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)     

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     

Effects of Leaf Chilling on Thylakoid Functions, Measured at Room Temperature, in Cucumis sativus L. and Oryza sativa L.

Photosynthetic functions in leaves of cucumber (Cucumis sativusL.) and rice (Oryza sativa L.) were examined before and aftervarious chilling treatments. Cucumber leaves lost the capacityfor the photosynthetic oxygen evolution after chilling at 0°Cin the dark for 48 h. Thyla-koids isolated from such leaveswere not able to reduce dichloroindophenol (DCIP), but the additionof diphenylcarbazide (DPC), an electron donor to PS II, restoredthe ability to reduce DCIP, indicating that the site of damageis in the water-splitting machinery of PS II. In moderate light (500 jumol quanta m^–2s^–1), chillingof cucumber leaves at 5°C for 5 h was sufficient to inducethe complete loss of the capacity for photosynthetic oxygenevolution. Electron transport rates measured in thylakoids wereunaltered, but thylakoids were totally permeable to protons.Since the addition of dicyclohexylcarbodiimide (DCCD) restoredcoupling and the capacity for proton uptake, the primary siteof damage was deduced to be in the ATPase. In rice, both chilling treatments had barely any effect on thylakoidfunctions, although some negative effects was apparent in photosynthesisin leaves. ¹Present address: Department of Botany, Faculty of Science,University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113 Japan. ²Present address: Department of Botany, Duke University, Durham,NC 27706, U.S.A. (Received January 11, 1989; Accepted June 12, 1989)     

Effects of Some Growth Regulators on Polyamine Biosynthetic Enzymes in Etiolated Pea Seedlings

This study was designed to examine possible links between polyaminebiosynthesis and effects of growth regulatory compounds. Anauxin (IAA), a cytokinin [benzyladenine; benzylaminopurine (BAP)],an ethylene source (ethephon) and abscisic acid (ABA) were individuallyapplied to terminal buds of excised etiolated or red light (R)-exposedpea epicotyls. Effects were noted on bud fresh weight and onthe two main enzymes of putrescine biosynthesis, arginine decarboxylase(ADC; EC 4.1.1.19 [EC] ) and ornithine decarboxylase (ODC; EC 4.1.1.17 [EC] ).As previously reported [Dai and Galston (1981) Plant Physiol.67: 266], both bud growth and ADC activity are increased byR light. In such buds, ADC is raised further by 1–10 µMBAP or ABA and inhibited by 1–10 µM IAA or ethylene(50 mg/liter or more of ethephon). In all cases, effects ofR-irradiation plus 1 mM growth regulators on ODC activity wasthe inverse of their effects on ADC, indicating independentcontrol of these pathways. These results do not support theview that putrescine biosynthetic activity is correlated withgrowth in etiolated pea seedlings. ¹Supported by a grant from NSF to A.W.G. ²Supported by a grant from the Turkish Government. Permanentaddress: Department of General Botany, University of Istanbul,S?leymaniye, Istanbul, Turkey. ³On sabbatical leave from the Department of Horticulture, HebrewUniversity of Jerusalem, Rehovot, Israel. (Received September 22, 1983; Accepted February 28, 1984)     

Effect of Plant Growth Regulators on Flower-Opening of Pharbitis nil

Flower buds of Pharbitis nil (due to open the next morning)cut from plants in the field before noon open very slowly bothin darkness and at a low temperature (20°C), unlike thebuds cut in the evening. On cool cloudy days, even the budscut in the evening open very slowly. Addition of sucrose, mineralnutrients or plant growth regulators other than ABA to the waterin which the cut buds were placed did not promote flower-openingunder such conditions, but addition of ABA (10–100 µM)greatly promoted it. IAA (100 µM) given alone or in combinationwith ABA suppressed floweropening completely. Mature flowerbuds placed in an ABA solution opened even under continuouslight at 25°C just as those kept in darkness without ABA;flower-opening occurred about 12 h after the application ofABA. ABA given to the buds in darkness at 25°C and thatgiven in continuous light at 20°C also advanced the timeof flower-opening. The action mechanism of ABA is discussed. ¹ This paper is dedicated to the memory of Dr. Joji Ashida,the first president of the Japanese Society of Plant Physiologist. (Received October 28, 1982; Accepted January 7, 1983)     

