Pre-treating paclobutrazol enhanced chilling tolerance of sweetpotato

The objective of this work was to study changes in low molecular weight antioxidants and antioxidative enzymes in chilling-stressed sweetpotato, as affected by paclobutrazol (PBZ) pre-treatment 24 h prior to exposure to chilling conditions. Sweetpotato ‘TN71’ and ‘TN65’ were treated with 300 mg PBZ/5 ml/plant, after which plants were subjected to 7°C/7°C (day/night) for periods of 1, 3 and 5 days, followed by a 3-day recovery period at 24°C/20°C (day/night). A factorial experiment in completely randomized design with four replications was used in this study. Young fully expanded leaves at each temperature and period of time were clipped for antioxidative system measurement. We concluded that different varieties displayed variations in their oxidative system, and the differential expressions of each genotype were associated with chilling stress response. Plants with various antioxidative systems responded differently to chilling stress according to the duration of the chilling period and subsequent re-warming period. ASA, GSH and GSSG contents were enhanced in TN71 prior to chilling stress. Increased APX, GR, ASA and MDA activities accounted for chilling tolerance in TN65. Furthermore, our results indicate that the elevated levels of the antioxidative system observed after PBZ pre-treatments afforded the sweetpotato leaf improved chilling-stress tolerance. The levels of ASA and GSSG of both TN71 and TN65 under chilling were significantly raised by pre-treating with PBZ. PBZ pre-treatment exhibited the important function of enhancing the restoration of leaf oxidative damage under chilling stress and increasing the chilling tolerance of plants to mitigate chilling stress effects.     

Light-dependent damage to photosynthesis in olive leaves during chilling and high temperature stress

Abstract The leaves of olive are long lived and likely to experience both chilling and high temperature stress during their life. Changes in photosynthetic CO₂ assimilation resulting from chilling and high temperature stress, in both dim and high light, are investigated. The quantum yield (φ) of photosynthesis at limiting light levels was reduced following chilling (at 5°C for 12 h), in dim light by approximately 10%, and in high light by 75%; the difference being attributed to photoinhibition. Similar reductions were observed in the light-saturated rate of CO₂ uptake (A_max). Decrease in A_max correlated with a halving of the leaf internal CO₂ concentration (c_i), suggesting an increased limitation by stomata following photoinhibition. Leaves were apparently more susceptible to photoinhibitory damage if the whole plant, rather than the leaf alone, was chilled. On return to 26 °C, I he photosynthetic capacity recovered to pre-stress levels within a few hours if leaves had been chilled in high light for 8 h or less, but did not fully recover from longer periods of chilling when loss of chlorophyll occurred. Leaves which were recovering from chilling in high light showed far more damage on being chilled a second time in high light. Three hours in high light at 38 °C reduced φ by 80%, but φ recovered within 4h of return to 26 °C. Although leaves of Olive are apparently less susceptible to photoinhibitory damage during chilling stress than the short-lived leaves of chilling-sensitive annual? crops, the results nevertheless show that photoinhibition during temperature stress is potentially a major factor influencing the photosynthetic productivity of Olive in the field.     

The role of phytochrome B,D and E in thermoperiodic responses of <Emphasis Type="Italic">Arabidopsis thaliana</Emphasis>

