Chilling Sensitivity of Photosynthetic Oil-Seedlings: I COTTON SUNFLOWER

Despite the high probability that sensitive post-emergent seedlingswill be exposed to suboptimal temperatures which significantlyaffect subsequent development and yield, growers of long-season,indeterminate crops must rely upon empirically determined ‘earliestplanting dates’ Most ‘chilling-stress’ studieshave dealt, not with photosynthetic seedlings, but rather withthe effect of low, non-freezing temperatures (< 10 ?) upongerminating seeds and pre-emergent seedlings. A photosyntheticseedling growth system was used to monitor the effects of temperaturesfrom 10 to 35? upon the roots and aerial portions of chilling-sensitivecotton and relatively chilling-resistant sunflower oil-seedlings.Length measurements of cotton seedlings were too variable tobe reliable indicators of temperature treatment effects, butroot and shoot fresh weights could be used as non-destructivemeasurements of differences in root and shoot temperature responsesin both cotton and sunflower seedlings. The fresh weights wereindicative of the relative water status of seedling roots andshoots, including that of seedlings returned to 30? after exposureto other temperatures. Growth of both cotton and sunflower seedlingswas inhibited to some degree at non-optimal temperatures andthe capacities of the roots and shoots to return to normal waterstatus, as indicated by fresh weights and relative water contents,was correlated with sensitivity to suboptimal temperatures Key words: Cotton, sunflower, temperature, water status     

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.     

外源脯氨酸对高温胁迫下黄瓜幼苗叶片AsA-GSH循环和光合荧光特性的影响

以抗热性较弱的黄瓜品种‘新泰密刺'为试材,在人工气候箱内采用营养液栽培法,研究了外源脯氨酸(Pro)预处理对高温胁迫下黄瓜幼苗叶片抗坏血酸-谷胱甘肽循环和光合荧光特性的影响.结果显示:(1)与清水处理相比,高温胁迫4 h和8 h时,Pro预处理黄瓜幼苗叶片单脱氢抗坏血酸还原酶(MDAR)活性、GSH(还原型谷胱甘肽)/GSSG(氧化型谷胱甘肽)比值及GSH含量显著升高;(2)在高温胁迫8 h时,Pro预处理幼苗的净光合速率(P_n)、气孔导度(G_s)及PSⅡ的最大光化学效率(F_v/F_m)、光化学淬灭系数(q_P)均显著升高,而蒸腾速率(T_r)和非光化学淬灭系数(NPQ)降低.研究表明,外源Pro预处理可显著提高高温胁迫下黄瓜幼苗叶片抗坏血酸-谷胱甘肽循环清除H_2O_2能力和叶片光合能力,有效缓解高温胁迫对黄瓜叶片抗氧化系统和光合系统的伤害,从而增强植株的耐热性.     

纯化腐植酸对氮胁迫下黄瓜幼苗生长和氮代谢的影响

为研究纯化腐植酸(PHA)在不同水平氮胁迫下对黄瓜植株生长和氮代谢的影响,探明PHA对逆境胁迫的缓解作用机制,采用水培方式,选用新泰密刺为供试品种,以正常氮水平(11 mmol·L^-1 NO₃^-)为对照,进行低氮(1.0 mmol·L^-1 NO₃^-)和高氮(101 mmol·L^-1 NO₃^-)胁迫处理,研究纯化腐植酸对氮胁迫下黄瓜幼苗生长和氮代谢的影响.结果表明: 低氮和高氮胁迫均抑制了黄瓜幼苗生长,株高、茎粗、叶面积、干物质积累量均低于正常氮水平处理.施用纯化腐植酸促进了正常氮水平及低氮胁迫下黄瓜干物质积累,在高氮胁迫下差异不显著.PHA影响了黄瓜幼苗NO₃^-的吸收,呈低氮下促进、高氮下抑制吸收的趋势;PHA显著降低了低氮、高氮胁迫下根系和叶片中的铵态氮含量;与正常氮水平相比,低氮、高氮胁迫下根系和叶片的硝酸还原酶(NR)、谷氨酰胺合成酶(GS)、谷氨酸合酶(GOGAT)、谷氨酸脱氢酶(GDH)活性及根系中亚硝酸还原酶(NiR)活性均显著降低,PHA不同程度地提高了NR、NiR、GS、GOGAT、GDH活性,还提高了根系和叶片中游离氨基酸、可溶性蛋白的含量.综上,添加PHA缓解了氮胁迫对黄瓜幼苗生长的抑制作用.     

