Carbon Translocation in the Tomato: Pathways of Carbon Metabolism in the Fruit-

The rate of carbon import by tomato fruits has been relatedto their carbon metabolism by examining the effects of fruittemperature on the metabolism of imported assimilates. ¹⁴C–sucrose,–glucose, –fructose, –malic acid and –citricacid were injected individually into young growing tomato fruitswhich were subsequently maintained at 25 or 5 °C for 48h. Fruit temperature greatly affected the proportions of ¹⁴Clost from the fruits by export and respiration. Only 40 percent of the injected ¹⁴C from ¹⁴C–sugars and 20 per centfrom ¹⁴C–acids was recovered from fruits at 25 °C.Less than 10 per cent of the injected ¹⁴C was exported, thebalance being respired. In contrast, more than 50 per cent ofthe injected ¹⁴C was recovered from cooled fruits, in whichthe import rate of carbon was presumably reduced, and 20–36per cent of injected ¹⁴C was exported. Cooling enhanced thesynthesis of ¹⁴C–sucrose from injected ¹⁴C–hexosesand inhibited the incorporation of ¹⁴C into starch and insolubleresidue. When ¹⁴C–sugars were injected, radioactivityexported from the cooled fruits was detected as sucrose in thephloem of the peduncles; radioactivity was also detected instems and roots when fruits were cooled. In almost fully–grownfruits injected ¹⁴C–compounds were metabolized less readilythan in smaller fruits. Conversion of ¹⁴C–hexoses to ¹⁴C–sucrosewas again enhanced by cooling (5 °C, but was less in fruitsmaintained at 35 °C than in controls. Lycopersicon esculentum, tomato, fruit, translocation, carbon metabolism     

Survival of carnation (Dianthus caryophyllus L.) shoot apices frozen to the temperature of liquid nitrogen

Effects of cooling and rewarming rates on the survival of carnationshoot apices frozen to the temperature of liquid nitrogen wereinvestigated. Ten percent dimethyl sulfoxide (DMSO), alone orin combination with 5% glucose, sucrose or sorbitol was mosteffective as a cryoprotectant for carnation shoot apices. Theshoot apices survived slow freezing at about –70?C inthe presence of 10% DMSO. About 80% of the shoot apices survivedfreezing at the temperature of liquid nitrogen after prefreezingat –50?C or below, regardless of the rewarming rates.Shoot apices in the presence of 10% DMSO were cooled at differentrates then rewarmed rapidly. The survival rate gradually decreasedto zero as the cooling rate increased from about 0.5?C/min to50?C/min. At cooling rates higher than 50?C/min, no survivalwas observed even at 5?10⁴?C/min. However, in apices prefrozenat –15?C or below then cooled ultrarapidly at 10⁴?C/min,all remained alive with subsequent rapid rewarming. These apicesdeveloped normal young plants. This ultrarapid cooling methodcombined with prefreezing seems to be useful for the cryopreservationof shoot apices from various plants. ¹Contribution No. 2207 from the Institute of Low TemperatureScience, Hokkaido University. This work was supported in partby a Grant-in-Aid (No. 434035) for Scientific Research fromthe Ministry of Education, Science and Culture. (Received November 13, 1979; )     

Freezing Tolerance in Hydrated Lactuca sativa (L) Seed: A Model to Explain Observed Variation Between Seed Lots

