Ulteriori ricerche sulla germinazione di Cercis siliquastrum L. Azione dell'acido gibberellico e ruolo dell'endosperma nel fenomeno della dormienza

Abstract

Further research on the germination of Cercis siliquastrum L. Effect of gibberellic acid (GA₃) and role of endosperm in dormancy.—In order to locate the causes of the dormancy in Cercis siliquastrum L., researches have been carried out also on non-scarified seeds without integument, as well as on isolated embryos.

We have noted that gibberellic acid can substitute the cold treatment to interrupt the dormancy and we have also investigated the optimal concentrations.

The results we have obtained do not show the inhibition to be located in the integument and point out a determinant role of the endosperm.

Histological investigations are being carried out to study better the possible occurrence of a mechanical restraint imposed by the albumen on the non-dormant embryo.     

Tegumento seminale e germinazione in Cercis siliquastrum L.

Abstract

Seminal integument and germination of Cercis siliquastrum L. – A histological study of the seminal integument of Cercis siliquastrum L. has been carried out, in order to explain whether the obstacle to the germination, removed by a cold-treatment, was caused by a mechanical action of the integument itself. We have noted that both the cold-treated seeds which germinate and the non-treated control seeds which don't germinate show in the long run the same modifications. We have therefore come to the conclusion that the inability to germinate found in the non-treated seeds is not due to the mechanical resistance of the integument and we think it necessary to return to further researches, also at a biochemical level.     

Untersuchungen über die Endospermschleime der Samen von Cercis siliquastrum L. und Ononis natrix L

Die Samen der Caesalpiniacee Cercis siliquastrum sowie die der Papilionacee Ononis natrix enthalten im unterschiedlich stark entwickelten Endosperm quellbare Zellwandschleime. Die Samen von Ononis natrix besitzen ein vergleichsweise gering entwickeltes Endosperm, jedoch sind die einzelnen Zellen bis zur völligen Reduktion des Lumens schleimerfüllt. Bei Wasserzugabe quellen diese Zellwandschleime beider Arten unterschiedlich stark auf. Die Anfärbbarkeit der Endospermschleime wird anhand der Samen von Cercis siliquastrum für verschiedene Farbstoffe beschrieben. Zur näheren Charakterisierung der Quellbarkeit der Endospermschleime werden Quellungsindex sowie Viskositätsveränderung wäßriger Lösungen untersucht. Besonderes Interesse gilt der Untersuchung der Endospermschleime während der Reifung und Keimung der Samen. Dazu werden aus zerkleinerten unreifen, reifen und gekeimten Samen die Schleimstoffe extrahiert, sauer hydrolysiert und chromatographisch analysiert. Anhand chromatogrammspek-tralphotometrischer Untersuchungen ließ sich für die unterschiedlichen Entwicklungsstadien der Samen das Verhältnis von Galaktose/Mannose ermitteln. Dabei wurden zwischen reifenden, reifen und gekeimten Samen von Ononis natrix nur geringe Schwankungen in der Zusammensetzung des Galaktomannans nachgewiesen. Demgegenüber nimmt bei heranreifenden Samen von Cereis siliquastrum der Galaktosegehalt des Galaktomannans bis zur Reife zu und während der Keimung deutlich ab.     

Effects of seed chilling or GA3 supply on dormancy breaking and plantlet growth in Cercis siliquastrum L.

Germination and post-germination events have been compared in seeds of Cercis siliquastrum whose dormancy was removed by fulfilling the natural chilling requirement or by exogenous GA₃ application.Compared to the chilled ones, the GA₃ treated seeds showed precocious embryo growth and an earlier reserve mobilization, which started before radicle emergence.Although the hormonal application was interrupted at seed germination, the plantlets of Cercis siliquastrum that originated from GA₃-supplied seeds were taller than those from chilled ones. Moreover, they produced a greater number of leaves but a reduced root mass and had some difficulty in maintaining a good water balance.Thus, the treatment of Cercis siliquastrum seeds with exogenous GA₃ broke dormancy and induced germination, but also caused long-lasting consequences on morphogenesis of the growing plantlet.     

Seed of Cercis siliquastrum L (Leguminosae,Caesalpinioideae): Reserves and their Utilization after Germination

An ultrastructural study on the reserves stored in cotyledons and endosperm and on their utilization after germination has been carried out in Cercis siliquastrum seeds. The observations have shown that all the cotyledonal reserves of proteins and lipids are used during seedling growth. However, inside the endosperm cells only the protein reserves are depleted, and large quantities of lipids remain undigested. In both cell walls and intercellular spaces of the endosperm cells huge masses of polysaccharide reserves are stored. However, only the polysaccharides inserted in the cell walls are dismantled, while those located in the intercellular spaces are not attacked by the lytic enzymes. Some hypotheses regarding the possible roles of those endospermic non-nutritional materials in the strategies of seed germination and seedling growth are suggested.     

