Estimation of Chilling Sensitivity and Injury in Gloxinia Leaves by the Thermal Hysteresis of NMR Relaxation Times of Water Protons

Thermal hysteresis of longitudinal relaxation times (T₁) ofwater protons in leaf tissues of gloxinia was investigated bypulse nuclear magnetic resonance (NMR) spectroscopy. The profilesof T₁ hysteresis during a slow cool-warm cycle (20 to 0?C) variedwith the degree of chilling injury. General trends of T₁ changesupon warming were as follows: (1) a small increase of T₁ wasobserved when no chilling injury occurred or the degree of injurywas minor, (2) a large increase of T₁ occurred when injury increased,(3) a large decrease of T₁ occurred from the earlier stage ofwarming when serious injury occured. The sum of T₁ ratio (theratio obtained from the difference between the T₁ value in thecooling process and that of the wanning process for eight stepsof cool-warm cycle, divided by the former) reflecting T₁ increaseor decrease during the warming process was related to varietaldifference and seasonal changes of chilling sensitivity. Therefore,T₁ hysteresis can be used as a diagnostic tool in detectingthe chilling sensitivity and the degree of chilling injury. (Received August 27, 1986; Accepted February 24, 1987)     

Ontogeny of Somatic Embryos of Vigna aconitifolia, Vigna mungo and Vigna radiata

Callus cultures were initiated from immature cotyledons of Vignaaconitifolia, V. mungo and V. radiata on MS medium supplementedwith NAA, picloram or 2, 4-D. On transfer to L-6 liquid mediumsupplemented with low concentrations of picloram, GA₃ and cytokinins,large number of somatic embryos differentiated from the callus.The cells destined to become somatic embryos divided to formspherical or filamentous proembryos. From the filamentous proembryo,the embryo proper developed either at single or multiple sites.Development of somatic embryos from multiple sites resultedin several embryos connected by a common suspensor at the radicleend. Continued divisions of the proembryos led to globular,heart shaped and dicotyledonary stages of somatic embryogenesis.The somatic embryos of V. mungo and V. aconitifolia differentiatedinto tiny plantlets at low frequency (1%) in liquid suspensioncultures supplemented with zeatin, picloram and GA₃. Vigna aconitifolia Jacq, Marechal, mothbean, Vigna mungo L. Hepper, urdbean, Vigna radiata L. Wilczk, mungbean, somatic embryo     

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)     

Flavonoids of someVigna-plants in leguminosae

Flavonoids in five lines ofVigna mungo, fifteen lines ofV. radiata var.radiata and two lines ofV. radiata var.sublobata, which belong to the subgenus Ceratotropis, were examined. In hypocotyls, seed-coats and mature leaves of those plants, twelve kinds of flavonoid including three anthocyanins, two leucoanthocyanins, two glycoflavones and five flavonol glycosides were found, and their distribution pattern in twenty-two lines of the legumes is discussed. The leaves ofV. radiata var.radiata and var.sublobata contained the glycosides (mainly rutin) of both quercetin and kaempferol, while those ofV. mungo contained only kaempferol glycosides, with robinin as the predominant pigment, and the purple-red hypocotyls of the former group contained delphinidin 3-p-coumaroylglucoside, while those of the latter contained cyanidin 3-glucoside, although delphinidin 3-glucoside was commonly found in all of the plants. With the exception of two lines, all of the seed-coats examined contained in common four compounds of vitexin, isovitexin, leucocyanidin and leucodelphinidin, whereas in addition to these pigments the black seed-coats ofV. mungo andV. radiata var.sublobata TC 1965 contained delphindin 3-glucoside.     

Characteristic Changes in Relaxation Times of Water Protons in Vigna radiata Seedlings Exposed to Temperature Stress

Water protons in hypocotyl tissues from etiolated seedlingsof Vigna radiata that were exposed to temperature stress showedcharacteristic relaxation behaviors for ¹H-NMR. Cold stresstreatment (0C) caused gradual prolongation of NMR relaxationtimes (T₁). After exposure of tissues to cold stress for 24h, T₁ returned to the initial value as a result of subsequentincubation at normal temperature (20C). By contrast, heat stresstreatment (40C) induced a time-dependent decrease in T₁, whichdid not return completely to the initial value upon subsequentincubation at 20C after exposure to heat stress for 4 h. Weexamined changes in various physical factors that influencethe response of T₁ to temperature stress, namely, water contentand the concentrations of protein, diamagnetic (K⁺, Na⁺, Ca²⁺and Mg²⁺) and paramagnetic (Mn²⁺ and Fe²⁺) ions in the tissues.From the relationships between T₁ and these factors in vitro,we could not interpret the responses of T₁ to the temperaturestress only in terms of a change in water content. A synergisticeffect of an Mn²⁺ -protein complex and pH might be essentialfor the mechanism of changes in T₁ that are due to cold stress.The influence of heat stress on structural water in tissuesis discussed in terms of water-protein interactions. (Received December 28, 1992; Accepted May 6, 1993)     

