Seed dormancy in relation to seed storage behaviour in Acer

Dormancy in seeds of Acer opalus is shown to be mainly caused by the seed coats, although a slight embryo dormancy exists in fresh seeds. The ability to germinate after drying indicates that seed storage behaviour is orthodox. Recalcitrant seeds were heavier than orthodox seeds not only within section Acer but also within the whole genus after statistical control of phylogeny, through a phylogenetic ANOVA with data from two different Acer phylogenies. An evolutionary change from orthodox to recalcitrant behaviour is postulated for genus Acer , but this change appears not to have been accompanied by a change in seed dormancy, at least in the taxonomic section in which Acer opalus belongs.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 203–208.     

Can seed characteristics or species distribution be used to predict the stratification requirements of herbs in the Australian Alps?

The germination requirements of 19 herbs in the Australian Alps were investigated to determine which species may be sensitive to predicted climate changes. Seeds were subjected to factorial treatments of cold stratification for 0, 4, 8 and 12 weeks, followed by incubation at constant temperatures of 10, 15, 20 and 25 °C and alternating temperatures of 20/5 and 20/10 °C. Germination responses were used to identify stratification‐dependent species, to classify dormancy and to determine optimum conditions for laboratory germination. Ordinal logistic regression was used to determine whether the duration of stratification required for ≥ 50% germination could be predicted by seed weight, seed length, embryo : seed ratio or species distribution (latitudinal range, altitudinal range and maximum altitude). The Kruskal–Wallis test was used to determine any significant differences in stratification requirement between endospermic and non‐endospermic seeds. Species varied considerably in their response to the treatment combinations, and therefore their dormancy class. No significant predictors of stratification requirement were identified by ordinal logistic regression (P > 0.9); however, there was a significant difference in stratification requirement between endospermic and non‐endospermic seeds (P = 0.003). Species with non‐endospermic seeds did not require any stratification to germinate well over a range of temperatures, and appear most likely to remain stable or expand in range in response to climate warming. Conversely, the need for ≥ 8 weeks of cold stratification was associated with the presence of endosperm and either a restricted distribution or upland ecotypes of widely distributed species. Alpine species with endospermic seed and a restricted distribution are most likely to contract in range under climate change and would be appropriate to prioritize for ex situ conservation. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 172 , 187–204.     

Structure and development of Medicago truncatula pod wall and seed coat

BACKGROUND AND AIMS: Medicago truncatula has gained much attention as a genomic model species for legume biology, but little is known about the morphology of its pods and seeds. Structural and developmental characteristics of M. truncatula pod walls and seed coats are presented. METHODS: Plants of M. truncatula ecotype A17 were grown under controlled conditions in a greenhouse. Flowers were date-tagged at anthesis, so that pods of known age could be collected. Harvested pods were fixed and sectioned for light microscopy. Structural attributes of pod walls and seed coats were characterized at four time points throughout early to mid-stages of pod development (3, 6, 13 and 20 d post-pollination). KEY RESULTS: Basic features of the pod wall are an exocarp comprised of a single epidermal layer, a mesocarp with seven to 14 layers of parenchyma cells, and an endocarp composed of an inner epidermal cell layer and three to five layers of sclerenchyma cells adjacent to it. Vascular bundles are abundant in the pod wall and include one lateral carpellary bundle, one median carpellary bundle and nine to 12 vascular bundles, all embedded within the mesocarp parenchyma. Seed coat features include an epidermal layer of macrosclereids, a sub-epidermal layer of osteosclereids, and two to five rows of internal parenchyma cells. The hilar region contains the tracheid bar and the chalazal vascular bundle, the latter of which expands to form only two short branches. CONCLUSIONS: This characterization provides a needed understanding of pod structure and development in this model legume, and should facilitate various molecular investigations into legume fruit and seed biology.     

