Osmotic Stress in Coleoptiles and Primary Leaves of Wheat. II. Main Phosphorylated Fractions

Seedlings of wheat (Triticum durum, cv. Balcarceno-INTA) werewater-stressed in darkness with 20% polyethylene glycol (PEG)6000 or 0.3 M mannitol added to the root medium. At differenttimes and up to a total of 36 h of treatment the coleoptilesand primary leaves were cut and analysed for acid soluble-P,lipid-P, protein-P, alkali-stable organic-P, and nucleic acid-P.All the phosphorylated fractions were expressed on 100 mg oftotal coleoptile and primary leaves dry wt. Acid soluble-P (14.6µmol) accounted for most of the phosphorus. The lipid-Pfraction remained at an unchanged level (6.2 µmol/100mg dry wt) in control or in mildly osmotic stressed shoots ofseedlings over the period of treatment. The protein-P representedonly 2.4% (0.8 µmol) of the total phosphorus found incoleoptiles and primary leaves. The alkali-stable organic-Pand nucleic acid-P fractions represented 22.2% (7.2µ mol)and 11.1% (3.6 µmol) of the total phosphorus content ofshoots, respectively. All the phosphorylated fractions, exceptingthe lipid-P fraction, underwent a significant (P < 0.025)fall over periods of up to 36 h of wheat seedlings growth indarkness. A common characteristic found in all the phosphorylatedfractions was the fact that there were not significant differencesbetween control and 20% PEG 6000 or 0.3 M mannitol treated seedlingsduring 36 h of treatment and growth in darkness. However, whenseedlings were pulse-labelled with 32P during imbibition, someeffects of the osmotic stressants on several fractions couldbe seen. Specific radioactivity fell in acid soluble-P of controlshoots, but increased in 20% PEG 6000 and in 0.3 M mannitoltreated seedlings. Radioactive phosphorus was not found in thealkali-stable organic-P fraction. Lipid-P, nucleic acid-P, andprotein-P fractions increased their specific activities during36 h of shoot growth in control plants. Such 20% PEG 6000 and0.3 M mannitol restricted this increase during the same periodof time, the former being more active. Possible implicationsof phospholipid and phosphoprotein turnover in relation to waterstress are discussed.     

Physiological and Biochemical Responses Reveal the Drought Tolerance Efficacy of the Halophyte Salicornia brachiata

The drought tolerance of Salicornia brachiata seedlings was assessed by monitoring growth, nutrient uptake, electrolyte leakage, lipid peroxidation, and biochemical responses under drought conditions simulated with 0, 10, 20, and 30 % polyethylene glycol (PEG 6000). After 7 days of drought induction, plants were harvested for measurement of various parameters. The biomass decreased and the plant height remained unchanged with PEG treatment. The total plant water content (TWC%) decreased by 11 % at the highest concentration of PEG (30 %). The electrolyte leakage and lipid peroxidation of shoots increased by 17 and 5 %, respectively, in 30 % PEG-treated plants. K⁺ and Ca²⁺ contents of shoots increased in a dose-dependent manner. However, in roots K⁺ content decreased and Ca²⁺ content remained unaffected by PEG treatment. Mg²⁺ content increased at high concentrations of PEG (20–30 %) in shoots and decreased at the highest concentration of PEG (30 %) in roots. Total free amino acids, proline, and polyphenol contents increased progressively with increase in severity of the drought stress. Total sugar content and reducing sugar content increased in 10 and 20 % PEG-treated plants and decreased in 30 % PEG-treated plants. Our results suggest that proline and other free amino acids, sugars, and polyphenols are the main compatible solutes in S. brachiata for maintenance of osmotic balance, protection of cellular macromolecules, detoxification of the cells, and scavenging of free radicals under drought stress. A greater accumulation of compatible solutes also facilitates the maintenance of nutrient uptake and adequate tissue water status and protection of membranes under drought conditions in S. brachiata. The results from the present study suggest that S. brachiata can be used for restoration of arid and semiarid lands of coastal ecosystems.     

