Fatty acid composition of microsomal phospholipids and H+-ATPase activity in the roots of Scots pine seedlings grown at different root temperatures during flushing

The fatty acid composition of phospholipids in the microsomesand the vanadate-sensitive H⁺-ATPase activity of the roots ofone-year-old Scots pine (Pinus sylvestris L.) seedlings werestudied during flushing in spring. The seedlings in hydroponiccultures were subjected to different root temperatures (5, 12or 20°C). The shoot was maintained at 20/15° C (day/night)during the 35 d experiment. After 35 d at 5° C, root growthwas totally inhibited and shoot growth partly inhibited. In roots grown at 5° C the fatty acid composition of themicrosomal phospholipids and the degree of fatty acid unsaturation(bond index) were unchanged, while in roots grown at 12 and20° C the fatty acid composition changed and bond indexdecreased. At those root temperatures, the most obvious changewas a decline in the proportion of linolenic acid (C18:3). Inthe new white roots grown either at 12°C or 20°C theproportion of C18:2 was higher and the proportion of C18:3 lowerthan in 1-year-old roots. Independently of root temperature,H⁺-ATPase activity, determined on a fresh weight basis, declinedto half of the original activity during the experiment. Thedecline in H⁺ -ATPase activity was most rapid during the firstweek. In the old roots the decline in H⁺-ATPase activity followedclosely the decline in amount of membrane protein. In new rootsH⁺-ATPase activity was high and increased with increasing roottemperature. These results suggest that in the roots of Scotspine seedlings, vanadate-sensitive H⁺-ATPase activity is dependenton age, while changes in the microsomal fatty acid compositionof phospholipids are regulated mainly by root temperature. Key words: Fatty acids of phospholipids, microsomes, H⁺-ATPase, root temperature, Scots pine     

Low-temperature pretreatment of the root system of Brassica rapa L. plants: effects on the xylem sap exudation and on the nitrate absorption rate

Brassica rapa plants were exposed for a 52 h period (as pretreatment) to a differential temperature (DT) between roots (5°C) and shoots (20°C), while control plants were maintained with both shoot and roots at 20°C (warm grown = WG). Measured at 20°C, volume flow of xylem exudate from roots of DT plants was enhanced compared with that from WG plants, while transpiration flows were similar in pretreated and control plants. Both transpiration and exudation flows were dependent upon shoot/root ratio. Differences in the volume flow of exudate were principally related to increases in root hydraulic conductance. Anion fluxes (notably nitrate) into xylem exudate of DT plants were significantly greater than those into exudate of WG plants. This enhancement of nitrate flow from the pretreated roots was associated with a two-fold increase in nitrate uptake rate. The relationship of the cold-induced change in nitrate uptake capacity with shoot/root ratio is discussed in terms of control of nitrate absorption by shoot sink strength.     

The effect of differential root and shoot temperature on the nitrate reductase activity,assayed in vivo and in vitro in roots ofHordeum vulgare (barley)

There was a large increase in nitrate reductase activity (NAR) assayed both in vivo and in vitro in roots of barley plants (cv. Midas_ grown with roots at 10°C and shoots at 20°C, compared with whole plants grown at 20°C. There were diurnal fluctuations in NRA in roots from both treatments, but they were much greater in roots grown at 20°C, where NRA fell to a very low value in the dark period. The diurnal fluctuations in the malate content of the roots were also related to the root growth temperature. Plants with roots grown at the lower temperature had a higher malate content, especially in the dark period where it was 20 times greater than in plants with roots at 20°C. At all times there was a three-fold increase in soluble carbohydrate in cooled roots and diurnal fluctuations were much less pronounced than those of malate. Growth at low temperatures increased the total flux of amino N into the xylem sap and increased the proportion of reduced N in the total N flux. At certain times of day both 10°C- and 20°C-grown roots responded to exogeneous malate by increasing the flux of amino acid into the xylem sap, although this effect was always more pronounced in 20°C-grown roots.     

