Effects of Waterlogging on Nitrogen Accumulation and Alleviation of Waterlogging Damage by Application of Nitrogen Fertilizer and Mixtalol in Winter Rape (Brassica napus L.)

A study on the physiological and yield effects of waterlogging and the alleviation of waterlogging damage by the application of nitrogen fertilizers and mixtalol in winter rape was conducted in experimental tanks especially designed for controlling soil moisture content. The results showed that waterlogging at the seedling and stem elongation stages causes a significant decrease in nitrogen content and rate of nitrogen accumulation. Leaf chlorophyll content, superoxide dismutase and catalase activities, and root oxidizability (capacity for root oxidation) and root exudate were also reduced by waterlogging. The experiments confirmed that the physiological function of rape plants was retarded during the time of waterlogging at the seedling stage, and its adverse effects remained. Plant height, stem width, and the number of primary branches per plant were decreased significantly by waterlogging at the seedling and stem elongation stages. Pods per plant and seeds per pod were also reduced significantly, giving a 21.3 and 12.5% decrease of seed yield from the control for treatments at the seedling and stem elongation stages, respectively. Foliar sprays of nitrogen fertilizers at the seedling stage or mixtalol at the flowering stage alleviated plant damage caused by waterlogging by retarding chlorophyll and nitrogen degradation, increasing superoxide dismutase and catalase activities and root oxidizability, and improving yield components and seed yield of waterlogged plants. Therefore, besides draining off water, alleviation of waterlogging damage may be controlled by applying nitrogen fertilizer and a suitable plant growth regulator at appropriate growth stages. Received July 3, 1996; accepted December 26, 1996     

Uniconazole-induced alleviation of freezing injury in relation to changes in hormonal balance, enzyme activities and lipid peroxidation in winter rape

Winter rape (Brassica napus L. cv. 601) seedlings were treated with 50 mg.l-1 of foliar-applied uniconazole and then exposed to freezing stress with a light/dark temperature regime of 2 °C/–3 °C for 5 days at the seedling stage. Stressed plants contained lower endogenous GA3 and IAA contents than the controls, while zeatin and ABA contents and ethylene levels were significantly increased. Uniconazole-treated plants had lower endogenous GA3 and IAA contents, and higher zeatin and ABA contents and ethylene levels. Leaf chlorophyll content and respiratory capacity of roots were reduced significantly after plants were subjected to freezing stress, and foliar sprays of uniconazole retarded the degradation of chlorophyll and increased respiratory capacity of roots. Uniconazole-induced freezing tolerance was accompanied by increased activities of various antioxidant enzymes, including superoxide dismutase, catalase and peroxidase. Foliar applications of uniconazole reduced electrolyte leakage and malondialdehyde accumulation caused by freezing stress, suggesting that uniconazole may have decreased freezing-induced lipid peroxidation and membrane damage.     

外源水杨酸对NaCl胁迫下大豆种子萌发和幼苗生长生理的影响

以大豆种子、幼苗为试验材料,采用砂培的方法,研究了0.2mmol·L-1外源水杨酸(SA)对100mmol·L-1 NaCl胁迫下大豆种子萌发、幼苗形态及生物量、膜脂过氧化和抗氧化酶活性的影响。结果显示:NaCl胁迫下,大豆种子萌发和幼苗生长受到显著抑制,且随着胁迫时间的延长(0~3d),大豆幼苗相对电解质渗漏率、硫代巴比妥酸活性产物(TBARS)含量显著升高,超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)活性均明显降低。外源SA促进NaCl胁迫下大豆种子萌发和根茎生长,增加幼苗生物量积累,降低幼苗叶片相对电解质渗漏率和TBARS含量,增强其叶片SOD、CAT、APX活性。研究表明,NaCl胁迫能显著抑制大豆种子萌发和幼苗生长,而一定浓度的外源SA能有效提高NaCl胁迫下大豆种子活力及幼苗抗氧化酶活性,减轻膜脂过氧化程度,缓解NaCl胁迫所造成的伤害,提高大豆幼苗抗盐胁迫的能力。     