Water Deficit Enhanced Cotton Resistance to Spider Mite Herbivory

We investigated the responses of cotton (Gossypium hirsutumL.)to the combined effects of soil water deficit and two-spottedspider mite (Tetranychus urticaeKoch) infestation. Two mitetreatments (-M: uninfested, +M: artificially infested 83 d aftersowing), and two water regimes (+W: well watered, -W: waterstressed) were combined factorially in four treatments. Mitecolonies developed at similar rates in well-watered and water-stressedcrops. Despite the similar intensity of infestation, visualsymptoms of mite injury were more marked in well-watered hostplants (+M+W) than in their water-stressed counterparts (+M-W).Lint yield of unstressed controls (-M+W) was 175 g m^-2. In uninfestedcrops, water deficit reduced yield by 30%, mites reduced theyield of well-watered crops by 92%, and the combination of miteinfestation and water deficit reduced yield by 72% (water effect:P<0.01;mite and interaction effect:P<0.0001). Differences in yieldresponses to mites between well-watered and water-stressed cropswere mostly related to differences in reproductive partitioning.The interaction between mites and water deficit was also significantfor other crop variables including canopy temperature, leafwater potential, concentration of nitrogen in reproductive structuresand seed oil concentration. The magnitude and consistency ofthe interaction between both stresses indicates that, underour experimental conditions, mechanisms of adjustment to waterdeficit may have enhanced cotton resistance to mites. This isfurther supported by (a) an increase in specific leaf weightand a parallel increase in leaf penetration resistance due towater deficit; (b) a negative association between macroscopicsymptoms of mite injury and leaf penetration resistance; and(c) a choice test showing that adult female mites preferredto feed and oviposit on leaves from well-watered plants.Copyright1998 Annals of Botany Company Gossypium hirsutumL.;Tetranychus urticaeKoch; leaf water potential; leaf penetration resistance; canopy temperature; multiple stresses; specific leaf weight; radiation use efficiency; nitrogen concentration; reproductive allocation.     

Leaf Water Relations, Osmotic Adjustment, Cell Membrane Stability, Epicuticular Wax Load and Growth as Affected by Increasing Water Deficits in Sorghum

A field experiment was conducted with a non-irrigated waterstress treatment and an irrigated control using four sorghum(Sorghum bicolor L. Moench) cultivars. We investigated the effectsof water deficits on leaf water relations, osmotic adjustment,stomatal conductance, cuticular conductance, cell membrane stability(CMS) measured by the polyethylene glycol (PEG) test, epicuticularwax load (EWL), cytoplasmic lipid content, solute concentrationin cell sap, and growth. Osmotic adjustment was observed under water deficit conditions.Lower osmotic potential enabled plants to maintain turgor anddecreased the sensitivity of turgor-dependent processes. Sugarand K were identified as the major solutes contributing to osmoticpotential in sorghum. Sugar and K concentrations in cell sapincreased by 37·4% and 27%, respectively, under waterdeficit conditions in favour of decreasing osmotic potential.Stomatal conductance and cuticular conductance were lower inthe non-irrigated plants. A wide range in CMS among four cultivarswas observed. CMS increased with increasing water deficits.EWL increased on leaves of water deficient plants and was positivelycorrelated with cuticular conductance and CMS. Membrane phospholipidcontent increased in water-stressed plants. CMS as measured by the PEG test, was influenced by EWL, cuticularthickness, and osmotic concentration of leaf tissues. The cultivarswhich maintained higher CMS, higher EWL, lower cuticular conductance,higher turgor and higher osmotic adjustment under water deficitconditions were identified as drought tolerant. Key words: Sorghum bicolor, cell membrane stability, leaf water relationsosmotic adjustment, water stress     

Absorption and Secretion of Polyethylene Glycol by Solanaceous Plants

The response of the following species of the Solanaceae to waterstress caused by polyethylene glycol (PEG) as an osmoticum,was examined: Solatium khasianum, S. laciniatum, S. melongena,S. nigrum, S. tuberosum, Capsicum annuum, Lycopersicon esculentumand Hyosciamus boveanus. Secretion of solution from the leaveswas observed in these plants when put into 4.5% solution ofPEG 1500, 4000 and 6000. Secretion of liquid started after 20min in seedlings with mechanically damaged roots, and after24 h in plants with intact roots. After evaporation of the liquid,deposits of white material which remained on the leaves wereidentified as PEG by high pressure liquid chromatography andby PEG induced protoplast fusion. All the species examined bear glandular and non-glandular hairson their leaves. In species with leaves which are highly tomentous,PEG secretion took place mainly through the non-glandular hairs.In species with a small number of hairs, secretion took placethrough ordinary epidermal cells. Under similar conditions mannitolsolution was secreted only through wounds and cracks, and NaClsolution was not secreted at all. Key words: Secretion, PEG, Solanaceous plants     