New invasive bruchine species (Chrysomelidae: Bruchinae) in the fauna of Romania,with a review on their distribution and biology

Four allochthonous seed beetles, associated with Gleditsia triacanthos L., Albizia julibrissin Durraz. and Cercis siliquastrum L., are reported from Romania for the first time. They are Megabruchidius dorsalis (Fåhraeus, 1839), M. tonkineus (Pic, 1914), Bruchidius terrenus (Sharp, 1886) and B. siliquastri Delobel, 2007 respectively. Their distribution (native, in Europe and Romania) is reviewed. Notes on biology are provided and morphological characters for the identification of these species are discussed. We also provide information about the parasitoid assemblages associated with these seed beetles, three of the parasitoid–host relationships being reported here for the first time.     

Studies on the Dormancy of Calluna vulgaris (L.) Hull, During Winter: Classification of Dormancy

Experiments are described in which plants of Calluna vulgariswere transferred from a high altitudinal blanket bog to controlledenvironment rooms under a range of conditions, to determinethe type of dormancy mechanism which occurs in this speciesduring the winter months. It was found that in autumn, Callunaexhibits semi-dormancy, bud break not occurring under shortphotoperiods. From December onwards, bud break will occur under short photoperiodsif warm temperatures are applied; at this time the plants arein a state of post-dormancy. Calluna lacks a period of truedormancy since it can always be forced to resume growth by longphotoperiods. Although in autumn, plants will not break dormancy under shortdays, after experiencing the natural outdoor conditions of winter,they will break dormancy equally readily under long and shortdays when brought into warm controlled environment rooms inthe spring. Calluna vulgaris (L.) Hull., heather, dormancy, pre-dormancy, post-dormancy, semi-dormancy     

Studies on the Dormancy of Calluna vulgaris (L.) Hull, during Winter: The Effect of Photoperiod and Temperature on the Induction of Dormancy and the Annual Cycle of Development

The effects of daylength and temperature on the induction ofdormancy in shoots of Calluna vulgaris were investigated usingcontrolled environment growth rooms. Short days did not induce dormancy in Calluna but floweringwas inhibited and shoots having a characteristic end-of-seasonmorphology were formed. Short days combined with low temperaturesarrested growth but the depth of dormancy was not as great asthat of plants in the field in late autumn. Long days combinedwith low temperature did not induce dormancy or the end-of-seasonmorphology. Results from the growth room experiments may be interpretedin relation to the annual cycle of development of Calluna underfield conditions. Calluna vulgaris (L.), photoperiod, temperature, dormancy, flowering, annual cycle of development     

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     

Apple Fruit Bud Development and Growth; Analysis and an Empirical Model

Analysis of the information available on apple bud developmentand growth after dormancy leads to an empirical model of growthto full bloom. The analysis and model are set in the frameworkof the physiological mechanisms considered to be responsiblefor dormancy and subsequent bud growth. It is necessary to introducean arbitrary ‘growth unit’ scale to describe theseprocesses quantitatively, which is done by the equation G = A/(I+be^–k(I).P) where G and A are in growth units, the value of k is controlledby a dormancy index I and P is a temperature summation. Themodel fulfils the main requirements laid down for it and thevalues of P at full bloom, derived from controlled environmentwork and field observations, are very similar.     

Bud Dormancy in the Kiwi Fruit, Actinidia chinensis Planch

A study of lateral bud dormancy in Actinidia chinensis has shownthat true dormancy can be induced, especially in short daysat warm and constant temperatures This dormancy can be brokenquantitatively by chilling but temperatures as high as 10 °Care effective The dormancy appears to be due to an inhibitor(possibly ABA), apparently stored in the special bud cover aspecial structure in Kiwi fruit which may represent fused stipulesRemoval of the cover also admits oxygen and light, both of whichhave promoting effects on bud break Application of ABA enhancesdormancy (as do crude extracts tentatively identified as ABA)while GA₃ application enhances dormancy before chilling andpromotes bud break only after chilling Actinidia chinensis, Kiwi fruit, dormancy, abscissic acid, gibberellic acid, chilling     

Are Seasonal Dormancy Patterns in Arabidopsis thaliana Regulated by Changes in Seed Sensitivity to Light, Nitrate and Gibberellin?

