Nucleolar vacuolation in soybean root meristematic cells during recovery after chilling

The nucleolar vacuole formation in soybean root meristematic cells from seedlings grown 3 d at temperature 25 °C (control), 3 d at temperature 25 °C and then transferred to 10 °C (chilling) for 4 d, and after recovery for 1.5, 3, 6, 12 and 24 h at 25 °C were observed on semi-thin sections. Simultaneously, autoradiographic studies with ³H-uridine on squashed preparations were carried out. During recovery of plants, the number of vacuolated nucleoli increased gradually from 24 % after 1.5 h up to 40 % after 24 h, while in the control there were 18 % of nucleoli with vacuoles and after 4-d chilling only 5 %. Labelling of cells during 20-min incubation in ³H-uridine and during 80-min post-incubation in non-radioactive medium was increased in recovered plants in comparison with the control and chilled plants. The conclusion has been drawn that nucleolar vacuoles in soybean plants are formed as a result of migration of granular component accumulated in nucleolus during 4-d chilling.     

Increased chilling tolerance and altered carbon metabolism in tomato leaves following application of mechanical stress

We investigated the effects of brushing on the chilling tolerance and metabolism of nonstructural carbohydrates (soluble sugars and starch) in tomato leaves before, during and after a chilling stress. Tomato plants ( Lycopersicon esculentum Mill. cv. Caruso) were cultivated either without mechanical stress application (control plants) or with daily brushing treatments for 15 days (brushed plants), prior to a 7-day chilling treatment (8/5°C day/night). Brushing resulted in shorter plants with a 34% reduction in leaf dry weight per area and a 59% reduction of soluble sugars and starch, on a dry weight basis. The sugar to starch ratio was not affected by brushing. A greater chilling tolerance in the brushed plants was demonstrated by the maintenance of a significantly higher PSII efficiency in brushed plants (42%) compared to that of the control plants (30%) after 7 days of chilling treatment, less visible damage to the leaf tissue, and a more rapid resumption of growth during 3 days of recovery as compared to control plants. During the chilling treatment levels of soluble sugars per leaf dry weight increased 15-fold in the brushed plants and 5-fold in control plants. In the present study we have demonstrated that brushing can increase chilling tolerance in tomato plants. The observed differences in chilling tolerance and concentration of soluble sugars in the leaves may indicate an involvement of soluble sugar levels in acclimation to chilling.     

低温胁迫下二倍体杂交种高山松光系统Ⅱ功能稳定性研究

以人工气候室内的高山松(Pinus densata)及其亲本油松(P.tabulaeformis)和云南松(P.yunnanensis)实生苗为材料,通过测定低温胁迫和恢复后其幼苗的快速叶绿素荧光诱导动力学(JIP-test)参数,分析高山松及其亲本的光系统Ⅱ(PSⅡ)功能稳定性以及对低温胁迫的响应差异,以探讨高山松适应高海拔低温环境的光合生理生态机制。结果表明:经过33 d的低温(12℃/5℃,昼/夜)处理后,高山松PSⅡ功能参数单位截面积吸收的能量(ABS/CSo)、捕获的能量(TRo/CSo)、电子传递的能量(ETo/CSo)、耗散的能量(DIo/CSo)、有活性反应中心的数量(RC/CSo),以及原初光化学反应的最大量子产额(φPo)、吸收光能用于QA-以后的电子传递的能量比例(φEo)、捕获光能用于QA-以后的电子传递的能量比例(Ψo)、光能利用能力参数(PIabs)、2 ms时相对可变荧光(VJ)、荧光上升的初始斜率(Mo)、荧光曲线与Fm所围面积(Area)、介于F0和Fm之间的相对面积(Sm)和QA氧化还原次数(N)均与处理前无显著差异;油松和云南松的φPo、φEo、Ψo、PIabs、Area与对照差异显著,云南松的VJ、Mo、Sm、N、ETo/CSo、DIo/CSo、ABS/CSo也与对照存在显著差异;温度恢复之后(25℃/18℃,昼/夜),这些荧光参数的恢复程度表现为高山松>油松>云南松。可见,低温胁迫显著影响了油松和云南松的光能传递和光能利用能力以及受体库大小,且云南松遭受伤害的程度高于油松,而高山松的PSⅡ功能及其稳定性在遭受低温胁迫时明显高于亲本油松和云南松,且胁迫解除后恢复程度高,从而使得高山松能够在高海拔低温环境中累积代谢所需的有机物,保证其正常的生长和发育。     