Smoke-water improves shoot growth and indigo accumulation in shoots of Isatis indigotica seedlings

Although smoke treatments have successfully been used for promoting the germination of many seeds, there are no reports on the effect of smoke on secondary metabolite production in plants. This study highlights the effects of smoke-water on shoot growth and accumulation of indigo in shoots of Isatis indigotica Fort., a Chinese medicinal plant. Results showed that seedlings treated with smoke-water at a dilution of 1:1000 achieved the highest fresh and dry shoot mass, which was significantly (P < 0.05) different from the control and other smoke-water dilutions tested. A higher concentration of smoke-water (1:500) significantly increased (P < 0.05) the indigo concentration in shoots compared with untreated seedlings. The effect of 1:1000 and 1:2000 dilutions gave non-significant increases in the concentration of indigo. These findings suggest the possible use of smoke-water for promoting the growth and accumulation of secondary metabolites in plants.     

INFLUENCE OF He-Ne LASER IRRADIATION ON PROTECTIVE ENZYME ACTIVITIES AND LIPID PEROXIDATION IN WHEAT SEEDLINGS BY DROUGHT STRESS DAMAGE

 用He-Ne激光(5.23 mW·mm^–2)处理经5%、10%、15% PEG6000胁迫的小麦幼苗, 分析了干旱胁迫条件下激光处理对小麦幼苗保护酶活性及脂质过氧化作用的影响。适度干旱胁迫的小麦幼苗经He-Ne激光辐照后, 丙二醛(MDA)含量和超氧自由基(O₂^–.)产生速率显著降低(p<0.05), 而过氧化物酶(POD)活性和抗坏血酸(AsA)、谷胱甘肽(GSH)含量却显著增加(p<0.05)。总体上看, 5%和10% PEG6000胁迫的小麦幼苗经激光辐照3 min后抗旱性增强。     

Effects of the fungal endophyte, Neotyphodium lolii, on net photosynthesis and growth rates of perennial ryegrass (Lolium perenne) are independent of In Planta endophyte concentration

• Background and Aims Neotyphodium lolii is a fungal endophyteof perennial ryegrass (Lolium perenne), improving grass fitnessthrough production of bioactive alkaloids. Neotyphodium speciescan also affect growth and physiology of their host grasses(family Poaceae, sub-family Pooideae), but little is known aboutthe mechanisms. This study examined the effect of N. lolii onnet photosynthesis (P_n) and growth rates in ryegrass genotypesdiffering in endophyte concentration in all leaf tissues. • Methods Plants from two ryegrass genotypes, Nui D andNui UIV, infected with N. lolii (E+) differing approx. 2-foldin endophyte concentration or uninfected clones thereof (E–)were grown in a controlled environment. For each genotype xendophyte treatment, plant growth rates were assessed as tilleringand leaf extension rates, and the light response of P_n, darkrespiration and transpiration measured in leaves of young (30–45d old) and old (>90 d old) plants with a single-chamber openinfrared gas-exchange system. • Key Results Neotyphodium lolii affected CO₂-limited ratesof P_n, which were approx. 17 % lower in E+ than E– plants(P < 0·05) in the young plants. Apparent photon yieldand dark respiration were unaffected by the endophyte (P >0·05). Neotyphodium lolii also decreased transpiration(P < 0·05), but only in complete darkness. There wereno endophyte effects on P_n in the old plants (P > 0·05).E+ plants grew faster immediately after replanting (P < 0·05),but had approx. 10 % lower growth rates during mid-log growth(P < 0·05) than E– plants, but there was noeffect on final plant biomass (P > 0·05). The endophyteeffects on P_n and growth tended to be more pronounced in NuiUIV, despite having a lower endophyte concentration than NuiD. • Conclusions Neotyphodium lolii affects CO₂ fixation,but not light interception and photochemistry of P_n. The impactof N. lolii on plant growth and photosynthesis is independentof endophyte concentration in the plant, suggesting that theendophyte mycelium is not simply an energy drain to the plant.However, the endophyte effects on P_n and plant growth are stronglydependent on the plant growth phase.     