Influence of Root and Content on the Temperature Response of Net and Uptake in Chilling Sensitive and Chilling Resistant Lycopersicon Taxa

We studied the influence of internal ammonium and nitrate contenton the temperature response of ammonium and nitrate uptake inboth chilling sensitive and chilling resistant tomatoes. Threetaxa were examined: Lycopersicon esculentum Mill. cv. T-5, achilling sensitive cultivar, Lycopersicon hirsutum Humb. andBompl. LA 1264, a wild, chilling sensitive accession from thelowlands of Ecuador, and Lycopersicon hirsutum LA1778, a chillingresistant accession from the highlands of Peru. Short exposures(4 h) of L. esculentum cv. T-5 to chilling temperatures irreversiblyinhibited ammonium absorption for at least 6 h. Nitrate absorptionin this taxon and ammonium and nitrate absorption in the L.hirsutum accessions recovered fully and immediately from suchexposures. The chilling resistant accession, L. hirsutum LA1778,showed a lower Q₁₀ for ammonium absorption (1?54?0?10, mean?s.e.)than its chilling sensitive relatives, L. hirsutum LA1264 (2?37?0?35)and L. esculentum cv. T-5 (1?92?0?11). The temperature responseof nitrate absorption depended on internal nitrate status; plantsgrown at high levels of ammonium and nitrate (200 mmol m^–3)showed higher Q₁₀'s for nitrate uptake (2?29?0?10) than thosedepleted of internal (1?86?0?12). Key words: Lycopersicon, ammonium, nitrate, temperature response, chilling     

Antitranspirant-induced Heat Stress in the Parasitic Plant Striga hermonthica--A Novel Method of Control

Leaf temperatures (T₁) of the parasitic plant Striga hermonthicaare substantially below those of the air (T_a), [T_a–T₁]reaching 7 ?C at T_a = 40 ?C. This results from high rates oftranspiration and the consequent evaporative cooling of theleaf. Application of an antitranspirant, which mechanicallyimpedes foliar loss of water vapour, reduced transpiration andstomatal conductance by 40% and 57%, respectively, and reduced[T_a– T₁] to 2 ?C at T_a = 40 ?C. The temperature sensitivityof photosynthesis in the host-parasite association differed,the optima (T_opt) being 37.2 and 40.1 ?C for S. hermonthicaand sorghum, respectively. Once Topt had been exceeded in S.hermonthica net photosynthesis declined rapidly, reaching thelethal limit (Tmax) at 42.6 ?C. S. hermonthica is particularlysensitive to high temperatures and antitranspirant-induced overheatingleads to blackening and shrivelling of the leaf after as littleas 4 h at T_a = 40 ?C. Application of an antitranspirant underfield conditions in the Sudan at T_a = 40 ?C resulted in 28%and 67% reductions in transpiration and stomatal conductance,together with a 5 ?C increase in T₁, and subsequent leaf death.In addition to these short-term physiological responses, antitranspirantspraying of the arasite increased the grain and straw yieldof the crop by factors of 3.4 and 2.6, respectively. Antitranspirantsmay have potential use as a method of controlling Striga inthe field. Key words: Striga hermonthica, sorghum, photosynthesis, transpiration, high temperature stress, anti-transpirant     

Statistical Studies Using AIC Method to Decide the Question of "Break" or "Straight" in Arrhenius Plots of Water Proton NMR Relaxation Times in Chilling-Sensitive Vigna and Insensitive Pisum Seedlings