Ultrastructural Localization of Adenosine Triphosphatase Activity in Cotyledon Cells of Tomato and Its Changes during Chilling Stress

The ultrastructural localization of adenosine tripkosphatase (ATPase) activity in cotyledon cells of tomato was carried out by use of the cytochemical method of lead phosphate precipitation, and the changes in ATPase activity during chilling stress of the tomato seedlings were studied. The following experimental results have been obtained: 1. The ATPase activity in the cotyledon cells of tomato seedlings germinated and grown at 28 ℃. was located at plasmolemma, plasmodesmata, nucleoli and nuclear chromatin chloroplast lamellae, many sites of cell wall, and the surface of cell wall bordering the intercellular spaces and their inclusions. 2. When the tomato seedlings were subjected to chilling treatment for 4 h. at 5 ℃., the ATPase activity in cotyledon cells was indifferent from that of non-chilling treated seedlings. After chilling treatment for 12 h. at 5 ℃., the reaction of ATPase activity at plasmolemma, and in cell wall and intercellular spaces was markedly reduced. though the high activity reaction of ATPase in nuclei and at chloroplast lamellae was still maintained. When the tomato seedlings were subjected to chilling stress for 24 h. at 5℃., the ATPase activity at plasmolemma and in cell wall was almost inactivated, while the ATPase activity in nuclei and at chloroplast lamellae was only slightly lowered. These results indicated that the chilling injury may influence firstly on the ATPase activity of cell surface (plasmolemma and cell wall). 3. The role of intercellular spaces used as the passage of materials and the process and mechanism of chilling injury are discussed.     

Electrolyte leakage and lipid degradation account for cold sensitivity in leaves of Coffea sp. plants

Five Coffea genotypes differing in their sensitivity to low positive temperatures were compared with regard to the effects of chilling on membrane integrity, as well as their ability to recover from cold-induced injury upon re-warming. Membrane damage was evaluated through electrolyte leakage, changes in membrane lipid composition and malondialdehyde (MDA) production in control conditions (25/20 degrees C, day/night), after a gradual temperature decrease period to 15/10 degrees C, after chilling treatment (3 nights at 4 degrees C) and upon re-warming to 25/20 degrees C during 6 days (recovery). C. dewevrei showed the highest electrolyte leakage at 15/10 degrees C and after chilling. This was due mainly to lipid degradation observed at 15/10 degrees C, reflecting strong membrane damage. Furthermore, MDA production after chilling conditions indicated the occurrence of lipid peroxidation. A higher susceptibility of C. dewevrei to cold also was inferred from the complete absence of recovery as regards permeability, contrary to what was observed in the remaining plants. Apoat? and Piat? presented significant leakage values after chilling. However, such effects were reversible under recovery conditions. Exposure to cold (15/10 degrees C and 3 x 15/4 degrees C) did not significantly affect membrane permeability in Catuaí and Icatú. Furthermore, no significant MDA production was observed even after chilling treatments in Apoat?, Piat?, Catuaí and Icatú, suggesting that the four genotypes had the ability to maintain membrane integrity and/or repair membrane damage caused by low temperatures. Apoat?, Piat? and, to a lower extent, Catuaí, were able to cope with gradual temperature decrease through an enhanced lipid biosynthesis. After acclimation, Piat? and Catuaí showed a lowering of digalactosyldiacylglycerol to monogalactosyldiacylglycerol ratio (MGDG/DGDG) as a result of enhanced DGDG synthesis, which represents an increase in membrane stability. The same was observed in Apoat? after chilling, in spite of phospholipids decrease. The studied parameters clearly indicated that chilling induced irreversible membrane damage in C. dewevrei. We also concluded that increased lipid synthesis, lower MGDG/DGDG ratio, and changes in membrane unsaturation occurring during acclimation to low temperatures may be critical factors in maintenance of cellular integrity under chilling.     