Effects of Temperature on Disease Severity in Plants of Subterranean Clover Infected Singly or in Mixed Infection with Bean yellow mosaic virus and Kabatiella caulivora

Many epidemics involve plants infected with more than one pathogen, but few experiments address climate change scenarios that influence mixed infections. This study addresses the interactive effects of co‐infection and temperature on disease development in plants of the annual pasture species subterranean clover (Trifolium subterraneum), which is widely sown in different world regions. Bean yellow mosaic virus (BYMV) and the fungus Kabatiella caulivora are two important pathogens causing considerable production losses in pastures containing this species. Both occur together in such pastures causing a severe necrotic disease when mixed infection occurs. Effects of temperature on symptom expression were investigated in subterranean clover plants infected singly or in mixed infection with these pathogens. Plants were maintained in controlled environment rooms at 18°C, 20°C or 22.5°C after sap inoculation with BYMV. K. caulivora conidia suspensions were inoculated to plants once systemic BYMV symptoms developed. Plants were assessed for three disease assessment parameters, dead petioles numbers, marginal leaflet necrosis and overall plant damage. In general, mixed infection caused most severe symptoms, K. caulivora least severe symptoms, and BYMV symptoms of intermediate severity. In single infections, effects of temperature on disease severity differed between pathogens: BYMV symptoms were most pronounced at 18°C, but K. caulivora induced more severe symptoms at 20°C and 22.5°C. In mixed infections, disease severity generally followed the pattern developed with BYMV alone as temperature increased. Also, synergistic increase in disease severity sometimes occurred at 18°C, but increases were only additive at 20°C and 22.5°C. These results reflected the greater BYMV multiplication detected in infected leaves at 18°C compared with 20°C or 22.5°C. Our findings indicate that in rainfed subterranean clover pastures, as global warming progresses disease severity from infection with BYMV and K. caulivora alone may decline or increase, respectively, and mixed infection with them may become less damaging.     

Assessment of conditions affecting <Emphasis Type="Italic">Agrobacterium</Emphasis> <Emphasis Type="Italic">rhizogenes</Emphasis>-mediated transformation of soybean

Agrobacterium rhizogenes-mediated transformation has become a powerful tool for studying gene function and root biology due to its quick and simple methodology. This transformation method is particularly suitable for those plants, including legumes, whose transformation using Agrobacterium tumefaciens has been challenging. Although there are some reports on A. rhizogenes-mediated transformation of legumes to produce ‘composite’ plants, conditions influencing A. rhizogenes-mediated transformation of soybean [Glycine max (L.) Merr.] have not been yet fully investigated. To better understand A. rhizogenes-mediated root transformation in soybean, we have evaluated the impact of genotype, plant age for infection, bacterial inoculating concentration, inoculation temperature, and other factors on transformation of soybean. The results have shown that there are significant differences among soybean genotypes in their susceptibility to A. rhizogenes. Soybean cv. Zigongdongdou is the most susceptible to A. rhizogenes strain K599 among 10 genotypes tested. The effects of seedling age have been evaluated, and 1-day-old plantlets are found to be optimal for hairy root induction. There are no significant differences in hairy root induction for bacterial suspension from OD₆₀₀ = 0.2 to OD₆₀₀ = 1.2. Under 16 h photoperiod, hairy roots can be induced both at 23°C/20°C and 28°C/25°C, but not at 33°C/30°C as day/night temperature regimes. Using this transformation protocol, almost 100% of the composite plants formed hairy roots within 2 weeks, and based on GUS histochemical analysis, 94.2% transformation frequency is obtained. Transgene integration has been also confirmed by Southern blot analysis. D. Cao and W. Hou contributed equally to this work.     

Selenium Modifies the Effect of Short-Term Chilling Stress on Cucumber Plants

The objective of this study was to investigate the effect of selenium (Se) supply (0, control; 2.5, 5, 10, or 20 μM) on cucumber (Cucumis sativus L.) cv. Polan F1 plants grown under short-term low temperature stress. About 14–16 day-old seedlings, grown at an optimal temperature (25/20°C; day/night), were exposed to short-term chilling stress with a day/night temperature of 10°C/5°C for 24 h, for a further 24 h at 20°C/15°C, and then transferred to 25/20°C (re-warming) for 7 days. Se did not affect the fresh weight (FW) of plants at a concentration of 2.5–10 μM, but in the presence of 20 μM Se, the biomass of shoots significantly decreased. The contents of chlorophylls and carotenoids witnessed no significant change after Se supplementation. Compared with the control, the Se-treated plants showed an increase of proline content in leaves, once after chilling and again after 7 days of re-warming. However, proline levels were much higher immediately after chilling than after re-warming. The malondialdehyde (MDA) content in the root of plants treated with 2.5–10 μM Se decreased directly after stress. This was in comparison with the plants grown without Se, whereas it increased in roots and leaves of plants exposed to 20 μM Se. Seven days later, the MDA level in the root of plants grown in the presence of Se was still lower than those of plants not treated with Se and generally witnessed no significant change in leaves. Although Se at concentrations of 2.5–10 μM modified the physiological response of cucumber to short-term chilling stress, causing an increase in proline content in leaves and diminishing lipid peroxidation in roots, the resistance of plants to low temperature was not clearly enhanced, as concluded on the basis of FW and photosynthetic pigments accumulation.     