Effect of Putrescine, 4-PU-30, and Abscisic Acid on Maize Plants Grown under Normal, Drought, and Rewatering Conditions

The experiments were carried out with maize (Zea mays L.) seedlings, hybrid Kneja 530, grown hydroponically in a growth chamber. Twelve-day-old plants were foliar treated with putrescine, N¹-(2-chloro-4-pyridyl)-N²-phenylurea (4-PU-30), and abscisic acid (ABA) at concentrations of 10⁻⁵ m. Twenty-four hours later the plants were subjected to a water deficit program, induced by 15% polyethylene glycol (PEG; molecular weight, 6,000). Three days after drought stress half of the plants were transferred to nutrient solution for the next 3 days. The effects of the water shortage, rewatering, and plant growth regulator (PGR) treatment on the fresh and dry weights, leaf pigment content, proline level, relative water content (RWC), transpiration rate, activities of catalase and guaiacol peroxidase, hydrogen peroxide content, and level of the products of lipid peroxidation were studied. It was established that the application of PGRs alleviated to some extent the plant damage provoked by PEG stress. At the end of the water shortage program the plants treated with these PGRs possessed higher fresh weight than drought-subjected control seedlings. It was found also that putrescine increased the dry weight of plants. Under drought, the RWC and transpiration rate of seedlings declined, but PGR treatment reduced these effects. The accumulation of free proline, malondialdehyde, and hydrogen peroxide was prevented in PGR-treated plants compared with the water stress control. The results provided further information about the influence of putrescine, 4-PU-30, and ABA on maize plants grown under normal, drought, and rewatering conditions. Received September 25, 1997; accepted August 10, 1998     

Uniconazole-induced tolerance of rape plants to heat stress in relation to changes in hormonal levels, enzyme activities and lipid peroxidation

Winter rape (Brassica napus L. cv. 601) seedlings were treated with 50 mg.l-1of foliar-applied uniconazole and then exposed to heat stress with a light/dark temperature regime of 43 °C/38 °C for 3 days at the stem elongation stage. Heat stressed plants contained lower endogenous GA3, IAA and zeatin contents than the controls, while ABA content and ethylene level were increased significantly. Uniconazole-treated plants had lower endogenous GA3 and IAA contents, and higher zeatin and ABA contents and ethylene levels. Leaf chlorophyll content and respiratory capacity of roots were reduced markedly after plants were subjected to heat stress, and foliar sprays of uniconazole retarded the degradation of chlorophyll and increased respiratory capacity of roots. Following exposure to heat, the activities of superoxide dismutase and peroxidase were significantly reduced. Uniconazole-induced heat tolerance was accompanied by increased activities of various antioxidant enzymes. Foliar applications of uniconazole reduced electrolyte leakage and malondialdehyde accumulation caused by heat stress, suggesting that uniconazole may have decreased heat-induced lipid peroxidation and membrane damage. Foliar sprays of uniconazole increased the tolerance of rape plants to heat stress.     

Uniconazole-induced thermotolerance in soybean seedling root tissue

Soybean [Glycine max(L.) Merr. cv. A2] seeds were germinated in 0 or 1 mg 1¹ (3.4 uM) uniconazole, after which seedling roots were excised and exposed to 22 or 48°C for 90 min. Prior to the temperature treatments there were few ultrastructural differences between uniconazole-treated seedling roots and the controls. Following exposure to 48°C, electron micrographs revealed near complete loss of normal ultrastructure in control epidermal root cells, whereas cellular integrity was maintained in treated roots, indicating that uniconazole conferred tolerance to high temperature. Total electrolyte, sugar and K⁺ leakage were all greater from control roots than treated roots during exposure to 48°C. Proline content in the roots was unaffected by uniconazole at 22°C but was 25–30% greater in treated tissue than in controls following exposure to 48°C. Malondialdehyde content was unaffected by uniconazole at 22°C but was nearly 20% less in treated tissue than in controls following high temperature exposure. This indicates that uniconazole decreased high-temperature-induced lipid peroxidation. Uniconazole elevated several antiox-idant systems in the roots, including water-soluble sulfhydryl concentration and catalase, peroxidase and superoxide dismutase activities. These findings are consistent with the hypothesis that uniconazole-induced stress tolerance is due, at least in part, to enhanced antioxidant activity which reduces stress-related oxidative damage to cell membranes.     