Some aspects of respiration and respiration inhibitors in low temperature effects of the cotton plant

Respiration of leaf tissue from cotlon plants in the nine leaf stage was found to be severely reduced at temperatures below 15°C. In another study, young cotton plants were exposed to chilling temperature (2.8°C) for 72 hours and the ability of the plant tissues to recover respiration at normal temperatures (15 and 25°C) was examined at periodic intervals. Chilling exposures of 12 hours injured cotton tissues as indicated by increased respiratiou of leaves and roots at 25°C. Further chilling malerially reduced the capacity of the leaves to re-estahlish normal respiration rales at higher temperatures. Picolinic acid, Dexon and matonate were used to study the influence of respiratory inhibitors on the chill damage of the collon plants. The chemicals were applied six hours before cold exposure aud fhe growth and development of cold injured plants was studied to indicate the effectiveness of the treatments. Tissue weights at the final harvests indicated that picolinic acid and Dexon treated plants recovered better after cold injury than the untreated plauts. The results suggest thai 15°C may be a critical temperaliire for many physiological processes of the cotton plant because the supply of energy needed for plant reactionsis restricted due to inadequate respiration. They also indicate that the disturhances in respiration are among the early effects of chilling colton plants and may be the cause of delayed growth and development of cotton plants subjccled to non-lethal chilling exposures. It is concluded that chemicals like picolinie acid and Dexon may he effective through protection of specific systems rather than a general reduction of respiration.     

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.     

Detection of QTLs associated with shoot wilting and root ammonium uptake under chilling temperatures in an interspecific backcross population from Lycopersicon esculentum ×L. hirsutum

The genetic basis for shoot wilting and root ammonium uptake under chilling temperatures was examined in an interspecific backcross (BC₁) population derived from Lycopersicon esculentum Mill. cv T5 and wild Lycopersicon hirsutum f. typicum accession LA1778. The chilling sensitivity of shoot wilting and ammonium uptake was evaluated in four replicated cuttings from each of 196 BC₁ plants. Wilting was evaluated at two different times: 2 hours (wilting 2 h) and 6 hours (wilting 6 h recovery) after root exposure to 4°C. The BC₁ plants were genotyped with 89 polymorphic RFLP markers, and composite interval mapping was used to detect quantitative trait loci (QTLs). Three QTLs, one each on chromosomes 5, 6 and 9, were detected for wilting 2 h. The presence of a L. hirsutum (H) allele at the QTL on chromosomes 5 and 9 decreased wilting, while the H allele at the QTL on chromosome 6 increased wilting. To analyze plant recovery from wilting at 6 h, subsets of the BC₁ population were selected, based on phenotype and genotype, because not all plants wilted at 2 h. The phenotype subset (wilting 6 h-PS) included plants that wilted to a greater degree at 2 h, and the genotype subsets included plants carrying specific allelic compositions at the QTL for wilting 2 h on chromosomes 5 (wilting 6 h-GS-ch5), 6 (wilting 6 h-GS-ch6), and 9 (wilting 6 h-GS-ch9). On chromosome 6, a QTL was located that was associated with three subsets (wilting 6 h-PS, wilting 6 h-GS-ch5 and wilting 6 h-GS-ch9), while on chromosome 7 a QTL was detected with two subsets (wilting 6 h-PS and wilting 6 h-GS-ch5). Three additional QTLs were detected within a single subset: chromosome 1 (wilting 6 h-GS-ch6), chromosome 11 (wilting 6 h-GS-ch5) and chromosome 12 (wilting 6 h-GS-ch9). The presence of the H allele at the QTL on chromosomes 7 and 12 had a positive effect, enhancing recovery from wilting, while the H allele at the other QTL had a negative effect. Three traits were used to evaluate the chilling sensitivity of root ammonium uptake: ammonium uptake before a chilling episode, ammonium uptake after the chilling episode, and the relative inhibition of uptake (difference in uptake rates before and after chilling divided by the rate before chilling). One QTL was detected on chromosome 3 for the rate before chilling and one on chromosome 6 for the relative inhibition of ammonium uptake. Our results demonstrate that shoot wilting and ammonium uptake under chilling are controlled by multiple QTLs. Received: 10 August 1999 / Accepted: 25 March 2000     