Root, Callus, and Cell Suspension Cultures, from Atropa belladonna, L. and Atropa belladonna, Cultivar lutea Doll

Root, callus, and cell suspension cultures have been establishedfrom seedlings of Atropa belladonna, L. and Atropa belladonna,cultivar lutea Döll. The growth of these cultures is described.Callus cultures transferred to auxin (-naphthaleneacetic acid)-freemedium initiated roots and shoots. Excised root cultures havebeen established from such roots and plants from such shoots.Extracts of the cultures have been submitted to the Vitali—Morinreaction and following chromatography, to the Dragendorff reaction.Cultured excised roots and plants raised from shoots initiatedon cultured callus were shown to contain atropine (hyoscyamine)and reactive substances corresponding in Rf to hyoscine andcuscohygrine. These alkaloids were absent from cultured callusand cultured cell suspensions and from leaves when initiatedwithout roots on callus. The cultured calluses and cell suspensionscontained choline (0.022–0.027 g per 100 g dry weightof root callus). The growth of cell suspension cultures wasnot inhibited by incorporating atropine sulphate, L-hyoscyamine,L-hyoscine hydrobromide, or DL-scopoline nitrate in the culturemedium at 250 mg/I. These alkaloids were absorbed by the cells,a high proportion of the added alkaloid could be recovered fromthe cultures even after 4 weeks' growth and no evidence wasobtained of the presence of degradation products of the alkaloids.The suppression of alkaloid formation in actively growing callusand cell suspension cultures is discussed.     

Influence of Osmotic Stress on Nitrate Reductase Activity in Wheat (Triticum aestivum L.) and the Role of Abscisic Acid

Wheat seedlings (Triticum aestivum L. cv. Timmo) were treatedwith up to 20% (w/v) polyethylene glycol (PEG, mol. wt. 3350)in the nutrient medium for 6 d. Shoot growth and nitrate transportand metabolism were substantially affected by PEG treatment.At 20% PEG (corresponding to a water potential of approximately–1.6 MPa), which caused plants to wilt within 1–2h, activity of nitrate reductase (NR) declined with a half-lifeof approximately 5 h in both roots and shoots. The decline wasconsiderably slower at lower PEG concentrations. Significantincreases in levels of abscisic acid (ABA) only occurred inshoots. Application of ABA to intact plants or excised shootsdid not induce or accelerate decline in shoot NR activity. Therapid decline in NR activity during wilting appears unrelatedto both nitrate flux and ABA. At lower PEG concentrations andin the long-term, however, NR activity corroborates rates ofboth transport and growth-related utilization of nitrate. Therole of ABA in this context appears to be indirect through itsaction on stomatal function which reduces water flux and gasexchange. Key words: Stress, nitrate reductase, abscisic acid (ABA)     

1-Aminocyclopropane-1-Carboxylic Acid Transported from Roots to Shoots Promotes Leaf Abscission in Cleopatra Mandarin (Citrus reshni Hort. ex Tan.) Seedlings Rehydrated after Water Stress

The effect of water stress and subsequent rehydration on 1-aminocyclopropane-1-carboxylic acid (ACC) content, ACC synthase activity, ethylene production, and leaf abscission was studied in Cleopatra mandarin (Citrus reshni Hort. ex Tan.) seedlings. Leaf abscission occurred when drought-stressed plants were allowed to rehydrate, whereas no abscission was observed in plants under water stress conditions. In roots of water-stressed plants, a high ACC accumulation and an increase in ACC synthase activity were observed. Neither increase in ACC content nor significant ethylene production were detected in leaves of water-stressed plants. After rehydration, a sharp rise in ACC content and ethylene production was observed in leaves of water-stressed plants. Content of ACC in xylem fluid was 10-fold higher in plants rehydrated for 2 h after water stress than in nonstressed plants. Leaf abscission induced by rehydration after drought stress was inhibited when roots or shoots were treated before water stress with aminooxyacetic acid (AOA, inhibitor of ACC synthase) or cobalt ion (inhibitor of ethylene-forming enzyme), respectively. However, AOA treatments to shoots did not suppress leaf abscission. The data indicate that water stress promotes ACC synthesis in roots of Cleopatra mandarin seedlings. Rehydration of plants results in ACC transport to the shoots, where it is oxidized to ethylene. Subsequently, this ethylene induces leaf abscission.     