Low temperature tolerance was investigated in the imbibed seedof 15 seed lots compnsmg seven cultivars of Lactuca sativa L.During rapid cooling (20 °C h^–1) some seeds of allseed lots survived to –16 °C but none to –20°C. The majority of seed lots retained over 50 per centviability above –14 °C due to isolation of the embryofrom external ice by the endosperm, and subsequent embryo super-cooling.Certain seed lots, including all three seed lots of cv. TomThumb, showed high mortality at temperatures above –10°C. Correlation of mortality with the formation of externalice suggested that the endosperm is not an effective nucleationbarrier in these seed lots. Survival to –20 °C was increased at slower coolingrates (6 to 1 °C h^–1) due to freeze desiccation ofthe embryo, but seed lots varied considerably in their toleranceof specific cooling rates. A model to explain this variationwas developed incorporatmg (1) seed lot super-cooling limittemperature, (2) the rate at which freeze dehydration of thesupercooled embryo took place, (3) the moisture content at whichnucleation (at –20 °C) was no longer certain and (4)the.initial equilibrium moisture content of the fully imbibedseed. Factors (1), (2) and (3) were found to be relatively constant,but low (or artificially reduced) seed moisture content wasclosely correlated with high survival at natural cooling rates.Seed size fractions of similar moisture content from a singlecultivar showed that more small seeds survive cooling at 3 °Ch^–1 to –20 °C than larger seed. Seed with pierced endosperms or ineffective nucleation barrierswere capable of surviving to at least –10 °C if cooledslowly (1 °C h^–1) but were killed by rapid (20 °Ch^–1) cooling. Lactuca sativa L, lettuce, seed germination freezing tolerance, super-cooling     

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     

Influence of Environmental Stress on the Germination of Anabaena vaginicola Akinetes

Germination of akinetes of Anabeana vaginicola v. fertilissimaPrasad in response to environmental stress was studied. Additionof nitrate to the medium induced early and maximum germination(96 per cent), whereas less than half of the akinetes germinatedwhen either nitrate or phosphate was omitted from the medium.The pH range over which germination occurred was 7.0–9.0.The desiccated akinetes after rehydration germinated after acertain lag period, depending upon the dehydration state. Thetemperature optimum for germination and vegetative growth wasthe same (25 °C) and germination did not occur at 5 °Cor above 35 °C. The limit of heat shock tolerated was 55°C for 4 min. In addition to white light, only the red partof the visible spectrum induced germination. Ultraviolet radiationreduced germination rate presumably by inducing thymine dimersin DNA. The photoreactivating system (s) in akinetes is certainlynon-photosynthetic. LD₅₀ photon flux densities were 300 Jm^–2for akinetes and 240 Jm^–2 for vegetative cells. Anabaena vaginicola, blue-green alga, akinete, germination, environmental stress     

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     

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     

Responses to Drying of Recalcitrant Seeds of Quercus nigra L.

It has been suggested that rate of desiccation can influencethe expression of recalcitrant behaviour in seeds, thus complicatingthe task of determining which seeds are truly recalcitrant.The objective of this study was to see if variable rates ofdesiccation influenced such behaviour inQuercus nigra L., atree seed known to be recalcitrant. Acorn moisture content, leachate conductivity, and germinationwere determined at various times during desiccation at threerates at 27 and 40°C. Moisture contents and germinationdecreased as the severity of desiccation increased. Leachateconductivity increased slightly but was not a sensitive indicatorof loss of viability. The critical (lethal) moisture contentfor these acorns was 10–15%, although rehydration within48 h of reaching this level prevented death in about 25% ofthe acorns. At 27°C any desiccation treatment that producedlosses of 30–50mg of moisture per g of acorn dry weightper day should be suitable as a test for recalcitrance in thegenus. Apparent physiological or fungal damage at 40°C rulesout the higher temperature for such a test. Quercus nigra L.; desiccation rate; temperature; recalcitrant; leachate conductivity; germination; viability     

The Carbon Economy of Rubus chamaemorus L. II. Respiration

Respiratory activity and seasonal changes in carbohydrate contentof the storage organs of Rubus chamaemorus L. have been investigated.Leaf dark respiration rate increases in a non-linear mannerfrom 0·7 mg CO₂ evolved dm^–2 h^–1 at 0 °Cto 4·6 rng CO₂ evolved dm^–2 hh^–1 at 30 °C.Root and rhizome respiration rates increase from 1 µ1O₂ uptake g^–1 fresh weight h^–1 at 0.7 ° C to10 µ10, uptake g^–1 f. wt h^–1 at 20 °C.Rhizome carbohydrate reserves decline from a September peakof 33 per cent alcohol insoluble d. wt to 16 per cent in May. The circumpolar distribution of R. chamaemorus is discussedin relation to the evidence presented here and in the precedingpaper of the series.     