Development of ovule,fruit and seed of Xyris (Xyridaceae,Poales) and taxonomic considerations

The development of the ovule, fruit and seed of Xyris spp. was studied to assess the embryological characteristics of potential taxonomic usefulness. All of the studied species have (1) orthotropous, bitegmic and tenuinucellate ovules, with a micropyle formed by both the endostoma and exostoma; (2) a cuticle in the ovules and seeds between the nucellus/endosperm and the inner integument and between the inner and outer integuments; (3) helobial, starchy endosperm; (4) a reduced, campanulate and undifferentiated embryo; (5) a seed coat formed by a tanniferous endotegmen, endotesta with thick‐walled cells and exotesta with thin‐walled cells; and (6) a micropylar operculum formed from inner and outer integuments. The pericarp is composed of a mesocarp with cells containing starch grains and an endocarp and exocarp formed by cells with U‐shaped thickened walls. The studied species differ in the embryo sac development, which can be of the Polygonum or Allium type, and in the pericarp, which can have larger cells in either endocarp or exocarp. The Allium‐type embryo sac development was observed only in Xyris spp. within Xyridaceae. Xyris also differs from the other genera of Xyridaceae by the presence of orthotropous ovules and a seed coat formed by endotegmen, endotesta and exotesta, in agreement with the division of the family into Xyridoideae and Abolbodoideae. © 2015 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 619–628.     

Multiple pleurograms in Chamaecrista Moench (Leguminosae, Caesalpinioideae)

According to the literature, the seeds of Chamaecrista lack pleurograms and have pitted testas aligned in vertical lines. Preliminary observations have revealed that these small structures consist of superficial alterations of the testa that are coloured differently to the rest of the seed coat and stand out as pits. However, no anatomical inspection has yet determined the precise composition of these pits. The present work examined the morphology, surface micromorphology, anatomy, and histochemistry of the seed coat of mature seeds of C. desvauxii var. latistipula , C. flexuosa , and C. nictitans var. patellaria in order to elucidate the structural nature of the seed coat pits. For this, seed coats were studied using scanning electron microscopy and light microscopy. Structural modifications were examined in the seed coats of the studied species, and variations were noted in the mucilaginous layer, in the thickness of the palisade layer, and in the presence of larger hypodermic cells. Based on the anatomical features observed, and comparing these with published data on pleurograms in the Caesalpinioideae, it was determined that the structures referred to previously as tegumental pits on Chamaecrista seeds are actually small and numerous pleurograms, reported here for the first time.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 487–492.     

Reproductive biology in Anagyris foetida L. (Leguminosae), an autumn–winter flowering and ornithophilous Mediterranean shrub

As most plants of the Mediterranean region bloom in spring, there have been few studies of the reproductive biology of species with autumn–winter flowering. In this study, we investigate the breeding system of Anagyris foetida , one of the few shrubs that blooms at this time. The floral, phenological, and reproductive aspects of two populations of this Mediterranean legume from south-west Spain were studied via field and laboratory experiments. The variability of fruit and seeds was studied in another 12 Iberian populations with respect to certain meteorological parameters (temperature and rainfall). Anagyris foetida shows cauliflory, marked floral longevity, and adichogamy. The peak of flowering is in January–February. It is self-compatible, with no clear advantage of cross- over self-pollination, and with virtually no autonomous self-pollination. This is because the stigma, like some other legumes, prevents the germination of pollen if its surface is not ruptured by pollinators. The number of seeds per fruit under natural pollination was positively correlated with the total rainfall during the fruiting period (from January to May), and significantly influenced the percentage of fruit weight represented by the pericarp, in the sense that the smaller the number of viable seeds in the fruit, the greater the percentage of pericarp weight.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 519–532.     

Morphology of fruits, seeds and embryos of Argentinian Capparis L. (Capparaceae)

Embryos, seeds and fruits of four species of Capparis L. (Capparaceae) from Argentina are described in this paper: C. flexuosa (L.) L. sensu lato, C. retusa Griseb., C. speciosa Griseb. and C. tweediana Eichl. Chlorophyllous embryos are found in C. flexuosa and C. retusa , species with thin seed coats, dehiscent siliques, and somewhat fleshy red endocarps. Nonchlorophyllous embryos are found in the berry-fruited C. speciosa and C. tweediana , the former with leathery indehiscent fruit wall, the latter with thin-walled dehiscent berries with massive fleshy pulp. The pulp is permeated by seed coat hairs in C. tweediana . The embryos of C. flexuosa , C. retusa and C. tweediana belong to the 'Axile Division, Foliate Subdivision, and Folded Type' of the classification devised by A. C. Martin in 1946. Some features of the embryo of C. speciosa (which are not considered in Martin's classification), support a new subdivision (Massive) and a new morphological type (Unequal cotyledons), characterized by profound anisocotyly, globose shape of the major cotyledon, presence of suberized cells and an undeveloped radicle. Anatomical studies of embryos and seedlings confirm the anisocotyly.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 209−218.     