The objective of this work was to study the role of the phytochromes (phy) B, D and E in the thermoperiodic control of elongation and flowering time in Arabidopsis thaliana. WT, and phyB, phyD and phyE single mutants, and phyB phyD and phyB phyE double mutants, were grown under day/night temperatures (DT/NT) of 12/22°C, 17/17°C or 22/12°C (negative, zero and positive DIF, respectively) for inflorescence stem length measurements, and under DT/NT 17/25°C or 25/17°C (negative and positive DIF, respectively) for leaf morphology and flowering time measurements. In WT final length of the stem, petiole and leaf blade were longer under positive DIF compared to negative DIF. The temperature effect was stronger in the leaf petiole than the stem, whereas only a slight change was seen in the leaf blade length direction and none in the width direction. The temperature effect on stem and petiole elongation was reduced or nearly eliminated in the genotypes lacking phyB, while a phyD or a phyE mutation had no influence or a slightly positive influence on the temperature effect, respectively. These results suggest that phyB, and not phyD or phyE, is needed for a complete thermoperiodic control of elongation growth in A. thaliana. For all genotypes tested, plants flowered earlier at negative DIF than positive DIF, suggesting that none of the three phytochromes B, D, or E is needed for a thermoperiodic control of flowering time in A. thaliana.     

Prior temperature exposure affects subsequent chilling sensitivity

The chilling sensitivity of small discs or segments of tissue excised from chillingsensitive species was significantly altered by prior temperature exposure subsequent to holding the tissue at chilling temperatures as measured by a number of physiological processes sensitive to chilling. This temperature conditioning was reversible by an additional temperature exposure before chilling, and mature-green and red-ripe tomato tissue exhibit similar chilling sensitivities. Exposing pericarp discs excised from tomato fruit (Lycopersicon esculentum Mill. cv. Castelmart), a chilling-sensitive species, to temperatures from 0 to 37°C for 6 h before chilling the discs at 2.5°C for 4 days significantly altered the rate of ion leakage from the discs, but had no effect on the rate of ion leakage before chilling and only a minimal effect on discs held at a non-chilling temperature of 12°C. Exposing chillingsensitive tissue to temperatures below that required to induce heat-shock proteins but above 20°C significantly increased chilling sensitivity as compared to tissue exposed to temperatures between 10 and 20°C. Rates of ion leakage after 4 days of chilling at 2.5°C were higher from fruit and vegetative tissue of chilling-sensitive species (Cucumis sativus L. cv. Poinsett 76, and Cucurbita pepo L. cv. Young Beauty) that were previously exposed for 6 h to 32°C than from similar tissue exposed to 12°C. Exposure to 32 and 12°C had no effect on the rate of ion leakage from fruit tissue of chilling tolerant species (Malus domestica Borkh. cv. Golden Delicious, Pyrus communis L. cv. Bartlett). Ethylene and CO₂ production were higher and lycopene synthesis was lower in chilled tomato pericarp discs that were previously exposed for 6 h to 32°C than the values from tissue exposed to 12°C for 6 h before chilling. Increased chilling sensitivity induced by a 6 h exposure to 32°C could be reversed by subsequent exposure to 12°C for 6 h.     

Effects of post-chilling temperature on growth and variegation in Solomon's Seal

Effects of temperature were studied on the current and following season's growth of shoots from chilled rhizomes of Variegated Solomon's Seal. The rate of progress to completed elongation of the aerial shoot in chilled plants increased linearly with increasing temperature up to 28°C (24 h mean). A post‐chilling thermal time of 658 ± 47°Cd (> ‐1.3°C) was required for aerial shoots to become fully extended. Temperatures of 28°C and 33°C accelerated aerial shoot senescence and decreased rhizome and root dry weights, as compared with 18°C and 23°C treatments. Leaf number and variegation were not affected by temperature treatments during current growth season and all plants produced 12–13 leaves with between 7% and 9% leaf area variegated. Leaf variegation, however, was significantly increased in plants that had been grown after chilling at 28°C during the preceding growing season. Proteins of approximately 26, 32 and 62 kDa were present in the green parts of leaves but not in the white parts.     