土壤水分对温室春黄瓜苗期生长与生理特性的影响

以津优1号黄瓜为试验材料．研究了土壤不同水分含量对温室春黄瓜苗期生长与生理特性的影响。结果表明,在土壤水分为田间持水量90％时．黄瓜幼苗长势健壮,茎粗大,根系活力强,叶绿素含量和光合速率高．与其它处理差异显著,说明土壤含水量过高或过低均不利于培育黄瓜壮苗。株高和叶面积随土壤含水量的升高而增加;细胞汁液浓度随土壤含水量的升高而降低．且对植株水分状况反应十分敏感,可以用来作为判断植株水分盈亏状况的生理指标。     

嫁接对铜胁迫下黄瓜幼苗根系多胺代谢的影响

采用营养液栽培法,研究了嫁接(以黑籽南瓜为砧木)对铜胁迫下黄瓜幼苗根系活力及多胺代谢的影响.结果表明:铜胁迫下黄瓜幼苗根系活力下降,电解质渗漏率升高,而嫁接苗的变化幅度显著小于黄瓜自根苗;铜胁迫下黄瓜嫁接植株根系中除游离态腐胺(Put)含量显著低于自根苗外,结合态和束缚态Put、3种形态亚精胺(Spd)和精胺(Spm)含量均显著高于自根苗,嫁接苗根系中游离态Put含量及腐胺/多胺(Put/PAs)显著低于自根苗;铜胁迫下,嫁接苗根系精氨酸脱羧酶(ADC)、鸟氨酸脱羧酶(ODC)和S-腺苷蛋氨酸脱羧酶(SAMDC)活性高于自根苗,而二胺氧化酶(DAO)和多胺氧化酶(PAO)活性显著低于自根苗.表明嫁接黄瓜幼苗根系PAs的合成增加,降解减少,使PAs含量维持在较高水平,从而提高了黄瓜幼苗抗铜胁迫能力.     

Physiological and biochemical mechanisms of silicon-induced copper stress tolerance in cotton (<Emphasis Type="Italic">Gossypium hirsutum</Emphasis> L.)

Accumulation of excess copper (Cu) in agricultural soils can decrease growth and quality of crops grown on these soils and a little information is available on the role of silicon (Si) in reducing Cu toxicity in plants. A hydroponic study was conducted to investigate the effects of Si (1.0 mM) on growth and physiology of cotton seedlings grown on different Cu (0, 25, and 50 µM) concentrations. Elevated levels of Cu decreased growth, biomass, photosynthetic pigments, and gas exchange characteristics, and increased the electrolyte leakage (EL), hydrogen peroxide (H₂O₂), and thiobarbituric acid reactive substances (TBARS) contents in leaf, stem, and roots of cotton seedlings. Cu stress alone decreased the activities of key antioxidant enzymes in cotton seedlings. Exogenous application of Si alleviated the toxic effects of Cu on cotton seedlings by improving growth, photosynthetic pigments, and gas exchange characteristics under Cu stress. The Si application decreased Cu concentrations in leaves, stem, and roots as compared with the control plants. Furthermore, Si decreased oxidative stress as evidenced by decreased EL, H₂O₂, and TBARS contents, and increased the antioxidant enzyme activities in cotton seedlings. This study provides evidences of Si-mediated reduction of Cu toxicity in cotton seedlings at physiological and biochemical levels.     