Chilling stress response of postemergent cotton seedlings

Early season development of cotton is often impaired by sudden episodes of chilling temperature. We determined the chilling response specific to postemergent 13-day-old cotton (Gossypium hirsutum L. cv. Coker 100A-glandless) seedlings. Seedlings were gradually chilled during the dark period and rewarmed during the night-to-day transition. For some chilled plants, the soil temperature was maintained at control level. Plant growth, water relations and net photosynthesis (P(n)) were analyzed after one or three chilling cycles and after 3 days of recovery. Three chilling cycles led to lower relative growth rate (RGR) compared with controls during the recovery period, especially for plants with chilled shoots and roots. Treatment differences in RGR were associated with net assimilation rate rather than specific leaf area. Both chilling treatments led to loss of leaf turgor during the night-to-day transition; this effect was greater for plants with chilled compared with warm roots. Chilling-induced water stress was associated with accumulation of the osmolyte glycine betaine to the same extent for both chilling treatments. Inhibition of P(n) during chilling was related to both stomatal and non-stomatal effects. P(n) fully recovered after seedlings were returned to control conditions for 3 days. We conclude that leaf expansion during the night-to-day transition was a significant factor determining the magnitude of the chilling response of postemergent cotton seedlings.     

Influence of mefluidide on growth,development, and cell wall digestibility of sorghum

Application of mefluidide (N-[2,4-dimethyl-5-([(trifluoromethyl)sulfonyl]amino) phenyl]acetamide) inhibits plant development in perennial grasses. This study examined the effect of mefluidide on the morphological development and digestibility of sorghum. In the greenhouse, 5.9 × 10^–5 g active ingredient (a.i.) plant^–1 applied at the seedling, eight-leaf and boot stages reduced mean plant height 70%, 59%, and 2%, respectively. Heights were also reduced 14%, 15% and 35% by 5.9 × 10^–8, 5.9 × 10^–7 and 5.9 × 10^–6 gram a.i. plant^–1 applied at the eight-leaf stage. Field application of 0.26 or 0.52 kg ha^–1 mefluidide at either the eight-leaf or flagleaf stage reduced mean plant height of all cultivars. Basal tiller numbers increased 319% 28 d, and dry matter production was reduced 65% 42 d following mefluidide application at the eight-leaf stage. Treated stems were 34% higher and treated leaves were 7% higher in cellulase dry matter digestibility than control plants following mefluidide application at the eight-leaf stage. These results indicate that mefluidide application to vegetative stages in sorghum may enhance the forage value of the plants while it inhibits normal plant growth.     

Hardly Increased Oxidative Stress After Exposure to Low Temperature in Chilling-Acclimated and Non-Acclimated Maize Leaves