Inhibition of Light-Stimulated Leaf Expansion by Abscisic Acid

Abscisic acid (ABA) applied to intact bean (Phaseolus vulgaris)leaves or to isolated leaf discs inhibits light-stimulated cellenlargement This effect may be obtained with 10^–4 molm^–3 ABA, but is more significant at higher concentrations.The inhibition of disc expansion by ABA is greater for discsprovided with an external supply of sucrose than for discs providedwith KC1, and may be completely overcome by increasing the KC1concentration externally to 50 mol m^–3. Decreased growthrate of ABA-treated tissue is not correlated with loss of solutesfrom growing cells, but is correlated with a decrease in cellwall extensibility. ABA does not prevent light-stimulated acidificationof the leaf surface, and stimulates the acidification of theexternal solution by leaf pieces. However, the capacity of thecell walls to undergo acid-induced wall loosening is diminishedby ABA-treatment. The possibility that ABA acts directly byinhibiting growth processes at the cellular level, or indirectlyby causing stomatal closure, is discussed. Key words: Phaseolus vulgaris, ABA, Inhibition, Leaf expansion     

New fava bean guard cell signaling mutant impaired in ABA-induced stomatal closure

We isolated a mutant from Vicia faba L. cv. House Ryousai. Itwilts easily under strong light and high temperature conditions,suggesting that its stomatal movement may be disturbed. We determinedresponses of mutant guard cells to some environmental stimuli.Mutant guard cells demonstrated an impaired ability to respondto ABA in 0.1 mM CaCl₂ and stomata did not close in thepresence of up to 1 mM ABA, whereas wild-type stomata closedwhen exposed to 10 µM ABA. Elevating external Ca²⁺caused a similar degree of stomatal closure in the wild typeand the mutant. A high concentration of CO₂ (700 µlliter^–1) induced stomatal closure in the wild type, butnot in the mutant. On the basis of these results, we proposethe working hypothesis that the mutation occurs in the regiondownstream of CO₂ and ABA sensing and in the region upstreamof Ca²⁺ elevation. The mutant is named fia (fava bean impairedin ABA-induced stomatal closure). ³ Corresponding author: E-mail, smoiwai{at}agri.kagoshima-u.ac.jp;Fax, +81-99-285-8556.     

Carrier-Mediated ABA Uptake by Suspension-Cultured Phaseolus coccineus L. Cells: Stereospecificity and Inhibition by Ionones and ABA Esters

Astle, M. and Rubery, P. 1987. Carrier-mediated ABA uptake bysuspension-cultured Phaseolus coccineus L. cells: Stereospecificityand inhibition by ionones and ABA esters.—J. exp. Bot.38: 150–163. The substrate for the abscisic acid (ABA) carrier in Phaseoluscoccineus L. suspension-cultured cells is shown to be the (S)ABAenantiomer, K_m = 1?0 mmol m^–3. The methyl (MeABA) andphenyl (PheABA) esters of ABA inhibit carrier-mediated uptakeof ABA with half-maximal inhibition achieved at about 7?0 mmolm^–3 and 10 mmol m^–3 respectively: with (S)MeABAthis value is decreased to about 2?0 mmol m^–3. There isno demethylation of radioactive MeABA by the cells during 5min incubations. Although MeABA reversibly inhibits the ABAcarrier, it is not a transport substrate: association of radioactiveMeABA with living cells is unaffected by non-radioactive MeABAor ABA and, by comparison with frozen-and-thawed cells, it isshown that the radioactivity remains extracellular. It is proposedthat MeABA binds to the carrier to form an abortive complexthat is not translocated. The terpenoid ABA analogue LAB 144143also inhibits carrier-mediated ABA uptake. At concentrationsup to about 20 mmol m^–3 - and ß-ionone specificallyinhibit the ABA carrier with the half-maximal effect at about0?6 mmol m^–3 ß-ionone. However, at higher iononeconcentrations, the uptake of ABA, indol-3-yl acetic acid andof 5,5-dimethyloxazolidine-2,4-dione (DMO) are all stimulated:this may reflect general permeabilization of the membrane toweak acids by ionone. Key words: Uptake carrier, abscisic acid, methyl and phenyl esters of ABA, ionone, Phaseolus coccineus L. suspension culture     