Uniconazole (S-3307) induced cadmium tolerance in wheat

Uniconazole, a triazole, was applied to seed at a concentration of 0. l g kg^–1 seed to protect wheat plants from the toxic metal cadmium (Cd). The degree of protection afforded by uniconazole against Cd toxicity was assessed by measuring fresh and dry weights of shoots and roots and by estimating the chlorophyll and solute leakage level in the leaves. Fresh weights and dry weights of roots and shoots were higher in Cd + uniconazole treated plants compared to uniconazole and cadmium treatment alone. Uniconazole + cadmium treated plants were darker in color, having more chlorophyll. Solute leakage was increased with the increasing concentrations of Cd and loss of membrane permeability was alleviated by the use of uniconazole.     

Endogenous Levels of Cytokinins, Indoleacetic Acid, Abscisic Acid, and Pigments in Variegated Somaclones of Micropropagated Banana Leaves

The banana (Musa spp. AAA) micropropagation shows a high incidence of off-types, among whose variegated plants are very common. Endogenous levels of growth regulators and pigment content were measured in normal and variegated leaves of the micropropagated banana plants growing in a greenhouse. Growth regulators were separated by high pressure liquid chromatography and submitted to enzyme-linked immunosorbent assay for quantification. Pigment content was measured using the colorimetric method. Green leaves contained 1.9 and 10 times more cytokinins compared with green and yellow sectors of variegated leaves, respectively. The levels of indoleacetic acid in normal leaves were significantly higher than those found in green and yellow sectors of variegated leaves; however, the levels of abscisic acid were lower in normal leaves. The lower content of chlorophylls in variegated leaves coincided with decreased endogenous levels of cytokinins, which indicated that variegation in banana leaves may be associated with alterations in the metabolism of this growth regulator. Received December 3, 1997; accepted February 2, 1998     

Seed Film Coating with Uniconazole Improves Rape Seedling Growth in Relation to Physiological Changes Under Waterlogging Stress

Waterlogging is an important constraint of global production of rape. The effects of seed film coating with 0.0075% uniconazole on the growth and physiology was investigated using seedlings from three varieties of rape (Brassica napus L.) subjected to waterlogging. While seed coating with uniconazole had no significant effect on germination percentage during waterlogging stress, it enhanced root vigour, increased root length, root volume and root dry weight. It also significantly enhanced leaf dry weight and ratio of root to shoot, but induced a significant decrease in shoot height and stem dry weight. Seed film coating with uniconazole also significantly increased the activities of the antioxidant enzymes, POD, CAT and SOD, and soluble sugar concentration during waterlogging. Thus, it suggests that seed film coating with uniconazole at a suitable concentration can improve rape seedling growth and increase seedling establishment during waterlogging.     

Exogenous spermidine alters in different way membrane permeability and lipid peroxidation in water stressed barley leaves

In order to see whether polyamines will modify membrane functioning in the water stressed plants, barley (Hordeum vulgare) seedlings were treated with spermidine (Spd) prior to dehydration and then the stress-evoked changes in membrane permeability (i.e. in electrolyte leakage from leaves) and lipid peroxidation (indicated by modifications of the malondialdehyde (MDA) level, and of the lipoxygenase (LOX) activity) were followed. The Spd treatement lowered injury index in plants subjected to water deficit, although it slightly increased the stress-promoted LOX activity and increased the MDA level in the studied leaves. Presented results confirm that spermidine stabilizes plant membranes under water stress conditions. However, this effect does not seem to be associated with the Spd-induced modifications in the lipid peroxidation activities.     

