Natural Ageing: Poly(A) Polymerase in Germinating Embryos of Triticum durum Wheat

The viability of seeds is associated with ageing and storageconditions. A loss of viability is accompanied by slow germination,reduced growth, and a decline in protein and poly(A)⁺RNA synthesis.This paper reports on the activity of poly(A) polymerase indry and germinating embryos of Triticum durum Desf. cv. Cappellicaryopses of different ages and viability. The enzyme was presentas a single form during ageing and germination. The poly(A)polymerase was active at decreasing levels in all aged dry embryos,in parallel with loss of viability. Its activity strongly increasedduring the germination only in viable embryos. The observedincrease was due to de novo synthesis of the enzyme. Poly(A)polymerase synthesis was low during germination of less viableembryos and absent in older ones. Reduced poly(A) polymeraseactivity in dry or germinated wheat embryos may cause a shorteningof poly(A) chains in vitro and a decline in poly(A)⁺RNA synthesis.Copyright1995, 1999 Academic Press Triticum durum Desf. cv. Cappelli, wheat, embryo, natural ageing, poly(A) polymerase     

Oxidative Phosphorylation in Germinating Lettuce Seeds

The effect of thiourea and coumarin, in vivo and in vitro, onthe phosphorylating activity of lettuce mitochondria was investigated,as well as the effect of coumarin on the P/O ratio. It was shownthat both substances in vitro inhibit phosphorylation; whilein vivo coumarin inhibits but thiourea under certain circumstancesstimulates. Coumarin was also shown to decrease the P/O ratioand therefore may be considered as an uncoupler. The difficulties in considering these effects of the substancesas a primary mechanism controlling germination are pointed outand discussed.     

The Possible Role of Low Temperature in Breaking the Dormancy of Seeds of Fraxinus excelsior L.

It has been shown that the growth-inhibiting substances presentin the embryo and endosperm of F. excelsior are not removedduring pretreatment or during the actual germination process.On the other hand, evidence is presented that the inhibitormay be physiologically effective in preventing germination.A biological assay technique using embryos of the same speciesfrom which the growth substances were extracted was used todemonstrate the production of a germination and growth-promotingsubstance during the process of low temperature after-ripeningand its apparent counteraction of the effect of the endogenousinhibitor.     

Regulation of Soybean Embryogenesis by Abscisic Acid

Abscisic Acid (ABA) stimulates growth and protein accumulationin soybean (Glycine max. L. Merr.) embryos during the earlyphases of embryogenesis. Growth of mid-stage embryos is suppressedby ABA, but protein accumulation is not impaired. Metabolitedistribution studies indicate that ABA alters partitioning ofsucrose in older embryos such that protein accumulation is sustainedat the expense of lipid accumulation. The responses of in vitrocultured embryos to ABA is consistent with the normal patternof ABA accumulation and disappearance that occurs during embryogenesisin situ. A close correlation exists between ABA levels and embryogrowth rates in situ in three cultivars of soybeans. Dependingon the age or stage of the developing embryo, ABA either servesto promote or inhibit embryo growth. Key words: Embryogenesis, ABA, Seeds, Soybean.     

PROPERTIES AND CHANGES OF GLUCOSE-6-PHOSPHATE DEHYDROGENASE IN GERMINATING LETTUCE SEEDS

Glucose-6-phosphate dehydrogenase is present in lettuce seedsand seedlings in a particulate, 20,000 g fraction and in a solublefraction of the cells. In both fractions the enzyme activityoccurs in the presence of either NAD or NADP. It seems probablethat an enzyme with two active sites is involved. Total activity does not change during 48 hours germination inwater. It is depressed by coumarin or thiourea treatment. Specificactivity rises in the soluble fraction when germination occurs,but not in the mitochondrial one. Coumarin treatment largelydepresses the increase in specific activity. In vitro 100 ppmcoumarin totally inhibit enzyme activity. 1,250 ppm thioureado not affect enzyme activity. The results are analysed and it is concluded that glucose-6-phosphatedehydrogenase is important, if at all, only in the very earlystages of germination. (Received August 13, 1965; )     

