Chilling injury in cotton (Gossypium hirsutum L.) : Effects of antimicrotubular drugs

When exposed to 4°C for more than three days, intact cotton(Gossypium hirsutum L.) seedlings and isolated cotyledonarydiscs suffered chilling injury as shown by the leakage of electrolytesfrom the tissue and the development of necrotic areas. Applicationof antimicrotubular drugs such as colchicine, demecolcine orpodophyllotoxin during chilling significantly accelerated andenhanced tissue damage. Lumicolchicine, the stereoisomer ofcolchicine, was ineffective. Non-chilled tissues showed hardlyany damage when treated with the same levels of antimicrotubulardrugs. Prior treatment with 10^–5 M abscisic acid (ABA)prevented the appearance of symptoms of damage caused by chillingand the antimicrotubular drugs during the first 2 to 3 daysand greatly reduced it at later stages. Our present resultssuggest that chilling damage may be due at least in part, tothe cold-induced disassembly of microtubules. Furthermore, themode of action of ABA might be related to factors which influencethe physiological stability of the microtubule network. ¹Preliminary report of this work was presented at the 10th InternationalConference on Plant Growth Substances, Madison, Wisconsin, 1979. ³Incumbent of the Seagram Chair in Plant Sciences. (Received April 15, 1980; )     

Alterations in Protein Synthesis in vivo in Chilling Sensitive Mung Bean Hypocotyls Caused by Chilling Stress

The effects of chilling on protein synthesis in vivo in etiolatedhypocotyls of Vigna radiata L. were investigated. After exposureof the tissues to 0?C for various periods of time, proteinswere labeled with [³⁵S]-methionine at 26?C. The total amountof ³⁵S incorporated into soluble and membrane proteins was reversiblyreduced by chilling for 24 h, during which time the tissuessuffered no injury. Further prolonged chilling produced an irreversibledecline both in the incorporation of radioactivity and in cellviability as assessed by the extent of leakage of electrolyte.The ³⁵S-labeled proteins in the soluble and the total membranefractions were analyzed quantitatively. Chilling of etiolatedhypocotyls for one or two days induced the syntheses of twosoluble proteins (82 and 74 kDa) and one membrane protein (80kDa). Moreover, three heat-shock proteins (HSPs) that were inducedby heat stress (41 ?C, 4h) had the same electrophoretic mobilitiesas those of the proteins induced directly or indirectly by thechilling treatment. ¹Contribution No. 3170 from the Institute of Low TemperatureScience. (Received April 22, 1988; Accepted September 30, 1988)     

Effect of Hormones on Sucrose Uptake and on ATPase Activity of Citrus sinensis L. Osbeck Leaves

Carbohydrate accumulation in young, fully expanded leaves ofCitrus sinensis L. Osbeck is affected by the presence of thefruitlet on the shoot. Previous work gave evidence that gibberellinsmay be involved in this 'fruit effect'. In the present workwe have studied the effect of gibberellic acid (GA₃) on ¹⁴C-sucroseuptake by leaf discs and whether its action could be due toa modulation of the plasma membrane ATPase, which maintainsthe H⁺ gradient that drives H⁺/sucrose co-transport. The effect of GA₃ on ¹⁴C-sucrose uptake depended on the osmolarityof the assay medium. At 300 mOsm a reduction in the uptake ratewas observed. The inhibitory effect of the hormone disappearedafter preincubating the leaf discs with para-chloromercuri-phenylsulphonicacid (PCMPS), a sulphydril binding inhibitor. ATPase activityof isolated plasma membrane vesicles was inhibited by IAA treatments,while GA₃ or ABA did not affect this enzyme, even after a 3h preincubation period. However, in the absence of a surfactantin the assay medium, GA₃, together with turgor pressure, modulatedplasma membrane ATPase activity, possibly through modificationsof membrane permeability. The hormone effect on ¹⁴ C-sucroseuptake may involve action on the sucrose carrier.Copyright 1994,1999 Academic Press Abscisic acid, Citrus sinensis, gibberellic acid, indoleacetic acid, orange, osmotic pressure, plasma membrane ATPase, ¹⁴C-sucrose uptake     

Proline and Polyamine Involvement in Chilling Tolerance of Maize Suspension Cultures