AM真菌种间差异对枳壳生长及耐热性效应的研究※

用地表球囊霉、莫西球囊霉、珠状巨孢球囊霉及其混合菌剂接种无菌根枳壳幼苗进行盆栽试验,25℃培养4个月,观察对枳壳菌根形成和营养生长的影响,在40℃高温胁迫30d,调查分析菌根枳壳的耐热性。试验结果表明:接种AM真菌的根系形成了20%～80%的菌根侵染率;菌根枳壳的苗高、苗质量、节间长、茎基粗、须根数量和须根长度等营养生长显著增加;叶片中的SOD,POD活性和根系活力显著增强,可溶性蛋白、可溶性糖含量显著升高,叶片中的MDA含量降低,膜透性显著变小,枳壳苗的耐热性显著提高;但是,AM真菌在促进枳壳苗菌根化、营养生长和提高耐热性方面存在着种间差异,地表球囊霉、莫西球囊霉、珠状巨孢球囊霉、混合菌剂与枳壳根系形成丛枝菌根的侵染率依次为20.4%±1.2%、61.8%±3.4%、85.7%±2.7%、83.3%±2.2%,促进枳壳苗营养生长提高枳壳苗耐热能力的AM真菌依次为:地表球囊霉<莫西球囊霉<珠状巨孢球囊霉<混合菌剂,认为珠状巨孢球囊霉和莫西球囊霉是枳壳耐高温胁迫菌根化育苗的重要优良菌种。     

外源NO对NaCl胁迫下黄瓜幼苗生长和根系谷胱甘肽抗氧化酶系统的影响

以津春2号黄瓜为材料,采用营养液水培的方法,研究了外源一氧化氮(NO)对黄瓜幼苗生长和根系谷胱甘肽抗氧化酶系统的影响.结果表明,(1)正常生长条件下添加NO能促进黄瓜幼苗生长,而添加亚甲基蓝(MB-1)显著抑制黄瓜幼苗的生长;(2)添加NO显著缓解了NaCl胁迫对黄瓜幼苗生长的抑制,提高根系还原型谷胱甘肽(GSH)含量、抗坏血酸过氧化物酶(APX)和谷胱甘肽还原酶(GR)活性,而氧化型谷胱甘肽(GSSG)含量略有下降,同时缓解了NaCl胁迫下抗坏血酸(ASA)含量的下降幅度;(3)NaCl胁迫下添加NO的同时添加MB-1可部分解除NO的作用,与NaCl胁迫下单独添加NO处理比较,GR活性、GSH和ASA含量均降低,GSSG含量提高,APX先升高后下降.研究发现,外源NO可能通过鸟苷酸环化酶(cGC)介导来调节NaCl胁迫下黄瓜幼苗根系GR活性和GSH、GSSG、ASA含量,提高抗氧化酶活性和非酶抗氧化物质含量,增强植株对活性氧的清除能力,减少膜脂过氧化,缓解NaCl胁迫对黄瓜幼苗造成的伤害.     

Interactive effects of water,light and heat stress on photosynthesis in Fremont cottonwood

Fremont cottonwood seedlings are vulnerable to water stress from rapid water‐table decline during river recession in spring. Water stress is usually cited as the reason for reduced establishment, but interactions of water stress with microclimate extremes are more likely the causes of mortality. We assessed photosynthetic responses of Fremont cottonwood seedlings to water, light and heat stresses, which commonly co‐occur in habitats where seedlings establish. Under moderate temperature and light conditions, water stress did not affect photosynthetic function. However, stomatal closure during water stress predisposed Fremont cottonwood leaves to light and heat stress, resulting in greatly reduced photosynthesis beginning at 31 °C versus at 41 °C for well‐watered plants. Ontogenetic shifts in leaf orientation from horizontal to vertical, which occur as seedlings mature, reduce heat and light stress, especially during water stress. When compared with naturally occurring microclimate extremes, seedling stress responses suggest that reduced assimilation and photoprotection are common for Fremont cottonwood seedlings on exposed point bars where they establish. These reductions in photosynthesis likely have negative impacts on growth and may predispose young (<90‐day‐old) seedlings to early mortality during rapid water‐table declines. Interactions with heat and light stress are more important in these effects than water stress alone.     