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.     

Physiological Responses of Apple Trees to Supraoptimal Root Temperature

Ungrafted apple rootstocks were grown in sand cultures at constant root temperatures between 20°C to 40°C. Temperatures of 30°C and above reduced root and shoot growth. Serious damage to the leaves occurred at 35°C and above. The O₂ consumption, CO₂ evolution and respiratory quotient (RQ) of the roots showed maximum values at 35°C. Different rootstock cultivars varied greatly in their susceptibility to damage by supraoptimal root temperatures apparently due to anaerobic respiration. The more susceptible ones differed from resistant types in the larger amount of ethanol they accumulated in their roots at supraoptimal root temperature, and the more severe reduction in the malic acid content of the roots at such temperature. Acetaldehyde was also found in roots and leaves at supraoptimal root temperatures, whereas the organic acid content of the leaves tended to decrease. Supraoptimal root temperature also caused a reduction of cytokinins in both roots and leaves accompanied by a reduction in the leaf chlorophyll content. This could be prevented by the application of kinetin or benzyladenine to the leaves. In a short experiment a rise in root temperature up to 40°C caused an increase in transpiration and a decrease in the resistance of the leaves to the passage of water vapor, whereas in prolonged experiments transpiration reached a maximum and leaf resistance a minimum at 30°C. The leaf water potential increased also with increasing root temperature. Leaf temperature increased with increasing root temperature, irrespective of increasing or decreasing transpiration rates.     

Plasma membrane fluidity and hydraulic conductance in wheat roots: interactions between root temperature and nitrate or phosphate deprivation

The hypothesis was tested that the negative effect of mineral nutrient deprivation (–N and –P) on the hydraulic conductance (L0) of wheat roots may be relieved by increasing the fluidity of plasma membrane (PM) lipids through elevated temperature. An increase in root temperature from 20 to 30°C increased the sap flow, J_v, from the excised roots of nutrient-deprived plants for 4 h, with a corresponding increase in L₀. In the same period, there was a decline in the flux of osmotically active solutes (J_s > to the xylem. As the duration of the period at 30°C increased, it was clear that the differential in L₀ between control and nutrient-deprived roots was maintained, even though L_u was significantly greater than the initial (20 °C) value after 48h. The lipid order parameter, determined by fluorescence polarization of 1, 6 diphenyl- 1, 3, 5-hexatriene (DPH), decreased markedly in two-phase purified PMs in the first 4 h of treatment at 30°C, but thereafter remained steady. The differential between control and nutrient-deprived roots was maintained throughout the 48h period. The correlation between lowered L₀ in nutrient-deprived roots and increased PM lipid ordering remained unchanged in conditions where the overall membrane fluidity was increased by elevated temperature.     

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.     

Adenylate control contributes to thermal acclimation of sugar maple fine‐root respiration in experimentally warmed soil

We investigated the occurrence of and mechanisms responsible for acclimation of fine‐root respiration of mature sugar maple (Acer saccharum) after 3+ years of experimental soil warming (+4 to 5 °C) in a factorial combination with soil moisture addition. Potential mechanisms for thermal respiratory acclimation included changes in enzymatic capacity, as indicated by root N concentration; substrate limitation, assessed by examining nonstructural carbohydrates and effects of exogenous sugar additions; and adenylate control, examined as responses of root respiration to a respiratory uncoupling agent. Partial acclimation of fine‐root respiration occurred in response to soil warming, causing specific root respiration to increase to a much lesser degree (14% to 26%) than would be expected for a 4 to 5 °C temperature increase (approximately 55%). Acclimation was greatest when ambient soil temperature was warmer or soil moisture availability was low. We found no evidence that enzyme or substrate limitation caused acclimation but did find evidence supporting adenylate control. The uncoupling agent caused a 1.4 times greater stimulation of respiration in roots from warmed soil. Sugar maple fine‐root respiration in warmed soil was at least partially constrained by adenylate use, helping constrain respiration to that needed to support work being performed by the roots.     