Abstract: Seedlings of Zea mays L. were grown at optimal (25 °C) and suboptimal (15 °C) temperature and then exposed to severe chilling temperature (6 °C) at their growth light intensity (450 ìmol quanta m⁻² s⁻¹) for 4 d. Photosynthetic parameters, hydrogen peroxide, antioxidant contents, and activity of scavenging enzymes were investigated before, during, and after chilling stress. This stress caused a stronger reduction in photosynthetic activity, maximum quantum efficiency of photosystem II primary photochemistry ( F _v/ F _m), and catalase activity in plants which had been grown at 25 °C rather than at 15 °C. Maize plants grown at suboptimal temperature de-epoxidized their xanthophyll cycle pool to a greater extent and exhibited a faster recovery from chilling stress than plants which had not been acclimated to chilling. Antioxidant content, activity of scavenging enzymes, with the exception of catalase, hydrogen peroxide formation, and the size of the xanthophyll cycle pool were hardly affected by chilling stress. However, chilling induced a temporary increase in the glutathione content and triggered the synthesis of á-tocopherol during the phase of recovery at 25 °C. The results indicate that leaves respond to chilling stress by down-regulation of photosystem II accompanied by de-epoxidation of the xanthophyll cycle pool, probably to prevent enhanced formation of superoxide radicals at photosystem I and, consequently, other reactive oxygen species.     

Ultrastructural and autoradiographic studies of the role of nucleolar vacuoles in soybean root meristem

Ultrastructural and autoradiographic studies of nucleoli in soybean root meristematic cells in seedlings: (1) grown for 3 days at 25 degrees C (control), (2) grown for three days at 25 degrees C and for 4 days at 10 degrees C, and (3) grown as in (2) and recovered for 1 day at 25 degrees C were carried out. Control nucleoli had dense structure and a few small nucleolar vacuoles. Chilled plant nucleoli had less dense structure and no vacuoles. Nucleoli of plants recovered at 25 degrees C had big nucleolar vacuoles. In autoradiograms of squashed preparations, the labeling of nucleoli and cytoplasm after 20-min incubation in 3H-uridine was 5- and 6-fold stronger, respectively, in control than in chilled roots. Following recovery, the labeling of nucleoli and cytoplasm was much stronger than after chilling or even than in control roots. After 80-min postincubation in non-radioactive medium, average labeling of particular areas of cells was the highest in recovered plants which indicated intensification of rRNA synthesis, maturation and transport into cytoplasm resulting from the resumption of optimal conditions which was correlated with the appearance of big nucleolar vacuoles. In autoradiograms of semi-thin sections from roots of seedlings chilled for 4 days then recovered and incubated for 20 min in 3H-uridine, practically only extravacuolar parts of nucleoli were labeled. After 80-min postincubation, the labeling of nucleolar vacuoles was observed. Thus, during postincubation the labeled molecules were translocated from the nucleolar periphery into nucleolar vacuoles in cells where intensive transport of these molecules to the cytoplasm takes place. On the basis of these results, a hypothesis has been put forward that nucleolar vacuoles may be involved in the intensification of pre-ribosome transport outside nucleolus.     

Nickel and Cadmium-related Changes in Growth, Plasma Membrane Lipid Composition, ATPase Hydrolytic Activity and Proton-pumping of Rice (Oryza sativa L. cv. Bahia) Shoots

Six-day-old rice plants (Oryza sativa L. cv. Bahia) were grownin the presence of 0.5 mol m^–3 Ni or Cd for 5 or 10 d.Five days after treatment, some plants were transferred to amedium containing no heavy metal for 5 or 10 d. Plasmalemmavesicles from shoots of treated, transferred (recovery experiments)and control plants were isolated, ATPase activity and proton-pumpingwere assessed, and free sterols and phospholipids determined.The ATPase hydrolytic activity was increased by 37% and 34%in 5 and 10 d Cd-treated plants, respectively; and by 66% in5 and 10 d Ni-treated plants. However, neither the initial rateof H⁺ transport nor the proton-pumping rate at steady-statewere significantly affected by the treatments. The relativeproportion (%) of the plasmalemma sterols campesterol and ⁵-avenasteroldecreased while sitosterol increased during heavy metal treatment.The overall plasmalemma phospholipid fatty acyl chain lengthand degree of unsaturation were also reduced. In experimentswhere plants recovered from Cd and Ni treatment, differencesbetween treated and control plants were reverted, particularlyin 10 d Ni-recovered plants. The possible involvement of lipidsin the regulation of the plasmalemma ATPase as well as the relationshipbetween growth, ATPase and adaptations to stress conditionsare discussed. Key words: Cadmium, nickel, sterols, phospholipids, ATPase     