Uniconazole inhibits stress-induced ethylene in wheat and soybean seedlings

Previous studies have shown that uniconazole inhibits ethylene synthesis and protects plants from various stresses. The present research was conducted to delineate the mechanism of ethylene inhibition by uniconazole [(E)-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol]. Following heat stress of 48°C for 3 h, the shoots of the control wheat seedlings became desiccated, and the seedlings lost 23% of their fresh mass 8 h after stress. The control soybean seedlings had epinastic unifoliate leaves 5 h after foliar application (4.4 g.a.i./ha) of the herbicide triclopyr [(3,5,6-trichloro-2-pyridinyl)oxyacetic acid]. Soil drench applications of uniconazole, a potent member of the triazole family, reduced these symptoms associated with heat and herbicide stress in wheat (5.0 mg/L) and soybean (0.4 mg/L) seedlings, respectively.Basal ethylene production was inhibited 32 and 48% by uniconazole in the wheat and acotyledonous soybean seedlings, respectively. Following a 48°C heat stress, 1-aminocyclopropane-1-carboxylic acid (ACC) levels increased 40% in both the control and uniconazole-treated wheat seedlings. After triclopyr application, ACC levels increased 400% in both the control and uniconazoletreated soybean seedlings. The increased ACC levels, following stress, were accompanied by increased ethylene production from the control, but not from the uniconazole-treated wheat and acotyledonous soybean seedlings. Uniconazole treatment did not significantly change the basal or stress-induced N-malonyl-1-aminocyclopropane-1-carboxylic acid (MACC) levels compared to controls. These results suggest that uniconazole inhibits ethylene synthesis by interfering with the conversion of ACC to ethylene in wheat and acotyledonous soybean seedlings. Ethylene production and ACC conversion were not inhibited by uniconazole in excised soybean cotyledons. These results indicate that different ethylene-forming enzyme (EFE) systems operate in the soybean acotyledonous seedling and cotyledon, and the system in the former is inhibited by uniconazole.     

Changes m Ethylene Production in Relation to l-Aminocyclopropane-l-Carboxylic Acid and Its Malonyl Conjugate in Waterlogged Wheat Plants

When wheat seedlings were subjected to waterlogging, 1-aminocyelopropane-l-carboxylic acid (ACC), an ethylene precursor, accumulated in large quantity in roots. In shoots, ACC and ethylene production also increased, but declined with the prolonged periods of waterlogging. However, ACC content in roots maintained in high level during the whole period of waterlogging. Drainage caused a drastic drop in both ACC content and ethylene production in waterlogged plants to control level. 1-(malonylamino) cyclopropane-l-carboxylic acid (MACC) level in roots subjected to waterlogging showed little changes. However, MACC content in shoots kept increasing during the 9-days period of waterlogging. At later period of waterlogging (longer than 5 days) when ACC and ethylene production bad dropped, the. level of MACC continued to increase. Draining stopped this increasing, but did not reduced its level. When exogenous ACC was introduced into the leaves via transpiration stream, the ability of leaves of waterlogged plant to convert ACC to MACC was much higher than control. The data presented showed that at the later stage of waterlogging, the conversien of a great quantity of ACC to MACC in waterlogged wheat plants is the cause of the reduction of ethylene production and ACC content. It was suggested that the formation of MACC is another way of regulation in ethylene biosynthesis. Among leaves of different ages, the enhancement of ethylene, ACC and MACC content was more pronounced in older leaves than in younger laves during the waterlogging period. The physiological significance of adaptation to waterlogging stress was discussed.     

Membrane permeability and micro- and macroelement accumulation in spring wheat cultivars during the short-term effect of salinity- and PEG-induced water stress