Proteins in the roots of the perennial weeds chicory (Cichorium intybus L.) and dandelion (Taraxacum officinale Weber) are associated with overwintering

Roots are the overwintering structures of herbaceous perennial weeds growing in temperate climates. During the fall they accumulated reserves which are remobilized when growth resumes in the spring. An 18kDa (kilodalton) protein increases in both chicory and dandelion roots during the fall months. The proteins in both species are antigenically similar, and are recognized also by an antibody to a storage-protein deposited in Jerusalem artichoke (Helianthus tuberosus) tubers. In chicory, the protein is root-specific, but in dandelion it is detectable in the flowers, vestigial stem and the seed. Electrophoretic characterization of the 18-kDa protein shows that it is a single polypeptide, without subunits, with charge isomers of pI values close to pH 6.5. The major protein present in chicory and dandelion roots is unlike the vegetative storage proteins recently found in soybean or the storage proteins in the bark of trees.     

Effects of Warming and Nitrogen Addition on Plant Photosynthate Partitioning in an Alpine Meadow on the Tibetan Plateau

Quantifying plant carbon (C) allocation among different pools is critical for understanding and predicting how C turnover responds to global climate change in terrestrial ecosystems. A field experiment with increasing warming and nitrogen (N) was established to investigate interactive effects on plant C allocation in alpine meadows. Open-top chambers (OTCs) were used to simulate warming. In OTCs, daytime air and soil temperature at 5 cm depth increased by 2.0 and 1.6 °C, respectively, compared with ambient conditions, but soil moisture at 5 cm depth decreased by 4.95% (v/v) from 2012 to 2014. Warming reduced aboveground biomass by 38, 36, and 43% in 2012, 2013, and 2014, respectively, and increased belowground biomass by 64% and 29% in 2013 and 2014, respectively, and the root-to-shoot ratio was significantly increased. Specifically, warming increased the proportion of plant roots in the deep layers (10–20 cm). Both N addition and its combination with warming substantially enhanced belowground biomass. Pulse-labeling experiments for ¹³C revealed that warming reduced the translocation of assimilated C to shoots by 8.8% (38.7% in warming, and 47.5% in the control [CK]), and increased the allocation to root by 12.2% (55.5% in warming, and 43.3% in CK) after 28 days labeling. However, N addition increased the proportion of assimilated C allocated to shoots by 6.5% (54.0% in N addition, and 47.5% in CK), whereas warming combined with N addition reduced this proportion by 10.9%. A decline in soil water content in the surface layer may be the main cause of plants allocating more newly fixed photosynthate to roots. Therefore, plants promoted root growth to draw water from deeper soil layers (10–20 cm). We concluded that climate warming will change the allocation patterns of plant photosynthates by affecting soil water availability, whereas N addition will increase plant photosynthates aboveground in alpine meadows and thus will significantly affect C turnover under future climate change scenarios.

     

Effects of salinity and temperature on Deschampsia antarctica

Deschampsia antarctica is one of two species of vascular plants native to Antarctica. Populations of D. antarctica have become established on recently exposed glacial forelands on the Antarctic Peninsula and these plants may rely upon nutrient inputs from hauled out mammals, seabirds and sea spray. However, not much is known about the ability of these plants to tolerate salinity stress. We examined the effects of salinity and temperature on growth, reproduction, chlorophyll fluorescence and water relations of D. antarctica. In addition, we analysed concentrations of free proline in leaves and roots as previous studies have found large increases in the concentration of this amino acid in response to environmental stress. The growth chamber experiment was a 3 × 3 (temperature × salinity) complete factorial. Plants were grown at three temperature regimes: 7°/7°C, 12°/7°C, and 20°/7°C day/night and three salinity levels: <0.02 decismen per metre (dS m⁻¹; “low salinity”), 2.5 dS m⁻¹ (“medium salinity”), and 5.0 dS m⁻¹ (“high salinity”) for 66 days. Warmer temperatures improved leaf and tiller production as well as leaf and root length, which is consistent with previous findings on this species. Salinity reduced final root length by 6 and 13% in the medium and high-salinity treatments, respectively. Plants growing in medium and high-salinity treatments had xylem pressures that were more negative and higher free-proline concentrations, suggesting that proline may act as an osmoregulant in D. antarctica.     