The generic position of Lithraea brasiliensis Marchand (Anacardiaceae): evidence from fruit and seed structure

In Lithraea brasiliensis Marchand the exocarp is characterized by brachysclereids and the parenchymatous mesocarp by large secretory ducts; inner sclerenchymatous ridges are absent in die mesocarp. The stratified endocarp s. s. comprises a crystal layer, palisade-like brachysclereids, osteosclereids and macrosclereids. The osteosclereids are characterized by a distinct light line or linea lucida , which has hitherto also been recorded in a species of Rhus. In the partially pachychalazal seed, a typical Anacardiaceae-like hypostase typifies the chalazal part of the seed coat, while the integumentary seed coat reveals a well preserved outer epidermis, a compressed endotegmen and well developed inner cuticular layer. Our comparison of die characters of the ovule, fruit and seed of L. brasiliensis with those of various species of Rhus and other genera of the tribe Rhoeae (some closely related) presents evidence that L. brasiliensis could be most closely associated with the genus Rhus.     

Standard yet unusual mechanisms of long-distance dispersal: seed dispersal of Corymbia torelliana by bees

Mellitochory, seed dispersal by bees, has been implicated in long-distance dispersal of the tropical rain forest tree, Corymbia torelliana (Myrtaceae). We examined natural and introduced populations of C. torelliana for 4 years to determine the species of bees that disperse seeds, and the extent and distance of seed dispersal. The mechanism of seed dispersal by bees was also investigated, including fruit traits that promote dispersal, foraging behaviour of bees at fruits, and the fate of seeds. The fruit structure of C. torelliana , with seed presented in a resin reward, is a unique trait that promotes seed dispersal by bees and often results in long-distance dispersal. We discovered that a guild of four species of stingless bees, Trigona carbonaria, T. clypearis, T. sapiens , and T. hockingsi, dispersed seeds of C. torelliana in its natural range. More than half of the nests found within 250 m of fruiting trees had evidence of seed transport. Seeds were transported minimum distances of 20–220 m by bees. Approximately 88% of seeds were dispersed by gravity but almost all fruits retained one or two seeds embedded in resin for bee dispersal. Bee foraging for resin peaked immediately after fruit opening and corresponded to a peak of seed dispersal at the hive. There were strong correlations between numbers of seeds brought in and taken out of each hive by bees ( r =  0.753–0.992, P  < 0.05), and germination rates were 95 ± 5%. These results showed that bee-transported seeds were effectively dispersed outside of the hive soon after release from fruits. Seed dispersal by bees is a non-standard dispersal mechanism for C. torelliana, as most seeds are dispersed by gravity before bees can enter fruits. However, many C. torelliana seeds are dispersed by bees, since seeds are retained in almost all fruits, and all of these are dispersed by bees.     

Ovule morphology, embryogenesis and seed development in three Hylocereus species (Cactaceae)

Pre-embryonic and embryonic stages and seed developments were studied in the diploids Hylocereus monacanthus and Hylocereus undatus and the tetraploid Hylocereus megalanthus. Ovule morphology was similar among species except for micropyle entrance. H. monacanthus had the thickest and most robust suspensor. Embryo developmental time, measured from fertilization to maturity, was significantly more prolonged in H. megalanthus. Typical to Cactaceae, the seed coat was formed by one layer of sclerenchymatous cells, but was more lignified in H. megalanthus. Morphological features common to all species included (1) cellular type endosperm with independent patterns of development in the chalazal and micropylar zones, forming a haustorium layer from the chalazal zone to the embryo; (2) an endothelial layer surrounding the embryo sac almost complete; (3) a nucellar summit growing into the micropyle; and (4) a placental obturator and a funicle connecting the ovarian tissue to the ovule. Seed development was typically endospermic (exendospermic orthodox seeds). Anomalies included two egg cells in the same embryo sac, two embryos developing in the same ovule, and embryos developing from the chalazal pole region. Total seed number and seed viability were significantly lower in H. megalanthus than in the other two taxa. Embryos at different developmental stages were observed in aborted H. megalanthus seeds.     