The In Vitro Culture of Immature Barley Embryos on Different Culture Media

Immature barley embryos (Hordeum distichum var. Julia) of between0•20 and 0•80 mm in length, were isolated from thedeveloping grain and cultured in vitro on various culture media.The subsequent development of the embryos was followed overa period of weeks, and where germination ensued the growth rateof shoot and root meristems was compared with in vivo germinationrates. Various growth media were assessed for their abilityto support normal development of immature embryos. A numberof published media failed to support satisfactory developmentof young embryos. The addition of 1–15 per cent coconutmilk to Norstog's Medium I (mineral + vitamin solns) enhancedembryo development and lowered the threshold of viability fromembryos of 0•50 mm in length to 0•35 mm. Althoughin many cases germination ensued, embryo development was largelyabnormal. A slightly greater enhancement of growth was achievedwith 0•05–0•30 per cent casein hydrolysate asthe growth medium supplement, although abnormal developmentwas not eliminated. A further lowering of the viability thresholdto include embryos of 0•25 mm in length was obtained bycombining 2•7 mM glutamine with the casein hydrolysatesupplement. Normal development and germination of embryos assmall as O25 mm was however obtained on Norstog's Medium JJand the results were reproduced in four additional if . distichumvarieties. In each case the critical threshold of viabilitywas found to lie in embryos of 0•20–0•30 mmin length.     

Premature Drying, Fluridone-Treatment, and Embryo Isolation During Development of Maize Kernels (Zea mays L.) Induce Germination, but the Protein Synthetic Responses are Different. Potential Regulation of Germination and Protein Synthesis by Abscisic Acid

Freshly harvested, developing kernels of maize (Zea mays L.)do not germinate up to 77 d after pollination, but can be inducedto do so by fluridone, premature desiccation, and isolationof the developing embryo. The pattern of protein synthesis indeveloping maize embryos is distinct from that during germinationand subsequent seedling growth. Premature desiccation at 35DAP elicits a pattern of protein synthesis upon rehydrationwhich is similar to that in germinated embryos from mature drykernels. Fluridone-induced viviparous germination is accompaniedby changes in the synthesis of some proteins to a post-germinativepattern, but some developmental proteins continue to be synthesized.Embryos isolated from developing kernels at 35 DAP germinatewhen incubated on water; they also produce some developmentalproteins during germination. Kernels from developing cobs at35 DAP which are detached from the mother plant and maintainedin an atmosphere of high relative humidity (moist controls)do not germinate, but neither do they continue a clearly definedpattern of either developmental or germinative protein synthesis.Drying is thus critical to effect a clear transition of proteinsynthesis from a developmental to a germinative mode in maizeembryos. Abscisic acid within the developing embryos is reduced by fluridone,but to a lesser extent by premature drying or maturation drying.Changes in sensitivity to abscisic acid by the developing embryomay be as, or more, important in permitting germination, andthe attendant synthesis of proteins, than changes in abscisicacid content. Key words: Maize (Zea mays L.), germination, vivipary, desiccation, abscisic acid     

Seed Dormancy in Acer: The Role of Testa-imposed and Embryo Dormancy in Acer velutinum

The embryo dormancy shown in freshly harvested samples of Acervelutinum seeds is weakly established and very short-lived.Loss of this embryo dormancy occurred during post-harvest fruitstorage at either 5 or 17 C. In contrast, the dormancy of intactfruits and seeds was overcome only during storage at the lowertemperature. Removal of the cotyledons from embryos of freshlyharvested fruits allowed more rapid germination of the embryonicaxes, indicating that the cotyledons exert an inhibitory effect,although the axes still retained a measure of innate dormancy.The inhibitory effect of the cotyledons became less marked withincreasing duration of fruit storage, this loss of inhibitoryeffect occurring at both storage temperatures. Applied ABA stronglysuppressed germinative capacity in intact embryos and isolatedembryonic axes from freshly harvested fruits, but when ABA wasapplied to embryos of fruits that had been stored for variousperiods at 5 or 17 C, the inhibitory effect was first weakenedand then lost with increased storage. Although dormancy in the seeds of A. velutinum may be describedas intermediate between testa-imposed dormancy and true dormancy,it is perhaps more properly included in the former category. Acer velutinum Boiss. var. vanvolxemii, abscisic acid, embryo dormancy, germination, seed storage, testa-imposed dormancy, tissue sensitivity     

Light-controlled Cycocel Reversal of Coumarin Inhibition of Lettuce Seed Germination and Root Growth

