposed to explain the greater reduction observed in root colonization than in root and hyphal growth.     

Activity of enzymatic antioxidant defense systems in chilled and heat shocked cucumber seedling radicles

Chilling whole cucumber seedlings that had 10‐mm long radicles for 4 days at 2.5°C significantly inhibited subsequent radicle growth both by increasing the time it took the seedlings to recover from chilling and attain a linear rate of radicle growth, and by decreasing the subsequent rate of linear growth. Exposing cucumber seedlings to 45°C for up to 20 min had no effect on subsequent radicle growth, while longer exposures produced reductions in growth. A heat shock at 45°C for 10 min induced the optimal protection to 4 days of chilling at 2.5°C by reducing chilling inhibition from 60 to 42%. Two hours after being chilled, heat shocked or heat shocked and then chilled, there was no difference in protein content of the apical 1 cm of the seedling radicle among these treatments and the non‐heat shocked, non‐chilled control. Two days after treatment, the protein content was still similar in tissue that had been heat shocked or heat shocked and chilled, while it was significantly reduced in tissue that had been chilled. In general, 2 h after treatment, the activity of the 5 antioxidant enzymes examined in this study [superoxide dismutase (SOD; EC 1.15.1.1), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), guaiacol peroxidase (GPX; EC 1.11.1.7) and glutathione reductase (GR; EC 1.6.4.2)] were reduced by chilling and unaffected or increased by heat shock. When heat shock was followed by chilling, there was a consistent effect of the heat shock treatment on preventing the loss of enzyme activity following chilling. This protective effect of the heat shock treatment was even more pronounced after 2 days of recovery at 25°C for SOD, CAT and APX. In contrast, the activity of GR and GPX was substantially higher in chilled tissue than in tissue that had been heat shocked before being chilled. Elevated levels of GR and GPX therefore appear to be correlated with the development of chilling injury, while elevated levels of SOD, CAT and APX appear to be correlated with the development of heat shock‐induced chilling tolerance.     

Variation in growth attributes of contrasting populations of Trifolium repens

A range of growth attributes was measured in seedlings of 10 Trifolium repens populations, differing in leaf size and origin, grown in three temperature and two glasshouse environments. Growth rates of large leaf types of Mediterranean origin were higher than those of smaller leaf types at 10°C. However, the greater temperature response of the smaller leaf types resulted in higher growth rates for S.100 and S.184 than for a large leaf type from Israel at 20°C. The increase of growth rate with temperature was associated with changes in leaf area ratio and net assimilation rate between 10° and 15°C but only with changes in net assimilation rate between 15° and 20°C. Within each temperature environment, population differences in growth rate were related to differences in net assimilation rate rather than leaf expansion. At low temperature a greater proportion of dry matter was distributed to leaf tissue in large leaf types particularly those of Mediterranean origin but they showed a proportionately smaller increase in allocation to leaves with increasing temperature compared with small leaf types. In the glasshouse environments growth rates in spring were more than double those in the autumn. This difference was associated with net assimilation rates which were about five times greater in the spring environment. However, leaf area ratios in the spring were only half those in the autumn. These differences in leaf area ratio between the glasshouse environments were closely related to differences in specific leaf area but not to differences in distribution of dry matter to leaf tissue which was greater in the spring environment.     

Temperature effects on the reactive oxygen species formation and antioxidant defence in roots of two cucurbit species with contrasting root zone temperature optima