We have assessed the effect of various medium supplements inpromoting the ability of maize (Zea mays L.) inbred FR27rhmsuspension cultures to grow following a period of 4 °C chillingstress. Following a 4 week exposure to 4 °C in culture mediumwithout proline, no cell growth occurred upon subsequent incubationat 28°C for 2 weeks. This inhibition was reversed when 3to 48 mol m^–3 proline or 0.1 mol m^–3 putrescineor 0.01 mol m^–3 spermidine were present in the mediumduring the chilling stress. On the other hand, suspensions weremade more sensitive to 4°C by blocking polyamine biosynthesiswith 1.0 mol m^–3 methylglyoxal bis (guanylhydrazone) (MGBG)or a combination of 1.0 mol m^–3 difluoromethylornithine(DFMO) and 1.0 mol m^–3 difluoromethylarginine (DFMA).The addition of 10 mol m^–3 putrescine to the suspensioncontaining DFMO and DFMA prevented the increased chilling sensitivity.Electrolyte leakage studies conducted to assess membrane integrityafter 4 weeks at 4°C and a 2 week regrowth period showedthat cells treated with no polyamines (control), 0.01 mol m^–3spermidine, 1.0 mol m^–3 putrescine, or 1.0 mol m^–3MGBG lost 43, 32, 14, and 100% of the total electrolyte pool,respectively. These results suggest that proline and polyaminesare beneficial for inducing chilling tolerance in FR27rhm suspension. Key words: Proline, polyamine, chilling stress     

Polyamine Titre in Relation to Chill-Sensitivity in Phaseolus sp.

Guye, M G., Vigh, L. and Wilson, J. M. 1986. Polyamine titrein relation to chill-sensitivity in Phaseolus sp.—J. exp.Bot. 37: 1036–1043. Endogenous levels of the polyamines putrescine, spermidine andspermine were quantified in the primary leaves of five cultivarsof bean (Phaseolus sp.) differing in their ‘wilting response’to a chilling exposure of 5 ?C for 24 h. Levels of polyamines prior to chilling treatment did not appearto be correlated with chill-tolerance as levels in the non-chilledcontrols were highest in cultivars of medium chill-sensitivity.Plants grown under a vapour saturation deficit (VSD) of 8?4gm^–3 day/6?1 g m^–3 night exhibited a mild hardeningas compared to plants grown under a VSD of 5?7 gm^–3 day/4?1gm^–3 night, as the former showed less wilting on chilling.Hardening at high VSD had the effect of slightly lowering theputrescine content of non-chilled tissue but total polyaminecontent remained unchanged. However, on chilling, the largestrelative increase in polyamine levels, in particular that ofputrescine, occurred in hardened plants. There was also a significantrelative increase in putrescine titre in response to chillingin non-hardened genotypes of high chill-tolerance, whereas morechill-sensitive genotypes remained unchanged or slightly declinedin putrescine content on chilling. Relative changes in putrescine content rather than absolutelevels appears to be correlated with chill-tolerance. Theseresults are discussed in view of present knowledge on the adaptivesignificance of stress-induced changes in polyamines, especiallywith regard to membrane stability Key words: Chilling, polyamines, Phaseolus sp.     

The Resolution by HPLC of RS-[2-14C]Me 1', 4'-cis-Diol of Abscisic acid and the Metabolism of (-)-R- and (+)-S-Abscisic Acid

The R- and S-enantiomers of racemic [2-¹⁴C]Me 1', 4'-cis-diolof abscisic acid have been separated by high performance liquidchromatography on an optically-active Pirkle column. R-[2-¹⁴C]-and S-[2-¹⁴C]abscisic acids, formed from the Me 1', 4'-cis-diolby oxidation and alkyline hydrolysis were fed to tomato shootsand the extracts analysed by reversed phase high performanceliquid chromatography. R-[2-¹⁴C]abscisic acid formed mainlythe abscisic acid glucose ester (ABAGE), abscisic acid l'-glucoside(ABAGS) and an uncharacterized conjugate. Dihydrophaseic acid4'-B-D-glucoside, the major metabolite of RS-abscisic acid intomato shoots, was found to be derived virtually exclusivelyfrom the natural, S-abscisic acid. Phaseic acid and conjugatesof abscisic acid were also found as products of the naturallyoccurring enantiomer. The resolution method was used to measurethe relative proportions of R and S enantiomers in the freeacid liberated from conjugates formed from RS-[2-¹⁴C]ABA fedto shoots. The ratios show an excess of the R-enantiomer: 5.8:1, ABAGE; 29.4: 1, ABAGE; 8.3: 1 for an uncharacterized conjugateand 6.1: 1 for the residual free [2-¹⁴C]ABA. Key words: ABA, HPLC, Tomato     