Lettuce seed germination or lettuce root elongation after germination in water was inhibited by coumarin and these inhibitions were reversed by Cycocel. 2.53 × 10³ M Cycocel reversed the inhibition of seed germination by 6.8 × 10⁴ M coumarin. and 6.32 × lO^?4 M Cycocel reversed the inhibition of root elongation by 3.4 × 10³ M coumarin. No other analogs of Cycocel reversed these coumarin induced inhibitions of growth. Cycocel reversal of coumarin inhibition of lettuce seed germination occurred in red light but not in far-red light or darkness. The red-far-red system was photoreversible. Cycocel and kinetin appear to act similarly in reversing coumarin inhibition of germination. Gibberellin A₃ and IAA were unable to reverse these coumarin induced inhibitions. A common mechanism is suggested for Cycocel reversal of coumarin and lAA inhibition of growth.     

In vitro Culture of Abscissed Immature Avocado Embryos

The efficiency of an avocado hybridization programme, usingsmall potted glasshouse plants, was reduced by a high rate ofabscission of immature fruitlets bearing embryos too young forconventional germination. This was overcome in part by culturein vitro of the shed embryos on a liquid medium supplementedwith 0.5 mg l^–1 benzyladenine. Most embryos younger than6 weeks did not survive in culture, but older embryos slowlyproduced multiple shoots, with axillary shoot growth being furtherstimulated by removal of both cotyledons. Embryo response wasnot related to cultivar. Shoots removed from culture could begrafted to seedling rootstocks. Grafting was considered morereliable than dependence on growth of the main root or adventitiousroots in vitro to produce established plants. Persea americana Miller, avocado, abscissed fruitlets, in vitro embryo culture     

Nuclear Replication Activity During Seed Development, Dormancy Breakage and Germination in Three Tree Species: Norway Maple (Acer platanoidesL.), Sycamore (Acer pseudoplatanusL.) and Cherry (Prunus aviumL.)

Flow cytometric analyses of nuclear DNA levels were carriedout during development, stratification and germination of dormantseeds from three tree species with contrasting characteristics.Norway maple (Acer platanoides) and sycamore (Acer pseudoplatanus)have orthodox (desiccation-tolerant) and recalcitrant (desiccation-sensitive)storage behaviours, respectively, and require only a periodof cold to break dormancy, whereas, orthodox cherry (Prunusavium) seeds require an initial warm period before cold stratificationto fully stimulate germination. Whole embryos and radicle tipsof both Norway maple and sycamore were found to have stablehigh levels of 4C DNA during the latter stages of developmentand both contained nuclei arrested at the 2C and 4C levels atmaturity. Mature cherry embryos had nuclei predominantly arrestedat the 2C level. This suggests that the acquisition of desiccationtolerance is not correlated with the arrest of the cell cycleat any particular nuclear DNA level. Neither DNA replicationin radicle cells nor germination occurred when seeds were maintainedmoist at a constant 20 °C. However, in the late stages ofcold treatment during stratification, nuclear DNA levels inradicle cells changed in advance of radicle emergence in theorthodox Norway maple and cherry, whereas in the recalcitrantsycamore, change was not recorded until after radicle emergence.These results show that DNA replication has potential use asan indicator of the progress of tree seeds through stratificationtreatments used to break some types of dormancy. The ways inwhich this indicator could be exploited for seed quality andperformance testing are discussed.Copyright 1998 Annals of BotanyCompany Norway maple,Acer platanoidesL., sycamore,Acer pseudoplatanusL., cherry,Prunus aviumL., DNA replication, flow cytometry, seed dormancy, stratification     

Somatic Embryogenesis in Brassica nigra (Koch)

Four genotypes of Brassica nigra were tested for their abilityto produce somatic embryos in vitro. Seedling-derived hypocotylexplants cultured in MS medium with p-chlorophenoxyacetic acid,-naphthaleneacetic acid and adenine gave rise to embryos thatcould germinate into seedlings with a high frequency on transferto medium containing benzylaminopurine riboside and p-chlorophenoxyaceticacid. Ebryogenesis was highest in leaf explants followed bystem and hypocotyls. Comparison of the embryogenic responseof hypocotyl segments differing in age indicated an increasein the frequency of response with increasing age of the explants.However, germination of embryos into seedlings declined withincreasing age of the explant. Embryogenesis was higher in MSmedium compared to five other media with similar growth regulatorcomposition. Genotypic differences exist for frequency of embryogenesisand subsequent maturation into seedlings. Key words: Brassica nigra, somatic embryogenesis, growth regulators, plant regeneration     

