Showing papers in "Plant Growth Regulation in 2002"
TL;DR: Theent of the cell membrane damage not only correlated well with the growthresponses of wheat seedlings belonging to various cultivars to withholding water but also with the recognised field performances of these cultivars.
Abstract: This work was carried out to adapt the electrolyte leakage technique to durum wheat and then to evaluate its relevance in the assessment of the cell membrane stability as a mechanism of water stress tolerance in this species. The method currently used is based on in vitro desiccation of leaf tissues by a solution of polyethylene glycol (PEG) and a subsequent measurement of electrolyte leakage into deionised water. It consists of three successive steps: (1) a washing treatment to remove solutes from both leaf surfaces and cells damaged by cutting; (2) a stress period during which the leaf tissues are plunged in a PEG-solution and (3) a rehydration period during which after-effects of the stress are evaluated. During the washing period, the major part of electrolytes was removed within 15 min. Varying the stress conditions influenced both the percent and the kinetics of electrolyte leakage during rehydration. Electrolyte leakage exhibited a characteristic pattern reflecting the condition of cellular membranes (repair and hardening). In practice, we recommend a 15-minute washing time, a 10-hour stress period and 4 h of rehydration. The extent of the cell membrane damage not only correlated well with the growth responses of wheat seedlings belonging to various cultivars to withholding water but also with the recognised field performances of these cultivars. The relative proportion of endogenous ions lost in the effusate during the rehydration step may vary strongly according to the element analysed and the precise nutritional status of the plant should therefore be considered. However, an increase in inorganic ion leakage does not fully explain the recorded PEG-induced increase in electrical conductivity (EC) during the subsequent rehydration step and organic ions are probably also involved in such an increase.
681 citations
TL;DR: The hyperhydrated state of shoots and the cancerous state of cells, both induced under conditions of stress in invitro cultures, are identified and detailed, because they perfectly illustrate the stress-induced state-change concept.
Abstract: Because the term stress is used, most often subjectively, with variousmeanings, this paper first attempts to clarify the physiological definition,andthe appropriate terms as responses in different situations. The flexibility ofnormal metabolism allows the development of responses to environmental changeswhich fluctuate regularly and predictably over daily and seasonal cycles. Thusevery deviation of a factor from its optimum does not necessarily result instress. Stress begins with a constraint or with highly unpredictablefluctuations imposed on regular metabolic patterns that cause bodily injury,disease, or aberrant physiology. Stress is the altered physiological conditioncaused by factors that tend to alter an equilibrium. Strain is any physicaland/or chemical change produced by a stress, i.e. every established condition,which forces a system away from its thermodynamic optimal state. The papersecondly summarises the Strasser's state-change concept which is preciselythat suboptimality is the driving force for acclimation (genotype level) oradaptation (population level) to stress. The paper continues with the actualknowledge on the mechanisms of stress recognition and cell signalling. Briefly:plasma membranes are the sensors of environmental changes; phytohormones andsecond messengers are the transducers of information from membranes tometabolism; carbon balance is the master integrator of plant response; betwixtand between, some genes are expressed more strongly, whereas others arerepressed. Reactive oxygen species play key roles in up- and down-regulation ofmetabolism and structure. The paper shows finally that the above concepts canbeapplied to plant tissue cultures where the accumulating physiological andgenetical deviations (from a normal plant behaviour) are related to thestressing conditions of the in vitro culture media and ofthe confined environment. The hyperhydrated state of shoots and the cancerousstate of cells, both induced under conditions of stress in invitro cultures, are identified and detailed, because they perfectlyillustrate the stress-induced state-change concept. It is concluded that stressresponses include either pathologies or adaptive advantages. Stress may thuscontain both destructive and constructive elements : it is a selection factoraswell as a driving force for improved resistance and adaptive evolution.
291 citations
TL;DR: The effectiveness of a LED system for plantlet growth and morphogenesis in space-based plant research chambers is demonstrated and the number of stomata was greater in mixed radiation of FL with LEDs in both the plants.
Abstract: The effects of light generated by monochromic blue, red or mixed radiation from a fluorescent lamp (FL) with light emitting diodes (LEDs) (blue, red, or far-red) on growth and morphogenesis of marigold and salvia seedlings were investigated and the responses compared with those of plantlets grown under a broad spectrum conventional fluorescent lamp (a 16 h photoperiod per day). Dry weight of marigold seedlings was significantly increased in monochromic red light (R), fluorescent light plus red LED (FLR) or fluorescent light (FL) but reduced when monochromic blue light (B) was used, whereas in salvia dry weight was significantly greater under fluorescent light plus blue LED (FLB), fluorescent light plus red LED (FLR) and fluorescent light plus far-red LED (FLFr) as compared to other treatments. Stem length in marigold was greatest in monochromic blue light, being three times greater than in FLR or FL treatments. In salvia, FLFr increased stem length but this was significantly decreased by R as compared to other treatments. The number of visible flower buds in marigold was much higher in FLR as well as in the control (FL), and it was about five times greater than in B or R. However, the number of open flowers in salvia varied slightly in all the treatments. Different light qualities also influenced the duration of the blooming period in both the species. No flower buds were formed when monochromic B or R was used in salvia and FLFr inhibited flower bud formation in marigold. In comparison with monochromic blue or red light, the number of stomata was greater in mixed radiation of FL with LEDs in both the plants. Our study demonstrates the effectiveness of a LED system for plantlet growth and morphogenesis in space-based plant research chambers.
