Glaucium Flavum Seed Germination - an Ecophysiological Approach
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Annals of Botany 63, 121-130, 1989 121 Glaucium flavum Seed Germination - an Ecophysiological Approach c. A. THANOS, K. GEORGHIOU and FLORA SKAROU Institute of General Botany, University of Athens, Athens 15784, Greece Accepted: 17 August 1988 . ABSTRACT The yellow horned-poppy Glaucium jiavum Crantz shows a final dark germination which is of characteristically 'mediterranean' type (maximal responseat the temperature range 5-15 °C), though a considerablebroadening is brought about, both by a red light pulse and a stratification treatment. Seeds . imbibed in darkness at 25 °C for even a few hours are induced to develop a secondary dormancy (thermodormancy) which can be releasedby light and stratification. The well known time dependenceof light sensitivity and the gradually imposed induction of light indifference at supraoptimal temperatures have also been shown. Seedsimbibed under regimes simulating those met naturally in Greece during November or April, do not germinate when illuminated with white light (I; = 1.26). Full manifestation of germination occurs either in complete darkness or under various, red-enriched light conditions (I; higher than 2.07). A partial promotion is observed with very low fluence rates of white light (in the order 10-:'- 10-4 of daylight). The existence of a surface-avoiding seedling emergencemechanism based on light- inhibited seedgermination was verified in a pot experiment under natural conditions, with seedsburied to various depths. Only those seedsburied at 0.5 cm germinate optimally and readily after the onset of the rainy season (November-December) although those at 1 and 2 cm also germinate to a considerable extent. Key words: Glauciumjiavum, yellow horned-poppy, seedgermination, light, phytochrome, stratification, thermodormancy, seedling emergence. The aim of the present study was to investigate in INTRODUCTION detail the germination characteristicsof G.fiavum The yellow horned.poppy, Glaucium fiavum seeds. Particular emphasis was given to the Crantz, is a perennial or biennial herb, recognized ecophysiological aspects in an attempt to gain by Theophrastus (Enquiry into Plants, IX, XII, 3) insight into the possible role of the germination as a medicinal plant growing on rocky sites by the mechanismsrevealed by laboratory experimentsin sea. The genus Glaucium (Papaveraceae)consists the natural situation. of nearly 20 species,chiefly of the Mediterranean region and also eastwardsto Afghanistan (Meikle, MATERIALS AND METHODS 1977). Glaucium fiavum occurs all along the Mediterranean shores but also on the coasts of Seeds of the yellow horned-poppy (Glaucium , . ~ W. Europe and northwards up to Norway fiavum Crantz) were collected In July 1986 from (Mowat, 1964; Eisikowitch, 1979/1980). the ripe capsules of several pla~ts.g~owing in the In sharp contrast to its wide distribution, there sand-gravel seashore of K. Dlmlnlo (Northern . is a marked scarcity of information on the Peloponnesus,Greece). The mean weight of 50 physiology of seed germination in the yellow seeds(Is.e.) was found to b.e 0.0565I 0.0005g horned-poppy, and only the requirement for (n = 10), thus mean seed .welght ~ .1'1 mg.. The stratification has been documented (Formano- seedswere stored dusted wIth fungIcIde (Thlram) wiczowa and Kozlowski, 1976; Mermerska, 1984). in light- and water proof plastic tins, both at room temperature (20 I 5 °C) and in the refrigerator Communicationpresented at a symposiumAdvances ~3;t 2 °C). No variation in germination characte~- in SeedBiology at the.Royal Botanic Gardens,Kew IStlCS :-vas o~served throughout the expen- (14-15 April 1988),organized by J. B. Dickie, H. w. mentatIon perIod. Pritchardand R. J. Probert. Germination tests were performed in Petri 0305-7364/89/010121 + 10 $03.00/0 @ 1989Annals of BotanyCompany 122 Thanoset al.-Glaucium flavum SeedGermination dishes(8 cm. diameter) lined with two filter papers Tables 4 and 5) were equipped with a white light and moistened with 3 ml of deionised water or source of an emission spectrum quite similar to appropriate mannitol (Merck) solution. For the natural daylight, with a ~ value equal to 1.26;;;' is stratification experiments the dishes were trans- defined as the R (660 nm): FR (730 nm) photon ferred to the refrigerator (in light-proof metal ratio (Smith, 1986).This source (light source A in cans) immediately after onset of seed imbibition. Tables 4 and 5) consistedof four white fluorescent Seeddesiccation included an initial surface drying tubes (Sylvania, Cool White F48Tl2/CW IHO, and afterwards seedswere left to dehydrate in air. 60 W) and four white incandescentbulbs (Osram The criterion of germination was visible radicle 40 W). Light source B (Table 4) consisted of the protrusion and measurementswere taken daily, as four fluorescent tubes only. Various coloured and a rule, though in certain casesonly once or twice neutral (diffuse