Phytophthora cryptogea root rot of tomato in rock woo] nutrient culture. II. Effect of root zone temperature on infection, sporulation and symptom development

The effect of root-zone temperature on Phytophthora cryptogea root rot was studied in tomato cv. Counter grown under winter and summer conditions in rockwool culture. A nutrient temperature of 25°C resulted in increased root initiation and growth, higher in winter-grown than in summer-grown plants. Rhizosphere zoospore populations were greatly reduced at 25°C and above. Growth of P. cryptogea in vitro was optimal between 20°C and 25°C and completely suppressed at 30°C. Encystment was enhanced by increased temperatures above 20°C. Zoospore release in vitro occurred in cultures maintained at constant temperatures in the absence of the normal chilling stimulus. Optimal release was at 10°C; no zoospores were released at 30°C. Inoculated, winter-grown tomato plants maintained at 15°C developed acute aerial symptoms and died after 21 days. Comparable plants grown at a root-zone temperature of 25°C remained symptomless for the 3-months duration of the experiment. Summer-grown infected plants at the higher root temperature wilted but did not die. Enhanced temperature was ineffective as a curative treatment in summer-grown plants with established infection. Aerial symptoms of Phytophthora infection are seen as a function of the net amount of available healthy root. With high root zone temperatures this is determined by new root production and decreased inoculum and infection.     

Absorption of nitrate and ammonium ions by Lolium perenne from flowing solution cultures at low root temperatures

Lolium perenne L. cv. 23 (perennial ryegrass) plants were grown in flowing solution culture and acclimatized over 49 d to low root temperature (5°C) prior to treatment at root temperatures of 3, 5, 7 and 9°C for 41 d with common air temperature of 20/15°C day/night and solution pH 5·0. The effects of root temperature on growth, uptake and assimilation of N were compared with N supplied as either NH₄ or NO3 at 10 mmol m^?3. At any given temperature, the relative growth rate (RGR) of roots exceeded that of shoots, thus the root fraction (Rf) increased with time. These effects were found in plants grown with the two N sources. Plants grown at 3 and 5°C had very high dry matter contents as reflected by the fresh weight: freeze-dried weight ratio. This ratio increased sharply, especially in roots at 7 and 9°C. Expressed on a fresh weight basis, there was no major effect of root temperature on the [N] of plants receiving NHJ but at any given temperature, the [N] in plants grown with NHJ was significantly greater than in those grown with NO₃. The specific absorption rate (SAR) of NH⁺₄ was greater at all temperatures than SAR-NO₃. In plants grown with NH⁺, 3–5% of the total N was recovered as NH⁺₄, whereas in those grown with NO^?₃ the unassimilated NO^?₃ rose sharply between 7 and 9°C to become 14 and 28% of the total N in shoots and roots, respectively. The greater assimilation of NH⁺₄ lead to concentrations of insoluble reduced N (= protein) which were 125 and 20% greater, in roots and shoots, respectively, than in NO^?₃-grown plants. Plants grown with NH⁺₄ had very much greater glutamine and asparagine concentrations in both roots and shoots, although other amino acids were more similar in Concentration to those in NO^?₃ grown plants. It is concluded that slow growth at low root temperature is not caused by restriction of the absorption or assimilation of either NH⁺₄ or NO^?₃. The additional residual N (protein) in NH⁺₄ grown plants may serve as a labile store of N which could support growth when external N supply becomes deficient.     

Response of rice plants to constant and cyclic submerged soil temperature regimes

Summary An experiment was conducted in controlled temperature water baths to compare the response of rice plant of variety Taichung (Native) 1 to cyclic soil temperature regime of 32°C/20°C and constant soil temperature regime of 26°C. These temperature regimes are reported to be highly favourable for rice growth and therefore selected for comparison. The plants growing at 32°C/20°C showed some superiority over those growing at 26°C in respect of root growth and tiller development. The grain yield at 32°C/20°C was higher which resulted from larger number of tillers and panicles than at 26°C, although the difference in other yield characteristics was not appreciable. NPK content of grains, straw and roots did not vary appreciably between 32°C/20°C and 26°C but the total uptake of these nutrients varied because of the difference in total dry matter production. The results suggest that the development of rice plants, particularly in reproductive phase, is practically as good at 26°C as at 32°C/20°C and there seems to be no sufficient ground for generalising the phenomenon of diurnal thermoperiodicity for rice plants.