Comparative Effects of Aromatic Compounds on Inhibition of Lettuce Fruit Germination

Germination of lettuce (Lactuca sativa L. cv. Great Lakes) wasinhibited by aromatic alcohols, aldehydes and carboxylic acidsin a way similar to that by aliphatic members. Increased lipophilicityusually leads to increased inhibitory activity. Thus methylationincreased activity while hydroxylation decreased it. Exceptionswere seen with ortho-hydroxylated compounds and other exceptionsindicated the presence of unrecognized factors. Many of thephenolic compounds often quoted as inhibitors were shown tobe not particularly activeagainst lettuce germination when comparedwith, for instance, abscisic acid or coumarin.     

Allelopathic impact of artificially applied coumarin on <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> f.sp. <Emphasis Type="Italic">niveum</Emphasis>

Watermelon production is threatened by fusarium wilt caused by Fusarium oxysporum f.sp. niveum (FON) in continuous cultivation system. Some elements, mainly allelochemicals, released from living roots or decayed plants might be associated with the disease. The purpose of this work was to evaluate the possible impact of coumarin, one kind of watermelon allelochemical, on FON. Furthermore, possible new mechanisms might be investigated during the ecological interactions of plant-microbe. Results showed that coumarin strongly inhibited growth of FON leading to a decrease in its biomass, dry weight of mycelia of FON in a liquid culture. The dry weight was decreased by 62.9% compared with control. The hyphal growth of FON on plates was stopped at high (>400 mg l⁻¹) concentrations of coumarin. At 320 mg l⁻¹, sporulation and enzyme activities of FON were also severely suppressed by coumarin. The yield of conidia, and the activities of proteinase, cellulase, and amylase were reduced by 98.9%, 79.7%, 29.8% and 15.9% respectively. However, conidial germination and mycotoxin (MT) production of FON were greatly stimulated, being increased by 55.7% and 14.9 fold at 320 mg l⁻¹ respectively. We conclude that coumarin acted as an allelochemical substance to inhibit growth and pathogenic enzyme activities of FON but to stimulate mycotoxin production and conidial germination. It was suggested that coumarin acted as a signal transduction element bridging plant and pathogen in the process of plant-microbe interactions.     

The First Appearance of Polyploid Nuclei in Primary Roots of Two Diploid Angiosperms

In Anchusa capensis, where the polyploid divisions are restrictedto a particular time and place in germination, cytophotometricanalysis showed that the polyploid cells arise at the time ofconversion of the globular-shaped embryo to the heart-shapedembryo. In Spinacia oleracea, where the divisions occur throughoutthe growth of the root, these polyploid cells do not arise duringembryogenesis but during germination and subsequent growth. Anchusa capensis Thunb., summer forget-me-not, Spinacia oleracea L., spinach, root meristem, polyploid divisions, determinate divisions, indeterminate divisions, germination, embryogenesis, cytophotometry     

Proteolytic Activities in x Haynaldoticum sardoum Seeds of Different Ages

Carboxypeptidase, aminopeptidase and proteinase activities weremeasured in endosperms from dry and germinating x Haynaldoticumsardoum naturally aged seeds. Carboxypeptidase activity, presentin dry seeds, decreased slightly during germination and remainednearly unchanged during the storage period. Aminopeptidase activityincreased during germination in younger seeds, but decreasedin non-viable seeds. Proteinase activity was absent in dry seeds,increased during germination in younger seeds and disappearedin the older ones. Proteinase activity was not recovered in old endosperms followingtransplantation of young embryos, and was recovered only toa very small extent in young endosperms following transplantationof old embryos. Young endosperms onto which young embryos hadbeen transplanted gave maximum recovery of enzyme activity,although this was lower than in young intact seeds. These results suggest that the reduced or delayed availabilityof nutrients to the embryo axis is not the only factor causingthe failure of seeds to germinate, the ageing process beinga progressive phenomenon affecting both embryo and endosperm. x Haynaldoticum sardoum, Denti de cani, seed ageing, proteolytic activities, embryo-transplantation     

Normalizing Development of Cultured Triticum aestivum L. Embryos: I. LOW OXYGEN TENSIONS AND EXOGENOUS ABA