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     

Germination of Sporangia of Phytophthora palmivora (Butl.) Butl.

Sporangia of Phytophthora palmivora germinated by either forminggerm tubes or producing zoospores. Two distinct modes of germ-tubedevelopment have been described. Sporangia in distilled waterformed zoospores at 10–34°C with an optimum at 22°Cbut germinated by means of germ tubes at 30 and 34°C only.Zoospore formation was inhibited to varying degrees by cocoapod extract, I.0 per cent (w/v) peptone and yeast extract, 100–500µg1^-1 thiamine, and by very low concentrations of severalamino acids, carbohydrates, and inorganic salts. Germ-tube formation was encouraged at 22°C by 1'0 per cent(w/v) peptone and yeast extract, by cocoa pod extract and exudate,10mM CaCl2, 1–10 mM MgSO₄. 7H₂O, 0.5 per cent (w/v) fructose,galactose, glucose, lactose, maltose, and sucrose, by 100 ppmarginine, aspartic acid, glutarnic acid, glycine, leucine, andtryptophane, and by 100–500 µg 1^-1 thiamine.     

Soya Bean Seed Growth and Maturation In vitro without Pods

Immature Glycine max (L.) Merrill seeds, initially between 50and 450 mg f. wt, were grown and matured successfully in vitro.Excised seeds were floated in a liquid medium containing 5 percent sucrose, minerals and glutamine in flasks incubated at25 °C under 300 to 350 µE m^–2 s^–1 fluorescentlight. During 16 to 21 d in culture, seeds grew to a matured. wt of 100 to 600 mg per seed at an average rate of 5 to 25mg d. wt per seed d^–1 depending on initial size. Growthrates were maximal during the first 8 to 10 d in vitro but declinedwith loss of green colour in the cotyledons. Seed coats rupturedwith rapid cotyledon expansion during the first 2 d in culture.Embryos were tolerant to desiccation and 80 to 90 per cent germinatedif removed from culture before complete loss of green colour.The growth of excised seeds in vitro exceeded the growth ofseeds in detached pods, but when windows were cut in pods topermit direct exposure of seeds to the medium, seed growth wascomparable. Glycine max (L.) Merrill, soya bean, seed culture, seed growth, seed maturation, germination     

Ethylene Involvement in Dormancy Release of Ricinodendron rautanenii Seeds

Ricinodendron rautanenii (manketti) seeds respond to as littleas 10^–2 µl I^–1 ethylene. Both dry and imbibedseeds respond to ethylene treatments. The length of the imbibitionperiod prior to the ethylene treatment is not important as seedswhich were simultaneously gassed and imbibed germinated successfully.Seeds were sensitive to the gas at temperatures between 25 and35 °C. No temperature effect was observed in seeds whichwere transferred from temperatures below 20 °C, or above35 °C, to 30 °C. There is no period of carbon dioxidesensitivity associated with the ethylene treatment and the effectsof the ethylene treatment persisted in both dry and imbibedseeds when subsequently maintained (desiccated) at room temperaturefor 8 d Ricinodendron rautanenii, manketti nut, ethylene, germination     

Osmoconditioning as a Means of Counteracting the Ageing of Pepper Seeds during High-temperature Storage