The comparative responses of ten spring wheat cultivars to water stress were investigated. Wheat plants were cultured under hydroponics conditions (Hoagland nutrient) to the stage of three-leaf seedlings. Then, the water medium was supplemented with PEG (drought) or NaCl (salinity) to obtain a water status equal to −1.5 MPa. After a 2-day treatment, the changes in the following parameters were determined: fresh and dry weight, macro- and microelement accumulation, membrane injury (electrolyte leakage, lipid peroxidation) and fatty acid content of the phospholipid fraction of plasmalemma (in comparison to plants not stressed, taken as a control). Generally, the plants were more significantly influenced by water stress stimulated by PEG than by NaCl treatment, as compared to the plants cultivated in the control media. The results of the decrease in water content in leaves and electrolyte leakage from cells corresponded well with the intensity of lipid peroxidation (determined by malondialdehyde—MDA-content) and were chosen for the selection of investigated genotypes for tolerance to both stresses. The more tolerant genotypes exhibited the opposite changes in phospholipid fatty acid unsaturation for two applied stresses i.e. NaCl treatment caused a decrease in unsaturation whereas in PEG-treated plants an increase in unsaturation was observed. These changes were reversed for less tolerant plants, i.e. NaCl treatment influenced an increase in fatty acid unsaturation whereas in PEG-treated plants a decrease in unsaturation was measured. The ratio of U/S (unsaturated to saturated fatty acids) correlated with the total amount of accumulated macroelements. The content of Mg, Ca and S in leaves of plants undergoing both stress factors (NaCl and PEG) dropped whereas the K and P content increased in leaves of wheat seedlings cultured on media containing NaCl only. For microelements, a decrease in the accumulation of these nutrients was detected in all investigated seedlings. However, a greater reduction in the level of these elements occurred in seedlings grown on media with PEG in comparison to those grown on NaCl containing media.     

Growth Responses and Allocation of Assimilates of Rice Seedlings by Paclobutrazol and Gibberellin Treatment

Paclobutrazol [(2RS,3RS)-1-(4-chlorophenyl)methyl-4,4-dimethyl-2-(1h-1,2,4-trizol-1-yl)penten-3-ol] effectively decreased vegetative growth of rice (Oryza sativa L.) seedlings and increased the chlorophyll content. The number of veins in a leaf, the calculated number of stomata per leaf, and the length of guard cells were not altered by the paclobutrazol treatment, suggesting an effect on cell elongation. The allocation pattern of carbohydrates was changed by either gibberellin (GA) or paclobutrazol treatment. GA₃ induced more shoot growth and less accumulation of starch than the control and paclobutrazol-treated seedlings. Photosynthetic ability was not affected by either paclobutrazol or GA₃ treatment. Paclobutrazol-treated plants allocated a smaller amount of photosynthates for vegetative shoot growth and stored more as starch in the crowns than the control and GA₃-treated plants. The same starch degrading activity in the crown tissue of paclobutrazol-treated seedlings as in control plants suggests that the accumulated starch is utilized in a normal activity for growth including leaf emergence, tiller formation, and root production, resulting in improved seedling quality. Received May 30, 1996; accepted December 10, 1996     

Uniconazole-induced tolerance of soybean to water deficit stress in relation to changes in photosynthesis, hormones and antioxidant system

This study investigated whether uniconazole confers drought tolerance to soybean and if such tolerance is correlated with changes in photosynthesis, hormones and antioxidant system of leaves. Soybean plants were foliar treated with uniconazole at 50 mg L-1 at the beginning of bloom and then exposed to water deficit stress at pod initiation for 7 d. Uniconazole promoted biomass accumulation and seed yield under both water conditions. Plants treated with uniconazole showed higher leaf water potential only in water-stressed condition. Water stress decreased the chlorophyll content and photosynthetic rate, but those of uniconazole-treated plants were higher than the stressed control. Uniconazole increased the maximum quantum yield of photosystemand ribulose-1,5-bisphosphate carboxylase/oxygenase activity of water-stressed plants. Water stress decreased partitioning of assimilated 14C from labeled leaf to the other parts of the plant. In contrast, uniconazole enhanced translocation of assimilated 14C from labeled leaves to the other parts, except stems, regardless of water treatment. Uniconazole-treated plants contained less GA3, GA4 and ABA under well-watered condition than untreated plants, while the IAA and zeatin levels were increased substantially under both water conditions, and ABA concentration was also increased under water stressed condition. Under water-stressed conditions, uniconazole increased the content of proline and soluble sugars, and the activities of superoxide dismutase and peroxidase in soybean leaves but not the malondialdehyde content or electrical conductivity. These results suggest that uniconazole-induced tolerance to water deficit stress in soybean was related to the changes of photosynthesis, hormones and antioxidant system of leaves.     

