Primary dormancy in tomato (Lycopersicon esculentum cv. Moneymaker): studies with the sitiens mutant

Intact wild-type tomato (Lycopersicon esculentum cv. Moneymaker)seeds do not complete germination to the same percentage orat the same speed as intact ABA-deficient sitiens (sit^w) mutantseeds when seeds of both genotypes are imbibed on polyethyleneglycol (PEG) solutions of –0.3 to –1.5 MPa osmoticpotential. However, if the thicker testas of wild-type seedsare removed (stripped) from the micropyle without damaging theendosperm, both the percentage and speed of germination at lowexternal water potential are similar to that of sit^w mutantseeds. Removing the micropylar end of the testa from sit^w seedsdid not enhance either the speed or percentage of germinationon PEG solution. Despite similar germination percentage and speed between strippedwild-type seeds and either stripped or intact sit^w seeds underosmotic stress, some differences in seed metabolism are evidentbetween genotypes. The activity of endo-ß-mannanasewas greater in the endosperm of sit^w mutant seeds compared tothe endosperm of wild-type seeds when seeds were exposed toosmotic stress. Although     

Soya Bean Seed Growth and Maturation by In Vitro Pod Culture

Immature Glycine max (L.) Merr. seeds initially at 50–70mg fresh weight were successfully grown and matured in vitroin detached pods. Surface sterilized pods were floated in aliquid medium containing 5 per cent sucrose, minerals, and glutaminein 125 ml Erlenmeyer flasks and incubated at 25 °C under350–400 µE m^–1 s^–1 white light. Seedswhich were matured in vitro increased tenfold in dry weight,were visually similar to commercial seeds of the same size,were tolerant to desiccation and germinated with normal seedlinggrowth. Excised pods transported dye from the pedicel to thegrowing seed within 120 min. Soya bean pod culture is a usefultechnique to study the influence of single or combinations ofchemical or environmental parameters on regulation of seed growth,seed maturation, and subsequent germination events without theconfounding interactions with the mother plant. Glycine max (L.) Merr., soya bean, pod culture, seed culture, seed growth, seed maturation, germination     

Seed Germination and Radicle Growth of a Halophyte, Kalidium caspicum(Chenopodiaceae)

Effects of temperature, light, NaCl and polyethylene glycol(PEG)-6000 on seed germination and radicle growth in a halophyticshrub, Kalidium caspicum(L.) Ung.-Sternb. were investigated.When seeds were incubated in deionized water at constant temperaturesbetween 10 and 30°C, the percentage germination in the darkexceeded 75%; light suppressed seed germination at alternatingtemperatures. Incubating seeds with a hypersaline solution ofNaCl for 30 d had no adverse effect on their germinability.The percentage germination of seeds incubated with a –0.8MPa NaCl solution was 73, 80 and 54% at 10, 20 and 30°C,respectively, but all radicles died before their length exceeded5 mm. In contrast, when seeds were incubated with a –0.8MPa PEG solution at 20°C, 68% of seeds germinated, and 95%of the emerging radicles survived beyond 5 mm. The high sensitivityof small radicles of this species to salinity indicated thatsalt must be removed from the soil surface for seedling establishment.Copyright2000 Annals of Botany Company Chinese desert, radicle growth, germination, halophyte, Kalidium caspicum, salinity     

Contrasted Effects of CO2 on the Regulation of Dormancy and Germination in Xanthium pennsylvanicum and Setaria faberi Seeds

The effects of CO₂ on dormancy and germination were examinedusing seeds of cocklebur (Xanthium pennsylvanicum Wallr.) andgiant foxtail (Setaria faberi Herrm.). The rate of germinationof the giant foxtail seeds as well as cocklebur was promotedby exogenously applied CO₂ at a concentration of 30 mmol mol^-1regardless of the sowing conditions. However, seeds which failedto germinate in the presence of CO₂, entered a secondary phaseof dormancy under unfavourable germination conditions. If CO₂was applied to seeds under conditions such as water stress imposedwith a 200 mol m^-3 mannitol solution, a hypoxic atmosphere of100 mmol mol^-1 O₂ or a treatment of 0·1 mol m^-3 ABA,development of secondary dormancy was accelerated. These contrastedeffects of CO₂ were observed in ecological studies. Under naturalfield conditions germination of buried giant foxtail seeds respondedpositively to CO₂ during a period of release from primary dormancyfrom Feb. to May, but CO₂ accelerated secondary dormancy commencingin early Jun. In other words, in the presence of CO₂, both theenvironmental conditions and the germination states of the seedsclearly showed secondary dormancy-inducing effects. Thus, itseems that CO₂ has contrasted effects on regulation of dormancyand germination of seeds depending on the germination conditions.Copyright1995, 1999 Academic Press Xanthium pennsylvanicum, cocklebur, Setaria faberi, giant foxtail, CO₂, water stress, hypoxia, ABA, germination, secondary dormancy     