Wheat (Triticum aestivum L.) embryos form in dynamically-regulatedovular environments. Our objectives were to improve developmentof cultured immature wheat embryos by simulating, in vitro,abscisic acid (ABA) levels and O₂ tensions as found in wheatovules during zygotic embryogenesis. We characterized from intactwheat kernels embryo respiration, embryo morphology and embryoand endosperm + ABA levels at 13, 19 and 25 d post-anthesis(DPA). Young (13 DPA) embryos were then excised and culturedin vitro, where they were exposed to 0·2 or 2·Ommol m^–3 ±ABA and 2.·1, 2·5 or 7·4mol m^–3 (6, 7 and 21%, respectively) gaseous O₂. At 6and 12 d in culture, + ABA levels, embryo respiration and embryomorphology were characterized by treatment. Thirteen-day-oldembryos from two different plant populations differed by 17-foldin initial ABA content. However, this difference did not affectprecocious germination in vitro, nor did it affect the amountof exogenous ABA required to reduce precocious germination by40%. In this respect, embryos from both populations were equallysensitive to exogenous ABA. Cavity sap O₂ levels (2·1to 2·5 mol m^–3) were much more effective in preventingprecocious germination of cultured embryos than were cavitysap levels of ABA (0·2 to 2·0 mmol m^–3).The combination of physiological levels of both ABA and O₂ largelynormalized DW accumulation and embryo morphology without alteringendogenous + ABA levels. Residual respiration of cultured embryoswas higher than that of embryos grown in situ, and was not influencedby the exogenous O₂ and ABA treatments Key words: Abscisic acid, embryo development, oxygen tensions, respiration, wheat     

Developmental Differences Between Germinating After-ripened and Dormant Excised Avena fatua L. Embryos

Based on physiological and molecular differences associatedwith the germination of after-ripened and dormant caryopsesand excised embryos, it has been hypothesized that various methodsof after-ripening are the only treatments that facilitate thetransition of dormant wild oat embryos to a non-dormant state.To further investigate this hypothesis, analytical methods wereused to evaluate physical and temporal changes associated withgermination and subsequent growth of after-ripened and dormantexcised embryos (AR-embryos and D-embryos, respectively) inducedto germinate with fructose (Fru) and/or gibberellic acid (GA).While chemical treatments of Fru, GA, and Fru+GA have littleeffect on the germination and short-term growth of AR-embryos,they do induce germination of D-embryos. Growth following germinationof D-embryos varied according to treatment with the combinationof Fru+GA inducing the greatest growth over the duration ofthe experiment. Even considering differences in the time tocomplete germination, growth of D-embryos was not comparablewith that of AR-embryos. This provides physical evidence thatchemical treatments induce germination without fulfilling therequirements for normal after-ripening-enhanced germination/growth,and indicates that fructose and/or gibberellic acid do not removethe dormancy-block or rate limiting step in the same manneras after-ripening. Avena fatua ; after-ripening; dormancy; fructose; germination; gibberellic acid; wild oats     

Production of a Fungistat and the Role of Fungi during Germination of Digitalis purpurea L.cv. Gloxiniaflora Seeds

The seed coats of Digitalis purpurea L. cv. Gloxiniaflora werecultured for indigenous fungi. Alternaria alternata (Fries)was identified as the sole fungus on seeds freshly harvestedfrom unopened capsules, whereas A. alternata, Rhizopus arrhizus(Fischer), Penicillium sp. and other fungi appeared on storedseeds. The appearance of fungi in seed cultures was seasonal,being more frequent in winter and early spring than in summerand autumn. Alternaria grew well on autoclaved seeds, on dehiscentseed coats, or on seed coats separated from the embryos of ungerminatedseeds. Rhizopus did not grow on these but grew weakly on theculture medium from viable seeds. A. alternata appears to functionas a degradation agent for the seed coat subsequent to germination.Neither fungus was found to be essential to germination of Digitalisseeds. Bioassay of the culture medium from germinating seedsshowed that a fungistat effective against both Alternaria andRhizopus is produced coincident with germination. Based on chromatographicanalysis, the fungistat appears to be a cardenolide. Alternaria alternata (Fries), cardenolides, Digitalis purpurea L. cv, Gloxiniaflora, fungistats, germination, Rhizopus arrhizus (Fischer)