186 citations
TL;DR: In this article, the effects of high temperature on antioxidant enzymes were investigated in three mulberry (Morus alba L.) cultivars (cv. K-2, MR-2 and BC2-59).
Abstract: The effects of high temperature on antioxidant enzymes were investigated in three mulberry (Morus alba L.) cultivars (cv. K-2, MR-2 and BC2-59). High temperature was imposed by maintaining the plants at 40°C for 120, 240 and 360 min in an environmental plant growth chamber. The activities of superoxide disumutase (SOD), catalase (CAT), guaiacol peroxidase (POD), ascorbate peroxidase (APX) and glutathione reductase (GR) were assayed in the leaf extracts of control and high temperature-treated plants. Antioxidant enzyme activities were high in all the mulberry cultivars in response to high temperature treatment. However, cv. BC2-59 showed significantly higher activities of all the five antioxidant enzymes in response to high temperature compared to those from the leaves of K-2, and MR-2 mulberry cultivars. The present study suggested that the cv. BC2-59 has an efficient antioxidant system among the three cultivars, which could prevent the oxidative damage in the leaves caused by high temperature stress.
172 citations
TL;DR: The ability of proline to activate the enzymes may suggest alimited conformational change and be important for characterisation of metabolic responses to environmental stresses and can be used as a stress indicator.
Abstract: Accumulation of proline in response to environmental stresses seems to be widespread among plants. To elucidate the role of proline in plant responses, in vivo and in vitro, we studied the effect of proline on catalase (CAT; EC 1.11.1.6), peroxidase (POD; EC 1.11.1.7) and polyphenol oxidase (PPO; EC 1.14.18.1). In vivo, these three enzymes were activated by proline, while CAT and POD were activated and PPO was inactivated by NaCl. In vitro, CAT and POD were activated and PPO was inactivated by proline. Proline appeared to protect these three enzyme activities. The significance of these findings with regard to environmental stress-induced proline accumulation in vivo is discussed. The ability of proline to activate the enzymes may suggest a limited conformational change. These results are important for characterisation of metabolic responses to environmental stresses and can be used as a stress indicator.
154 citations
TL;DR: The higher amylase activity in shoot of primed seedlings enhanced the rapid hydrolysis of transitory starch of the shoot leading to more availability of glucose for shoot growth and this was confirmed by the low level of starch in shoots of primed Seedlings.
Abstract: Seven-day-old seedlings obtained from seeds primed with mannitol (4%)and water showed three to four fold more growth with respect to root and shootlength in comparison with seedlings obtained from non-primed seeds. Seedlingswere grown under water deficit stress conditions created by 15% polyethyleneglycol (PEG) 6000 in the medium. Priming of chickpea seeds with NaCl and PEGwasnot effective in increasing seedling growth under these water deficit stressconditions. The activities of amylase, invertases (acid and alkaline), sucrosesynthase (SS) and sucrose phosphate synthase (SPS) were higher in shoots ofprimed seedlings. An increase in the activities of SS, and both the acid andalkaline invertases was also observed in roots of primed seedlings. The twofoldincrease in specific activity of sucrose phosphate synthase was observed incotyledons of primed seedlings. The higher amylase activity in shoots of primedseedlings enhanced the rapid hydrolysis of transitory starch of the shootleading to more availability of glucose for shoot growth and this was confirmedby the low level of starch in shoots of primed seedlings.
148 citations
TL;DR: Overall, gibberellic acid treatment stimulated the vegetative growth of both cultivars ofwheat under salt stress, but it caused a slight reduction in grain yield.
Abstract: A sand culture experiment assessed whether gibberellic acid(GA3) could alleviate the adverse effects of salt stress on thegrowth, ion accumulation and photosynthetic capacity of two spring wheatcultivars, Barani-83 (salt sensitive) and SARC-I (salt tolerant).Three-week-oldplants of both cultivars were exposed to 0, 100 and 200 molm−3 NaCl in Hoagland's nutrient solution. Threeweeks after the initiation of salt treatments, half of the plants of eachcultivar were sprayed overall with 100 mg L−1GA3 solution. Plants were harvested 3 weeks after theapplication of GA3. Fresh and dry weights of shoots and roots, plantheight and leaf area were decreased with increasing supply of salt, butgibberellic acid treatment caused a significant ameliorative effect on both thecultivars with respect to these growth attributes. However, GA3caused no significant change in grain yields but increased grain size in boththe cultivars. Saline growth medium caused a marked increase in theconcentrations of Na+ and Cl− in shoots androots of both the lines. However, with the application of GA3accumulation of Na+ and Cl− was enhanced inboth shoots and roots of both wheat lines, but more ions accumulated in saltsensitive Barani-83 than in salt tolerant SARC-1. Net CO2assimilation rate (A) of both wheat lines decreased consistently withincreasingsupply of NaCl, but application of GA3 alleviated the effect of saltstress on this variable in both the cultivars. However, the ameliorative effectof the hormone was more pronounced in Barani-83 than in SARC-1. Althoughwater-use efficiency (A/E = CO2assimilation/transpiration) and intrinsic water use efficiency(A/gs = CO2 assimilation/stomatalconductance) decreased significantly with increasing salt concentration of thegrowth medium in both the cultivars, GA3 was more effective inenhancing both the water-use attributes in Barani-83 than in SARC-1. Overall,GA3 treatment stimulated the vegetative growth of both cultivars ofwheat under salt stress, but it caused a slight reduction in grain yield.GA3 treatment enhanced the accumulation of Na+ andCl− in both shoots and roots of wheat plants under saltstress.It also caused a significant increase in photosynthetic capacity in both linesat the vegetative stage under both saline and non-saline media.