Gynoecium, fruit and seed structure of Paullinieae (Sapindaceae)

Despite an emphasis on fruit characters in Paullinieae taxonomy, few detailed morphological and anatomical studies of the gynoecia, fruits and seeds exist. The aims of the present study were (1) to provide a detailed documentation of gynoecium, fruit and seed structure and ontogeny in selected Paullinieae taxa; (2) to determine whether the gynoecium, seed and seedling provide additional characters of systematic value within the tribe; and (3) to relate the structural findings to mechanisms of fruit dehiscence and dispersal within these taxa. Newly described characters of systematic value within Paullinieae are shape and surface of the obturator, type of pollen tube transmitting tract, indumentum of the inner and outer surface of the carpels, ovary wall anatomy, aril anatomy, pseudo-hilum form, seedling germination mode and structure of first leaves. The fruits of Paullinia are septifragal, and conspicuous colour contrasts between the pericarp, aril and seed in most species of this genus are suggestive of a bird dispersal syndrome. Interestingly, it appears that relatively minor structural changes are associated with switches to rodent dispersal in Paullinia sphaerocarpa and water dispersal in P. clathrata and P. hystrix. Anemochorous fruits are septifragal ( Cardiospermum and Urvillea ) or schizocarpic ( Houssayanthus , Lophostigma , Serjania ). They are structurally similar and Cardiospermum with septifragal capsules may also show septicidal dehiscence.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 147 , 159–189.     

Ovule,fruit and seed development in Abolboda (Xyridaceae,Poales): implications for taxonomy and phylogeny

Xyridaceae belongs to the xyrid clade of Poales, but the phylogenetic position of the xyrid families is only weakly supported. Xyridaceae is divided into two subfamilies and five genera, the relationships of which remain unclear. The development of the ovule, fruit and seed of Abolboda spp. was studied to identify characteristics of taxonomic and phylogenetic value. All of the studied species share anatropous, tenuinucellate and bitegmic ovules with a micropyle formed by the inner and outer integuments, megagametophyte development of the Polygonum type, seeds with a tanniferous hypostase, a helobial and starchy endosperm and an undifferentiated embryo, seed coat derived from both integuments with a tanniferous tegmen and a micropylar operculum, and fruits with a parenchymatous endocarp and mesocarp and a sclerenchymatous exocarp. Most of the ovule and seed characteristics described for Abolboda are also present in Xyris and may represent a pattern for the family. Abolboda is distinguished by the ovule type, endosperm formation and the number of layers in the seed coat, in agreement with its classification in Abolbodoideae. The following characteristics link Xyridaceae to Eriocaulaceae and Mayacaceae, supporting the xyrid clade: tenuinucellate, bitegmic ovules; seeds with a tanniferous hypostase, a starchy endosperm and an undifferentiated embryo; and a seed coat with a tanniferous tegmen. A micropylar operculum in the seeds of Abolboda is described for the first time here and may represent a synapomorphy for the xyrids. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175 , 144–154.     

A water drop-shaped slingshot in plants: geometry and mechanics in the explosive seed dispersal of Orixa japonica (Rutaceae)