The Effects of Cytokinins and ABA on Stomatal Behaviour of Maize and Commelina

Epidermal strips and leaf fragments of Commelina and leaf fragmentsof maize were incubated on solutions containing naturally-occurringor synthetic cytokinins and/or ABA. The effects of these treatmentson stomatal behaviour were assessed. Cytokinins alone did notpromote stomatal opening in either species but concentrationsof both zeatin and kinetin from 10^–3 to 10^–1 molm^–3 caused some reversal of ABA-stimulated closure ofmaize stomata. The reversal of the ABA effect increased withincreasing cytokinin concentration. Cytokinins had no effecton ABA-stimulated closure of Commelina stomata. When appliedalone, at high concentration (10^–1 mol m^–3), toCommelina epidermis or leaf pieces both zeatin and kinetin restrictedstomatal opening. Key words: ABA, Cytokinins, Stomata, Maize, Commelina     

Correlation of cytokinins and abscisic acid with monocarpic senescence in soybeans

The involvement of cytokinins and abscisic acid (ABA) in themonocarpic senescence (foliar yellowing following fruit development)of soybeans was examined. Foliar sprays of cytokinin (10^–4M zeatin or 10^–5 M benzyladenine), begun when the plantsfirst set fruit and repeated every other day, significantlydelayed, but did not prevent, monocarpic senescence. Foliarsprays of 10^–4 M ABA, applied in the same manner, significantlyhastened senescence of fruiting soybeans but apparently hadno effect on depodded plants. Leaf and stem material from pre-senescentand senescent plants was extracted, chromatographed, and bioassayedfor cytokinin-lilce activity (Amaranthus betacyanin productionassay) and ABA-like activity (oat coleoptile straight growthassay for inhibitors). ABA-like activity increased, and cytokinin-likeactivity decreased in shoot tissue before the plants began tosenesce. Cytokinin-like activity in the fruit also declinedduring this period. These results implicate a decrease in cytokininsand an increase in ABA-like inhibitors in the control of monocarpicsenescence of soybeans, but neither alone is causal. ¹ Supported in part by Research Grant 416-15-79 from the USDACooperative State Research Service under PL 89–106. ² Present address: Biology Dept., College of St. Benedict'sSt. Joseph, Minn. 56374, U.S.A. (Received February 4, 1978; )     

Interaction of Abscisic Acid and 6-Benzylaminopurine on the Metabolism of Lemna minor L.

The effects of abscisic acid (ABA) and 6-benzylaminopurine (BAP)on growth and the contents of chlorophyll, protein and nucleicacid of fronds of Lemna minor were studied. The frond multiplicationrate was reduced by 10^–6 M ABA but increased by 10^–6M BAP. When both substances were added simultaneously to theculture medium, the growth inhibition expected from ABA wasreduced considerably by the presence of BAP. The chlorophyll content per frond was increased by ABA whilethat per flask was reduced by ABA and increased by BAP. WhenABA and BAP were added together, the ABA effect was reducedby BAP. A similar response was detected in the nucleic acidcontent; ABA caused a decrease during the early phase of treatmentwhile BAP increased it. In this case, treatment with ABA$BAPalso showed that BAP could reduce the ABA effect. However, thiseffect was not observed on the protein content. ² Present address: Departamento de Agricultura, Facultad deVeterinaria, Universidad Aut?noma de Barcelona, Bellaterra,Barcelona, Spain. (Received June 6, 1984; Accepted September 10, 1985)     