135 citations
TL;DR: Results indicate that genotype 24367 is more tolerant to stresses induced by water andnitrogen deficiency and that increased fibrous root development may be a major factor in increasing sap flow via a concomitant enhancement of aquaporinactivity.
Abstract: The responses of two sugar beet genotypes, 24367 (putative drought tolerant) and N6 (putative drought intolerant), to drought and nutrient deficiency stress were investigated in an attempt to identify reliable and sensitive indicators of stress tolerance. In glasshouse-grown plants of both genotypes, relative water content (RWC) of the leaves decreased and leaf temperature increased in response to drought stress. Genotype differences in response to drought included leaf RWC, glycine betaine accumulation, alteration of shoot/root ratio and production of fibrous roots. Thus, in comparison to N6, genotype 24367 lost less water from leaves, produced more fibrous roots, produced more glycine betaine in shoots and tap roots and had a much reduced shoot/root ratio in response to withholding water for up to 215 h. The hydraulic conductance and sap flow of sugar beet seedlings grown in nutrient culture decreased when subjected to nitrogen deficiency stress. Under nitrogen sufficient conditions sap flow was greater in 24367 than in N6. The results indicate that genotype 24367 is more tolerant to stresses induced by water and nitrogen deficiency and that increased fibrous root development may be a major factor in increasing sap flow via a concomitant enhancement of aquaporin activity.
115 citations
TL;DR: Overall the results indicate that differences in polar auxin transport ability between lilac and forsythiac contribute to differences in rooting ability.
Abstract: Therooting responses of cuttings of difficult-to-root lilac (Syringavulgaris) and easy-to-root forsythia(Forsythia × intermedia)were compared. The rooting ability of lilac cuttings declined over the growingseason (May–June). There was also a decline in the initial concentrationof free IAA at the base of the cuttings, but there was not a tight relationshipbetween basal IAA concentration and rooting ability. Polar auxin transportability was measured in lilac and forsythia during the period of maximum growthby [3H]IAA application to stem internodal tissue. Transport abilitydeclined in lilac over this time period, particularly in terms of transportintensity and percentage of [3H]IAA transported. In contrast thechanges in polar auxin transport ability in forsythia were less marked. Thisdifference between species was maintained in winter hardwood cuttings, withforsythia tissue showing greater polar auxin transport ability than lilac. Theimportance of polar auxin transport for adventitious rooting was demonstratedinboth lilac and forsythia softwood cuttings by use of the polar transportinhibitor 2,3,5-triiodobenzoic acid (TIBA). Overall the results indicate thatdifferences in polar auxin transport ability between lilac and forsythiacontribute to differences in rooting ability.
96 citations
TL;DR: It is proposed that depression of corn seedlings shoot growth is not an effect of potassium leakage or lead accumulation but of an unknown signal induced inroots, as a response to exposure to lead, which is transmitted to shoots.
Abstract: It was observed that dry weight yield is not a sensitive parameter withwhich to assess lead toxicity to plants. Elongation growth of corn seedlingroots was more sensitive to lead than shoot growth and was inhibited by allconcentrations tested (10−5, 10−4, and 10−3 M).It was positively correlated with potassium concentration and negativelycorrelated with lead concentration in the roots. Negative correlation also wasobserved between lead concentration and potassium concentration in roots. It ispostulated that inhibition of corn root growth is connected with potassiumleakage from root cells. The toxic action of lead on corn seedling mesocotylandcoleoptile growth was not correlated with potassium concentration in planttissue and correlation between growth and lead concentration was low. Inseedlings treated with 10−4 and 10−3 M lead the growthof mesocotyl and coleoptile was affected similarly, although the concentrationof lead was threefold higher in mesocotyl tissue than in coleoptile tissue. It isproposed that depression of corn seedlings shoot growth is not an effect ofpotassium leakage or lead accumulation but of an unknown signal induced inroots, as a response to exposure to lead, which is transmitted to shoots. Thepositive correlation between lead and calcium concentrations found in seedlingroots might be connected with high constitutional tolerance of corn to lead.Since the first 8 mm of an apical root accounts for 50% of thelead accumulated by the whole root, it is postulated that rhizofiltration oflead contaminated waters should be more efficient when plant species withhighly branched root systems are used.
94 citations
TL;DR: Production of some new compounds, and increase in the activity of theenzymes peroxidase and polyphenol oxidase, following inoculation was observed in the dual inoculated plants.