Chilling Injury in Cotton {Gossypium hirsutum L.): Light Requirement for the Reduction of Injury and for the Protective Effect of Abscisic Acid

Pretreatment by darkness increased chilling (4°C) injuryin whole cotton (Gossypium hirsutum L.) seedlings and isolatedcotyledonary tissue. Addition of sucrose in the dark periodprevented the effect of darkness. Application of the photosyntheticinhibitor DCMU in light simulated the effect of darkness. ABA(10^–5 M) decreased chilling injury when applied in lightas a pretreatment before the onset of chilling. The same pretreatmentin darkness was almost ineffective, unless sucrose was added.ABA applied in light together with DCMU was ineffective in decreasingchilling injury. Lower light intensity resulted in increasedchilling injury and a decreased effect of ABA in the preventionof chilling injury. The antimicrotubular drug colchicine increased the chillinginjury. Pretreatment with ABA in light decreased the chillingand colchicine injury while the same pretreatment in darknesswas ineffective. These results suggest that a deficiency of a photosyntheticproduct increases the chilling sensitivity of the tissue. ABAapparently increases chilling resistance through a metabolicprocess which depends on photosynthetic activity. ³ Incumbent of the Seagram Chair in Plant Sciences (Received November 20, 1980; Accepted January 31, 1981)     

Effect of LAB 173 711, an ABA analogue,on low-temperature resistance of mung bean seedlings

The effect of LAB 173 711, a synthetic analogue of abscisic acid, has been evaluated on chilling-sensitive mung bean (Vigna radiata L. cv. Local V.) seedlings. Electrical conductivity was used for assessing the degree of chilling injury. Exposure of 8-day-old mung bean seedlings to 4°C for 35 h resulted in a 50% electrolyte leakage and induced irreversible chilling injury. The seedlings gained the best protection against chilling injury by pretreatment with LAB 173 711 (5 × 10^–4 M) for 3 days. The protection effect could be sustained for 4 days. The LAB 173 711 pretreatment at 28°C did not cause a significant difference in the electrolyte leakage over the ambient temperature (28°C) control. Application of LAB 173 711 at 28°C reduced visible injury and the treated seedlings had higher ethylene production and respiration rate over the untreated control. LAB 173 711 helped maintain the integrity of the cell membrane and thus reduced the leakage of soluble sugar and amino acids. These combined effects led to a higher chilling tolerance in the mung bean seedlings.     

Ethylene and 1 -Aminocyclopropane-1-Carboxylic Acid Production in flacca, a Wilty Mutant of Tomato, Subjected to Water Deficiency and Pre-treatment with Abscisic Acid

Neill, S. J., McGaw, B. A. and Horgan, R. 1986. Ethylene and1-aminocyclopropane-l-carboxylic acid production in flacca,a wilty mutant of tomato, subjected to water deficiency andpretreatment with abscisic acid —J. exp. Bot. 37: 535–541. Plants of Lycoperstcon esculentum Mill. cv. Ailsa Craig wildtype and flacca (flc) were sprayed daily with H²O or 2?10^–2mol m^–3 abscisic acid (ABA). ABA treatment effected apartial phenotypic reversion of flc shoots; leaf areas wereincreased and transpiration rates decreased. Leaf expansionof wild type shoots was inhibited by ABA. Indoleacetic acid (IAA), ABA and l-aminocyclopropane-l-carboxylicacid (ACC) concentrations were determined by combined gas chromatography-massspectrometry using deuterium-labelled internal standards ABAtreatment for 30 d resulted in greatly elevated internal ABAlevels, increasing from 1?0 to 4?3 and from 0?45 to 4?9 nmolg^–1 fr. wt. in wild type and flc leaves respectively.Endogenous IAA and ACC concentrations were much lower than thoseof ABA. IAA content ranged from 0?05 to 0?1 nmol g^–1 andACC content from 0?07 to 0?24 nmol g^–1 Ethylene emanationrates were similar for wild type and flc shoots. Wilting of detached leaves induced a substantial increase inethylene and ACC accumulation in all plants, regardless of treatmentor type. Ethylene and ACC levels were no greater in flc leavescompared to the wild type. ABA pretreatment did not preventthe wilting-induced increase in ACC and ethylene synthesis. Key words: ABA, ACC, ethylene, wilting, wilty mutants     