Release of Guttation Fluid from Passive Hydathodes of Intact Barley Plants. II. The Effects of Abscisic Acid and Cytokinins

Guttation was used as a non-destructive way to study the flowof water and mineral ions from the roots and compared with parallelmeasurements of root exudation. Guttation of the leaves of barley seedlings depends on age andon the culture solution. Best rates of guttation were obtainedwith the primary leaves of 6- to 7-day-old seedlings grown onfull mineral nutrient solution. The growing leaf tissue becomessaturated with K⁺ below 1.5 mM K⁺ in the medium, whereas K⁺concentration in the guttated fluid still increases furtheras K⁺ concentration in the medium is raised. At 3 mM K⁺ averagevalues of guttation were 1.4–2.4 mm³ h^–1 per plantwith a K⁺ concentration of 10–20 mM; for exuding plantsthe flow was 4.2–7.6 mm³ h^–1 per plant and K⁺ concentration35–55 mM. Abscisic acid (ABA) at 10^–6 to 10^–4 M 0–2h after addition to the root medium increased volume flow ofguttation and exudation and the amount of K⁺ exported. Threeh after addition of ABA both volume and amount of K⁺ were reduced.There was an ABA-dependent increase in water permeability (Lp)of exuding roots shortly after ABA addition. Later Lp was decreasedby 35 per cent and salt export by 60 per cent suggesting aneffect of ABA on salt transport to the xylem apart from itseffect on Lp. Benzyladenine (5 x 10^–8 to 10^–5 M)and kinetin (5 x 10^–6 M) progressively reduced volumeflow and K⁺ export in guttation and exudation and reduced Lp. Guttation showed a qualitatively similar response to phytohormonesas found here and elsewhere using exuding roots. Hordeum vulgare L., barley, guttation, abscisic acid, cytokinins, benzyl adenine, kinetin     

Different Sets of cis-Elements Contribute to the Expression of a Catalase Gene from Castor Bean during Seed Formation and Postembryonic Development in Transgenic Tobacco

Deletion analysis of the promoter region of a gene for catalase,cat2, from castor bean (Ricinus communis) was performed to identifythe cis-regulatory elements responsible for the expression ofa rß-glucuronidase (GUS) fusion gene during seed formationand postembryonic development in transgenic tobacco. The analysisshowed that multiple cis-elements contribute to the activityof the cat2 promoter during seed formation and postembryonicdevelopment. The 5'-upstream regions from –1,241 to –816bp, from –720 to –682 bp, and from –632 to–535 bp, relative to the site of initiation of translationof cat2, contributed positively to the activity of the cat2promoter during both stages. By contrast, the region from –816to –720 bp had a negative effect at both stages. The regionfrom –682 to –632 bp contributed positively to theactivity during seed formation but negatively during postembyonicdevelopment. Histochemical analysis revealed that the multiplecis-elements determined not only the level of expression ofthe chimeric gene but also the tissue-specificity of such expression.For example, the region from –1,241 to –816 bp allowedexpression of the chimeric gene in the axis of the embryo ofthe dry seed, as well as in the cortex of the middle part ofthe hypocotyl and at the base of epicotyl in the young seedling. ¹Present address: Department of Plant Molecular and Cell Biology,University of Florida, Gainesville, Florida 32611-0511, U.S.A. ²Present address: Center for Molecular Biology and Genetics,Mie University, 1515 Kamihama, Tsu, Mie, 519 Japan ³Present address: Faculty of Biotechnology, Fukui PrefecturalUniversity, 4-1-1 Kenjojima, Matsuoka-cho, Yoshida-gun, Fukui,910-11 Japan     