Abstract: Mycorrhizal and Rhizobiuminoculation resulted in a significant increase in the quantities of phenoliccompounds in roots and shoots of groundnut plants, as compared to uninoculatedplants. Production of some new compounds, and increase in the activity of theenzymes peroxidase and polyphenol oxidase, following inoculation was observed.Accumulation of phenolics and the activation of oxidative enzymes were morepronounced in the dual inoculated plants.
TL;DR: The retention of the germination cue by the seeds, and thereversal of the inhibitory effects of high concentrations of smoke afterrinsingsuggest the existence of dual regulatory cues in smoke.
Abstract: The stimulation of seed germination by smoke and aqueous smoke extractshas received much attention in recent years However, the mode of action andtheidentity of the active compound(s) in smoke which promote seed germinationremain unknown Consequently, experiments were conducted to gain furtherinsightinto the nature of smoke-stimulated seed germination, using Grand Rapidslettuceseeds Imbibition of seeds prior to incubation with diluted smoke extract,resulted in reduced levels of germination in comparison to seeds imbibedcontinuously on smoke extract This suggests that the promotion of germinationby smoke is dependent on the initial uptake of the active component, and mostlikely, on the presence of this component in the embryonic axisPulse-treatmentof lettuce seeds revealed that there is a required threshold level of thisactive component The retention of the germination cue by the seeds, and thereversal of the inhibitory effects of high concentrations of smoke afterrinsingsuggest the existence of dual regulatory cues in smoke This competitiveinteraction, in which the germination promoter cannot be leached while theinhibitor can, may be important in post fire environments – providing amechanism to prevent germination until sufficient rainfall leaches theinhibitory compounds and then allowing the stimulatory compound(s), which areactive over a broad concentration range, to function
TL;DR: It was showed that changing of induction medium 15h after microspore isolation produced higher spontaneous doubling efficiency, as compared with medium change 6 h after isolation, which was less effective on embryogenesis and doubling efficiency.
Abstract: The effect of colchicine on embryogenesis induction and chromosomedoubling during microspore culture was evaluated in two F1 hybridsofwinter oilseed rape (Brassica napus L.). Colchicinetreatment (50 and 500 mg/L) of isolated microspores during thefirst 15 h in culture stimulated embryogenesis and produced large amounts ofhealthy-looking embryos. These normal embryos germinated well at 24°C after being transferred to solid regeneration medium and aninitial period of low temperature (2 °C) for 10 days, andcoulddirectly and rapidly regenerate vigorous plants. A high doubling efficiency of84–88% was obtained from 500 mg/L colchicine treatment for15h with low frequency of polyploid and chimeric plants. Acolchicinetreatment duration of 6 h was less effective on embryogenesis anddoubling efficiency. The present experiment also showed that changing of induction medium 15h after microspore isolation produced higher spontaneous doublingefficiency, as compared with medium change 6 h after isolation.
TL;DR: Under lowassimilate supply, cell division is a main limiting factor for fruit growth, although cell enlargement during further fruit development is also affected, but the number of fruit cells during tomato plant development is investigated.
Abstract: Fruit sink strength or its ability to attract assimilates depends bothon sink activity and size. This study investigated one main component of sinksize, that is the number of fruit cells during tomato plant development. Plantswere grown in a controlled climate chamber under a limiting (LS, six fruits pertruss) and non-limiting (NLS, two fruits per truss and CO2enrichment) supply of carbon assimilates. Under NLS conditions, fruit cellnumber was homogeneous among successive trusses, and fruits contained onaverage1.2 × 106 more cells than under LS conditions,though differences were not significant on the first truss which underwent thelowest competition. Under LS conditions, an ontogenetic increase in cell numberwas observed in proximal fruits of the upper trusses attributed to theenlargement of the apical meristem during plant development. The decrease ofcell number from proximal to distal fruits within a truss, that was expectedfrom the literature, was generally observed in the LS experiment, with anaverage significant difference of about1.6 × 106cells between the first and fifth fruits. Nevertheless, whereas the gradient incell number from proximal to distal fruits was steep in the upper trusses, itwas not significant on the lower trusses indicating that this gradient largelydepended on the level of competition during floral development. Thus, under lowassimilate supply, cell division is a main limiting factor for fruit growth,although cell enlargement during further fruit development is also affected,butwas not measured in this work.
TL;DR: Al3+-induced inhibition of root growth is preceded by significantchanges in CK content and composition and enhanced ethylene evolution, which indicates that CK can induce ethylene production, and the rapid increase in CK, particularly Z and dZ, may contribute to inhibition ofRoot-growth either directly or indirectly by affecting plant hormone homeostasis.