Physiological and biochemical changes related to methyl jasmonate-induced chilling tolerance of rice (Oryza sativa L.) seedlings

Physiological and biochemical changes related to methyl jasmonate (MeJA)-induced chilling tolerance of rice (Oryza sativa L. cv. Taichung Native 1) seedlings were investigated. Treatment of whole plants with 10 mmol m^?3 MeJA for 48 h before chilling (5 °C) was optimal for the induction of chilling tolerance. MeJA greatly improved the survival ratio of chilled seedlings and ameliorated chilling injury such as demolition of membrane structure (estimated by electrolyte leakage). MeJA also prevented water loss in chilled seedlings by reducing the opening of stomata and decreasing the root bleeding rate. Putrescine and spermine levels in shoots increased but spermidine levels decreased on exposure to MeJA. In roots, putrescine levels also increased and spermidine levels increased transiently on exposure to MeJA. Activities of arginine decarboxylase (ADC; EC 4.1.1.19) and S-adenosylmethionine decarboxylase (SAMDC; EC 4.1.1.50) in both shoots and roots increased on exposure to MeJA, while the activity of ornithine decarboxylase (ODC; EC 4.1.1.17) remained unchanged. The MeJA-induced putrescine increase was inhibited by 50 mmol m^?3α-difluoromethylarginine (DFMA), an irreversible inhibitor of ADC, but not by 50 mmol m^?3α-difluoromethylornithine (DFMO), an irreversible inhibitor of ODC. The effect of MeJA on the induction of chilling tolerance was also reduced by 50 mmol m^?3 DFMA. The effects of DFMA were partly prevented by 1 mol m^?3 putrescine. This indicates that putrescine accumulation is required for the induction of chilling tolerance of rice seedlings by MeJA.     

Relationships between Acetylene Reduction Activity, Hydrogen Evolution and Nitrogen Fixation in Nodules of Acacia spp.: Experimental Background to Assaying Fixation by Acetylene Reduction under Field Conditions

Hansen, A. P., Pate, J. S. and Atkins, C. A. 1987. Relationshipsbetween acetylene reduction activity, hydrogen evolution andnitrogen fixation in nodules of Acacia spp.: Experimental backgroundto assaying fixation by acetylene reduction under field conditions.—J.exp. Bot. 38: 1–12 Glasshouse grown, symbiotically-dependent seedlings of Acaciaalata R.Br., .A. extensa Lindl., and A. pulchella R.Br. wereexamined for acetylene reduction in closed assay systems usingundisturbed potted plants, excavated whole plants, nodulatedroots or detached nodules. Nitrogenase activity declined sharplyover the first hour after exposure of detached nodules to acetylene(10% v/v in air), less steeply or not at all over a 3 h periodin assays involving attached nodules. Using detached nodules,rates of acetylene reduction, nitrogen (¹⁵N₂) fixation, andhydrogen evolution in air (¹⁵N₂) and acetylene-containing atmosphereswere measured in comparable 30 min assays. Total electron flowthrough nitrogenase in air was determined from rates of nitrogen(¹⁵N₂) fixation ( ? 3) plus hydrogen evolution, that in thepresence of acetylene from rates of acetylene reduction andhydrogen evolution in air: acetylene. Values for the ratio ofelectron flow in air: acetylene to that in air ranged from 0?43to 0?83 in A. pulcheila, from 0?44 to 0?66 in A. alala and from0?37 to 0?70 in A. extensa, indicating substantial inhibitionof electron flow through nitrogenase of detached nodules byacetylene. Relative efficiencies of nitrogenase functioningbased on hydrogen evolution and acetylene reduction were from0?15 to 0?79, those based on nitrogen (¹⁵N₂) fixation and hydrogenevolution from 0?53 to 0?87. Molar ratios of acetylene reducedto nitrogen (¹⁵N₂) fixed were 2?82 ? 0?24, 201 ? 0?15, and 1?91? 0?11 (?s.e.; n = 7) for A. pulcheila,A. extensa and A. alata respectively A standard 5–10 min acetylene reduction assay, conductedon freshly detached unwashed nodules in daytime (12.00–14.00h), was calibrated for field use by comparing total N accumulationof seedlings with estimated cumulative acetylene reduction overa 7-week period of glasshouse culture. Molar ratios for acetylenereduced: nitrogen fixed using this arbitrary method were 3?58for A. alata, 4?82 for A. extensa and 1?60 for A. pulchella.The significance of the data is discussed. Key words: Acacia spp, nitrogenase functioning     