Effects of Temperature and dl-Strigol on Seed Conditioning and Germination of Witchweed (Striga asiatica)

Seed conditioning and germination in witchweed (Striga asiatica(L.) Kuntze) were temperature-dependent. With higher conditioningtemperatures, shorter conditioning time was required for germinationwith terminal dl-strigol (strigol) treatment at 30 °C. Maximumgermination (80–100%) was obtained by conditioning inwater at 20, 25, 30 and 35 °C for 14, 7, 5 and 3 d, respectively,and terminally treating with 10^–6 M strigol at 30 °C.Seeds conditioned in 10^–8 M strigol instead of water germinatedmuch less with the same terminal strigol treatment. Generally,conditioning was slower when seeds were conditioned in strigolrather than water. The reduction in germination rate by pretreatmentin strigol or pretreatment at low temperatures could be overcomeby increasing the terminal strigol concentration in the germinationtest. Conditioned seeds did not germinate at 10 and 15 °Cwith a terminal 10^–6 M strigol treatment but yielded closeto maximum germination at 25, 30 and 35 °C with the sameterminal strigol treatment. To obtain maximum germination, boththe minimum conditioning temperature and the minimum germinationtemperature for conditioned seeds were 20 °C. Factors suchas conditioning time, and strigol concentration and temperatureduring conditioning and/or germination determine whether seedsremain in the conditioning phase or shift to a germination phase. dl-Strigol, germination stimulation, parasitic plants, seed conditioning, seed germination, Striga asiatica, temperature, weed control     

Effects of combining priming and plant growth regulator treatments on the synchronisation of carrot seed germination

Osmotic priming of carrot seeds for 2 wk in polyethylene glycol (PEG, — 10 MPa) at 15 °C led to more rapid and synchronous germination at 20 °C compared to untreated seeds. These responses were enhanced by a 24 h pre-priming soak in water or a change of solution after the first 24 h of priming to remove leachate. The inclusion of 200 mg litre^-1N-substituted phthalimide in the pre-priming soak and/or in the PEG further enhanced the results of priming. Leachate removal combined with phthalimide inclusion gave 79% and 86% germination from seeds of two carrot cultivars during the first day in 20°C water following priming. In contrast, cumulative germination of untreated seeds of the same cultivars was 18% and 61% respectively after 3 days in 20°C water. Seeds primed in PEG containing 200 mg phthalimide litre^-1with the solution replaced after the first 24 h germinated earlier and more synchronously than untreated seeds over a range of germination temperatures (5, 10, 15, or 20°C), but the effects of priming were most marked at 5°C.     

防风种子发芽特性及促进发芽的试验研究

防风种子发芽率和发芽势均较低,其主要原因包括个体之间的差异及物种特性。种子发芽率较低首先表现在个体发芽率上的差异,试验所用15株防风发芽率从28.0%到92.0%,从整体 上表现发芽率较低。防风本身发芽率低,由于物种因素,种子刚刚采收后的休眠,个体之间解除休眠时间和进入衰老的时间不一致,致使所有的种子不能全部在同一时间进入发芽高峰,同时,防风发芽的启动日有所差异,15株防风启动日和发芽持续时间相差均为两周以上。采用5~50 mg·kg^-1 GA、1~10 mg·kg^-1 6-BA、1%KNO₃和3%H₂O₂可提高休眠防风种子的发芽率,GA、6-BA可除防风种子的休眠,而1% KNO₃和3% H₂O₂对解除休眠的种子无明显影响。采用多种微量元素,即10~100 mg·kg^-1 Mn²⁺、10 mg·kg^-1 Cu²⁺和1 mg·kg^-1 Mo对种子进行处理可显著提高防风种子的发芽率,提示在植株绿果期喷施该类元素也可提高防风种子的发芽率。采用GA、NAA处理幼果,也可以提高种子的发芽率。     