Abstract: The role of plant hormones in aluminium (Al3+)-inducedinhibition of root growth was investigated in roots of Phaseolusvulgaris L. cv. Strike. Changes in ethylene evolution and changes inthe content and composition of cytokinins (CKs), at intervals up to 150min after treatment with Al3+, were determined by gaschromatography (GC) and combined gas chromatography-mass spectrometry (GC-MS),respectively. Seedlings were cultivated in a continuously aerated nutrientsolution at pH 4.5 with and without Al3+. The growth rate ofAl3+-treated roots was significantly decreased after 360min. Ethylene evolution from excised root tips doubled after 15min of Al3+ treatment and reached a maximum 30min after treatment. Levels of CK nucleotides declined 60 to 80%after only 5 min of Al3+ treatment whereas the zeatin(Z) content increased six-fold. The increase in Z continued over the entire 150min-sampling period and reached a level 80 times higher than thatin roots not exposed to Al3+. These results show thatAl3+-induced inhibition of root growth is preceded by significantchanges in CK content and composition and enhanced ethylene evolution. Since CKcan induce ethylene production, the rapid increase in CK, particularly Z anddihydrozeatin (dZ), may contribute to inhibition of root-growth either directlyor indirectly by affecting plant hormone homeostasis.
TL;DR: It was found that red light promotes development of root growth and development, flowering, and de-etiolation of stem and leaf of Americancranberry and anthocyanin biosynthesis as phytochemical response in cranberry plants was most sensitive to red light.
Abstract: Morphological responses of American cranberry (Vacciniummacrocarpon Ait, Ericaceae) to different light conditions (red,far-red, white light and sunlight) were examined. Root growth and development,stem elongation, leaf enlargement, de-etiolation of stem and leaf, flower budformation, and flowering of American cranberry were measured under each lightcondition and in the dark. It was found that red light promotes development ofroots and leaves, flowering, and de-etiolation of stem and leaf of Americancranberry. Stem elongation and etiolation of stem and leaf were shown infar-redlight and dark. Anthocyanin biosynthesis as phytochemical response in cranberryplants was most sensitive to red light. Estimation of anthocyanin levels indifferent parts of cranberry plant suggested that anthocyanins were presentonlyin red fruit skins, and not in peeled fruits, green fruits, green leaves, greenstems, roots and seeds.
TL;DR: In this paper, a relationship between the antioxidant defence system and metal ion tolerance in two types of sunflower callus differing in metal ion sensitivity was studied, where the antioxidant defense system of callus subjected to anadaptationtreatment of Cd(II), Al(III) and Cr(III), responded differently to 150μM of each metal compared with the corresponding controls undershock treatment.
Abstract: A relationship between the antioxidant defence system and metal iontolerance in two types of sunflower callus differing in metal ion sensitivitywas studied. The antioxidant defence system of callus subjected to anadaptationtreatment of Cd(II), Al(III) and Cr(III) responded differently to 150μM of each metal compared with the corresponding controls undershock treatment. The GSH/GSSG ratio remained similar to control values for thethree metal-acclimated calli and in the chromium shock treatment, decreasingmoderately in the acute treatment with cadmium and aluminum. In contrast, theAs/DAs ratio was decreased in the two different treatments for the three metalsions, but the decrease was greater with acute stress. The antioxidant enzymesresponded differently according to the metal and treatment used. In chromiumadapted callus, all antioxidant enzymes increased except for glutathionereductase. However, in the shock treatment ascorbate peroxidase activity wasdiminished with each metal ion assayed. Guaiacol peroxidase was decreased bycadmium and chromium and remained similar to control values with aluminum.Glutathione reductase was only decreased by cadmium, and superoxide dismutaseand catalase activities were less increased than in tolerant cells. Theseresults suggest the involvement of an antioxidant defence system in theadaptiveresponse to heavy metal ions in Helianthus annuus L.cells.
TL;DR: The application of the synthetic auxin 3,5,6-TPA at the cell enlargementstage increased hexoses in developing fruit from foliated and fully defoliated plants of Satsuma mandarin, suggesting the occurrence of pathways for induction of fruit abscission, linked to carbon availability, relatively independent of the stage of development.
Abstract: The application of the synthetic auxin 3,5,6-TPA at the cell enlargementstage increased hexoses in developing fruit from foliated and fully defoliatedplants of Satsuma mandarin, cv ‘Okitsu’ (Citrusunshiu Marc) Although the sucrose concentrations also increased,ingeneral the differences were not statistically significant The plant growthregulator reduced fruit abscission in defoliated trees while it stimulatedfruitgrowth in the foliated ones The carbohydrate accumulation induced by 3,5,6-TPAindicates that its stimulatory effect on fruit growth might operate viapromotion of sink strength The results also suggest the occurrence of pathwaysfor induction of fruit abscission, linked to carbon availability, relativelyindependent of the stage of development
TL;DR: The present results lend further support to the emerging consensus that the tryptophan-dependent pathwayacts to maintain very high IAA levels required for mediating rapid cellproliferation in wounded tissues and, as previously shown, young embryos.