The question of "break" or "straight" in Arrhenius plots forthe temperature dependency of NMR relaxation times (T₁) of waterprotons in etiolated intact seedlings for chilling-sensitivetwo Vigna species and chilling-insensitive Pisum was statisticallystudied using the Akaike's Information Criterion (AIC), a versatileprocedure for statistical model identification. Among sevenmodels, the most appropriate was based on the following assumptions:individual k (preparation numbers) two-half lines connectingat the break point (TCB) and imposing no restrictions for thegradient and the break point (Model 7). The worst two modelswere one straight line or one TCB (Model 1 or 4). Thus, thedata obtained from replicated preparations should not be treatedas a whole but as individual in each sample case. Break pointsdetermined with Model 7 ranged around 11-5°C for V. radiataand 17-10°C for V. mungo. The implication of the occurrenceof "break" for Pisum clearly differed from Vigna judging bythe model fitness based on the AIC values. The question of "break"or "straight" in Arrhenius plots is therefore fairly dependenton the validity of the model selection in the statistical analysis,and the AIC method is a useful procedure for the resolutionof the problem of the "use" or "misuse" of Arrhenius plots inplant physiology. (Received November 2, 1988; Accepted January 17, 1989)     

Effects of two free radical scavengers and intermittent warming on chilling injury and polar lipid composition of cucumber and sweet pepper fruits

Cucumber (Cucumis sativus L.) and sweet pepper (Capsicum annuumL.) fruits were chilled at 2.5?C for different periods and thentransferred to 20?C and subsequently evaluated for chillinginjury. Sodium benzoate at 10 nw or ethoxyquin at 9.2 mM, appliedas a 5-min dip before chilling, increased the degree of unsaturationof 18-carbon fatty acids in the polar lipids and reduced theseverity of chilling injury. Intermittent warming to 20?C for24 hr at 3-day intervals also alleviated the chilling symptomsand increased fatty acid unsaturation of the polar lipids incucumber and pepper fruits. (Received August 22, 1978; )     

The Influence of Temperature on Seed Germination Rate in Grain Legumes: I. A COMPARISON OF CHICKPEA, LENTIL, SOYABEAN AND COWPEA AT CONSTANT TEMPERATURES

For a single seed population of each of four species of grainlegume positive linear relationships were shown between temperatureand rate of germination for different fractions (G) of eachpopulation, from a base temperature, T_b(G), at which germinationrate is zero, to an optimum temperature, T_o(G) at which germinationrate is maximal. At constant temperatures warmer than T_o(G)there were negative relations (probably linear) between temperatureand rate of germination to the maximum temperature for germination,T_m(G), Within each population T_b(G) did not differ, but it didvary between species, viz.0.0?C, 0.25?C, 4.and 8.5?C for chickpea(Cicer arietinum L.), lentil (Lens culinaris Medic.), soyabean(Glycine max [ Merr.) and cowpea (Vigna unguiculata [L.] Walp.),respectively. In contrast, T_o(G) varied both within each populationand also between the four species: 80% of seeds in each populationhad T_o(G) values within the range 31.8?C to 33.8 ?C, 24.0?Cto 24.4?C, 34.0?C to 34.5?C and 33.2?C to >40?C, respectively.Values of T_m(G) were much more vanable: the 80% population rangewas 48 .0?C to 60.8?C for chickpea, 31.8?C to 34.4?C for lentiland 46.8?C to 55.2?C for soyabean; reliable estimates couldnot be made for cowpea, but the results suggest higher and morevariable values of T_m(G) than in the other three species. Atsub-optimal temperatures the distribution of thermal time forthe different fractions of each population was normal, exceptfor lentil where it was log-normal. A single equation is proposedto describe the influence of sub-optimal temperatures on ratesof germination for whole seed populations. At supra-optimaltemperatures, variation in thermal time for the different fractionsof each population was only slight. The implications of thesefindings for the adaptation of grain legume crops to differentenvironments, and for the screening of germplasm, are discussed. Key words: Seed germination rate, temperature, grain legumes     

ERRATA

Delete: J. Ineffective nodule with outer cells filled with ared pigment (x40) Insert: J . Coiled, branched and swollen root hairs in the axilof laterals, with no infection threads (x 100). Delete: C, G Insert: C, E, F. Insert: D. Latus hispidus Delete: D, E. Coiled, branched, and swollen root hairs in theaxils of laterals with no infection threads. Insert: D. Ineffective nodules of L. hispidus with outer cellsfilled with a red pigment (x40). Delete: F. Insert: E Delete: G. Insert: F. Abstract, 4th Line: Delete: 40 ?C Insert: 4 ?C Please.note equation (3) on page 959 should read V₂ = V₁ l?27^{(T₂ - T₁)} and NOT: V₂ = V₁ (l?27)T₁ - T₂ as printed.     