Background and AimsIn angiosperms, many species disperse their seeds autonomously by rapid movement of the pericarp. The fruits of these species often have long rod- or long plate-shaped pericarps, which are suitable for ejecting seeds during fruit dehiscence by bending or coiling. However, here we show that fruit with a completely different shape can also rely on pericarp movement to disperse seeds explosively, as in Orixa japonica.MethodsFruit morphology was observed by hard tissue sectioning, scanning electron microscopy and micro-computed tomography, and the seed dispersal process was analysed using a high-speed camera. Comparisons were made of the geometric characteristics of pericarps before and after fruit dehiscence, and the mechanical process of pericarp movement was simulated with the aid of the finite element model.Key ResultsDuring fruit dehydration, the water drop-shaped endocarp of O. japonica with sandwich structure produced two-way bending deformation and cracking, and its width increased more than three-fold before opening. Meanwhile the same shaped exocarp with uniform structure could only produce small passive deformation under relatively large external forces. The endocarp forced the exocarp to open by hygroscopic movement before seed launching, and the exocarp provided the acceleration for seed launching through a reaction force.ConclusionsTwo layers of water drop-shaped pericarp in O. japonica form a structure similar to a slingshot, which launches the seed at high speed during fruit dehiscence. The results suggest that plants with explosive seed dispersal appear to have a wide variety of fruit morphology, and through a combination of different external shapes and internal structures, they are able to move rapidly using many sophisticated mechanisms.     

Role of trichomes and pericarp in the seed biology of the desert annual Lachnoloma lehmannii (Brassicaceae)

In many angiosperms, the fruit rather than the seed is the dispersal/germination unit, and this is the case with Lachnoloma lehmannii, a desert annual ephemeral in central southwestern Asia with indehiscent nonmucilaginuous silicles covered with trichomes. The primary aim of this study was to assess the role of trichomes and pericarp in dispersal, anchorage of diaspores, and seed germination of this species. Mature silicles are dispersed by wind and gravity, and trichomes not only significantly increased their dispersal distance, adherence to sandy soil particles, mass of water imbibed and moisture content, but also decreased the rate of water loss and moisture content of seeds. A significantly higher percentage of seeds within silicles than of isolated seeds retained viability after exposure to 60 °C for 24 h. Seed dormancy is due to the pericarp and to nondeep physiological dormancy, as shown by the increase in germination percentage of isolated seeds following dry storage and treatment with GA₃. Removal of pericarp increased germination of 6-month-old seeds from 0 to 80–90 %, and leachate from both pericarp and trichomes significantly inhibited germination of isolated seeds. Ninety-five percent of seeds within silicles buried in soil for 2 years were viable, but only 28 % of them germinated in light at 15/2 °C; thus L. lehmannii forms a persistent soil seed bank. The pericarp and its trichomes may maximize plant fitness by determining the settlement location of silicles, thus helping to ensure that seeds germinate during the cool season for seedling survival in the desert environment.     

Transfer cells in the seeds of Boraginales

The presence of transfer cells (TCs) in the seeds of Boraginales (Boraginaceae s.s. , Hydrophyllaceae, Heliotropiaceae, Ehretiaceae, Cordiaceae and Lennoaceae) has been reported but has not hitherto been studied systematically. This study, surveying the seed anatomy of 50 species of Boraginales, demonstrates that in Heliotropiaceae, Cordiaceae, Ehretiaceae and Lennoaceae, TCs are found in an uninterrupted course from the placenta via the funicle to the seed coat. These families are characterized by indehiscent fruits with a protective endocarp. The TCs may act as a sponge, thus promoting rapid germination when sufficient water is available. In Hydrophyllaceae, which have capsular fruits, TCs are often found but have a different structure and are restricted to the seed coat. Boraginaceae s.s. on the other hand are characterized by a complete absence of TCs in their seeds. The presence of TCs in seeds is considered as a synapomorphic trait and appears to be phylogenetically informative.  © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 140 , 155−164.     

Anatomical and chemical characteristics of the seed coat of <i>Medicago sativa</i> L. (alfalfa) cv. Baralfa 85 seeds and their association with seed dormancy

Seeds of alfalfa (Medicago sativa L.) can exhibit seedcoat imposed dormancy, which produces hard seeds within a seed lot. These seeds do not germinate because they do not imbibe water due to a barrier to water entry in the seed coat. The aim of this work was to analyze the anatomical and chemical characteristics of the testa of alfalfa seeds with respect to water permeability levels. The anatomy of seeds of the cv. Baralfa 85 was studied and structural substances, polyphenols, tannins and cutin present in the testa of seeds of different water permeability levels were determined. The anatomical characteristics of the seed coat and the proportions of components were found to determine the permeability level of the seed coat, an aspect that is associated with the physical seed dormancy level. Anatomically, increased thickness of the testa was associated with a lower permeability level. The difference may be attributed to the variation in cuticle thickness, length of macrosclereids and thickness of the cell wall, and presence and development of osteosclereids. From the physiological and chemical points of view, the mechanism of physical dormancy of the testa is explained by a greater amount of components that repel water and cement the cell wall, such as polyphenols, lignins, condensed tannins, pectic substances, and a lower proportion of cellulose and hemicellulose.     