Isolation of four heat shock protein cDNAs from grapefruit peel tissue and characterization of their expression in response to heat and chilling temperature stresses

In order to continuously supply horticultural products for long periods, it is essential to store them after harvest in low temperatures. However, many tropical and subtropical fruits and vegetables, such as citrus, are sensitive to chilling. In previous studies, the authors have shown that a short hot water rinsing treatment (at 62°C for 20 s) increased chilling tolerance in grapefruit. In order to gain more insight into the molecular mechanisms involved in heat‐induced chilling tolerance, PCR cDNA subtraction analysis was performed which isolated four different PCR fragments whose expression was enhanced 24 h after the heat treatment, and that showed high sequence homology with various plant HSP18‐I, HSP18‐II, HSP22 and HSP70 genes. It was found that the short hot water treatment given at 62°C for 20 s, but not at lower temperatures of 20 or 53°C, increased the expression of the various HSP cDNAs in grapefruit peel tissue. However, when the fruits were kept at ambient temperatures, the increases in HSP mRNA levels following the hot water treatment were temporary and lasted only between 6 and 48 h. Similar temporary increases in the HSP mRNA levels were detected following exposure of the fruit to a hot air treatment at 40°C for 2 h. Nevertheless, when the fruits were treated with hot water but afterwards stored at chilling temperatures of 2°C, the mRNA levels of the various HSP18‐I, HSP18‐II, HSP22 and HSP70 cDNAs increased and remained high and stable during the entire 8‐week cold‐storage period, suggesting their possible involvement in heat‐induced chilling‐tolerance responses. The chilling treatment by itself increased the expression of the HSP18‐I cDNA, but had no effect on the mRNA levels of any of the other HSP cDNAs. Exposure of fruit to other stresses, such as wounding, UV irradiation, anaerobic conditions and exposure to ethylene, had no effect on the expression of the various HSPs. Overall, the study explored the correlation between the expression and persistence of various HSP cDNAs in grapefruit peel tissue during cold storage, on the one hand, and the acquisition of chilling tolerance, on the other hand, and the results suggest that HSPs may play a general role in protecting plant cells under both high‐ and low‐temperature stresses.     

Effects of growth temperature and winter duration on leaf phenology of a spring ephemeral (Gagea lutea) and a summergreen forb (Maianthemum dilatatum)

Effects of growth temperature and winter duration on leaf longevity were compared between a spring ephemeral, Gagea lutea, and a forest summergreen forb, Maianthemum dilatatum. The plants were grown at day/night temperatures of 25/20°C and 15/10°C after a chilling treatment for variable periods at 2°C. The temperature regime of 25/20°C was much higher than the mean air temperatures for both species in their native habitats. Warm temperature of 25/20°C and/or long chilling treatment shortened leaf longevity in G. lutea, but not in M. dilatatum. The response of G. lutea was consistent with that reported for other spring ephemerals. Air temperature increases as the vegetative season progresses. The decrease in leaf longevity in G. lutea under warm temperature condition ensures leaf senescence in summer, an unfavorable season for its growth. This also implies that early leaf senescence could occur in years with early summers. Warm spring temperatures have been shown to accelerate the leafing-out of forest trees. The decrease in leaf longevity due to warm temperature helps synchronize the period of leaf senescence roughly with the time of the forest canopy leaf-out. Prolonged winter due to late snowmelt has been shown to shorten the vegetative period for spring ephemerals. The decrease in leaf longevity due to long chilling treatment would correspond with this shortened vegetative period.     

Photosynthetic responses to chilling in a chilling‐tolerant and chilling‐sensitive Miscanthus hybrid

Miscanthus is a C₄ perennial grass being developed for bioenergy production in temperate regions where chilling events are common. To evaluate chilling effects on Miscanthus, we assessed the processes controlling net CO₂ assimilation rate (A) in Miscanthus x giganteus (M161) and a chilling‐sensitive Miscanthus hybrid (M115) before and after a chilling treatment of 12/5 °C. The temperature response of A and maximum Rubisco activity in vitro were identical below 20 °C in chilled and unchilled M161, demonstrating Rubisco capacity limits or co‐limits A at cooler temperatures. By contrast, A in M115 decreased at all measurement temperatures after growth at 12/5 °C. Rubisco activity in vitro declined in proportion to the reduction in A in chilled M115 plants, indicating Rubisco capacity is responsible in part for the decline in A. Pyruvate orthophosphate dikinase activities were also reduced by the chilling treatment when assayed at 28 °C, indicating this enzyme may also contribute to the reduction in A in M115. The maximum extractable activities of PEPCase and NADP‐ME remained largely unchanged after chilling. The carboxylation efficiency of the C₄ cycle was depressed in both genotypes to a similar extent after chilling. Φ_P:Φ_CO2 remained unchanged in both genotypes indicating the C₃ and C₄ cycles decline equivalently upon chilling.     