Cloning and characterisation of a pepper aquaporin,CaAQP, which reduces chilling stress in transgenic tobacco plants

Ubiquitous cell membrane proteins called aquaporins are members of major intrinsic proteins (MIPs), which control the specific transport of water molecules across cell membranes. A pepper aquaporin gene (CaAQP), which exhibits the structural features of tonoplast intrinsic proteins of the MIP subfamily, was isolated from the leaves of chilling-treated seedlings of pepper (Capsicum annuum L.) cv. P70. Assays indicated high levels of expression in young seeds, green fruits and flower buds and low levels of expression in the stems, leaves and roots of pepper. The expression patterns were strongly and rapidly induced by HgCl₂, low temperature, abscisic acid, fluridone and osmotic stresses. The responsiveness of pepper seedlings pretreated with abscisic acid at low temperatures demonstrated up-regulation of CaAQP by chilling, which is potentially involved in ABA signalling. Our results indicated that overexpression of CaAQP decreased chilling stress in transgenic plants, likely by increasing the stomatal aperture under stress, increasing the rate of membrane damage during the recovery stage, thereby affecting the intercellular CO₂ concentration with lower stomatal conductance and transpiration rates. VIGS of CaAQP in pepper plants caused significant growth retardation. These results suggested that CaAQP played a crucial role in the plant response to abiotic stresses.     

The possible role of cyclic AMP in the control of genetic tumor induction

Young seedlings of the tumor-prone amphiploid Nicotiana suaveolensx N. langsdorffii, grown aseptically on nutrient medium, weretreated with 1x10^–2 M cyclic adenosine 3': 5'-monophosphate(cyclic AMP). The incidence of tumor formation was scored atregular intervals subsequent to exposure. Cyclic AMP causeda significant reduction in the rate of tumor formation. In addition,untreated plants grown on nutrient medium were harvested atregular intervals after the seeds had been sown. Cyclic AMPwas extracted, partially purified, and assayed radioimmunologically.The endogenous level of cyclic AMP in stem tissue was highestin young seedlings, rapidly fell reaching a low point in 18day-old plants, and eventually leveled off. The presence ofindoleacetic acid (IAA) in the growth medium at a final concentrationof 2x10^–5 M prevented the decline in cyclic AMP that occurredin seedlings grown on unsupplemented medium. (Received May 21, 1976; )     

ABA Levels and Effects in Chilled and Hardened Phaseolus vulgaris

Leaf abscisic acid (ABA) levels of chilled P. vulgaris weremeasured after 18 h chilling at 5°C, at a saturation deficitof 1.24 g m^–3 (SD), and after chilling in a water-saturatedatmosphere. Changes were also followed during a chill hardeningperiod of 4 d at 12°C, 2.1 g m^–3 SD. It was foundthat hardening resulted in an almost 5. fold increase in ABAlevels after 3 d at 12°C, and this decreased to approximatelycontrol levels on the fourth day. Subsequent chilling of hardenedplants produced no change in ABA levels from that of controlplants (22° C). In contrast, non-hardened plants chilledat 1.24 g m^–3 SD had ABA levels almost 3 times the levelof control plants. However, chilling in a water-saturated atmosphereresulted in a decrease in ABA levels. In addition, the response of leaf diffusion resistance (LDR)to exogenous ABA fed via the transpiration stream was measuredat 5 ° C and 22° C in hardened and non-hardened plants.Use of tritium-labelled ABA was made to calculate the stomatalsensitivity to ABA. It was found that exogenous ABA caused anincreased in LDR at 22°C in both hardened and non-hardenedplants. However, the sensitivity of the hardened plants to ABAwas greater in terms of rate of closure and amount of ABA requiredto close the stomata. At 5°C, however, ABA caused stomatalopening and the maintainance of open stomata in non-hardenedplants. In hardened plants, ABA caused stomatal closure at 5°C.These results are discussed in relation to the locking-openresponse of chilled P. vulgaris stomata. Key words: Chilling, Stomata, ABA, Phaseolus vulgaris     