Changes in the Morphology of Roots and Leaves of Carob Seedlings Induced by Nitrogen Source and Atmospheric Carbon Dioxide

Carob seedlings were grown hydroponically for 9 weeks under360 and 800 µl l^-1CO₂. One of two nitrogen sources, nitrateor ammonium, was added to the nutrient medium at concentrationsof 3 mol m^-3. Root systems of the developing plants suppliedwith nitrate compared to those supplied with ammonium were characterizedby:(a)more biomass on the lower part of the root;(b)fewer lateralroots of first and second order;(c)longer roots;(d)higher specificroot length;(e)a smaller root diameter. The morphology of theroot systems of nitrate-fed plants changed in the presence ofelevated carbon dioxide concentrations, resembling, more closely,that of ammonium-fed plants. Total leaf area was higher in ammonium-than in nitrate-fed plants. Nitrate-fed plants had greater totalleaf area in the presence of high carbon dioxide than in normalCO₂, due to an increase in epidermal cell size that led to developmentof larger leaflets with lower stomatal frequency. The observedchanges in the morphology of roots and shoots agreed with theresults observed for total biomass production. Nitrate-fed plantsincreased their biomass production by 100% in the presence ofelevated CO₂compared to 15% in ammonium-fed plants, indicatingthat the response of carob to high CO₂concentrations is verydependent on the nitrogen source. Under elevated CO₂, nitrate-grownplants had a larger content of sucrose in both roots and shoots,while no significant difference was observed in the contentof sucrose in ammonium-grown plants, whether in ambient or enrichedcarbon dioxide. Hence, the differences in soluble carbohydratecontents can, at least partly, account for differences in rootand shoot morphology.Copyright 1997 Annals of Botany Company Ceratonia siliquaL.; carob; ammonium; carbohydrate; carbon dioxide; nitrate; morphology; sucrose     

Closure of Stomata in Water-Stressed Pine Needles Results from the Decreased Water Potential of the Mesophyll Apoplast in the Substomatal Cavity

Pine (Pinus sylvestris L.) seedlings grown under controlled conditions were subjected to water deficit (external water potentials ranging from–0.15 to–1.5 MPa) by adding polyethylene glycol 6000 (PEG) to the nutrient solution. Following this treatment, the dry weights of plant shoots and roots, as well as the ratio of variable to maximum chlorophyll fluorescence (F_v/F_m), nonphotochemical quenching (NPQ) of chlorophyll excitations, photosynthetic CO₂/H₂O exchange, dark respiration of needles, and water potential of mesophyll apoplast in the substomatal cavity of pine needles, were measured. The imposed water deficit was followed by the inhibition of seedling growth, suppression of photosynthesis and transpiration, and by the decreased content of photosynthetic pigments. It is shown for the first time that the closure of stomata in the needles of water-stressed pine seedlings falls into the physiological reaction norm and is caused by the reduction of water potential in the mesophyll apoplast of the substomatal cavity.     

Natural Inhibitors in Normal and Dwarf Peas

Extracts of light- and dark-grown, normal and dwarf pea seedlings(Pisum sativum L. cv. Alaska and Radio respectively) were purifiedby solvent partitioning, column, paper and thin layer chromatography.Conventional acid-base partitioning was modified because thelarge volumes of material processed caused considerable crosscontamination between neutral and acidic phases. At each stepof the purification, fractions were tested for inhibitory activitywith the wheat coleoptile and pea section tests. Recovery ofabscisic acid was monitored using ¹⁴C-abscisic acid. Estimatesof abscisic acid content were marie using gas-liquid chromatographyand the wheat coleoptile bioassay. Two main inhibitors were found; one of these was identifiedas (+)-abscisic acid, the other (inhibitor Y) has not been identifiedbut displays chromatographic properties which suggest that itis neutral in nature. Abscisic acid was found in both rootsand shoots of light- and dark-grown pea seedlings. InhibitorY was found in trace amounts in the roots of dark-grown plantsbut could not be detected in the shoots. Growth in light induceda manifold increase in inhibitor Y concentration compared withdark-grown plants. The level of Y was threefold greater in light-growndwarf shoots than in comparable light-grown tall shoots. Therewas, thus, a correlation between the concentration of inhibitorY and the light-induced inhibition of stem elongation.     