Abstract: A facile radiotracer method for discriminating between the activities of tryptophan-dependent and tryptophanindependent pathways for IAA biosynthesis is described. This method utilized the simultaneous exposure of plants to [ 14 C]anthranilate in the presence or absence of excess unlabeled tryptophan in order to determine if tryptophan feeding can affect the relative enrichment of the IAA pool. Using this radiotracer method, the activities of the two biosynthetic pathways were analyzed in isolated axes of germinating bean seedlings at various times after cotyledon excision. Unlabeled tryptophan suppressed [ 14 C]anthranilate conversion into IAA in isolated axes of different ages immediately following cotyledon excision. On the other hand, tryptophan feeding did not inhibit [ 14 C]IAA accumulation in isolated axes 36 or 120 h after cotyledon excision. Thus, this method was able to resolve time-dependent differences following cotyledon excision in the biosynthetic activities of the two pathways. Moreover, the present results lend further support to the emerging consensus that the tryptophan-dependent pathway acts to maintain very high IAA levels required for mediating rapid cell proliferation in wounded tissues and, as previously shown, young embryos.
TL;DR: In this article, the changes in activity of peroxidase (POD) extracted from the cellwalls and the level of H2O2 in rice seedling rootstreated with mannitol and their correlation with root growth were investigated.
Abstract: The changes in activity of peroxidase (POD) extracted from the cellwalls and the level of H2O2 in rice seedling rootstreatedwith mannitol and their correlation with root growth were investigated.Increasing concentrations of mannitol from 92 to 276 mM, which isiso-osmotic with 50 to 150 mM NaCl, progressively reduced rootgrowth and increased POD activities extracted from the cell walls of riceroots.The reduction of growth was also correlated with an increase inH2O2 level. Both diamine oxidase (DAO) and NADHperoxidase(NADH-POD) are known to be responsible for the generation ofH2O2. Mannitol treatment increased DAO but not NADH-PODactivities in roots of rice seedlings, suggesting that DAO contributes to thegeneration of H2O2 in the cell walls of mannitol-treatedroots. An increase in the level of H2O2 and the activityof POD extracted from the cell walls of rice roots preceded root growthreduction caused by mannitol. An increase in DAO activity coincided with anincrease in H2O2 in roots caused by mannitol. Since DAOcatalyses the oxidation of putrescine, the demonstration that mannitolincreasesthe activity of DAO in roots is consistent with those that mannitol decreasesthe level of putrescine. In conclusion, cell-wall stiffening catalysed by PODispossibly involved in the regulation of root growth reduction caused bymannitol.
TL;DR: In this paper, a sunflower (Helianthus annuus L. cv Giza2) was treated with 5 and 10mg L−1 of thiamin either sprayed on the shoot or applied to the root.
Abstract: Plants of sunflower (Helianthus annuus L. cv Giza2) were salt-stressed with a combination of NaCl and CaCl2 inconcentrations having different osmotic potentials (ψs from 0 to −1.0MPa) and were treated with 5 and 10mg L−1 of thiamin either sprayed on the shoot orapplied to the root. The membranes of leaf discs from salt-stressed plantsappeared to be less stable (more injured) under heat(51 °C) and drought (40% polyethylene glycol6000) stresses than control plants. Salinity slowed the rate of growth (lengthand dry mass production), lowered leaf relative water content (RWC) and leafandroot water potential (ψw), decreased the contents of chlorophyll (Chl),soluble sugars (SS) and the K+/Na+ ratio butenhanced total free amino acids (TAA), Na+,Ca2+and Cl− accumulation in the shoot and root system. Root orshoot application of thiamin reduced membrane injury by either heat ordehydration stress, lowered leaf ψw, improved uptake of K+,and increased leaf RWC, Chl, SS, TAA contents and dry mass production. Theeffects of salinity (ψs), thiamin (Thi.) and their interaction(ψs × Thi) on the parameters tested were significant.Salinity was dominant (as indicated by η2 values) in affectingthe contents of Ca2+, Cl−, TAA and membranestability to heat and leaf ψw. The role of thiamin was dominant forNa+, K+ and SS contents and the contribution ofinteraction was dominant for growth parameters, Chl. and root ψw.
TL;DR: Several plant growth regulators used in practical farming to restrict shoot height and control lodging were examined for their impact on root growth in naturally short or tall cultivars of barley, oat, and wheat, finding root elongation in barley was strongly inhibited byethylene, with oat demonstrating an intermediate responsiveness.
Abstract: Several plant growth regulators (PGRs) commonly used in practicalfarming to restrict shoot height and control lodging were examined for theirimpact on root growth in naturally short or tall cultivars of barley (cvsKymppi and Saana), oat (cvs Veli and Pal), and wheat (cvs Mahti and Tjalve)The possible involvement of ethylene in the responses was also examined Shootswere sprayed at the two-leaf stage with the gibberellin biosynthesis inhibitorsCycocel (chlormequat chloride) (CCC) or Moddus (Trinexapac-ethyl) (TE), or withthe ethylene-releasing agent Cerone (ethephon) (ETH) at 0, 01, 1, 10 or 50times the recommended agricultural rate (RR) Root elongation and ethyleneproduction by roots or shoots were unaffected by CCC at all application ratesorby TE at ×01 or ×10 RR At ×10 and ×50 RR, TE wasinhibitory to root extension but did not increase ethylene biosynthesis bytheseroots or the shoots ETH at ×01 or ×10 RR did not affect rootextension or ethylene production in roots or shoots At all higher rates ofapplication ETH stimulated ethylene production strongly in shoots and roots ofall three species, while root elongation was retarded severely in barley,moderately in oat and only slightly in wheat These differences in elongationresponse are attributed to differences in sensitivity to ethylene released byethephon Accordingly, root elongation in wheat was only slightly affected whenethylene gas was supplied at concentrations up to 100 ppm for 3d In contrast, root elongation in barley was strongly inhibitedbyethylene, with oat demonstrating an intermediate responsiveness
TL;DR: Results show that proline accumulation caused by NaCl was associated with ammonium ion accumulation, and the content of the precursors of proline biosynthesis,ornithine and arginine was increased.