Control of Hypocotyl Hook Angle in Phaseolus mungo L. Role of Growth Substances

Effects of growth hormones on the hook angle and light responseof Phaseolus mungo L. hypocotyl hooks are described and theresults are discussed with reference to the functions of otherparts of the seedling in controlling the growth and shape ofthe hook. Apically applied IAA (indolyl acetic acid) prevented hook openingin decapitated seedlings in the dark and in all the red-irradiatedseedlings. [¹⁴C]IAA experiments showed that only a small quantityof IAA (2–6 ?g per hook) was required to produce theseeffects, and that transport of IAA through the hook was negligibleand unaffected by red irradiation. ABA (abscisic acid) had little effect on the hooks or theirlight response. Applied ethylene and IAA-induced ethylene slightly closed thehooks, but only slightly reduced light-induced opening. IAAreduced the effect of ethylene in the dark, but after irradiationthe hooks appeared more sensitive to the ethylene in the presenceof IAA, resulting in light-induced hook closure. Basally applied kinetin (6-furfurylaminopurine) prevented decapitatedhooks from opening in the dark, especially when GA₃ (gibberellicacid) was also present. Some combinations of kinetin and GA₃(with high kinetin concentrations) also prevented light-inducedopening, but combinations with lower kinetin concentrationsallowed almost as much opening as was found in intact hooks. It is proposed that the terminal parts act by regulating thesupply of cytokinins and gibberellins from the basal parts,and that IAA does not mediate this funotion in this species. The results are compared with those reported for other species.     

Asparagusic acid, a new plant growth inhibitor in etiolated young asparagus shoots

Yellow prisms of asparagusic acid, with a molecular formulaof C₄H₆O₂S₂ were isolated from etiolated asparagus tissues (Asparagusofficinalis L.). This acid inhibits growth in lettuce and otherseedlings when applied in concentrations of 6.67x10^–7Mto 6.67xl0^–7M. The extent of activity was very similarto that of abscisic acid. ¹ A well known shift reagent in the NMR spectrum (1). (Received April 12, 1972; )     

Genetic engineering of rice capable of synthesizing fructans and enhancing chilling tolerance

Fructans are water-soluble fructose oligomers and polymers thatare based on sucrose, and have been implicated in protectingplants against water stress. Rice (Oryza sativa L.) is highlysensitive to chilling temperatures, and is not able to synthesizefructans. Two wheat fructan-synthesizing enzymes, sucrose:sucrose1-fructosyltransferase, encoded by wft2, or sucrose:fructan6-fructosyltransferase, encoded by wft1, were introduced intorice plants, and rice transformants that accumulate fructanswere successfully obtained. The mature leaf blades of transgenicrice lines with wft2 or wft1 accumulated 16.2 mg g^–1 FWof oligo- and polysaccharides mainly composed of inulin oligomersof more than DP7, and 3.7 mg g^–1 FW of oligo- and polysaccharides,mainly composed of phlein oligomers of more than DP15, respectively.The transgenic rice seedlings with wft2 accumulated significantlyhigher concentrations of oligo- and polysaccharides than non-transgenicrice seedlings, and exhibited enhanced chilling tolerance. Theoligo- and polysaccharide concentrations of seedlings expressingwft1 were obviously lower than those of lines expressing wft2,and no correlation between oligo- and polysaccharide concentrationsand chilling tolerance was detected in wft1-expressing ricelines. The results suggest that transgenic rice lines expressingwheat-derived fructosyltransferase genes accumulated large amountsof fructans in mature leaf blades and exhibited enhanced chillingtolerance at the seedling stage. This is the first report owingthat fructan accumulation enhanced tolerance to non-freezinglow temperatures. Key words: Chilling tolerance, fructan, fructosyltransferase, Oryza sativa, transgenic plant     