Suboptimal root zone temperature (14°C) was imposed on chilling-sensitive cucumber (Cucumis sativus L.) and chilling-tolerant figleaf gourd (Cucurbita ficifolia Bouché) plants. Exposure of roots to low temperature for up to 10 days caused a strong growth inhibition in cucumber compared with figleaf gourd. Physiological analysis showed that generation of reactive oxygen species (ROS) such as hydrogen peroxide and superoxide anion was significantly induced in cucumber plants as fast as 1 day after low root zone temperature treatment. In addition to the significant induction of antioxidant superoxide dismutase activity, low root zone temperature also increased the mitochondrial electron transport allocated to alternative pathway while decreased cytochrome pathway salicylhydroxamic acid-resistant respiration. However, these defense responses could not compensate for the ROS production, resulting in membrane lipid peroxidation and loss of root cell viability in the low root zone temperature treated cucumber roots. In contrast, 14°C root zone temperature had no significant effects on figleaf gourd plant growth, antioxidant enzymes, ROS levels and alternative respiratory pathway. Hence, difference in ROS metabolism would be associated with the remarkable difference in adaptability of cucumber and figleaf gourd plants in response to suboptimal root zone temperature condition.     

Temperature-dependent growth and emergence of functional leaves: an adaptive mechanism in the seedlings of the western Himalayan plant Podophyllum hexandrum

As an adaptive mechanism, hypocotyl dormancy delays emergence of functional leaf until favorable season of growth in Podophyllum hexandrum, an endangered medicinal plant of the western Himalayas. However, upon exposure of the freshly germinated seedlings to favorable temperature (25°C), functional leaves emerged within 20 days. Therefore, we examined regulation mechanisms of growth and development of this alpine plant by temperature under laboratory conditions. The seedlings were exposed to (1) 25°C (temperature prevailing at the time of maximum vegetative growth), (2) 4°C (mean temperature at the onset of winter in its natural habitat), and (3) 10°C (an intermediate temperature). Slackened growth at 4°C was followed by senescence of aerial parts and quiescence of roots and predetermined leaf primordia. Rapid development of leaf primordia at 25°C was associated with increased starch hydrolysis. This was evident from higher α-amylase activity and reducing sugars. These parameters decreased on sudden exposure to 4°C. In contrast, the roots (perennating organs) showed a slight increase (1.36-fold) in α-amylase activity. Growth and development in seedlings growing at 10°C (temperature less adverse than 4°C) were comparatively faster. The content of reducing sugars and α-amylase activity were also higher in all the seedling parts at 10°C as compared to 4°C. This indicated larger requirements for sugar by the seedlings at 10°C. Irrespective of temperature, maximum changes in nitrate and nitrate reductase occurred during the initial 10 days, i.e., when the readily available form of sugars (reducing sugar) was highest. This indicated that a temperature-dependent availability of carbon, but not temperature itself, was an important regulator of uptake and reduction of nitrogen. IHBT Publication number 508a.     

Acclimatization of K+ uptake to changes in root temperature: experiments with oilseed rape and barley in flowing solution culture

Abstract Changes in the net uptake rate of K⁺ and in the average tissue concentration of K⁺ were measured over 14 d in response to changes in root temperature with oilseed rape (Brassica napus L. cv. Bien venu) and barley (Hordeum vulgare L. cv. Atem). Plants were grown in flowing nutrient solutions containing 2.5 mmol m^?3 K⁺ and were acclimatized over 49 d (rape) or 28 d (barley) to low root temperature (5°C) prior to steady–state treatments at root temperatures between 3 °C and 25 °C, with common air temperature. Uptake of K⁺ was monitored continuously over 14 d and nitrogen was supplied as NH₄⁺+ NO^?₃ or NH⁺₄ or NO^?₃. Unit absorption rates of K⁺ increased with time and with root temperature up to Day 4 or 5 following the change in root temperature. Thereafter they usually approached steady-state, with Q₁₀? 2.0 between 7 °C and 17°C, although rates became similar between 7 °C and 13°C. Uptake of K⁺ by rape plants was invariably greater under NO^?₃ nutrition compared with NH⁺₄. The percentage K⁺ in the plant dry matter increased with temperature from 2% at 3 °C to 4% at 25 °C in rape, but there was less effect of temperature on the average concentrations of K⁺ in the plant fresh weight or plant water content. Concentrations of K⁺ in the leaf water fraction of rape plants decreased with increasing root temperature, but in barley they increased with increasing root temperature. Concentrations of K⁺ in the root water fraction were relatively stable with respect to root temperature. The results are discussed in terms of compensatory changes in K⁺ uptake following a change in root temperature and the relationships between growth, shoot: root ratio and K⁺ composition of the plant.     