Abstract: The regulation of proline accumulation in detached leaves of rice(Oryza sativa cv. Taichung Native 1) was investigated.Increasing concentrations of NaCl from 50 to 200 mM progressivelyincreased proline content in detached rice leaves. NaCl induced prolineaccumulation was mainly due to the effect of both Na+ andCl− ions. Proline accumulation caused by NaCl was related toprotein proteolysis, an increase in ornithine-δ-aminotransferaseactivity,a decrease in proline dehydrogenase activity, a decrease in prolineutilisation,and an increase in the content of the precursors of proline biosynthesis,ornithine and arginine. Results also show that proline accumulation caused byNaCl was associated with ammonium ion accumulation.
TL;DR: In this paper, the authors evaluated the protective effect of NO against senescence of rice leaves enhanced by water deficit, and found that NO donors[N-tert-butyl-α-phenylnitrone (PBN), sodiumnitroprusside (SNP), 3-morpholinosydnonimine (SIN-1), and ascorbic acid +NaNO2] were effective in inhibiting senescences of dehydrated and polyethylene glycol (PEG) and sorbitol (ST) treatments were used toind
Abstract: In the present study, we evaluated the protective effect of nitric oxide(NO) against senescence of rice leaves enhanced by water deficit. Dehydration(DH), polyethylene glycol (PEG) and sorbitol (ST) treatments were used toinducewater deficit. Senescence of rice leaves was determined by the decrease ofprotein content. NO donors[N-tert-butyl-α-phenylnitrone (PBN), sodiumnitroprusside (SNP), 3-morpholinosydnonimine (SIN-1), and ascorbic acid +NaNO2] were effective in inhibiting senescence of dehydrated andPEG-treated rice leaves, but had no effect on senescence of ST-treated riceleaves. PEG or DH resulted in a marked increase in malondialdehyde (MDA)contentand decrease in superoxide dismutase (SOD) activity, but ST had no effect onMDAcontent and SOD activity. Treatment with NO donors caused a reduction of PEG-and DH-induced increase in MDA content and decrease in SOD activity. Theprotective effect of NO donors on promotion of senescence, increase in lipidperoxidation and decrease in SOD activity induced by PEG and DH was reversed by2-(4-carboxy-2-phenyl)-4,4,5,5- tetra-methylinmidazoline-1-oxyl-3-oxide, a NOspecific scavenger, suggesting that the protective effect of NO donors isattributed to NO released. The inhibition of PEG- and DH- enhanced senescenceofrice leaves by NO is most likely mediated through increasing SOD activity anddecrease in lipid peroxidation.
TL;DR: Somatic embryogenesis was achieved directly from pseudo-bulblettransverse thin cell layers (tTCL) of Lilium longiflorum and the highest number of embryo-like structures (globular embryos) were obtained from different sizeexplants.
Abstract: Somatic embryogenesis was achieved directly from pseudo-bulblettransverse thin cell layers (tTCL) of Lilium longiflorum.Embryo-like structures (globular embryos) were obtained from different sizeexplants of pseudo-bulblet tTCLs after 45 days culture on Murashige and Skoog,1962 (MS) medium containing 5.4 μM naphthalene acetic acid(NAA)and 1.1 μM thidiazuron (TDZ). The embryo-like structures werethen isolated and mass proliferated on MS medium, containing 5.4μM NAA and 0.4 μM TDZ, every 45 days. A0.8–1.0 mm thick explant was shown to be optimal forobtaining the highest number of embryo-like structures. For plant regenerationthese structures were transferred to hormone-free MS medium with 30g/l sucrose. All of these structures formedplantlets after 90 days culture.
TL;DR: Some changes observed in root anatomy and most of the variations in leaf anatomy features caused by the treatments could be ascribed to osmotic stress, however, there were evident differences in the morphology of the root system as well as in chlorophyll levels as afunction of the stress treatment.
Abstract: Drought and salinity are the major abiotic factors limiting productivityin rice (Oryza sativa L.). Although both generate osmoticstress, ion toxicity is an additional and important component of salinity. Tostudy the morphological and anatomical responses to those types of stress, weused in vitro grown rice seedlings. Based on an initialscreening of several non-penetrating osmotica on seedling growth, we selectedsorbitol to compare its osmotic effects during seedling development with thosegenerated by NaCl stress. At comparable levels of osmolality, the reduction inroot and leaf growth as well as their delayed development were similar for bothsaline- and osmotically-generated stress. Some changes observed in root anatomyand most of the variations in leaf anatomy features caused by the treatmentscould be ascribed to osmotic stress. However, there were evident differences inthe morphology of the root system as well as in chlorophyll levels as afunctionof the stress treatment. Furthermore, the larger size of epidermal andbulliformcells was distinctively related to saline stress. The results obtained providetools for the in vitro identification of either specificorcross-tolerant phenotypes.