Stress relaxation properties of the cell wall of growing intact plants

The cell wall of dark-grown Avena coleoptiles and the epidermisof light-grown mungbean hypocotyls was subjected to stress-relaxationanalysis and the following results were obtained. 1. Actively growing apical regions of the organs, either coleoptilesor hypocotyls, had certain threshold values of minimum stress-relaxationtime, T_O, 0.04 sec for coleoptile cell wall and 0.03 sec forthe epidermal cell wall of hypocotyls. The cell wall of thebasal region of the organs, which were mature and not growing,had a higher value of To. 2. When the apical regions of the organs, either coleoptilesor hypocotyls, ceased to grow, their cell walls showed T_O valuesabove these thresholds. 3. The relaxation rate, b, was small in the cell wall of activelygrowing regions of the organs, compared with that of non-growingregions. 4. The maximum relaxation time, T_m, was variable and no significantrelationship with growth capacity was found. 5. The extensibility, mm/gr, was large not only in activelygrowing regions of the organs but also in fully grown regions,suggesting that the value represents complex properties of thecell wall including the history of cell wall extension. From these results, we concluded that biochemical modificationsoccur in the cell wall matrix of actively growing organs ofeither monocots or dicots, and these are the bases of the capacityof the cell wall to extend and are represented chiefly by T_oand possibly by b. (Received August 12, 1974; )     

Further Evidence in Support of an Interactive Model in Stomatal Control

The interaction between CO₂ IAA, ABA, and temperature in thecontrol of stomatal behaviour, was investigated in the chill-resistantPisum sativum and chill-hardened Phaseolus vulgaris. It wasfound that the ability of kBA to induce stomatai closure wasdependent upon the presence of CO₂ in both species, at bothtemperatures (22 ?C, 5?C) Similarly, the ability of IAA to decreasestomatal resistance, was dependent upon the presence of CO₂in both species, at both temperatures. Chilling at 5?C in thelight did not influence the response characteristics of stomatato CO₂ ABA or IAA, in either species. These results are discussedin relation to a model of the interactions of these regulatorsof stomatal aperture. Key words: Stomata, modelling, chilling     

Comparison of Atrazine-Resistant and -Susceptible Biotypes of Senecio vulgaris L.: Effects of High and Low Temperatures on the in vivo Photosynthetic Electron Transfer in Intact Leaves

The effects of temperature on the yield of in vivo modulatedchlorophyll fluorescence were measured in intact leaves of atrazineresistantand -susceptible biotypes of the weed Senecio vulgaris L. At25 ?C, the photochemical quenching (q_Q of steady-state chlorophyllfluorescence was reduced by around 30% in the atrazine-resistantmutant as compared to the susceptible wild type, indicatinga higher reduction state of the primary electron acceptor Q_Aof photosystem II in the former biotype. Moderately elevatedtemperatures (above 30 ?C) further increased the steady-stateconcentration of reduced in the mutant. Analysis of the temperature dependence of both the photochemicalquenching q_Q and the initial fluorescence level F_o clearly indicateda drastically enhanced heat-sensitivity of the photochemicalapparatus in the atrazine-resistant Senecio leaves. The heat-inducedchanges in F₀ and q_Q were closely correlated, suggesting thatthe phenomenon responsible for the rise in F₀ was also involvedin the inhibition of the photosynthetic electron flux. Low temperaturesalso affected reoxidation but, in contrast to heating, no apparent differences were observed in the behaviourof the two biotypes exposed to chilling stress. Key words: Atrazine-resistance, chlorophyll fluorescence, heat stress, Senecio vulgaris     