Imbibed seeds of Arabidopsis thaliana (L.) Heynh., passed annuallythrough a pattern of changes in dormancy. Dormancy was brokenin summer and re-induced in autumn-winter. A second small germinationflush occurred in early spring. The role of sensitivity to light,nitrate and gibberellins (GAs) in regulating annual dormancypatterns and germination was studied with the use of GA-deficient(gal-2) and wild-type seeds. Dark-incubated seeds were exposedto a natural temperature regime for periods up to 18 monthsand at regular intervals germination capacity of portions ofseeds was tested at laboratory conditions. Germination datafitted as logistic dose response curves showed that sensitivityto light varied with the seasons in both genotypes. From interpretationof curve parameters, it is proposed that the observed sensitivitychanges involve alterations in the number of receptors, in thebinding characteristics of the receptors and/or in the responsechain initiated by ligand-receptor interaction. In this responsechain GA biosynthesis is stimulated (wild type) and sensitivityto GAs is enhanced (wild type, gal -2). GA sensitivity is alsodirectly influenced by temperature, thus without the interferenceof light. However, the significance of direct regulation ofGA requirement seemed to diminish with prolonged incubationoutdoors, whereas reversible changes in light sensitivity remainedclear. Therefore, we propose that seasonal dormancy patternsare mainly regulated by changes in sensitivity to light. GAsensitivity contributes to this pattern but is not primarilycontrolling dormancy. The GA requirement for germination isobvious as gal-2 seeds did not germinate at any time of theyear when deprived of applied GAs. However, GA biosynthesisis not required for dormancy control, as a dormancy patternwas also observed in the absence of the capacity to synthesizeGAs. Nitrate or sensitivity to nitrate did not contribute tothe regulation of dormancy and germination of this species.Copyright1994, 1999 Academic Press Arabidopsis thaliana (L.) Heynh., curve fitting, dormancy, fluence response curve, germination, gibberellin, gibberellin dose response curve, hormone mutant, light, mouse-ear-cress, nitrate, phytochrome, receptor, seasonal dormancy pattern, sensitivity     

Seed Coat Dormancy in Two Species of Grevillea(Proteaceae)

The role played by the seed coat in seed dormancy of Grevillealinearifolia(Cav.) Druce and G. wilsonii(A. Cunn.) was testedby a series of manipulations in which the seed coat was dissectedand removed, dissected and returned to the decoated seed, ordissected, removed and given a heat shock, and returned to thedecoated seed. Germination of intact seeds of both species wasalso examined after exposure to heat shock, smoke, or heat shockand smoke combined. Water permeability of the seed coat wasinvestigated by examining imbibition. For intact seeds, virtuallyno germination occurred under any treatment (G. wilsonii), orgermination was increased by exposure to either heat or smoke(G. linearifolia). Removal of the seed coat led to germinationof all decoated seeds for G. linearifolia, or a proportion ofdecoated seeds for G. wilsonii. Inclusion of smoked water inthe incubation medium led to a higher proportion of decoatedseeds germinating for G. wilsonii. Returning the seed coat,either with or without heat shock to the seed coat, did notsignificantly affect germination in either species. Seed coatswere permeable to water in both species. For the two Grevilleaspecies, there were different dormancy mechanisms that werecontrolled by the seed coat (G. linearifolia) or by both theseed coat and embryo (G. wilsonii). Copyright 2000 Annals ofBotany Company Grevillea linearifolia, Grevillea wilsonii, dormancy, seed coat dormancy, seed coat permeability, smoke, heat shock, germination     

Breaking of Seed Dormancy by Nitrate as a Gap Detection Mechanism

Germination of Planlago lanceolata seeds buried in a chalk grasslandwas higher in bare soil than in vegetated soil, and measurementof soil nitrate concentrations showed that they were high enoughto account for this stimulation. When seeds of P. lanceolatawere sown in pots of soil with or without plants, and wateredwith nutrient solution containing either no nitrate, or 14 mMnitrate (sufficiently high that not all nitrate was absorbedby the plants), the presence of plants inhibited germinationonly when the nutrient solution contained no nitrate. It wasconcluded that breaking of seed dormancy by nitrate can functionas a gap detection mechanism if nitrate concentrations in baresoil are high enough to break seed dormancy, but are too lowto break dormancy when vegetation is present Plantago lanceolata, seed, dormancy, germination, nitrate, gap detection     

Localization of Glucose-6-phosphate Dehydrogenase Activity in Seeds and its Possible Involvement in Dormancy Breakage

A quantitative cytochemical analysis of glucose-6-phosphatedehydrogenase activity of deeply dormant seeds of Avena fatuashowed that although the enzyme activity is present in mostcell types of the embryo and seed, it is only in the embryothat activity is increased on treatment with GA₃ to break dormancy.This would appear to happen prior to any measurable embryonicaxis growth, and supports the idea that activation of the pentosephosphate pathway is an early event in dormancy break. A similar,though less marked, change occurred in less dormant seeds ofA. fatua, but could not be detected in dormant seeds of Lactucasaliva. Dry seeds of L. sativa and weakly dormant A. fatua containedtwice the activity seen in seeds imbibed with either water orGA₃, indicating that this might be a marker of low levels ofdormancy. Avena fatua, Lactuca sativa, seeds, dormancy, pentose phosphate pathway, cytochemistry, glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase     