Effects of growth temperature and chilling duration on leaf phenology of <Emphasis Type="Italic">Fauria crista</Emphasis>-<Emphasis Type="Italic">galli</Emphasis> subsp. <Emphasis Type="Italic">japonica</Emphasis>, an alpine snowbed geophyte

I examined the effects of growth temperature and winter duration on the leaf phenology of Fauria crista-galli plants, which have an indeterminate growth habit. After a 220-day chilling treatment, the leaf expansion and green periods of plants maintained at 25/20°C were much longer than those of plants maintained at 15/10°C and of plants at the natural habitat obtained in a previous study. The results indicate that early growth cessation and early leaf senescence in the natural habitat are not only due to endogenous rhythm but determined to some extent by cool summer temperatures. When grown at 15/10°C, the green period of individual leaves and plants was much shorter after a long chilling treatment (220 days) than after a short chilling treatment (110 days). The plants sprouted during or immediately after the termination of chilling treatment, suggesting that the decrease in the green period results partly from an advance of endogenous developmental stages during the chilling treatment and that the timing of snowmelt potentially affects the time of leaf senescence in the natural habitat.     

The effects of development at sub-optimal growth temperatures on photosynthetic capacity and susceptibility to chilling-dependent photoinhibition in Zea mays

When plants of Zea mays L. cv. LG11 that have been grown at optimal temperatures are transferred to chilling temperatures (0–12°C) photoinhibition of photosynthetic CO₂ assimilation can occur. This study examines how growth at sub-optimal temperatures alters both photosynthetic capacity and resistance to chilling-dependent photoinhibition. Plants of Z. mays cv. LG11 were grown in controlled environments at 14, 17, 20 and 25°C. As a measure of the capacity for photosynthesis under light limiting conditions, the maximum quantum yields of CO₂ assimilation (φ^a.c) and O₂ evolution (φ^a.o) were determined for the laminae of the second leaves at photon fluxes of 50–150 μmol m^-2s^-1. To determine photosynthetic capacity at photon fluxes approaching light saturation, rates of CO₂ uptake (A₁₅₀₀) and O₂ evolution (A₁₅₀₀) were determined in a photon flux of 1500 μmol m^-2s^-1. In leaves developed at 14°C, φ and φ were 26 and 43%, respectively, of the values for leaves grown at 25°C. Leaves grown at 17°C showed intermediate reductions in φ and φ, whilst leaves developed at 20°C showed no significant differences from those grown at 25°C. Similar patterns of decrease were observed for A₁₅₀₀ and A_1500.0 with decreasing growth temperature. Leaves developed at 25°C showed higher rates of CO₂ assimilation at all light levels and measurement temperatures in comparison to leaves developed at 17 and 14°C. A greater reduction in A₁₅₀₀ relative to A_1500.0 with decreasing growth temperature was attributed to increased stomatal limitation. Exposure of leaves to 800–1000 μmol m^-2 s^-1 when plant temperature was depressed to ca 6.5°C produced a photoinhibition of photosynthetic CO₂ assimilation in all leaves. However, in leaves developed at 17°C the decrease in A₁₅₀₀ following this chilling treatment was only 25% compared to 90% in leaves developed at 25°C. Recovery following chilling was completed earlier in leaves developed at 17°C. The results suggest that growth at sub-optimal temperatures induces increased tolerance to exposure to high light at chilling temperatures. This is offset by the large loss in photosynthetic capacity imposed by leaf development at sub-optimal temperatures.     