Linear Relations between Carbon Dioxide Concentration and Rate of Development Towards Flowering in Sorghum, Cowpea and Soyabean

Negative linear relations were detected (P < 0·005)between the rate of progress from sowing to panicle initiationand CO₂ concentration (210-720 µmol CO₂ mol^-1 air) fortwo genotypes of sorghum [Sorghum bicolor (L.) Moench]. Relationsbetween CO₂ concentration and the rate of progress from sowingto first flowering were also negative in soyabean [Glycine max(L.) Merrill] (P < 0·025), but positive in cowpea[Vigna unguiculata (L.) Walp.] (P < 0·025), albeitthat in both grain legumes sensitivity was much less than insorghum. Thus CO₂ elevation does not delay flowering in allshort-day species. The considerable effect of CO₂ concentrationon times to panicle initiation resulted in large differencesamong the sorghum plants at this developmental stage; with increasein CO₂ concentration, plants were taller with slightly moreleaves and more pronounced apical extension. At the same timeafter sowing however, sorghum plants were heavier (P < 0·05)at 210 than at 360 µmol CO₂ mol^-1 air. In contrast, relationsbetween the dry masses of the soyabean and cowpea plants andCO₂ concentration were positive and curvilinear (P < 0·05).It is suggested that the impact of global environmental changecould be severe for sorghum production in the semi-arid tropics.Copyright1995, 1999 Academic Press Sorghum bicolor (L.) Moench., sorghum, Glycine max (L.) Merrill, soyabean, Vigna unguiculata (L.) Walp., cowpea, development, flowering, CO₂, dry matter accumulation, environmental change     

Antioxidant enzyme activities, malondialdehyde, and total phenolic content of PEG-induced hyperhydric leaves in sugar beet tissue culture

Hyperhydricity is a physiological abnormality that frequently affects shoots that are vegetatively propagated in vitro. In this study, sugar beet (Beta vulgaris L. cv. Felicita) shoot tip explants were cultured on Murashige and Skoog medium supplemented with different concentrations of polyethylene glycol (PEG) 6000. We observed that higher concentrations of PEG 6000 and longer exposure (up to 4 wk) resulted in increasing levels of hyperhydration as well as browning and/or blackening of tissues in culture. A comparison of hyperhydric shoots with controls on the 28th day showed a marked increase in the content of water, phenolics, and malondialdehyde (MDA), which was positively correlated with an increase in the accumulation of PEG 6000. Selected antioxidant enzyme activities, including superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), guaiacol peroxidase (POX), and polyphenol oxidase (PPO) also increased in hyperhydric shoots, especially at lower concentrations of PEG 6000. Regression analysis indicated that strong linear relationships exist between SOD–APX (R ²?=?0.932), SOD–CAT (R ²?=?0.753), SOD–total phenolic content (R ²?=?0.966), APX–PPO (R ²?=?0.842), APX–total phenolic content (R ²?=?0.904), POX–CAT (R ²?=?0.751), and CAT–total phenolic content (R ²?=?0.806). Despite the correlation between different antioxidant enzymes and between the antioxidant enzymes and antioxidant compounds, was not able to prevent ROS damage in hyperhydric shoots. The negative correlation between SOD–MDA, POX–MDA, CAT–MDA, and MDA–total phenolics also indicated an increase in antioxidant enzyme activities, yet the increase in these antioxidant compound contents did not prevent lipid peroxidation of in vitro propagated beet shoots.     