Sweet pepper seeds were osmotically conditioned in 0.4 M mannitolsolution for 4 d (at 25 °C, in darkness) before or afterstorage at 35 °C for up to six months, and their germinationand viability was compared with that of untreated seeds storedunder the same conditions. Seeds that had been osmoconditionedprior to storage retained a high rate of germination and germinatedto a high final percentage (from 80 to 50 per cent) at both15 and 25 °C throughout the storage period. By contrast,both the rate and total level of germination of untreated pepperseeds declined rapidly at both germination temperatures, andby three months of storage the total level of seed viabilitywas already less than 10 per cent. Seeds that were first storedat 35 °C, and then osmoconditioned just prior to germination,showed a decline in germinability which when tested at 25 °Cwas the same as for untreated seeds, while tested at 15 °Coccurred at a slightly slower rate than for untreated seeds. It is evident that osmoconditioning prior to storage, in additionto the acceleration of germination, resulted in a dramatic delayof the ageing rate, thus increasing considerably the longevityof seeds. On the other hand, osmoconditioning after storagedid not seem to have any significant effect on seed viability,though it enhanced the germination rate. Capsicum annuum, sweet pepper, seed, germination, osmoconditioning, priming, storage, viability, ageing, longevity     

Azetidine-2-carboxylic Acid and Lily Pollen Tube Elongation

Azetidine-2-carboxylic acid (AZC), which occurs naturally inLiliaceous plants, is reported to be a proline (pro) analoguePlant cell walls contain ‘extensin’, which is richin hydroxyproline (hyp). Peptidyl hyp arises through hydroxylationof peptidyl pro followed by glycosylation (arabinose attachment)of hyp Because AZC replaces peptidyl prolyl residues, it maybe a useful tool for evaluating the significance of hyp-o-arabinoselinkages in cell elongation. Therefore, we determined the effectof AZC on [¹⁴C]pro uptake, incorporation and conversion to wall-bound[¹⁴C]hyp in relation to elongation of lily pollen tubes whosewalls consist, in part, of hyp-containing glycopeptides TheAZC suppressed pollen germination 9–42 per cent (1–10mM) and subsequent tube elongation 40–54 per cent (0·1–1mM without affecting respiration In contrast, similar hyp concentrationswere without effect on tube elongation Whereas uptake of [¹⁴C]prowas 16·5–6·2 per cent of the control at0·1–1 mM AZC, [¹⁴C]leucine uptake was 85–25per cent of the control. Light microscope radioautography revealedfewer silver grains over tubes elongated in 0·1–1mM AZC than in its absence. Incorporation of [¹⁴C]pro into tnchloroaceticacid (TCA)-precipitable cytoplasm was reduced by only 10 percent at 0·01–1 mM but 43 per cent at 10 mM AZCGel filtration of cytoplasm from pollen germinated without AZCbut with [¹⁴C]pro resulted in labelled void volume (V) and threeretarded peaks (RI–III) Incorporation into V and RI wasinhibited at both 0·01 and 1 mM AZC These AZC concentrationsreduced conversion of [¹⁴C]pro to wall-bound hyp by 20 percent However, total incorporation of [¹⁴C]pro into salt-water-purifiedwall fractions was suppressed 47–53 per cent (0·1–1mM AZC). Lilium longiflorum, lily, hydroxyproline, proline, azetidine-2-carboxylic acid, pollen, pollen tube elongation     

Carbon and Nitrogen Transfer from Vegetative Organs to Ripening Seeds of Field Pea (Pisum arvense L.)

The fate of the carbon from photosynthetically assimilated ¹⁴CO₂and the nitrogen of rootapplied ¹⁵NO₃ was studied by harvestingplants at intervals after a week's feeding period, either early(34–41 d after sowing) during vegetative growth, or late(112–19 d) as plants were fruiting. Only 23 per cent of the early fed ¹⁴C but more than 90 per centof the early-fed ¹⁵N survived in plants until maturity (155d). Efficiency of transfer of early-fed ¹⁴C to seeds was 2 percent, that for early-fed ¹⁵N, 51 per cent. Assimilatory activitybefore flowering had little direct relevance to the carbon nutritionof seeds but provided approximately one-fifth of the seeds'requirement for nitrogen. Early or late-fed ¹⁵N was mobilized slowly for reproductivedevelopment, seeds at all 15 reproductive nodes deriving benefit,late-forming ones more so than those developing earlier. Vegetative organs on a young shoot lost previously acquired¹⁵N at rates within the range 0.5–2.4 per cent per day.The released nitrogen was first taken up by the root and youngerparts of the shoot, but much was later traced to the seeds. Late feeding of ¹⁴C or ¹⁵N resulted in a high (74–6 percent) efficiency of transfer to seeds, most of this appearingto be donated by, or cycled through, vegetative parts of thereproductive zone of the shoot. The significance of past and current assimilation in fruit nutritionis discussed.     