Contribution of Oxidative Stress to the Development of Cold-Induced Damage to Leaves of Chilling-Sensitive Plants: 3. Injury of Cell Membranes by Chilling Temperatures

Changes in permeability of cell membranes (judged from electrolyte leakage) were examined on leaves of 7- to 11-day-old seedlings of maize (Zea mays L.), cucumber (Cucumis sativus L.), millet (Panicum miliaceum L.), and on etiolated shoots of potato (Solanum tuberosum L.) immediately after cooling plants for 1–24 h at 2°C and one day after a 24-h chilling treatment. A gradually increasing leakage of ions from the cells was observed upon prolongation of chilling exposure, with the maximum attained by the end of 24-h chilling treatment. The leakage of electrolyte was slightly reduced in the post-treatment period but it was still higher than the electrolyte leakage from the control samples (untreated plants). The cold treatment of chilling-sensitive plants (but not of potato) revealed a positive correlation between the rates of lipid peroxidation, indicative of chilling injury, and the electrolyte efflux (r = 0.61–0.96). The evaluation of plant susceptibility to injury showed that millet and potato plants recovered from the chilling damage in 24 h after the treatment, whereas maize and cucumber plants did not show such a recovery.     

Uniconazole inhibits stress-induced ethylene in wheat and soybean seedlings

Previous studies have shown that uniconazole inhibits ethylene synthesis and protects plants from various stresses. The present research was conducted to delineate the mechanism of ethylene inhibition by uniconazole [(E)-(p-chlorophenyl)-4,4-dimethyl-2-(1,2,4-triazol-1-yl)-1-penten-3-ol]. Following heat stress of 48°C for 3 h, the shoots of the control wheat seedlings became desiccated, and the seedlings lost 23% of their fresh mass 8 h after stress. The control soybean seedlings had epinastic unifoliate leaves 5 h after foliar application (4.4 g.a.i./ha) of the herbicide triclopyr [(3,5,6-trichloro-2-pyridinyl)oxyacetic acid]. Soil drench applications of uniconazole, a potent member of the triazole family, reduced these symptoms associated with heat and herbicide stress in wheat (5.0 mg/L) and soybean (0.4 mg/L) seedlings, respectively. Basal ethylene production was inhibited 32 and 48% by uniconazole in the wheat and acotyledonous soybean seedlings, respectively. Following a 48°C heat stress, 1-aminocyclopropane-1-carboxylic acid (ACC) levels increased 40% in both the control and uniconazole-treated wheat seedlings. After triclopyr application, ACC levels increased 400% in both the control and uniconazoletreated soybean seedlings. The increased ACC levels, following stress, were accompanied by increased ethylene production from the control, but not from the uniconazole-treated wheat and acotyledonous soybean seedlings. Uniconazole treatment did not significantly change the basal or stress-induced N-malonyl-1-aminocyclopropane-1-carboxylic acid (MACC) levels compared to controls. These results suggest that uniconazole inhibits ethylene synthesis by interfering with the conversion of ACC to ethylene in wheat and acotyledonous soybean seedlings. Ethylene production and ACC conversion were not inhibited by uniconazole in excised soybean cotyledons. These results indicate that different ethylene-forming enzyme (EFE) systems operate in the soybean acotyledonous seedling and cotyledon, and the system in the former is inhibited by uniconazole.     

Riboflavin spraying impairs the antioxidant defense system but induces waterlogging tolerance in tobacco