Biosynthesis, accumulation and degradation of theobromine in developing Theobroma cacao fruits

We have studied the purine alkaloid content and purine metabolism in Theobroma cacao fruits at differing growth stages: Stage A (young small fruit, fresh weight, ca. 2 g); stage B (medium size fruit, fresh weight, ca. 100 g) and stage C (large size, fresh weight, ca. 500 g). The major purine alkaloid in stage A fruits (mainly pericarp) was theobromine (0.7 micromol g(-1) fresh weight), followed by caffeine (0.09 micromol g(-1) fresh weight). The theobromine content of the pericarp decreased sharply with tissue age, and the caffeine content decreased gradually. A large amount of theobromine (22 micromol g(-1) fresh weight) had accumulated in seeds (mainly cotyledons) of stage C fruits. Theobromine was found also in the seed coat and placenta. Tracer experiments with [8-(14)C]adenine show that the major sites of theobromine synthesis are the young pericarp and cotyledons of T. cacao fruits. Limited amounts of purine alkaloids may be transported from the pericarp to seed tissue, but most purine alkaloids that accumulated in seeds appeared to be synthesised in cotyledons. Degradation of [8-(14)C]theobromine and [8-(14)C]caffeine to CO2 via 3-methylxanthine and ureides (allantoin and allantoic acid) was detected only in the pericarp of stage C fruits.     

The relationship of Sophora sect. Edwardsia (Fabaceae) to Sophora tomentosa, the type species of the genus Sophora, observed from DNA sequence data and morphological characters

Sophora tomentosa , the type species of the genus Sophora , is shown by phylogenetic analyses of rbc L and ITS sequence data to be sister to Sophora sect. Edwardsia . S. tomentosa and most of the species from sect. Edwardsia share hypogeal germination, exstipulate leaves, and terete filaments. These species have buoyant seeds, and are distributed by ocean currents throughout the pantropics ( S. tomentosa ) and around southern temperate oceanic islands (sect. Edwardsia ). S. tomentosa differs from the species of sect. Edwardsia by its frutescent growth habit, terminal elongate inflorescence and smooth-walled legume. S. macrocarpa is unusual in sect. Edwardsia as its leaves have stipules, the filaments are winged, and the legume is smooth-walled.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 439–446.     

Ontogeny of the mycoheterotrophic species Afrothismia hydra (Burmanniaceae)

The complete ontogeny of the mycoheterotrophic Afrothismia hydra (Burmanniaceae) from seed to seed dispersal is presented. The oblong–ovoidal seeds are up to 0.7 mm long. They germinate with root tissue only, disrupting the seed coat and developing a primary ovoid root tubercle. At the proximal end of the tubercle, a second tubercle arises and further root initials indicate the sequential growth of more root tubercles with filiform extensions resulting in a small root aggregate. The seed coat often remains attached to this structure. When the root aggregate enlarges, a central axis to which all roots are connected becomes visible. This axis has a growth pole where new root tubercles arise. The same growth pole will later develop into a stem with scale leaves finally terminating in a flower. Flowers develop sympodially when the mature plant is only several centimetres long. After anthesis, the corolla tube disintegrates, leaving a pyxidium which opens by means of a peculiar elongating placenta, here called 'placentophore'. The placentophore elevates the placenta with attached seeds above the flowering level and is interpreted as an adaptation to ombrohydrochory. The reduction of hypocotyl, cotyledon and primary shoot is discussed with regard to the classical germination concepts of monocotyledons and with mycoheterotrophic dicotyledons.  © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society , 2008, 157 , 31–36.