The Use of Abscisic Acid to Synchronize Carrot Seed Germination Prior to Fluid Drilling

Abscisic acid (ABA) was used as a reversible block to the progressof carrot seed germination in a practical seed treatment. Pre-treatingseeds with 10^–4M ABA solution at 15 °C for 12 d gave93% germination of viable seeds on subsequent transfer to waterbefore radicle lengths became too long for fluid drilling. Thiscompared with only 31 % without pre-treatment ABA pretreatment significantly increased the synchrony of carrotseed germination and did not affect final percentage germinationor early seedling growth rates. Seedling emergence from ABA-treatedgerminating seeds was earlier and more uniform than from untreatedgerminating seeds and seedlings from both these treatments emergedbefore those from ungerminated seeds Daucus carota L., carrot, germination, seed treatment, fluid drilling, abscisic acid, radicle extension     

Deep and intermediate complex morphophysiological dormancy in seeds of Ferula gummosa (Apiaceae)

We tested the hypothesis that seeds of the monocarpic perennial Ferula gummosa from the Mediterranean area and central Asia have deep complex morphophysiological dormancy. We determined the water permeability of seeds, embryo morphology, temperature requirements for embryo growth and seed germination and responses of seeds to warm and cold stratification and to different concentrations of GA₃. The embryo has differentiated organs, but it is small (underdeveloped) and must grow inside the seed, reaching a critical embryo length, seed length ratio of 0.65–0.7, before the seed can germinate. Seeds required 9 weeks of cold stratification at <10°C for embryo growth, dormancy break and germination to occur. Thus, seeds have morphophysiological dormancy (MPD). Furthermore, GA₃ improved the germination percentage and rate at 5°C and promoted 20 and 5% germination of seeds incubated at 15 and 20°C, respectively. Thus, about 20% of the seeds had intermediate complex MPD. For the other seeds in the seed lot, cold stratification (5°C) was the only requirement for dormancy break and germination and GA₃ could not substitute for cold stratification. Thus, about 80% of the seeds had deep complex MPD.     

Light Actions in the Germination of Cocklebur Seeds: IV. DISAPPEARANCE OF RED LIGHT-REQUIREMENT FOR THE GERMINATION OF UPPER SEEDS SUBJECT TO ANOXIA, CHILLING, CYANIDE OR AZIDEPRETREATMENT

Esashi, Y., Fuwa, Nn Kojima, K. and Hase, S. 1986. Light actionsin the germination of cocklebur seeds. IV. Disappearance ofred light-requirement for the germination of upper seeds subjectto anoxia, chilling, cyanide or azide pretreatmenL—J.exp. Bot. 37: 1652–1662. The effects on the germination of positively photoblastic uppercocklebur (X anthium pennsylvanicum Wallr.) seeds by pretreatingwith anoxia, chilling, cyanide or azide, which stimulates theirdark germination, were examined in relation to light actions.Prior to experiments, seeds were pre-soaked at 23 °C inthe dark for 1 or 2 weeks to remove the pre-existing Pfr. Whenthe prctreatment conditions were suboptimal for germinationinduction, the stimulating effects of the pretreatments on germinationduring a subsequent dark period at 23 °C were manifest onlywhen seeds were irradiated with red light before or after thepretreatment Red light promotion was reversed by blue or far-redlight treatment. However, both prc-chilling for 6 d at 8 °Cand prctreatment with 1· 5 mol m ^{– 3} NaN³ for 2d could induce full germination without red light exposure.On the other hand, both pre-exposure to anoxia for 8 d and pretreatmentwith 30 mol m^–3 KCN could induce the dark germinationonly when germination occurred at 33 °C which is known toaugment the ratio of an alternative respiration flux to a cytochromeone. Moreover, the dark germination in response to these inductionswere strongly inhibited by the inhibitors of alternative respiration,propyl gallate and benzohydroxamic acid, applied during a subsequentdark period. It was thus suggested that Pfr has some relationto the operation of two respiration systems of cocklebur seeds,but it is not indispensable to germination of this positivelyphotoblastic seed. Key words: Anoxia, azide, blue light, chilling cyanide, dark germination, far-red light, red light, seed germination, X anthium pennsylvanicum     

Identification and Biological Activity of Germination-Inhibiting Long-Chain Fatty Acids in Animal-Waste Composts