TL;DR: In this article, a field experiment was conducted during 1997-98 in which foliar applied Gibberellic acid (GA3) could enhance crop growth and increasenitrogen-use efficiency.
Abstract: Mustard is cultivated throughout the world for oil in its seeds. Itrequires high nitrogen input for improved productivity but the nitrogen appliedto the soil is not fully utilised by the crops due to various constraints. Theobjective of the reported research was to determine if foliar- appliedgibberellic acid (GA3) could enhance crop growth and increasenitrogen-use efficiency. A field experiment was conducted during 1997–98in which GA3 (10−5 M) was applied tofoliage at 40d after sowing (pre-flowering) to mustard grown with 0, 40(sub-optimal), 80 (optimal) and 120 (supra-optimal) kgN ha−1. Foliar spray of GA3 was effectiveonly when plants received sufficient N (80 kgN ha−1). GA3 sprays significantly enhancedplant dry mass, leaf area, carbon dioxide exchange rate, plant growth rate,cropgrowth rate and relative growth rate. GA3 -treated plants showedenhanced nitrogen-use efficiency through redistribution of N to seeds.
TL;DR: The results indicate that high levels of JA and GAs are found indifferent tissues, especially during stolon growth and tuber set, and that gibberellic acid was the most abundant in all the organs.
Abstract: Among the multiple environmental signals and hormonal factors regulatingpotato plant morphogenesis and controlling tuber induction, jasmonates (JAs)andgibberellins (GAs) are important components of the signalling pathways in theseprocesses. In the present study, with Solanum tuberosum L.cv. Spunta, we followed the endogenous changes of JAs and GAs during thedevelopmental stages of soil-grown potato plants. Foliage at initial growthshowed the highest jasmonic acid (JA) concentration, while in roots the highestcontent was observed in the stage of tuber set. In stolons at the developmentalstage of tuber set an important increase of JA was found; however, in tubersthere was no change in this compound during tuber set and subsequent growth.Methyl jasmonate (Me-JA) in foliage did not show the same pattern as JA; Me-JAdecreased during the developmental stages in which it was monitored, meanwhileJA increased during those stages. The highest total amount of JAs expressed asJA + Me-JA was found at tuber set. A very important peak ofJA in roots was coincident with that observed in stolons at tuber set. Also, aprogressive increase of this compound in roots was shown during the transitionof stolons to tubers. Of the two GAs monitored, gibberellic acid(GA3) was the most abundant in all the organs. While GA1and GA3 were also found in stolons at the time of tuber set, noothermeasurements of GAs were obtained for stolons at previous stages of plantdevelopment. Our results indicate that high levels of JA and GAs are found indifferent tissues, especially during stolon growth and tuber set.
TL;DR: In this paper, the responses of Pueraria lobata hairy roots and normal roots to treatment with three auxins, indole-3-acetic acid (IAA),indole 3-butyric acid (IBA), and naphthalene acetic acid(NAA), were different.
Abstract: Pueraria lobata hairy roots have faster elongationand more branches than normal roots. The responses of hairy roots and normalroots to treatment with three auxins, indole-3-acetic acid (IAA),indole-3-butyric acid (IBA), and naphthalene acetic acid (NAA) were different.In normal roots, all three auxins strongly stimulated lateral root formation atall tested concentrations. Responses to IAA and IBA in primary root growth andlateral root elongation were similar and depended on concentration; promotionat0.1 μM, no effect at 1.0 μM, and inhibition at2.5 μM. In hairy roots, lateral root formation varied inresponseto the different auxins, i.e. depressed by NAA, unaffected by IAA, and promotedby IBA. Primary root growth was slightly inhibited by IBA and was unaffected byIAA. However, mean lateral root length was reduced in response to IAA and IBA.Only NAA exerted strong inhibition on primary and lateral root elongation inboth root types. The similar free IAA and conjugated IAA content but quitedifferent basal ethylene production and biosynthesis in hairy and normal rootssuggested different mechanisms of response to exogenous auxins in the two roottypes.
TL;DR: It appears that the IAA-induced ethylene production may be a factor involved in the stimulation of adventitious root formation in mung bean hypocotyl cuttings.
Abstract: The relationship between ethylene and adventitious root formation in mung bean hypocotyl cuttings was studiedEthephon, an ethylene-releasing compound, at 5 x 10 -5 M increased root number and root dry weight on hypo-cotyl cuttings When ethephon was applied to hypocotyl at different times after excision, there were two effectivetimes for root production ie between 06 h and 18-24 h These two time periods correspond to the induction phase and the late initiation phase of root development, respectively After excision, three peaks of ethylene productionwere observed The first peak commencing at 6 h started the sequence of reactions leading root formation, the second peak appearing at 12 h coincided with the beginning of the increase of the IAA level during primordia initiation, and the third peak showing at 48 h played a role in root differentiation and growth Ethylene stimulated rooting by enhancing the increase in auxins Thus it appears that the IAA-induced ethylene production may be a factor involved in the stimulation of adventitious root formation