冷胁迫下大麦幼苗根质膜水通道蛋白基因的表达

植物质膜水通道蛋白（plasma membrane intrinsic proteins,PIPs）是位于细胞质膜上具有选择性、高效转运水分的一类膜内在蛋白,参与植物生长发育的多个生理活动。本研究以大麦‘Haruna—nijo’为材料,对水培幼苗进行4℃冷胁迫,采用实时荧光定量PCR技术对胁迫期（4℃,48h）和温度恢复期（16℃,48h）两个过程的水通道蛋白PIPSs基因表达进行了分析;同期测定了根水导度（Lpr）、根长和苗高,分析冷胁迫下大麦根mF基因的表达与水分生理的关系。结果表明：大麦幼苗经4℃低温胁迫48h后,苗的生长明显受抑,根的生长无显著变化;温度恢复48h后,苗恢复生长,根的生长无显著变化;根水导度在胁迫期下降,恢复期急剧升高,均无显著差异。实时荧光定量PCR结果显示,根中表达量最高的是HvPIP1;2和HvPIP1;3,最低的是HvPIP1;1和HvPIP2;3;冷处理后HvPIPs表达童与对照比较总体百降,其HvPIP1;2、HvPIP1;3、HvPIP1;4、HvPIP1;5、HvPIP2;1、HvPIP2;2明显下调。恢复后大多数HvPIPS表达童增加．HvPIP1;1、HvPIP1;2、HvPIP1;5、HvPIP2;3显砉增如,HvPIP1;4、mPIP2;5表达量降低,但无显著轰异,研菀发现,冷弼迫后夫菱粮HvPIPs的表达情况总体下调,恢复生长大部分HvPIPs上调,结合根水导度的变化,推测大麦HvPIPs在抗冷反应中的作用复杂,冷害的不同阶段HvPIPs对水分吸收所起的作用不同。     

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.     

Different responses of tobacco antioxidant enzymes to light and chilling stress

The effect of elevated light treatment (25 degrees C, PPFD 360 mumol m-2 sec-1) or chilling temperatures combined with elevated light (5 degrees C, PPFD 360 mumol m-2 sec-1) on the activity of six antioxidant enzymes, guaiacol peroxidases, and glutathione peroxidase (GPx, EC 1.11.1.9) protein accumulation were studied in tobacco Nicotiana tabacum cv. Petit Havana SR1. Both treatments caused no photooxidative damage, but chilling caused a transient wilting. The light treatment increased the activities of ascorbate peroxidase (APx, EC 1.11.1.11) and guaiacol peroxidases while catalase (EC 1.11.1.6), superoxide dismutase (SOD, EC 1.15.1.1), monodehydroascorbate reductase (MDHAR, EC 1.6.5.4), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (EC 1.6.4.2) were unchanged. In contrast, chilling treatment did not increase any of the antioxidant enzyme activities, but decreased catalase and to a lesser extent DHAR activities. Glutathione peroxidase protein levels increased sporadically under light treatment and constantly under chilling. Both chilling and light stress caused induction of glutathione synthesis and accumulation of oxidised glutathione, although the predominant part of the glutathione pool remained in the reduced form. Antioxidant enzymes from the chilling treated plants were measured at both 25 degrees C and 5 degrees C. Measurements at 5 degrees C revealed a 3-fold reduction in catalase activity, compared with that measured at 25 degrees C, indicating that the overall reduction in catalase after four days of chilling was approximately 10-fold. The overall reduction in activity for the other antioxidant enzymes after four days of chilling was 2-fold for GR and APx, 1.5-fold for MDHAR, 3.5-fold for DHAR. The activity of SOD was the same at 25 and 5 degrees C. These results indicate that catalase and DHAR are most strongly affected by the chilling treatment and may be the rate-limiting factor of the antioxidant system at low temperatures.     