Long-chain fatty acids in germination-inhibiting animal-wastecomposts were identified by gas chromatography-mass spectrometryas myristic, palmitic, stearic, oleic, linoleic, and linolenicacids. These acids were found at concentrations greater than0.25 mg (g dry compost)^–1. The identified acids, togetherwith lauric acid, and five kinds of short- and medium-chainfatty acid, were tested for their effects on the germinationprocess of sorghum seeds. The authentic long-chain fatty acids, which were dissolved ina 1:9 (v/v) mixture of methanol and distilled water at 40 mgliter^–1, significantly reduced the -amylase activity,physiological water uptake, and ATP content of the germinatingseeds during the first 24h of imbibition, as well as the rateof germination of seeds. Among the tested fatty acids, myristicand palmitic acids were the most potent inhibitors of germination.The inhibitory effects of long-chain fatty acids were strongerthan those of the phenolic acids. The short- and medium-chainfatty acids did not have any significant germination-inhibitoryeffects at 40 mg liter^–1. The results indicate that thelong-chain fatty acids are the dominant inhibitors of germinationin animal-waste composts, and that the inhibition of the -amylaseactivity in germinating sorghum seeds is one aspect of the modeof action of these long-chain fatty acids. ¹On leave from the Department of Crop Science, Faculty of Agriculture,University of Peradeniya, Sri Lanka.     

The Effects of Kinetin and Gibberellin on the Germination of Dehusked Seeds of Indica and Japonica Rice (Oryza sativaL.) under Anaerobic and Aerobic Conditions

The effects of kinetin and gibberellin were examined under anaerobicconditions (0% oxygen) and aerobic conditions (20% oxygen) onthe germination of dehusked seeds of indica and japonica ricecultivars that had been harvested at different times duringthe formation of seeds. Surjamkhi was used as a representativeof deep dormant indica cultivars and Assam IV as a less dormantindica cultivar. Sasanishiki was used as the japonica rice cultivar.Both phytohormones were applied at a concentration of 10^-3Mwhichproved to have the greatest stimulatory effect in preliminarywork at concentrations of 10^-3–10^-5M. Under aerobic conditions,inhibition of germination by dehusking of Sasanishiki seedsthat had been harvested either 30 or 60 d after anthesis wasovercome by kinetin and all seeds germinated. Complete germinationinduced by kinetin under aerobic conditions was also achievedwith the dehusked seeds of the indica rice cultivar Assam IVthat had been harvested on two occasions and of Surjamkhi thathad been harvested 28 d after anthesis. In contrast, germinationof dehusked japonica seeds stimulated by anaerobiosis was inhibitedby kinetin. The stimulatory effects of gibberellin on the germinationof indica and japonica rice seeds were observed under aerobicand anaerobic conditions. Under anaerobic conditions, the responsesof dehusked indica and japonica rice seeds to kinetin and gibberellindiffered, being negative with kinetin and positive with gibberellin.Under aerobic conditions, the stimulatory effects of kinetinon germination of dehusked seeds were greater than those ofgibberellin. Thus, treatment with kinetin appears to be usefulfor breaking the considerable dormancy commonly observed inthe dehusked seeds of indica rice. Mechanisms are proposed toexplain the stimulatory effects of these phytohormones on thegermination of dehusked seeds of indica and japonica rice underaerobic and anaerobic conditions. Rice; Oryza sativaL.; seed germination; dehusking treatment; gibberellin; indica; japonica; kinetin; oxygen; dormancy; germination inhibition; seed formation     

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     

The Effects of Priming and Ageing on Seed Vigour in Tomato

A comparison was made of the effects of seed priming or ageingtreatments on the performance of tomato (Lycopersicon esculentumMill. cv. UC204C) seeds according to a number of indices ofseed vigour. A single lot of tomato seeds was primed in 120mol m^–3 K2HPO4 + 150 mol m^–3 KNO₃ for 5 d at 20?C, or aged at 13% moisture content (dry weight basis) and 50?C for 6 d. Germination percentage (>98%) was unaffectedby priming and reduced to 85% by ageing. X-ray photographs andlongitudinal sections revealed the formation of free space surroundingthe embryo in dry primed seeds, which was not evident in controlor aged seeds. Priming increased the rate of germination atall temperatures above the base temperature (T_b), while ageingdecreased it. T_b was unaffected by priming and only slightlyincreased by ageing. The variation in individual times to germinationwas approximately doubled in both primed and aged seed comparedto the control, based upon the slopes of probit germinationpercentage versus log thermal time curves. Root growth aftergermination tests and seedling growth in both greenhouse andfield tests were not influenced by either priming or ageing.The conductivity test was found to be unreliable as a vigourtest for tomato seeds. The results identify several indiceswhich can be used to quantify seed vigour in tomato. They alsoillustrate that seed priming can enhance seed performance accordingto some criteria, while having no effect or decreasing qualityaccording to other criteria. Seed vigour can apparently be separatedinto various components which can be independently influencedby seed enhancement treatments. Key words: Tomato, seed germination rate, seed priming, seed vigour     