A Technique for Determining Quantitative Expressions of Dormancy in Seeds

A method of quantifying the heterogeneity of dormancy withinseed populations is described. The method compares germinationresponses of unstratified and stratified seeds of Pinus taedaL. (loblolly pine). Mathematical functions were fitted to cumulativegermination curves of unstratified and stratified seeds andfunctions were integrated to determine areas beneath respectivecurves. The area between respective curves was calculated bydifference and was considered to be a measure of dormancy withinseed lots. The method may be used to help identify various controlsof seed dormancy. seed germination, stratification, germination curves, Pinus taeda, loblolly pine, dormancy     

The Expression of an Abscisic Acid-Responsive Glycine-Rich Protein Coincides with the Level of Seed Dormancy in Fagus sylvatica

By differential screening of a cDNA library constructed frompoly (A⁺) RNA of ABA-treated seeds of Fagus sylvatica L., wehave isolated an ABA-responsive clone that is present in dormantseeds and under conditions that maintain dormancy, but it tendsto disappear under conditions breaking seed dormancy. A searchof the sequence data bases showed that the clone codes for aGlycine-Rich Protein and has sequence similarity to RNA-bindingproteins. The clone, which exibits the characteristics of lea-genes,is up-regulated by ABA and down-regulated by GA3. Paclobutrazolabolishes the effect of GA³, which is restored upon additionof GA3. The possible relationship of this Glycine-Rich Proteinto seed dormancy in F. sylvatica is discussed. (Received May 23, 1997; Accepted September 22, 1997)     

Growth Substances in Relation the the Rooting of Salix fragilis Cuttings

An attempt has been made to correlate seasonal variations inthe rooting responses of Salix fragilis cuttings with theircontent of growth-promoting substances. Although they were bothlow in early dormancy and higher in late dormancy and in summerthere was not an exact correlation in all months. It was found that extracts of S. fragilis cuttings taken indormancy strongly inhibited the action of IAA on the growthof Avena coleoptile segments. This inhibitory influence wasless in extracts of cuttings taken at the end of dormancy andin summer. Extracts of cuttings which had been left in waterto root showed a striking decrease in their inhibitory actionon IAA.     

Effects of Kinetin and Salinity on Germination of Tomato, Barley and Cotton Seeds

The effects of kinetin and the interaction between kinetin andsalinity on seed germination of three plant species namely Lycopersiconesculentum, Hordeum vulgare and Gossypium hirsutum were studiedKinetin was applied exogenously to the seeds in order to determinewhether this growth-promoting hormone would promote germinationand to see if osmotically-induced dormancy caused by NaCl couldbe alleviated The results indicate that kinetin is capable ofbreaking dormancy in these species and there is a significantinteraction with salinity in tomato and cotton Kinetin, germination, salinity, water stress, salt stress, Lycopersicon esculentum Mill, tomato, Hordeum vulgare L, barley, Gossypium hirsutum L, cotton     

Changes in Ultrastructure and Abscisic Acid Level, and Response to Applied Gibberellins inTaxus maireiSeeds Treated With Warm and Cold Stratification

Seeds ofTaxus maireiare known for their deep dormancy whichcan only be broken by a procedure involving warm stratificationfollowed by cold stratification. Treatments with alternatingtemperatures of 25/15 or 23/11 °C (12 h light) for 6 monthsfollowed by 5 °C for 3 months were successful in overcomingseed dormancy. After 6 months of warm stratification, cytologicalchanges observed included: enlargement of the embryo; a decreasein the number of lipid bodies; appearance of ER; and increasesin mitochondria, plastids, dictyosomes, vacuoles and microbodiesin the shoot apical meristem. Cold stratification followingthe warm treatment induced cell division, and one or two distinctnucleoli in the shoot apical meristem cells were observed. Bothwarm and cold stratification reduced endogenous ABA concentrationsfrom the original 8888 pg per freshly harvested seed to 392and 536 pg, respectively. Treatment with exogenous gibberellinsafter seeds had been warm-stratified showed that GA₄and GA₇wereeffective at promoting seed germination, but GA₃was not. Theseresults suggest that the strong seed dormancy ofT. maireicouldbe caused by a high ABA content and underdevelopment of theembryos in freshly shed seeds. We conclude that warm stratificationwith alternating temperatures increases the growth of embryosby cell expansion and enlargement and decreases ABA content,but seeds still remain ungerminated. Cold stratification mayinduce the response to GAs and initiate cell division resultingin release from physiological dormancy and subsequent germinationofT. maireiseeds.Copyright 1998 Annals of Botany Company Taxus mairei; ultrastructure; abscisic acid; gibberellin; seed dormancy; stratification; germination.