Ethylene, Nitrate and Nitrite Interactions in the Promotion of Dark Germination of Common Purslane Seeds

Ethylene (10 µ1^–1) caused about one-third of highlydark-dormant seeds of common purslane (Portulaca oleracea L.)to germinate in the dark. Attempts were made to increase germinationin the dark with nitrate and ethylene combinations. When applieddirectly to the seeds, KNO₃ did not stimulate germination andKNO₃ plus ethylene did not increase germination above that ofethylene alone. Pre-incubation of seeds in KNO₃ for 4 to 7 dbefore the ethylene applications significantly increased germination.The effects of the KNO₃ pre-incubation were additive at eachof four ethylene concentrations (0.1–100 µ11^–1).Potassium nitrate was effective only when ethylene followedthe KNO₃ pre-incubation period. Potassium nitrite stimulatedabout 25 per cent of the seeds to germinate without a pre-incubationperiod and without ethylene. Also, ethylene plus KNO₂ enhancedgermination above that achieved by either stimulus alone. Silvernitrate did not block the ethylene promotion of germination,but reversed the typical ethylene inhibition of seedling growthfollowing germination. The results support the views that nitrateexerted its effect via conversion to nitrite within the seedand that the rate of nitrate conversion may be a limiting factorin the dark germination of common purslane seeds. Ethylene mayfacilitate nitrite activity by increasing seed sensitivity tothe stimulus. Common purslane, Portulaca oleracea L., ethylene, nitrate, nitrite, germination, dormancy     

The Effects of Temperature on 86Rb Uptake by Two Species of Chlamydomonas (Chlorophyta, Chlorophyceae)

⁸⁶Rb uptake was examined in two species of unicellular greenalgae, Chlamydomonas nivalis isolated from snow, and a cellwall-less mutant of the temperate freshwater Chlamydomonas reinhardii.In C. reinhardii cells grown at 20°C and cooled rapidlyto 0°C, ⁸⁶Rb uptake was abolished. Cells cooled rapidlyto –5°C in the absence of ice accumulated ⁸⁶Rb veryrapidly but the time course of this uptake suggested non-selectiveaccumulation through a damaged plasmalemma. Cells grown at 8°Cwere viable, able to divide and motile; they showed no signsof cold-shock and ⁸⁶Rb uptake, albeit slow, was measurable at–5°C in the absence of extracellular ice. Cells ofC. nivalis grown at 20°C were damaged at sub-zero temperaturesalthough they did show an enhanced ⁸⁶Rb uptake at 0°C. Cellsgrown at 5°C were able to accumulate ⁸⁶Rb from media undercooledto -5°C in the absence of extracellular ice, and again showedenhanced uptake at 0°C. The process of acclimation to lowtemperature appears to differ in the two species. Key words: Chlamydomonas, temperature, ⁸⁶Rb uptake, membrane     

Response of Seed Germination in Three Genera of Compositae to White Light of Varying Photon Flux Density and Photoperiod