The Responses of White Spruce and Yellow Birch to Some Selected Organophosphorus Insecticides and the Adjuvants Atlox and Arotex

At concentrations of 10 and 100 parts 10^–6 the insecticidesfenitrothion, acephate (Orthene^?), and phosphamidon inhibitedsome germination characteristics of white spruce seeds. Thelevel of inhibition was dependent upon the applied pesticideconcentration. By contrast, at these concentrations acephateand phosphamidon enhanced germination of yellow birch seeds,while 10 parts 10^–6 fenitrothion slightly stimulated germination.Higher concentrations of fenitrothion (25–50 and 100 parts10^–6) seriously depressed the germination of yellow birchseeds. Gross morpho-genetic changes and lack of seedling vigourcharacterized the growth of seedlings exposed to the higherconcentrations of fenitrothion. The metabolite S-methylfenitrothiondecreased germination of yellow birch seeds at concentrationsof 10 or 100 parts 10^–6; however, the emergent seedlingsgrew normally and did not show any dwarfing effects.     

Germination of Talinum triangulare L. Seeds as Affected by Various Chemical and Physical Treatments

Three-month ‘old’ and ‘fresh’ seedsof Talinum triangulare were subjected to various treatmentsto induce early and rapid germination. Scarification and activated carbon were the most effective treatmentsin improving total germination in fresh seeds, while the 3 and5 per cent thiourea treatments were most effective in improvingtotal germination in old seeds. Activated carbon, scarificationand 5 per cent thiourea treatments enhanced early germinationin both old and fresh seeds. Cumulative percentage germinationwas very high in fresh seeds after scarification or after treatmentwith activated carbon and 5 per cent thiourea, and lowest inseeds treated with 3 per cent thiourea and hot water. In oldseeds, highest cumulative percentage germination was obtainedwith 3 and 5 per cent thiourea treatments and scarification.Generally, higher germination was obtained with fresh seedsthan with old seeds. Partial seed-coat removal and treatment with 5 per cent thiouriaresulted in a higher rate of and cumulative percentage germinationcompared with seeds with the coat partially removed but nottreated with thiourea. Constantly high temperature (34 °C) increased both rateand total germination compared with seeds planted at room temperature(20–23 °C). Treatments that did not induce germinationwere 1 per cent thiourea, H₂SO₄, cold water soaking at roomtemperature, 6 per cent hydrogen peroxide and soil planting.These treatments effected less than 3 per cent germination. Talinum triangulare L, seed scarification, activated charcoal, thiourea, germination     

Increases in nuclear volume and cell size in meristematic cells arrested by 5-aminouracil

Summary Lateral roots ofVicia faba were treated with a solution of 5-aminouracil (3.93 × 10^–3 M). They were either treated for 6 hours and allowed to recover for up to 10 hours, or were treated continuously for up to 24 hours. Mitotic index decreased as the duration of treatment increased,e.g., it was < 0.5 after 6 hours treatment and 4 hours recovery and 0.23 after 12 hours continuous treatment. During this period of low mitotic activity nuclei and cells increased in size: mean nuclear volume, for example, was 1505±651 m³ 8 hours after the end of a 6 hours treatment. In roots treated continuously, nuclear volume increased from 559±204 m³ at 0 hour to 1272±636 m³ at 12 hours. In the first 3 hours it was the larger nuclei that grew,i.e., nuclei that would have proceeded into mitosis if they had not been blocked by 5-AU. But between 3 and 12 hours of continuous exposure to 5-AU all nuclei increased in volume. Cells, on the other hand, showed no response during the first 6 hours of treatment; their areas did not increase till 6–12 hours had elapsed. It appears that in cells blocked by 5-AU growth continues for about 12 hours. Initially, nuclei grow disproportionately large, suggesting that synthesis of nuclear components is favoured at the expense of cytoplasmic constituents, at least during the first 6 hours of treatment; there is an internal imbalance between nuclear and cell growth and a temporary change in the nuclear cytoplasmic ratio. When cells recover from the 5-AU block and enter mitosis their prophase nuclei are also much larger than those of untreated cells. The response to 5-AU is discussed in terms of internal restrictions on cell growth, due to the presence of cell walls, and the heterogeneity in nuclear volumes.     