Morphological adaptations byGlehnia littoralis to the biomass and heights of peripheral herbaceous plants in coastal sand dunes

To clarify the effects of peripheral herbal plants onGlehnia littoralis growth in coastal sand dunes, the morphology of their aboveground portions was surveyed in five communities:Carex kobomugi, Calystegia soldanella, Ischaemum anthephoroides, Oenothera biennis, andElymus mollis. Correlation coefficients (CC) were generally significant at the 1% level between community properties [total aboveground biomass (B) and height (H) of dominant species per unit area] and those ofG. littoralis [leaf number (Nl), petiole angle (Anp), petiole length (Lp), petiole weight (Wp), Lp/Wp, Lp/weight of leaf blade (Wb), Wp/total weight (Wt), specific leaf area (SLA), stem length (Ls), and Ls/weight of stem (Ws)J The exceptions were among four pairings: B and NI, B and Wt, H and Nl, and H and Wt. Of the two community properties, biomass had the greatest association with leaf properties while H was most closely related to those of the stems. Petiole angle increased along with leaf order, from 0° to 42° for the C.kobomugi community, from 5° to 55° forCalystegia soldanella, from 49° to 74° forI. anthephoroides, from 54° to 80° forO. biennis, and from 75° to 85° forE. mollis. In all communities, the properties of Wp, SLA, and Wb increased up to the third or fourth leaf, but then decreased; the exception was for Lp/Wp, which was the reverse. Leaf order of the largest one moved from first position to third as either B or H increased in a community.     

Differences between the effects of partial and whole plant chilling on carbon translocation of a C4 grass

Abstract Experiments were conducted with Echinochloa crus-galli to partition the effects of chilling the leaf vs. chilling the whole plant on subsequent ¹¹C translocation. The results clearly demonstrated that whole plant chilling was very detrimental whereas chilling only the leaf had no effect on subsequent translocation nor on ¹¹C uptake. The inhibition of translocation was due to a reduced rate and percentage of export while ¹¹C fixation rate was not significantly altered. When the leaf of a chilled plant was maintained at 22 °C, there was no impairment of the transport system nor of photosynthesis. The decrease in export with whole plant chilling may have been due to carbon movement into storage carbohydrates, resulting in a low sucrose gradient.     

Spontaneous and induced blocking and unblocking of phloem transport

Abstract Steady-state labelling with ¹¹CO₂ was used to observe the blocking of phloem transport, induced by chilling short regions of stems or petioles of velvetleaf (Abutilon theophrasti Medic.) or cotton (Gossipium hirsutum L.). The abruptness of these blockages was evidenced by sharp decreases in ¹¹C activity below, and increases above a 2 to 3 cm region cooled from 28°C to 18 or 13°C for periods as short as 2 min. Abrupt unblocking of transport in velvetleaf occurred a few minutes after rewarming, as evidenced by a sharp rise and and overshoot in ¹¹C activity. Recovery of transport in cotton was more prolonged and was marked by occasional spontaneous blocking and unblocking of transport at various points along the petiole or stem, not necessarily in the cooled region. Similar spontaneous events were often observed in undisturbed cotton plants, but only rarely in velvetleaf.     