Interactions of seed water content with phytochromeinitiated germination of Rumex crispus (L.) seeds

Light-initiated germination levels of Rumex crispus L. seedswere reduced equally by imbibition in mannitol or polyethyleneglycol 6000 (PEG 6000) solutions of the same w, indicating thatthe effects of each were through w. Reduction of the water contentof the seeds with these osmotica decreased the effectivenessof the far-red absorbing form of phytochrome (P_tr) in causinggermination. However, reduced water content had no effect onthe slopes or saturation points of fluence/response curves whichindicates that has no effect on the number of P_tr receptor sites.The time during which a portion of the seeds were still photoreversibleby far-red light was increased by imbibition in PEG 6000, indicatinga direct effect of w on a reaction involving phytochrome. Noqualitative effect of PEG 6000 on the Onset of secondary dormancywas seen; however, its effect on the relative rate of appearanceof secondary dormancy was equivocal. ¹ Mississippi Agricultural and Forestry Experiment Station cooperating. (Received February 23, 1978; )     

Effects of PEG-induced drought stress on regulation of indole alkaloid biosynthesis in Catharanthus roseus

Catharanthus roseus (C. roseus) plants were used to investigate the terpenoid indole alkaloids (TIAs) accumulation under the condition of PEG-induced drought stress. Multivariate analysis showed that 35% PEG6000 could induce more obvious and stable accumulation on proline (PRO) content and the relative water content (RWC). The results indicated that there were gradual increase and then decrease (p?<?.05) in the contents of vindoline (VIN) and catharanthine (CAT) under 35% PEG6000 stress, but the content of vinblastine (VBL) increased gradually. In addition, the expression levels of tryptophan decarboxylase (TDC), strictosidine synthase (STR) and deacetylvindoline-4-O-acetyltransferase (DAT) were upregulated in plants under 35% PEG6000 stress. Further correlation analysis indicated that CAT accumulation was significantly correlated with TDC gene expression, and VBL accumulation was significantly correlated with peroxidase (p?<?.05). Our results suggest that the cultivation of C. roseus in drought stress would serve as effective treatment for accumulating TIAs.     

壳斗科五树种幼苗叶片结构型性状及其相关关系

通过种子的人工采集、低温沙藏和温室培育后,将幼苗移栽到环境条件相同的同质园中自然生长,研究了中亚热带壳斗科丝栗栲(Castanopsis fargesii)、苦槠(C.sclerophylla)、锥栗(Castanea henryi)、板栗(C.mollissima)和麻栎(Quercus acutissima)2年生幼苗生长季节的叶面积、叶厚度、比叶面积、叶干物质含量、叶氮浓度、叶磷浓度和叶氮磷比7种结构型性状的差异及其相关关系。结果表明:(1)在5树种幼苗中,锥栗幼苗的叶面积和比叶面积最大、叶氮浓度最高,其叶干物质含量最低;丝栗栲幼苗的叶面积最小、叶氮浓度和叶磷浓度最低;苦槠幼苗的叶厚度和比叶面积最小,其叶干物质含量最高;板栗幼苗则是叶厚度最小;同时5树种幼苗叶片的氮磷比均无显著差异(P0.1)。(2)Pearson相关和线性回归分析表明,壳斗科5树种幼苗的叶面积与叶氮浓度极显著正相关(P0.01),并与比叶面积显著正相关(P0.05);叶厚度与比叶面积极显著负相关(P0.01),其与叶干物质含量显著正相关(P0.05);比叶面积与叶干物质含量极显著负相关(P0.01),并与叶氮浓度极显著正相关(P0.01),同时与叶磷浓度显著负相关(P0.05);叶氮浓度与叶干物质含量、叶磷浓度分别为显著负相关(P0.05)和显著正相关(P0.05)。该研究结果表明壳斗科5树种幼苗叶片的7种结构型性状表现出了一定的种间差异性,但同一结构型性状的大小顺序和种间差异的显著性不同;同时所有树种幼苗叶片各结构型性状间的相关性及其显著程度不同。     

Effect of water deficit and sulphur dioxide on total soluble proteins,nitrate reductase activity and free proline content in sunflower leaves

Sunflower (Helianthus annus L. cv. PSH-7) plants were subjected to different osmotic potentials, using polyethylene glycol-6000 (PEG-6000), after, prior to and during SO₂ fumigation. Total soluble proteins and nitrate reductase activity (NRA) decreased, and free proline content increased with the increasing water stress. These biochemical parameters were more adversely affected in fumigated plants than in non-fumigated ones, when mild water stress was provided prior to and during fumigation. When severe water stress was given prior to and during fumigation, total soluble proteins, NRA and free proline content were nearly the same in fumigated and non-fumigated water-stressed plants; it is because the stomatal closure was observed in water-stressed plants. The leaf water potential decreased with the increasing water stress; however, it was not significantly affected due to SO₂ fumigation.