The laboratory germination of crisp lettuce seeds under moisture stress

Seeds of the crisp lettuce cultivar Pennlake were germinated using all combinations of six ‘initial’ solutions of polyethylene glycol 6000 (PEG) with osmotic potentials ranging from 0 to -8 bars and seven ‘secondary’ solutions of PEG with osmotic potentials ranging from 0 to -10 bars, to which seeds were moved after 24 or 48 h in the ‘initial’ solution. The number of seeds germinating decreased at more negative osmotic potentials of both ‘initial’ and ‘secondary’ solutions but there was an interaction between germination temperature and the osmotic potential of the ‘initial’ solution. At an ‘initial’ solution osmotic potential of 0 bars germination at 20°C exceeded that at 10°C. As the osmotic potential of the ‘initial’ solution decreased germination at 20°C decreased more than at 10°C so that at the more negative osmotic potentials germination at 10°C exceeded that at 20°C. However seeds ungerminated after 14 days germinated normally when transferred back to water, so that the average final germination was 99.5%. The results suggest that major fluctuations in soil water potential in a seedbed are unlikely to influence seed germination per se provided that a period of 24 to 48 h at 0 bars tension is available at some time. The timing of such a period relative to sowing will have a considerable effect on the time of germination and hence the time of emergence. It is concluded that factors other than the direct effect of soil moisture content on germination are involved in reducing seedling emergence under fluctuating soil moisture conditions in the field.     

The effects of phosphate supply on uptake of potassium ions, 2,4-D and atrazine by wheat and maize

The germination percentage of peach [ Prunus persica (L.) Batsch cv. Halford] seeds at 20°C was low (< 20%) after incubation at 5°C for as long as 35 days, but then increased considerably (> 40%) when the seeds were maintained at 5°C for longer than 42 days. Four zones of gibberellin-like activity were found in partially purified seed extracts. Gibberellin-like activity remained low in seeds incubated at 5°C for as long as 28 days, but increased significantly in three of these zones after 35 days, and in the fourth zone after 49 days. The increase in gibberellin-like activity was evident prior to the transfer of the seeds to 20°C. Moreover, seeds maintained at 5°C germinated at this temperature after 63 days. For seeds incubated and germinated at 20°C, both the germination percentage and the gibberellin-like activity remained low throughout the experimental period. Application of the growth retardant paclobutrazol to seeds after 28 days of a 49 day total incubation period at 5°C did not substantially reduce seed germination, although the increase in gibberellin-like activity was prevented. Seeds did, however, require a longer time to germinate after transfer to 20°C and were dwarfed in appearance. Application of GA₃ to seeds prior to stratification increased the percentage germination of seeds only when they had been incubated at 5°C for at least 35 days. The major changes in gibberellin-like activity are, therefore, associated not so much with the processes which allow germination to take place in peach, but more with those processes which allow normal growth and development of the seedling.     

3H-THYMIDINE INCORPORATION INTO CELL NUCLEI IN GERMINATING LETTUCE SEEDS

Lettuce seeds were soaked in a ³H-thymidine solution and autoradiogramof sections of these seeds, fixed prior to and after germination(root protrusion), were prepared. Labeled nuclei in intact,punctured, as well as broken seeds began to appear approximatelyat the time of root protrusion. In the nuclei of the radicle,the beginning of ³H-thymidine incorporation precedes the divisionof nuclei by one to two hours, and all the dividing cells incorporate³H-thymidine before their first division. Occasional dividingcells in the epidermis of the hypocotyl were not found to be³H-labeled. In intact seeds, the nuclei observed in the coneof the plumule showed radioactivity approximately 3–4hr after germination, while in punctured and broken seeds the³H-incorporation occurred some hours earlier. (Received December 3, 1962; )