Chill-Induced Changes in the Activity and Abundance of the Vacuolar Proton-Pumping Pyrophosphatase from Mung Bean Hypocotyls

Changes in the properties of extractable vacuolar H+-pumping pyrophosphatase (V-PPase) and vacuolar ATPase activities in chilling-sensitive seedlings of mung bean (Vigna radiata) were investigated. Following chilling at 4[deg]C for 48 h, both hydrolytic and proton-pumping activities of the V-PPase increased 1.5- to 2-fold over controls and remained elevated even after 72 h at low temperatures. Vacuolar ATPase levels did not change significantly throughout the chilling regime. However a large increase in alcohol dehydrogenase activity during chilling suggests a shift toward fermentative metabolism, which can be expected to decrease ATPase activity in situ. Western blotting of vacuolar membrane-enriched fractions from control and treated plants has confirmed that the changes in V-PPase activity are mirrored by increases in the amount of pump protein. Results suggest a specific role for the V-PPase in protecting chill-sensitive plants from the injurious effects of low temperatures via the maintenance of the proton gradient across the vacuolar membrane.     

Effects of paclobutrazol and chilling temperatures on lipids, antioxidants and ATPase activity of plasma membrane isolated from green bell pepper fruits

The effects of paclobutrazol treatment on plasma membrane lipid composition and ATPase activity of bell pepper fruit ( Capsicum annuum ) subjected to chilling temperatures were assessed. Application of the growth regulator paclobutrazol affected plant growth and fruit morphology. The plants were more compact and the fruits were less elongated than control fruits. There was about 60% more plasma membrane on a fresh weight basis from treated fruits. At harvest there was no difference in sterol to phospholipid ratio, or in phospholipid fatty acid composition of control compared with paclobutrazol treated fruit. However, plasma membrane ATPase acitivity of treated fruit was two times higher than that of control fruit. After storage at chilling temperature (2°C), the control fruit developed more chilling iniury, and had greater weight loss and a higher rate of K⁺ leakage than paclobulrazol treated fruit. Plasma membrane phospholipid content decreased and saturation of phospholipid fatty acids was higher than in control fruit. These two changes were largely absent in plasma membrane from treated fruit. At harvest antioxidant levels in the plasma membrane of paclobutrazol treated peppers were higher than in those of controls and changed little during storage, whereas levels in control fruit plasma membrane decreased 66%. ATPase activity increased and then decreased in control fruit held at low temperature, whereas in treated fruit activity was constant. The protective effect of paclobutrazol against chilling injury of pepper fruit may result from a combination of its effect on fruit morphology, and protection of the lipids against oxidative stress.     

花榈木组培苗茎段低温胁迫培养及耐冷性诱导

以花榈木组培苗茎段为试材,在低温胁迫条件下进行耐冷性愈伤组织诱导培养。结果表明,5℃是花榈木茎段低温胁迫培养及耐冷性诱导的最适温度。经过5℃低温胁迫培养获得的耐冷性愈伤组织在分化培养基MS+6-BA 2.0 mg/L+NAA 0.25 mg/L上的分化率达70.0%,且再生植株的低温伤害率明显低于对照。     

短期夜间低温后番茄光合作用及叶绿体超微结构的恢复效应

为明确短期夜间低温后番茄光合作用在常温下的恢复效应,研究了番茄幼苗经夜间15 ℃（对照）、12 ℃、9 ℃和6 ℃处理7 d后植株光合作用和叶绿体超微结构的变化.结果表明：短期夜间低温处理有利于恢复期番茄叶片的光合作用;12 ℃和9 ℃处理叶片叶绿素含量均可恢复至对照水平,6 ℃处理叶绿素含量则不可恢复;夜间低温处理并未严重抑制叶片气孔的形成,相反刺激了恢复期叶片气孔的形成与发育;6 ℃处理后叶绿体基粒片层排列较松散,片层数减少.恢复7 d时,夜间处理温度越低,叶绿体中淀粉粒越小、数量越少,基粒片层排列越整齐致密.另外,短期夜间低温处理促进了番茄植株叶片在恢复期的光合产物运输.