Growth of Plants in Different Oxygen Concentrations

Dwarf french beans (Phaseolus vulgaris var. Canadian Wonder)were grown in chambers at 25?C with the roots aerated at 20per cent oxygen and tops variously maintained at: T₁ O₂ 0.21;CO₂ 270?10^–6: T₂; O₂ 0.05, CO₂, CO₂ 270?10^–6: T₃;O₂ 0.21; CO₂ 550?10^–6. Experiment 1 (T₁ and T₂) lasted2 weeks: Experiment 2 (T₁ T₂ and T₃) only one week. Hourly estimatesof CO₂ uptake were made by gas analysis and weekly estimatesof fresh weight, dry matter in tops and roots, and leaf area,by sampling. Light intensity was 80 W m^–2 of photosyntheticallyactive radiation. An attempt was made to explain the results in terms of a simplelight absorption model such that where dV/dt is the rate of CO₂ uptake per plant, ßis the photosynthetic efficiency, I₀ is the incident light intensity,f is the fraction of incident light absorbed by unit leaf layerand L is the leaf area index. The analysis showed that ß(T₂)was at least double ß(T₁), whilst f(T₂) was smallerthan f(T₁) at a given leaf area. The results also required thatthroughout the period of the experiment, fL(T₁)=fL(T₂) at anygiven time, i.e. the treatment with the larger leaf area (T₂)has the smaller value of f, and therefore intercepts less lightper unit leaf area. This could be advantageous for plant growth,but requires further experiments. The photosynthetic rates per unit leaf are about 40 per centgreater in T₂ than T₁. Over the relatively short period of the experiment the resultsare adequately described by U=btⁿ, where U is the accumulatedcarbon dioxide uptake, b is related to the photosynthetic efficiency(different for the differing treatments), and n is a constant(similar for all treatments). This relationship with time isbelieved to be a relationship with accumulated radiation, forthe light was constant throughout the experiments. Comparisons of carbon fixed (measured gas uptake) and dry matteraccumulation (sampling) show great scatter with an average valueof 0.43. The first week's results were generally smaller thanthis value and the second week's greater. Energy fixation as a fraction of photosynthetically active radiationon the ground area covered by the plants ranged from 3.5 to10 per cent. The results from treatment T₃ were similar to T₂ suggestingthat increasing CO₂ concentration decreases the growth inhibitionat 21 per cent O₂.     

Effects of Chilling, Light and Nitrogen-containing Compounds on Germination, Rate of Germination and Seed Imbibition of Clematis vitalba L.

Effects of chilling (5 °C) period, light and applied nitrogen(N) on germination (%), rate of germination (d to 50% of totalgermination; T_50%) and seed imbibition were examined inClematisvitalba L. In the absence of chilling, light and N, germinationwas minimal (3%). When applied alone, both chilling and N increasedgermination. Chilling for 12 weeks increased germination to64%, and 2.5 mM NO^-₃or NH⁺₄increased germination to 10–12%.Light did not increase germination when applied alone, but didwhen applied in combination with chilling and/or N. Half theseed germinated when light was combined with 2.5 mM NO^-₃or NH⁺₄.The influence of chilling, light and/or N on germination wasgreater when combined, than when either factor was applied alone.Both oxidized (NO^-₃) and reduced (NH⁺₄) forms of N increasedgermination, but non-N-containing compounds did not, suggestingthe response was due to N and not ionic or osmotic effects. Without additional N, T_50%decreased from 16–20 d at zerochilling, to around 5 d at 8 and 12 weeks chilling. AlthoughT_50%was not influenced by an increase in NO^-₃or NH⁺₄from 0.5to 5.0 mM , it did increase with additional applied N thereafter.However, the magnitude of the N effect was small compared tothat of chilling. Like germination, seed imbibition increasedwith a longer chilling period, but in contrast imbibition decreasedslightly with increased applied NO^-₃or NH⁺₄. It is argued thatincreased imbibition is not directly related to an increasein total germination, but that it may be related to the rateof germination. Possible mechanisms involved in the reductionin dormancy ofC. vitalba seed are discussed. Clematis vitalba L.; germination; dormancy; imbibition; rate of germination; chilling; light; nitrate; ammonium; nitrogen; phytochrome     

Time, Temperature and Germination of Pearl Millet (Pennisetum typhoides S. & H.): I. CONSTANT TEMPERATURE

The germination of pearl millet (Pennisetum typhoides S. &H.) seeds was investigated at constant temperatures between12 ?C and 47 ?C on a thermal gradient plate. The rate of germination increased linearly with temperaturefrom a base T_b to a sharply defined optimum T_o beyond whichthe rate decreased linearly with temperature, reaching zeroat T_m. The linearity of the response both above and below T_oallowed time and temperature to be combined in a thermal timeat which a specified fraction of the seeds germinated. Withinthe population T_b and T_m were constant.     

