Germination of Coffee Seeds (Coffea arabica L. cv. Mundo Novo)

The life-span of coffee seeds is extended when seeds are storedwith high moisture content. Germination in darkness is alwayshigher than in the light. Exogenous gibberellic acid and abscisicacid inhibit germination while kinetin reverses this inhibitoryeffect. Low levels of endogenous gibberellin- and abscisic acid-likeand high levels of cytokinin-like substances favour germinationwhile the opposite combination of regulators delays germination.     

Growth and Dormancy in Lunularia cruciata (L.) Dum: VI. GROWTH REGULATION BY DAYLENGTH, BY RED, FAR-RED, AND BLUE LIGHT, AND BY APPLIED GROWTH REGULATORS AND CHELATING AGENTS

Experiments with photoperiods ranging from 2 to 24 h confirmthat 8 h light per day is optimal for Lunularia: there is nogrowth in the dark or in continuous light, which causes therapid onset of dormancy. Short-day cycles intercalated amonga series of continuous light cycles promote growth; in cycleslonger than 24 h very long dark periods are detrimental. Withvery short photoperiods (5 min) red light promotes growth moreeffectively than white light at higher intensity; far-red actsas dark. The growth effects of red and far-red light breaks(3 min) depended on the time of application; red light inhibitedin the middle but promoted at the beginning of the 16-h darkperiod of a short day; far-red light had the opposite effect;in each case red and far-red effects were reversible by theother wavelength. Blue light gave the same response as red includingthe reversibility of far-red effects and vice versa. Surprisingly,significant effects of 5 min red, blue, and far-red irradiationwere also found in the middle of the main high-intensity white-lightperiod, red and blue promoting growth, far-red reducing it;again there was ready reversibility of the effects. Growth promoters of higher plants are generally inhibitory toLunularia or have little effect; among growth retardants TIBA,Phosphon D, and CCC gave a slight promotion of growth. EDTApromoted growth (cell numbers) very significantly while 8-hydroxyquinolinewas initially inhibitory, but had a marked latent promotingeffect when subsequently washed from the thalli.     

Effects of Moisture Content on Germination of Seeds of Hancornia speciosa Gom. (Apocynaceae)

Seeds of Hancornia speciosa germinated best at a temperatureof 20–30 °C. The viability of the seeds during storagewas short and the best storage conditions for viability entailedkeeping the seeds in polyethylene bags. Seed viability was maintainedonly when the seeds were stored at a moisture content above30%; storage conditions which allowed dehydration resulted ina rapid loss of viability (the seeds showed recalcitrant behaviour). Low temperature during storage did not improve longevity. Arelationship between germination and moisture content was established,but when the moisture content fell below 25% there was a drasticreduction of germination. After 9 weeks of storage, even athigh moisture content, seeds lost viability. Loss of seed viability during seed dehydration was associatedwith increased leakage of electrolytes and organic solutes,and reduced tetrazolium staining during subsequent imbibition. Hancornia speciosa, germination, recalcitrant seeds, storage, moisture     

Growth and Dormancy in Lunularia cruciata (L.) Dum.: IV. LIGHT AND TEMPERATURE CONTROL OF RHIZOID FORMATION IN GEMMAE

The first sign of initiation of growth in dormant gemmae ofL. cruciata is the formation of rhizoids. Gemmae in the cupcannot ‘germinate‘ until exposed to substrate conditionsallowing the outward diffusion of a growth inhibitor. Rhizoidproduction depends on temperature and light. With long lightperiods rhizoids are formed over a wide range of temperatures.Transference to darkness after 2 h white light causes about50 per cent of gemmae to produce rhizoids, and these are formedonly between 20 and 25 °C. Outside these temperature limitsthe percentage of gemmae with rhizoids soon drops to zero. Althoughrhizoid production is prevented in total darkness, gemmae remainalive for well over 6 months. Red light for as little as 5 spromoted, and far-red light inhibited, rhizoid formation inthe dark. Coumarin and indol-3yl-acetic acid can substitutefor light and partly reverse the effect of far-red irradiation.     

Growth and Dormancy in Lunularia cruciata (L.) Dum: V. THE CONTROL OF GROWTH BY A NATCRAL, ENDOGENOUS INHIBITOR

The production of an endogenous growth inhibitor by Lunulariahas been demonstrated in tests with diffusates from gemmae andthalli. Increased growth made by bisected gemmae compared withintact controls suggests that self-inhibition also occurs andpoints to the growing tip as the locus of inhibitor production.More inhibitor is produced in short-day (optimum growth) thanin long-day (dormancy inducing) conditions, but even in shortdays the growth of thalli depends on conditions allowing theinhibitor to diffuse away. Thalli prevented from doing thisby resting the apical 2 mm on non-wettable cover slips stoppedgrowth and showed morphological changes of incipient dormancy.Some of the ecological implications of these tests are discussed.     

Growth and Dormancy in Lunularia cruciata (L.) Dum: VII. THE ISOLATION AND BIOASSAY OF LUNULARIC ACID

The extraction, purification, and isolation of the growth inhibitorpreviously postulated are described. Methanol extraction andseparation into acid, neutral, and basic fractions was followedby paper chromatography of the acid and neutral fractions withdistilled water, re-extraction with methanol, and thin-layerchromatography, the peak of inhibition being located at Rf 0.7–0.8(isopropanol: ammonia: water, 100:5:5), or Rf 0.3–0.4(chloroform: ethyl acetate: acetic acid, 60:40:5) Lunularia gemmae, grown directly on the chromatographic stripwith added nutrient solution, served as the most appropriateand direct bioassay. Area measurements after 5–10 days'growth yielded significant differences. Other bioassays included:Marchantia polymorpha gemmae, lettuce hypocotyl growth, cress-seedgermination, oat coleoptile, and radish cotyledon disc tests.An active inhibitor, i.e. dihydrohydrangeic acid, now named‘lunularic acid’, was isolated in crystalline form.Lunularic acid was found to increase with long-day treatmentof Lunularia thalli, though present even in short-day. Its concentrationcould be altered rapidly when daylength conditions were changed.The growth inhibition was linearly related to concentrationover the range from 0.1 to 10 ppm, very high concentrationsbeing lethal. Abscisic acid, though inhibitory to Lunulariain low concentrations, was not detected in extracts, and couldeasily be separated from lunularic acid.     

Correlative Growth in Seedlings of Phaseolus vulgaris L. : Inhibition of Stem Growth by the Primary Leaves

Primary leaves of one-week-old seedlings of dwarf beans effectivelyinhibit stem elongation either in natural daylight or in continuousdarkness. Stem elongation is promoted by exogenous gibberellicacid and kinetin and inhibited by indol-3-ylacetic acid (IAA)or abscisic acid, and it is suggested that IAA is the inhibitorysubstance emanating from the primary leaf blades which affectsthe growth of the stem.     

Effect of Endogenous Coumarin on the Germination of Seeds of Coumarouna odorta Aublet

Seeds of Coumarouna germinate readily at 33?C in darkness orlight in spite of high levels of endogenous coumarin. The concentrationof coumarin on a dry-weight basis remained constant in the cotyledonsand increased in the embryos during germination. Applied coumarin(0.4 and 4 mM) did not inhibit germination of Coumarouna butenhanced the growth of embryos; yet a single seed of Coumarouna,placed at the centre of a Petri-dish, drastically inhibitedgermination of other neighbouring seeds (lettuce, radish, andtomato). The presence of coumarin in the soil of potted seedlingssuggest that coumarin exuded by the radicle can inhibit germinationand growth of other species in its vicinity, thus eliminatingcompetition during the first stages of growth.