D-精氨酸对低氧胁迫下黄瓜幼苗根系多胺含量和无氧呼吸代谢的影响

采用营养液水培法,研究了根际低氧胁迫下D-精氨酸（D-Arg）对两个抗低氧能力不同的黄瓜品种根系中多胺含量和无氧呼吸代谢的影响.结果表明,低氧处理下,黄瓜幼苗根系中多胺含量显著增加,无氧呼吸代谢能力提高;与抗低氧能力弱的‘中农八号’相比,抗低氧能力强的‘绿霸春四号’根系中乙醇发酵活性较高,乳酸发酵活性较低;低氧胁迫下,D-精氨酸能显著降低黄瓜幼苗根系中腐胺、亚精胺和精胺含量,根系中乙醇脱氢酶（ADH）和乳酸脱氢酶（LDH）活性增加,乙醇和乳酸含量升高,植株生长受到抑制,而外源腐胺能缓解D-精氨酸的这种作用.说明黄瓜幼苗根系中较高的多胺含量可能有利于缓解低氧胁迫对植株造成的伤害.     

低氧胁迫下24-表油菜素内酯对黄瓜幼苗叶片光合特性及多胺含量的影响

采用1/2 Hoagland营养液培养,研究了低氧胁迫下24-表油菜素内酯(EBR)对黄瓜幼苗叶片光合特性及多胺含量的影响.结果表明：低氧胁迫下黄瓜幼苗的净光合速率(P_n)、气孔导度(g_s)、蒸腾速率(T_r)、胞间CO₂浓度(C_i)显著下降,而叶绿素含量显著提高,幼苗生长受抑;低氧胁迫显著提高了黄瓜幼苗叶片的腐胺(Put)、亚精胺(Spd)、精胺(Spm)、多胺(PAs)含量和Put/PAs,但降低了(Spd+Spm) /Put.低氧胁迫下,外源EBR不仅显著提高了黄瓜幼苗的P_n、g_s、T_r及叶绿素含量,也显著提高了黄瓜幼苗叶片的游离态Spm、结合态Spd、Spm及束缚态Put、Spd、Spm含量,促进了PAs的进一步积累,且降低了Put/PAs,提高了(Spd+Spm)/Put．可见,外源EBR调节了黄瓜幼苗内源多胺含量及形态的变化,维持了较高的光合性能,促进了叶面积和干物质量的显著增加,缓解了低氧胁迫对黄瓜幼苗的伤害.     

外源一氧化氮对镉胁迫下黄瓜幼苗生长、活性氧代谢和光合特性的影响

镉是植物生长的非必需元素,它具有很大的生物毒性,与其它重金属相比,更易被植物吸收积累。通过采用营养液水培试验的方法,研究了外源一氧化氮（Nitric oxide,NO）对不同浓度Cd^2＋（100μmol L^-1．300μmol L^-1,500μmol L^-1）胁迫下黄瓜幼苗生长、叶片光合特性以及活性氧代谢的影响。结果表明：300μmol L^-1NO供体硝普钠（Sodium nitrop russide,SNP）能显著缓解镉胁迫时黄瓜植株造成的伤害,对300μmol L^-1 Cd^2＋处理的黄瓜幼苗缓解效果最好,可提高幼苗的生长量,增强幼苗叶片超氧物歧化酶（SOD）、过氧化物酶（POD）活性;提高了叶片叶绿素和脯氨酸（Pro）含量;降低了叶片内二醛（MDA）含量。     