Temperature dependence of seedling establishment of a perennial, Dioscorea tokoro

The temperature dependence of seed germination and seedling growth was analyzed in Dioscorea tokoro, an East Asian summer-green perennial. Seeds were able to germinate fully only at 11°–20°C. At around 17°–20°C the first leaf petiole of the seedling elongated and quickly set the first leaf blade at a position enabling photosynthesis. At temperatures higher than 20°C petiole elongation was retarded, and seedlings formed a rhizome and established as a perennial. The rhizome size increased with temperature up to 29°C. Thus, during growth immediately after germination, temperature appears to be a key factor in determining whether the plant establishes as a perennial or grows rapidly without rhizome thickening. Received: April 6, 2001 / Accepted: September 14, 2001     

Chilling stress and oxygen metabolizing enzymes in Zea mays and Zea diploperennis*

Abstract. The activities of five active-oxygen scavenging enzymes were compared for cold-lability and three were compared for chilling induction in two Zea genotypes of contrasting susceptibility to photoinhibition during chilling. Activities of superoxide dismutase (SOD, EC 1.15.1.1), ascorbate peroxidase (APX, EC 1.11.1.11), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GTR, EC 1.6.4.2) in leaf extracts from plants grown without chilling stress were assayed at 19°C and 5°C. Enzymes from the chilling-susceptible Z. Mays cv. LG11 had lower specific activities at 5°C than did enzymes from the chilling-tolerant Z. diploperennis, except for MDHAR where no significant differences were observed. The activities of SOD and APX from Z. diploperennis were double those of Z. mays at both assay temperatures. Monodehydroa-scrobate reductase and glutathione reductase activities in both species were reduced by 63–78% at a 5°C assay temperature. The dehydroascorbate reductase (DHAR) showed the greatest low-temperature lability losing 96% (Z. diploperennis) and 100% (Z. mays) of its activity at 5°C. To examine possible chilling-induced changes in levels of enzyme activity, plants of both Zea genotypes were transferred to growth chambers at 10°C at moderate light intensities. Glutathione reductase activity was found to increase within 24h in Z. diploperennis, but it decreased slightly in Z. mays. MDHAR activity decreased by 50% in Z. diploperennis but showed only a transient increase in activity in Z. mays.     

Low temperature acclimation of root fatty acid composition, leaf water potential, gas exchange and growth of soybean seedlings

Abstract Root fatty acid composition, photosynthesis, leaf water potentials, stomatal resistances, leaf specific weights, and root: shoot ratios of soybean were measured in two temperature regimes. Groups of soybean plants were grown in controlled chambers of the Duke University Phytotron under two thermoperiods. One group of the plants was grown from seed for 3 weeks in either 29/23°C or 17/11°C thermoperiods, and another group was grown for 2 weeks in 29/23°C and then transferred to the 17/11°C thermoperiod where it remained for 8 days. Broccoli was also grown in either 29/23°C or 17/11°C thermoperiods. Soybean roots contained more unsaturated fatty acids than broccoli roots, although broccoli roots showed a larger increase in unsaturation than soybean roots with decreased temperature. The fatty acid unsaturation in the roots of soybean began to increase rapidly after the temperature regime was changed. The increase was in the new roots produced in the cold regime rather than in the pre-existing roots. The soybean leaf water and osmotic potentials decreased about 0.4 MPa, beginning one day after the transfer from 29/23°C to 17/11°C, but recovered significantly after 8 d. Plants grown at 17/11 °C had lower rates of photosynthesis and adaxial stomatal resistances, but higher root: shoot ratios and specific leaf weights compared to plants grown at 29/23°C. Plants grown and maintained at 29/23°C showed a steady increase in photosynthetic rates over the 8-d experimental period, whether rates were measured in 1 mol m^?3 or 9 mol m^?3 oxygen. Plants transferred to 17/11°C however maintained constant rates of photosynthesis at 1 mol m^?3 O₂, whereas at 9 mol m^?3 rates declined for 2 d then were constant for the remaining 6 d of the experimental period. These results suggest that changes in membrane fatty acid unsaturation is an important aspect of plant acclimation to chilling temperatures in terms of maintaining root permeability and water uptake. However, the degree of unsaturation is not a good indicator of differences in chilling tolerance among species. The apparent acclimation of photorespiration to a constant percentage of photosynthesis suggests a role of photorespiration in the plant.