white) filters made of glass, per week. After each count, the germinated seeds Plexiglas and gelatine were used (Tables 4 and 5); were discarded and the tests were considered certain characteristics of the light transmitted finished when no additional seeds germinated. through thesefilters are appropriately indicated. A Each value is the mean from at least five samples part of the experiment presented in Table 5 was of 50 seedsand :t numbers (in Tables) and vertical carried out in a cabinet equipped with light source . bars (in Figures) represent standard error (s.e.). C, i.e. one white fluorescent(Philips TLD 18W 133) 1;.0is the time neededfor manifestation of half of and one white incandescent tube (Philips the final germination level and it was calculated Philinea 6276 x 60 W). The broad band red and . from the two median values. far-red light sources used for brief illumination The experimentswere performed in temperature (Table 3, Figs I, 2 and 3) consisted of eight red controlled plant growth cabinets (Model BK 5060 fluorescent (Philips T~ 20 W 118) and eight white EL, W.C. Heraeus GmbH, W. Germany) or incandescenttubes (Philips Philinea 6276x 60 W), chambers (Enviratrol, Conviron, Canada), where respectively, filtered through either one red (501) in all casestemperature was kept constant within or one red (501) and two blue (627) sheets of :to.5 °c. The growth chambers (experiments of Plexiglas filters, 3 mtn thick each (R6hm GmbH, . i t !...;e c 51 g E- ... '"Q; ",. "0 c i;: . 15 25 Temperature(OC) FIG. I. Final germination of G/auciumflavum seedsas a function of temperature. Seedswere tested: untreated (.), illuminated with a short (15 mins red light (0) and stratified for 20 d (.). The R illumination was given 8,4 and 4 h after onset of imbibition at 20, 25 and 30 °C, respectively. Vertical bars, 2 s.e. The circles enclose the corresponding 7:;0 values. Thanoset al.-Glaucium flavum Seed Germination 123 100 ~ 60 c .2 [; c E ~ co g 40 - i:L: . DC J . 2 3 I Time after anset af imbibitian (d) FIG. 2. Final seed germination of Glauciumflavum in response to a short (15 mins) red irradiation given after various periods of time from the onset of imbibition, at 20 and 25 °C (curves A and 8, respectively). DC, corresponding dark controls, vertical bars, 2 s.e. W. Germany). Total fluence rates at the regions 400-750 nm, for an overcast or a sunny day, 600-725 and 675-750 nm was 2 and 4 W m-2, respectively). The pots were subjected only to respectively. All manipulations of imbibed seeds natural fluctuations of environmental factors and were carried out under a dim green safelight (one the seedlingsemerging from the surfaceof the sand green fluorescent tube F l5T8.G.6, 15 W Green- were counted (and subsequently removed) twice Photo, General Electric; two sheets of Plexiglas per week. At the same dates the minimum and filter, 3 mm thick each, one red orange, 478, and maximum air temperature as well as rainfall were one green, 700, Rohm GmbH, W. Germany; also recorded. emission at 525-575 nm, maximum at 550 nm, total flu~nce rate I? mW ~-2). Total fluence rates RESUL TS were estImated by IntegratIng the spectral fluence rate curves constructed after the measurements The germinability of G. fiavum seedsat various taken with a spectroradiometer (ISCO SR, temperaturesis shown in Fig. 1. Dark germination USA). was restricted to temperaturesbelow 20 °C, where For the experiment describedin Fig. 4, 30 small it occurred at a very slow pace, especiallyat 5 °C. plastic pots (height 10 Cffi, diameter 8-9 cm) were Both a short red light (R) and a 20 d chilling pre- . filled (up to 8 ClT.from the bottom) with dry sea treatmentconsiderably expanded the temperature sand. The majority of the sand particles had a range of germination (by about 5 and 15 °c, diameter of 0.02-0.5 mm, the rest being consider- respectively). When a short (30 min) pulse of ably larger (0.5-2 mm); on wetting, the sand diffuse daylight was given, instead of the R one, a compacted to about 90 % of its initial volume. In significant promotion of germination at 20 and each pot, 25 seedshad been previously buried at 25 °c was also obtained (data not shown), though various depths (0, 0.5, 1,2,4 and 6 cm), eachdepth the effect was reduced in comparison to the representedby five pots. The pots were established corresponding R light pulse. on bare ground, in a well-protected place outdoors When the seeds were imbibed in mannitol and received only diffuse daylight (the maximum solutions at 15 °c, in darkness, a significant value of which ranged from 15 to 30 W m-2, at decrease of germinability was observed as a 124 Thanoset al.--Glaucium flavum SeedGermination 100 0 ~;e 60 c: 0 + ~c: 'E ~ 0- g 40 ii: . 20 6 0 Stratification(d) FIG. 3. The photosensitivity of stratified Glauciumflavum seedsat 20 A or 25 °C B: Final germination was scored after various stratification periods and in responseto either a short (15 mins) red pulse (0) or a short red pulse followed by a short (15 mins) far-red one «».