Various photon doses (net number of photons per unit area perday), provided by varying both photon flux density and photoperiod,were applied to imbibing seeds of seven lots of four speciesof Compositae in various germination test regimes. In all fourspecies germination was dependent upon photon dose, the productof photon flux density and daily duration of exposure. The responsewas quantified by linear relations between the probit of percentagegermination and the logarithm of photon dose. In general, photonflux density and photoperiod only influenced the stimulationof germination by the low energy reaction indirectly (as factorsof daily photon dose), whereas there was a tendency for photoperiodto have a direct influence on the inhibition of germinationby the high irradiance reaction. Reducing the germination testtemperature from 25?C to 20?C and 15?C not only increased thedark germination of L. sativa L., but also broadened the photondose range at which full germination occurred by reducing theminimum value necessary for the germination of the most dormantseeds, and increasing the maximum value which failed to inhibitthe germination of any seeds. Differences between L. sativaand L. serriola L. in the response of germination to white lightwere only quantitative, rather than qualitative. The singlemost promotory dose for all four species was 3 ? 10^–3mol m^–2 d^–1, although the inhibitory action of dosesup to 10– mol m– d– was generally only slight. Key words: Light, seed germination, seed dormancy, Compositae     

Quantal Response of Seed Germination in Seven Genera of Cruciferae to White Light of Varying Photon Flux Density and Photoperiod

The response of the germination of seeds of Barbarea vema (Mill.)Aschers, Brassica chinensis L., Brassica juncea (L.) Czern.& Coss., Brassica oleracea L. var. gongylodes L., Camelinasaliva (L.) Crantz, Eruca saliva Mill., Lepidium sativum L.,Nasturtium officinale R. Br., and Rorippa palustris (L.) Besserto white fluorescent light of different photon flux densitiesapplied for different daily durations in a diurnal alternatingtemperature regime of 20 °C/30 °C (16 h/8 h) was quantifiedby linear relations between probit percentage germination andthe logarithm of photon dose, the product of photon flux densityand duration. The low energy reaction, in which increasing dosepromotes germination, was detected in all the seed populationsbut in Barbarea vema and Brassica Juncea the lowest photon doseapplied (10^–5–2 and 10^{–5 7} mol m^–2 d^–1,respectively) was sufficient to saturate the response. Comparisons,where possible, between photoperiods demonstrated reciprocity,i.e. germination was proportional to photon dose irrespectiveof photoperiod, for the low energy reaction in Brassica oleracea(1 min d^–1 to 1 h d^–1), Camelina saliva (1 min d^–1to 8 h d^–1), Eruca saliva (1 min d^–1 to 24 h d^–1),Lepidium sativum (I min d^–1 to 8 h d^–1) and Rorippapalustris (1 min d^–1 to 8 h d^–1), but not in Brassicachinensis and Nasturtium officinale. The high irradiance reaction,in which increasing dose inhibits germination, was detectedin Barbarea vema, Brassica chinensis, Brassica juncea, Brassicaoleracea, and Camelina saliva. The minimum dose at which inhibitionwas detected was lO^–0–3 mol m^–2 d^–1.These results are discussed in the context of devising optimallight regimes for laboratory tests intended to maximize germination The response of germination to photon dose was also quantifiedwith 3 x 10^–4 M GA₂, co-applied (Brassica chinensis, Camelinasaliva, and Lepidium sativum) and with 2 x 10^–2 M potassiumnitrate co-applied (Brassica chinensis). In the latter casepotassium nitrate had no effect in the dark and inhibited germinationin the light, but GA₂, promoted germination substantially inall three species. Variation amongst seeds in the minimum photondose required to stimulate germination was not affected by co-applicationof GA₂, in Brassica chinensis and Camelina saliva, whereas seedsof Lepidium salivum showed a narrower distribution of sensitivitiesto the low energy reaction in the presence of GA₂ Barbarea vema (Mill.) Aschers, Brassica chinensis L., Brassica juncea (L.) Czern. & Coss., Brassica oleracea L. var. gongylodes L., Camelina saliva (L.) Crantz, Eruca saliva Mill., Lepidium satiaum L., Nasturtium officinale R. Br., Rorippa palustris (L.) Besser, Cruciferae, light, gibberellic acid, seed germination, seed dormancy