油菜素内酯对氯化钠胁迫下黄瓜幼苗的缓解效应

研究了2,4-表油菜素内酯(EBR)对氯化钠胁迫下黄瓜幼苗叶片光合作用及抗氧化系统的影响．结果表明： 与对照相比,氯化钠胁迫导致黄瓜幼苗叶片超氧阴离子产生速率、过氧化氢和丙二醛含量、细胞膜透性显著升高,净光合速率、气孔导度、蒸腾速率、胞间CO₂浓度显著下降,幼苗生长显著受抑．EBR可提高黄瓜幼苗叶片超氧化物歧化酶、过氧化物酶、过氧化氢酶等抗氧化酶活性,降低超氧阴离子产生速率、过氧化氢和丙二醛含量及细胞膜透性,维持良好的光合性能,从而促进幼苗生长,有效缓解氯化钠胁迫造成的伤害.
     

Seed reserve-dependent growth responses to temperature and water potential in carrot (Daucus carota L.)

Both temperature and soil moisture vary greatly in the surface layers of the soil through which seedlings grow following germination. The work presented studied the impact of these environmental variables on post-germination carrot growth to nominal seedling emergence. The rapid pre-crook downward growth of both the hypocotyl and root was consistent with their requirement for establishment in soil drying from the surface. At all temperatures, both hypocotyl and root growth rates decreased as water stress increased and there was a very distinct temperature optimum that tended to occur at lower temperatures as water stress increased. A model based on the thermodynamics of reversible protein denaturation was adapted to include the effects of water potential in order to describe these growth rate responses. In general, the percentage of seedlings that reached the crook stage (start of upward hypocotyl growth) decreased at the extremes of the temperature range used and was progressively reduced by increasing water stress. A model was developed to describe this response based on the idea that each seedling within a population has lower and upper temperature thresholds and a water potential threshold which define the conditions within which it is able to grow. This threshold modelling approach which applies growth rates within a distribution of temperature and water potential thresholds could be used to simulate seedling growth by dividing time into suitable units.     

Seedling vigour and the early growth of transplanted rice (Oryza sativa)

Previous studies suggest that the positive response of transplanted rice (Oryza sativa L.) to nursery fertiliser application was due to increased seedling vigour or possibly to increased nutrient content. This paper presents results of two glasshouse experiments designed to test the hypothesis that seedling vigour was responsible for the response of transplanted seedlings to nursery treatments. The aim of the present study was to explore the concept of seedling vigour of transplanted rice and to determine what plant attributes conferred vigour on the seedlings. Seedling vigour treatments were established by subjecting seedlings to short-term submergence (0, 1 and 2 days/week) in one experiment and to leaf clipping or root pruning and water stress in another to determine their effect on plant growth after transplanting. Submerging seedlings increased plant height but depressed shoot and root dry matter and root:shoot ratio of the seedling at 28 days after sowing. After transplanting these seedlings, prior submergence depressed shoot dry matter at 40 days. Nursery nutrient application increased plant height, increased root and shoot dry matter, but generally decreased root:shoot ratio. Pruning up to 60% of the roots at transplanting decreased shoot and root dry matter, P concentration in leaves at panicle initiation (PI) and straw dry matter and grain yield at maturity. By contrast, pruning 30% of leaves depressed shoot and root dry matter by 30% at PI, and root dry matter and straw and grain yield by 20% at maturity. The combined effects of leaf clipping and root pruning on shoot, root and straw dry matter were largely additive. It is concluded that the response of rice yield to nursery treatments is largely due to increased seedling vigour and can be effected by a range of nutritional as well as non-nutritional treatments of seedlings that increase seedling dry matter, nutrient content, and nutrient concentration. Impairment of leaf growth and to a lesser extent root growth in the nursery depressed seedling vigour after transplanting. However, rather than increasing stress tolerance, seedling vigour was more beneficial when post transplant growth was not limited by nutrient or water stresses.     