The Metabolism of Abscisic Acid

The light-catalysed isomerization of (+)-abscisic acid (ABA)to its trans isomer during isolation from leaves was monitoredby the addition of (±)-[2-¹⁴C]ABA to the extraction medium.(+)Trans-abscisic acid (t-ABA) was found to occur naturallyin rose (Rosa arvensis) leaves at 20µg/kg fresh weight;(+)-ABA was present at 594µg/kg. (±)-[2-¹⁴D]Trans-abscisicacid was not isomerized enzymically to ABA in tomato shoots. (±)-Abscisic acid was converted by tomato shoots to awater-soluble neutral product, ‘Metabolite B’, whichwas identified as abscisyl-ß-D-glucopyranoside. When(±)-[2-¹⁴C]trans-abscisic acid in an equimolar mixturewith (±)-[2-¹⁴C}ABA was fed to tomato shoots it was convertedto its glucose ester 10 times faster than was ABA. Trans-abscisyl-ß-D-glucopyrano8ide only was formedfrom (±)-[2-¹⁴C]t-ABA in experiments lasting up to 30h. Glucosyl abscisate was formed slowly from ABA and the freeacid fraction contained an excess of the unnatural (–).ABAas did the ABA released from abscisyl-ß-D-glucopyranosideby alkaline hydrolysis. The (+).ABA appeared to be the solesource of the acidic ‘Metabolite C" previously noted. The concentrations of endogenous (+)-, (+)-[2-¹⁴C]-, and (–)-[2-¹⁴C]ABAremaining as free acid, and also in the hydrolysate of abscisyl-ß-D-glucopyranoside,were measured by the ORD, UV absorption, and scintillation spectrometryof highly purified extracts of ABA from tomato shoots whichhad been supplied with racemic [2-^l4C]ABA.     

Chilling injury in cotton (Gossypium hirsutum L.) Prevention by abscisic acid

Cotton (Gossypium hirsutum L.) intact seedlings and isolatedcotyledonary discs were exposed to chilling (4?C) under humidconditions which prevented dehydration. The damage resultingfrom chilling was estimated by means of electrolyte leakageand survival in whole seedlings and by the electrolyte leakageand necrotic areas in isolated cotyledonary discs. Also, theeffect of chilling on membrane phospholipids and cellular reducedglutathione was determined. Within the first two and three daysof chilling, there was a marked reduction in the reduced glutathioneand membrane phospholipid levels without electrolyte loss andnecrosis. This reduction was completely prevented by pretreatmentwith abscisic acid. Prolonging the chilling period resultedin decreased survival in whole seedlings and in progressiveincrease in electrolyte leakage and necrosis in isolated cotyledonarydiscs. Pretreatment with abscisic acid prior to chilling almostcompletely prevented this chilling injury when exposure to 4?Cwas less than 5 days. Even with longer chilling periods, theabscisic acid pretreatment greatly reduced the damage. ³Incumbent of the Seagram Chair in Plant Science. (Received July 21, 1979; )     

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.     

Changes in the Translatable RNA Population during Abscisic Acid Induce Freezing Tolerance in Bromegrass Suspension Culture