Riboflavin, which causes plants to produce reactive oxygen species (ROS) when exposed to light, is an excellent photosensitizer for biocidal reactions. This study explores the possible protective role of riboflavin against waterlogging stress in tobacco plants. Tobacco seedlings (4 weeks old) were divided into four groups and pretreated with 0, 0.2, 0.5 or 1.0 mM riboflavin for 1 week, after which all groups were exposed to waterlogging stress for 7 days. We observed delayed leaf senescence and extended survival time, suggesting that riboflavin can confer increased waterlogging tolerance to plants as compared with the control (0 mM riboflavin). Enhanced stomatal closure was observed in the riboflavin-pretreated tobacco. We evaluated the levels of oxidative damage (H₂O₂ and lipid peroxidation), antioxidant enzyme (superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase) activity and antioxidant metabolites (including ascorbate and glutathione) in tobacco leaves that were pretreated with riboflavin. However, the results show that riboflavin pretreatment caused a decrease in chlorophyll content, antioxidant enzyme activity and redox values (AsA/DHA and GSH/GSSG), while causing a significant increase in lipid peroxidation, H₂O₂ accumulation and total ascorbate or glutathione content. In addition, the survival time and stomatal aperture of riboflavin-treated plants were significantly modified by exogenous application of GSH, well-known ROS scavenger. To explain the stomatal closure observed in tobacco plants, we propose a “damage avoidance” hypothesis based on riboflavin-mediated ROS toxicity. The protective function of the photosensitizer riboflavin may be highly significant for farming in frequently waterlogged areas.     

New Plant Growth Regulators Protect Photosynthesis and Enhance Growth Under Drought of Jack Pine Seedlings

To determine whether natural plant growth regulators (PGRs) can enhance drought tolerance and the competitive ability of transplanted seedlings, 1.5-year-old jack pine (Pinus banksana Lamb.) seedlings were treated with homobrassinolide, salicylic acid, and two polyamines, spermine and spermidine, triacontanol, abscisic acid (ABA), and the synthetic antioxidant, Ambiol. PGRs were fed into the xylem for 7 days and plants were droughted by withholding water for 12 days. ABA, Ambiol, spermidine, and spermine at a concentration of 10 μg L⁻¹ stimulated elongation growth under drought, whereas ABA, Ambiol, and spermidine maintained higher photosynthetic rates, higher water use efficiency, and lower Ci/Ca ratio under drought compared with control plants. The damaging effects of drought on membrane leakage was reversed by Ambiol, ABA, triacontanol, spermidine, and spermine. Because ABA, Ambiol, and both polyamines enhanced elongation growth and also reduced membrane damage in jack pine under drought, they show promise as treatments to harden seedlings against environmental stress. The protective action of these compounds on membrane integrity was associated with an inhibition of ethylene evolution, with a reduction in transpiration rate and an enhancement of photosynthesis, which together increased water use efficiency under drought. Although most of the tested compounds acted as antitranspirants, the inhibition in membrane leakage in ABA-, Ambiol-, and polyamine-treated plants appeared more closely related to the antiethylene action. Received December 30, 1998; accepted October 14, 1999     

烯效唑干拌种对小麦氮素积累和运转及籽粒蛋白质品质的影响

通过田间试验,研究了不同烯效唑干拌种剂量对3个不同筋力小麦品种植株氮素积累、运转和籽粒蛋白质品质的影响,结果表明,基因型、环境及烯效唑处理对小麦品质的影响效应依次减小,且均达到了极显著水平,但三者的互作效应较小。烯效唑处理后提高了不同生态点下不同小麦品种籽粒蛋白质含量和产量,处理后的面筋含量和沉淀值增加,面团形成时间和稳定时间延长;干拌种增加了开花期各营养器官中的氮素含量和单株氮素积累量,花后氮素总转移量、总转移率及其对籽粒氮的贡献率极显著提高,且处理后旗叶中可溶性蛋白质含量在花后15 d内均显著高于对照;对籽粒中氮含量而言,烯效唑处理后提高了灌浆初期籽粒中的非蛋白氮含量,花后5—20 d内均高于对照,灌浆期间籽粒蛋白氮含量均高于对照,因而处理后的粗蛋白质含量变化动态特点为谷底高、回升快。研究认为,烯效唑处理如同基因、环境一样独立影响小麦籽粒品质,而烯效唑处理后提高了开花初期旗叶中的可溶性蛋白质含量和花前营养器官中氮素含量及花后氮素转运量,可能是其提高籽粒非蛋白氮含量、促进籽粒蛋白质含量增加和蛋白质质量提高的重要原因之一,烯效唑干拌种对小麦籽粒蛋白质品质的改善具有广适性。