Reversible and Irreversible Reduction of ACC-dependent Ethylene Formation in Mung Bean (Vigna radiata [L] Wilczek) Hypocotyls Caused by Chilling

Etiolated seedlings of mung bean (Vigna radiata [L] Wilczek)grown at 26?C in the dark were chilled at 0?C for various periodsand then returned to 26?C to follow the development of chillinginjury and changes in ACC-dependent ethylene-forming activity(EFA). After chilling for one day, they could grow normallyat 26?C, but not after chilling for more than two days. Thelonger chilling caused a remarkable increase in electrolyteleakage from the hypocotyl tissues, suggesting plasma membraneinjury. The ACC-dependent EFA in vivo in hypocotyls was foundto be sensitive to chilling and progressively declined as afunction of the chilling period. After 1-day chilling, the activitydeclined to less than 50 per cent of the unchilled tissues,but it returned to the normal level within 3 h after the returnto 26?C. However, chilling more than two days caused irreversibleloss of the activity. Thus, there seems to be an intimate relationshipbetween irreversible loss of the EFA and chilling injury ofthe tissues. The recovery of EFA after chilling for one daycould be markedly inhibited by cycloheximide and monensin, suggestingthat the recovery requires protein synthesis and, presumably,includes repair of partially injured cellular membranes, mediatedthrough the Golgi apparatus. ¹Contribution No. 2894 from the Institute of Low TemperatureScience (Received June 23, 1986; Accepted November 7, 1986)     

The Effect of EGTA, Calcium Channel Blockers (Lanthanum Chloride and Nifedipine) and their Interaction with Abscisic Acid on Seed Germination of Brassica juncea cv. RLM-198

Recent investigations have shown that abscisic acid (ABA) dependsupon the availability of Ca²⁺ for its action in certain systems.In order to check whether ABA requires Ca²⁺ to inhibit seedgermination, the effects of ABA, CaCl₂, EGTA (a Ca²⁺ chelator)and lanthanum chloride and nifedipine (Ca²⁺ channel blockers),individually and in combination, on seed germination of Brassicajuncea L. cv. RLM-198 were studied. ABA inhibited germinationin a concentration dependent manner. ABA-induced inhibitionwas abolished with the lapse of time after application. Calciumneither affected germination nor altered the ABA-induced inhibition.EGTA. La³⁺ and nifedipine suppressed seed germination when testedindividually and further elevated the ABA effect, in a synergisticway, when applied simultaneously. They also prevented the time-dependentreduction in ABA-induced inhibition. The findings indicate thatCa²⁺ is not essential for ABA to cause germination inhibition. EGTA, Ca²⁺ channel blockers, abscisic acid, seed germination, Brassica juncea     

Effects of Some Amino Acid Analogues on the Uptake and Transport of K+ and Ca2+ in Wheat and Mung Bean Seedlings: II. UPTAKE AND TRANSLOCATION IN WHOLE SEEDLING PLANTS

The effects of some amino acid analogues (o-, m- and p-fluorophenylalanineand azetidine-2-carboxylic acid) on uptake of⁴²K and ⁴⁵Ca intothe roots and transport to the shoots of whole wheat and mungbean seedlings were measured. The effect of each analogue oneither K⁺ or Ca²⁺ movement could be placed into one of fourcategories: (1) No effect on either ion uptake or transport;(2) No effect on ion uptake, but a reduction in transport; (3)Similar reductions in ion uptake and transport; (4) A relativelygreater reduction in ion transport than in uptake. At leasttwo independent sites of protein involvement in ion movementwere required to account for all four types of analogue effectobserved; one site of protein involvement was probably at theplasmalemma of root cortex cells and the second site, involvinga protein that turned over more quickly, was within the stele.Some evidence was found that Ca²⁺ transport is a passive process.Light did not stimulate uptake. Key words: Triticum aestivum, Vigna radiata, Two pump hypothesis