Effects of temperature on growth and efficiency of food utilization in fifth-instar caterpillars of the tobacco hornworm, Manduca sexta

Fifth-instar larvae of Manduca sexta were reared from hatching on artificial diet at 15, 20, 25, 30 and 35°C. Total development time decreased with increasing temperature. Very few larvae (12%) survived at 15°C, so this temperature was not considered further. There was some mortality at 30°C (11%), and at 35°C (50%).The absolute rate of growth in the fifth instar was faster at 25 than at 20°C, but was similar at 25, 30 and 35°C. This was true both for caterpillars that were chronically exposed to experimental temperatures (i.e. since hatching) and for those acutely exposed (i.e. reared up to fifth instar at 25°C).There was a progressive decrease with higher rearing temperatures in both the initial and final sizes of chronically exposed fifth-instar larvae. Acutely exposed caterpillars matched for initial size showed smaller temperature related differences in final size. Because of these size differences there were differences in relative growth rate which did not reflect true differences in absolute growth rate.Total food consumed by chronically exposed caterpillars was greatest at the lowest temperature (20°C), and decreased progressively with increasing temperature. The absolute rate of food consumption increased from 20 to 25°C, but did not vary significantly between 25 and 35°C. Differences in the sizes of the insects at the different temperatures meant that there were differences among relative measures of consumption that did not reflect absolute food consumption.For chronically exposed caterpillars, none of the three usual indices of food conversion efficiency (AD, ECI and ECD) varied significantly with temperature between 20 and 35°C. This implies that the effects of temperature on metabolic costs are closely matched to food consumption.Oxygen consumption increased with temperature between 20 and 25°C but was temperature compensated between 25 and 35°C.These findings are discussed in terms of their implications for the optimal temperature for growth in Manduca.     

Heat-stress induced inhibition in growth and chlorosis in mungbean (<Emphasis Type="Italic">Phaseolus aureus</Emphasis> Roxb.) is partly mitigated by ascorbic acid application and is related to reduction in oxidative stress

The rising temperatures (>35°C) are proving detrimental to summer-sown mungbean genotypes that experience inhibition of vegetative and reproductive growth. In the present study, the mungbean plants growing hydroponically at varying temperatures of 30/20°C (control), 35/25, 40/30, and 45/35°C (as day/night 12 h/12 h) with (50 μM) or without ascorbic acid (ASC) were investigated for effects on growth, membrane damage, chlorophyll loss, leaf water status, components of oxidative stress, and antioxidants. The ASC-treated plants showed significant improvement in germination and seedling growth especially at 40/30 and 45/35°C. The damage to membranes, loss of water, decrease in cellular respiration, and chlorophyll were significantly prevented by ASC treatment to plants growing at these temperatures. The oxidative stress measured as malondialdehyde and hydrogen peroxide content was observed to be significantly lower at high temperatures with ASC application. The activities of superoxide dismutase, catalase, ascorbate peroxidase, and glutathione reductase increased at 40/30°C but decreased at 45/35°C in the absence of ASC while with its application, the activities of these enzymes were appreciably resorted. Among all the antioxidants, the endogenous ASC content decreased to the greatest extent at 45/35°C grown plants indicating its vital role in affecting the response of mungbean to heat stress. Exogenously applied ASC raised its endogenous content along with that of glutathione and proline at 45/35°C. The findings indicated that heat stress-induced inhibition in growth and chlorosis was associated with decrease in leaf water status and elevation of oxidative stress, which could partly be prevented by exogenous application of ASC. Its role in imparting protection against heat stress is discussed.     