Relationship of Nuclear Magnetic Resonance Relaxation Time to Water Content and Cold Hardiness in Flower Buds of Evergreen Azalea

The longitudinal relaxation time (T₁) of water protons in floretsof R. ? akebono flower buds was measured with a pulse NMR spectrometerto determine the relationship of T₁ to water content and coldhardiness (supercooling ability). Seasonal changes of T₁ inflorets were closely correlated with water content and supercoolingability of florets. T₁ of florets was short for acclimated budshaving a low water content and long for non-acclimated budshaving a high water content. Flower buds collected in Novemberand stored at 0 and 5?C for 4 weeks had shorter T₁ values thanbuds stored at 10?C even though the floret water content andsupercooling ability were similar. Thus, the short T₁ of coldacclimated buds hardened naturally or by storage at low temperaturesis due to a combination of both reduced water content and temperature. (Received August 27, 1983; Accepted May 26, 1984)     

Changes in Respiratory Metabolism during Aging in Seeds and Isolated Axes of Soybean

Cyanide-sensitive O₂ uptake was observed in the isolated embryonicaxis of soybean [Glycine max L. merr. cv. ‘Essex’]within 5 min after wetting and the O₂ uptake rate during thefirst h of imbibition was directly proportional to axis moisturecontent. Within 10 min after wetting, O₂ uptake was lower inaged low vigor (LV) axes than in high vigor (HV) axes imbibedeither in water (LV axes sustain imbibition injury) or in 30%w/v polyethylene glycol (LV axes do not sustain imbibition injury).Mitochondria isolated from LV axes after 4- and 24-h imbibitionwere characterized by lower O₂ uptake, ADP:O, and respiratorycontrol ratios relative to HV mitochondria. A plot of O₂ uptakevs temperature between 10 and 25?C revealed a break in the slopebetween 13 and 16?C for HV, but not LV, axes. Since LV axessustained water uptake injury at all temperatures tested, whereasHV axes sustained chilling injury only below 16?C, the dataindicate two temperature-O₂ uptake relationships: one for injuredtissues and one for non-injured tissues. We conclude that deteriorationper se involves impairment of respiratory metabolism in thesoybean embryonic axis. Chilling (10?C; HV and LV axes) andimbibitional (25?C; LV axes) injuries during the initial minof inbibition further disrupt respiratory metabolism and interferewith subsequent mitochondrial development and axis growth. ¹Scientific Articles No. A-3548, Contribution No. 6623 of theMaryland Agricultural Experiment Station. (Received May 25, 1983; Accepted September 28, 1983)     

Effects of Priming and Endosperm Integrity on Seed Germination Rates of Tomato Genotypes: I. GERMINATION AT SUBOPTIMAL TEMPERATURE

The bases of differences in germination rates (GR_g = inverseof time to germination [t_g] of percentage g) among three cold/salt-toleranttomato (Lycopersicon esculentum Mill.) accessions (PI 341988,PI 120256, and PI 174263) and one cold/salt-sensitive tomatocultivar (T5) were investigated. The effects of seed priming(6 d imbibition in aerated –1.2 MPa polyethylene glycolsolution at 20 ?C followed by redrying) and of removing theendosperm/testa cap covering the radicle on the temperaturesensitivity of GR_g, and the interaction of these treatmentswith genotypes, were also examined. GR_g decreased linearly withdecreasing temperature for all genotypes and seed treatments.The minimum or base temperatures for germination (T_b) variedby 1 ?C among the tomato lines, so genotypic differences inGR_g were due to differing thermal time requirements for germination.The mean thermal time requirement for germination of T5 seeds was 22% and 19% greater than that of PI 341988 andPI 120256 seeds, respectively, but only 9% greater than thatof PI 174263 seeds. Seed priming did not lower Tb of any genotype,but significantly reduced by 24, 49, 41, and 49% in T5, PI 341988, PI 120256, and PI 174263, respectively,indicating that priming increased the rate at which the seedsprogressed towards germination when T>T_b, but did not lowerthe minimum temperature at which germination could occur. Primingincreased the GR_g of T5 seeds to equal or exceed those of control(non-primed) seeds of the cold/salt-tolerant genotypes at anyT>T_b, but the PI lines exhibited an even greater responseto priming. Times to germination within each seed lot were normallydistributed on a logarithmic scale. Priming increased the variancein tg within a seed lot when compared to control seeds. However,the variation in thermal time for germination between the 10thand 90th percentiles of the seed population (_T(10–90))was relatively unaffected by priming due to the reduction in in primed seeds. Removing the endosperm cap and testa opposite the radicle tip decreased almost 6-fold and and reduced T_b by 5 ?C in T5 and PI 341988,implicating processes in the endosperm/testa as the limitingfactors in germination at suboptimal temperatures. Key words: Lycopersicon esculentum Mill., tomato, genetic variation, seed priming, thermal time, germination rate