亚精胺和丛枝菌根真菌对黄瓜生长的影响

以黄瓜品种‘津春2号’为材料,在育苗基质中添加亚精胺(Spd)和丛枝菌根真菌(AMF),研究外源Spd和AMF对黄瓜幼苗生长、光合作用、果实产量和品质以及根际微生物和酶活性的影响.结果表明:育苗基质中同时添加Spd和AMF,可促进黄瓜幼苗生长,提高根系活力和果实产量,改善品质,并促进养分吸收;Spd和AMF提高黄瓜幼苗净光合速率、实际光化学效率、表观量子效率、羧化效率和光呼吸速率,增加基质中细菌和放线菌数量,而降低真菌数量,并提高蔗糖酶、中性磷酸酶、过氧化氢酶和脲酶的活性.说明育苗基质中同时添加Spd和AMF,可提高黄瓜植株光能利用效率,促使黄瓜幼苗根际微生物区系从低肥力的"真菌型"向高肥力的"细菌型"转化,加速有机磷和有机态氮的分解与转化,为黄瓜生长发育提供比较充足的N、P等养分,从而促进黄瓜植株生长,提高产量并改善品质.Spd可提高AMF侵染率,两者对黄瓜幼苗生长具有明显的叠加效应,说明在接种AMF的基质中添加Spd,是一种可增强AMF侵染率的有效方法.     

Maximum axial and radial growth pressures of plant roots

Summary The axial root growth force exerted by seedlings of pea (Pisum sativum cv. Greenfeast), cotton (Gossypium hirsutum cv. Sicot 3) and sunflower (Helianthus annuus cv. Hysun) was measured. Effects of different seedling age and different batches of seeds on axial root growth pressure were investigated. Mean values of the maximum axial root growth pressure (P_a) estimated from the maximum axial root growth force (F_max) and root diameter were 497, 289, and 238 kPa respectively for pea, cotton and sunflower seedlings of same size. P_a and F_max were significantly influenced by seedling age and for pea seedlings of same age they varied with the seed batch. A new technique was developed for estimating radial root growth pressure and was tested on pea seedlings. Each pea root was confined both in the axial and radial directions in a cylindrical chalk sample at a constant water potential. The roots exerted radial stress which caused tensile failure in a proportion of the chalks. The measurement of tensile strength of duplicate chalks enabled estimation of the maximum radial pressures exerted by the roots. The maximum axial and radial root growth pressures were of comparable magnitude.     

Chilling tolerance in February seeded Chaite rices (Oryza sativa) of Nepal

Five Chaite and three main season rices Oryza sativa genotypes were examined to assess the effect of low temperature on the germination and growth of roots and shoots, root regeneration capacity, the extent of chlorophyll synthesis of etiolated seedlings, total chlorophyll content and photo-chemical efficiency (Fv/Fm) of chilled plants. Cultivated differences in the ability to germinate and grow at low temperatures have been found. The poor ability of Chaite rices to tolerate photo-oxidative tissue damage during January and February seemed to be the major factor resulting in poor seedling growth.     

Influence of Ultraviolet Radiation on Germination and Early Seedling Growth

The influence of UV-B radiation (280–320 nm) from filtered and unfiltered FS-40 fluorescent sunlamps on germination and early seedling growth was examined for a range of vegetables (tomato, radish, cucumber, lettuce, and bean) and field crops (wheat, cotton, soybean, and millet). Continuous exposure of seeds for 3 days to 26.9 × 10⁻² W × m⁻² UV-B radiation (280–320 nm) at 25°C, had a slight effect on fresh weight of seedlings but no appreciable influence on germination percentage, or dry weight of seedlings. Extending the time of exposure to 6 days, however, resulted in abnormal seedling growth in all species but wheat. Typical responses were short, stubby roots, bronzing of the cotyledons, increased pigmentation, and abnormal curvature of the shoots.