Peroxidases in Relation to Removal of Dormancy and Germination of Apple Embryos

The changes in germination, peroxidase activity and isoperoxidase spectrum have been studied in apple embryos at 5°C (stratification) and at 20°C in the presence or absence of seed coats. The embryo dormancy is progressively released at 5°C, but not at 20°C. The peroxidase activity in embryos covered with seed coats is very low at 5°C as well as at 20°C which corresponds to a restricted number of isoenzymes. In isolated embryos the peroxidase activity increases significantly. This is due to an increase in both the number and the activity of the isoperoxidases and it is more pronounced at 20°C than at 5°C. The obtained results suggest that the soluble peroxidases are not involved in the process of the release of embryo dormancy. The variations observed are attributed to the growth process following germination, which can occur even at low temperature.     

Effects of temperature and photoperiod on thermogenesis in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus)

We examined the effects of temperature and photoperiod on metabolic thermogenesis and the thermogenic characteristics of brown adipose tissue in plateau pikas (Ochotona curzoniae) and root voles (Microtus oeconomus), the dominant species of small mammals in the alpine meadow ecosystems on the Qinghai-Tibetan Plateau. Pikas and voles were acclimated in the following groups: (1) Long day – warm temperature (16L:8D, 23 °C), (2) Long day – cold temperature (16L:8D, 5 °C), (3) short day – warm temperature (8L:16D, 23 °C), and (4) short day – cold temperature (8L:16D, 5 °C). Both temperature and photoperiod were important environmental cues for changes in thermogenesis for both species. Low temperature and short photoperiod induced increases in metabolic rate, nonshivering thermogenesis (NST), mitochondrial protein contents of brown adipose tissue, and cytochrome C oxidase activity of brown adipose tissue mitochondria in both species. Plateau pikas were more sensitive to cold (79% of the total NST response) than to short photoperiod (21%), while root voles were more sensitive to short photoperiod (60% of the total NST response) than to cold (40%), although cold clearly enhanced thermogenesis. Their thermogenic characteristics correlated with their preferred habitats: plateau pikas are found mainly in more exposed microhabitats in open sunny meadow, while root voles live in more sheltered microhabitats in relatively closed shrub. Our results also showed that temperature and photoperiod combined induce thermogenic adjustments in both species in seasonal acclimatization in their alpine meadow macrohabitat. Accepted: 10 November 1998     

Ribonuclease activity in roots of soybean seedlings subjected to chilling stress and recovery

Many developmental and physiological changes, including alterations of enzyme activities, occur in plants under low temperature stress. In this study the total ribonuclease activity was determined in crude extracts from root tips of soybean seedlings germinated at 25 °C, subjected to chilling conditions (10°C) and recovered at optimal temperature (25°C). Measurements of RNase activity were performed every 24 hours starting from the third to the 10-th day of growth. We found that chilling caused a considerable increase in ribonuclease activity (in comparison with the control), with an activity peak on the fourth day of the cold treatment. The enzyme activity in root extracts of the plants recovered after cold stress decreased along with the time of recovery. No differences were found in approximate molecular weight (35 kDa) and pH optimum (6.0) for ribonucleases extracted from control and chilled soybean roots.     

Further Studies on Factors Affecting the Efflux of Betacyanin from Beet Root: A Note on Thermal Effects

As judged by betacyanin efflux, beet root tissue differs in stability toward O₂ at low and high temperatures (45–60°C and 60–100°C respectively). The effect of temperature itself can he divided into a high activation energy (93 Kcal mol^?1) process in the lower temperature range and a low activation energy process (19 Kcal mor^?1) in the higher range (> 60°C). From these data it is suggested that initially, elevating temperatures bring about reversible conformational changes in the membrane. With continuing increase in temperature in the presence of O₂, membrane chemical groups susceptible to oxidation are exposed and, upon oxidation, render conformational changes irreversible.