Abscisic acid (ABA) has been shown to increase freezing toleranceof bromegrass (Bromus in-ermis Leyss cv. Manchar) cell suspensioncultures from a LT₅₀ (the temperature at which 50% cells werekilled) of –7 to – 30?C in 5 days at 23?C. Our objectivewas to study the qualitative changes in the translatable RNApopulation during ABA induced frost tolernace. In vitro translationproducts of poly(A)⁺ RNA isolated from bromegrass cells withor without 75 µM ABA treatment for various periods oftime were separated by 2D-PAGE and visualized by fluorography.SDS soluble proteins from the same treatments were also separatedby 20-PAGE. After 5 days treatment, at least 22 new or increasedabundance SDS soluble polypeptides were observed. From fluorographs,29 novel or increased abundance in vitro translation productscould be detected. The pattern of changes between ABA inducedSDS-soluble proteins and translation products from the 2D gelswere similar. A time course study (0–7 days) showed that17 of the 29 translation products were detected after 1 dayABA treatment, and at least 14 were present after 1 h. Coldtreatment (+4?C) induced fewer changes in the pool of translatableRNA than with ABA treatment. Three translation products inducedby cold appear to be similar to 3 of the ABA induced translationproducts. The majority of the ABA inducible translatable RNAsappeared at 10 µM or higher which coincides with the inductionof freezing tolerance. Many of these ABA inducible RNAs persisted7 days after ABA was removed from the media and correspondinglythe LT₅₀ (–17?C) was still well above the control level(–17?C). The results suggest that ABA alters the poolof translatable RNAs during induction of freezing tolerancein bromegrass suspension culture cells. ¹Oregon Agricultural Experiment Station Technical Paper No.9256. (Received August 3, 1990; Accepted October 18, 1990)     

Phase Transition Temperatures Determined for Chloroplast Thylakoid Membranes and for Liposomes Prepared from Charged Lipids Extracted from Thylakoid Membranes of Higher Plants

Lipid phase separation temperatures of intact thylakoid membranesfrom a number of chilling sensitive plants were measured usingchlorophyll a as the intrinsic fluorescent probe. The phospho-and sulfolipids were extracted from the thylakoid lamellae ofthese plants and purified by silicic acid column and thin layerchromatographies. These separated lipids were eluted and recombinedto give a total charged anionic thylakoid lipid fraction thatwas used to prepare liposomes containing purified chlorophylla as the fluorescent probe. The phase separation temperaturesof these liposomes were compared to phase separation temperaturesin intact thylakoid membranes isolated from the same plants. The chilling-sensitive plants—corn, pepper, tomato andwater hyacinth — showed phase separation temperaturesranging from 9 to 19°C for both the liposomes and the thylakoidmembranes. In addition, low temperature phase separations wereseen from –21 to –27°C. Mimulus, which is notas chilling sensitive as the former plants, had a phase separationtemperature near 0 to 2.5°C and at –27°C. In general,there was a good agreement between the phase separation temperaturesof intact thylakoids and the purified anionic lipid fractionextracted from these thylakoids. Similar results were obtained using either trans-parinaric acidor chlorophyll a as the fluorescent probe in liposomes madefrom anionic thylakoid lipids or in liposomes prepared frompure dimyristoyl phosphatidyl choline, distearoyl phosphatidylcholine, or mixtures of equal amounts of these phospholipids. ¹ CIW-DPB Publication # 728. ³ Present address: Laboratory of Experimental Physics, Departmentof Biophysics, State University of Utrecht, Princetonplein 5,Utrecht, The Netherlands. (Received January 18, 1981; Accepted July 2, 1981)     

The Effect of Priming Treatments on the Viability and Accumulation of Chromosomal Damage in Aged Pea Seeds

A range of post-storage priming treatments were evaluated todevelop a protocol for priming pea seeds. Post-storage primingtreatments at 16 °C with PEG-8000 (-0·5, -1·0and -1·2 MPa), ABA (10^-1 M) and distilled water for 3,5 and 7 d ameliorated some of the damage which resulted fromageing. Most of the benefits occurred during the first 3 d withPEG or ABA and during the first 5 d distilled water. Primingtreatments increased the final germination and decreased themean germination time (MGT) and the frequency of chromosomalaberrations, possibly due to the repair of some age-induceddamage. The results of the priming experiment suggest that thecritical moisture content that facilitates repair of chromosomaldamage in pea seeds is likely to be between 32 and 46%. ABAhas been identified as a possible chemical which arrests germinationand facilitates repair of age-induced genetic damage.Copyright1995, 1999 Academic Press Pisum sativum, Pea, PEG, Polyethylene glycol, ABA, Abscisic acid, MGT, Mean germination time, seed priming, chromosome repair