A new amine,stizolamine, from Stizolobium hassjoo

A new pyrazine derivative, stizolamine (1-methyl-3-guanidino-6-hydroxymethylpyrazin-2-one), has been isolated from seeds of Stizolobium hassjoo. This amine, which has a blue fluorescence, gives guanidine, N-methyl-alanine, oxalic acid, alanine and glycine on treatment with 6 N HCl. The permanganate oxidation product of stizolamine is 4-amino-6-methylcarbamoyl-1,3,5-triazine-2-carboxylic acid.     

Distribution of stizolamine in some leguminous plants

The seeds of 38 species of 29 genera in 21 tribes of the Leguminosae were screened for stizolamine. It was detected in 19 species of the subfamily Lotoideae. Its occurrence in Lotoideae was wide (82% in tribes, 56% both in genera and species) but sporadic. The content was fairly varied (0·249–9540 nmol/g of seeds), the largest amount occurring in Stizolobium hassjoo.     

Natural selection drives the fine-scale divergence of a coevolutionary arms race involving a long-mouthed weevil and its obligate host plant

Background

One of the major recent advances in evolutionary biology is the recognition that evolutionary interactions between species are substantially differentiated among geographic populations. To date, several authors have revealed natural selection pressures mediating the geographically-divergent processes of coevolution. How local, then, is the geographic structuring of natural selection in coevolutionary systems?

Results

I examined the spatial scale of a "geographic selection mosaic," focusing on a system involving a seed-predatory insect, the camellia weevil (Curculio camelliae), and its host plant, the Japanese camellia (Camellia japonica). In this system, female weevils excavate camellia fruits with their extremely-long mouthparts to lay eggs into seeds, while camellia seeds are protected by thick pericarps. Quantitative evaluation of natural selection demonstrated that thicker camellia pericarps are significantly favored in some, but not all, populations within a small island (Yakushima Island, Japan; diameter ca. 30 km). At the extreme, camellia populations separated by only several kilometers were subject to different selection pressures. Interestingly, in a population with the thickest pericarps, camellia individuals with intermediate pericarp thickness had relatively high fitness when the potential costs of producing thick pericarps were considered. Also importantly, some parameters of the weevil - camellia interaction such as the severity of seed infestation showed clines along temperature, suggesting the effects of climate on the fine-scale geographic differentiation of the coevolutionary processes.

Conclusion

These results show that natural selection can drive the geographic differentiation of interspecific interactions at surprisingly small spatial scales. Future studies should reveal the evolutionary/ecological outcomes of the "fine scale geographic mosaics" in biological communities.     

The genetic constitutions of complementary genes Pp and Pb determine the purple color variation in pericarps with cyanidin-3-O-glucoside depositions in black rice

The purple pericarp color in rice was controlled by two dominant complementary genes, Pb and Pp. Crossing black rice ‘Heugnambyeo’ variants with three varieties of white pericarp rice gave a segregation ratio of 9 purple: 3 brown: 4 white. The Pp genes were segregated by homozygous PpPp alleles for the dark purple pericarps, heterozygous Pppp alleles for the medium and mixed purple pericarps, and homozygous pppp alleles for either brown or white pericarps with a 1 PpPp: 2 Pppp: 1 pppp segregation ratio, indicating that the Pp allele in rice is incompletely dominant to the recessive pp allele. Among the purple seeds, the amount of cyanidin-3-O-glucoside was higher in the dark purple seeds (Pb_PpPp) than in the medium purple seeds (Pb_Pppp). Moreover, no cyanidin-3-glucoside was detected in brown (Pb_pppp) or white pericarp seeds (pbpbpppp). These findings indicated that the level of cyanidin-3-glucoside was determined by the copy number of the Pp allele. Further genotype investigation of the F₃ progeny demonstrated that the dominant Pb allele was present in either purple or brown pericarp. A 2-bp (GT) deletion from the DNA sequences of the dominant and functional Pb was found in the same DNA sequences of the recessive and non-functional pb allele. These findings suggested that the presence of at least a dominant Pb allele was an essential factor for color development in rice pericarps. In conclusion, the Pp allele in rice is incompletely dominant to the recessive pp allele; thus, the number of dominant Pp alleles determines the concentration of cyanidin-3-O-glucoside in black rice.     

The role of fleshy pericarp in seed germination and dispersal under flooded conditions in three wetland forest species

In flooded habitats, inundations affect important forest regeneration processes, such as seed dispersal and germination. The main seed dispersal mechanism used by species in Austral South American temperate swamp and riparian forests is endozoochory, which releases seeds from the fleshy pericarp. Endozoochory could be favorable or unfavorable in wetland habitats, since this mechanism exposes seeds directly to water and can, in some cases, be detrimental to germination. In this study, we studied whether or not the fleshy pericarp favors germination after the flooding period's end. Furthermore, we quantified if the number of days which the fruit was found to be floating related to its germination success. We used the seeds of three common fleshy fruit species of flooded habitats from southern Chile, the trees Luma apiculata and Rhaphithamnus spinosus, and the vine Luzuriaga radicans. We simulated flooding periods of 7, 15, 30 and 45 days submerging seeds, with and without pericarps, in water. We found that the pericarp's presence significantly increased Luma's germination success and significantly decreased that of Luzuriaga. The germination of Rhaphithamnus was low after periods of flooding in both seed treatments, with no significant differences found between them. The fruits could float for an average of one to four weeks, depending on the species, which did not relate to their germination success. These results show that germination was affected by the presence of fleshy pericarps in flooded conditions and furthermore, that flotation allows for hydrochory from one week to one month. We suggest that in swamp forests multiple seed dispersal mechanisms are advantageous, especially for fleshy-fruited species.     

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.     

Accumulation of ions during seed development under controlled saline conditions of two Suaeda salsa populations is related to their adaptation to saline environments

Controlled conditions were used to investigate the relationship between ion distribution in developing seeds of two Suaeda salsa populations and seed germination and seedling emergence. Seeds were harvested from S. salsa plants that had been treated with 1 or 400 mM NaCl for 122 (saline inland population) or 135 days (intertidal zone population) in a glasshouse. Germination and seedling emergence were evaluated under salinity. In both populations, more ions were accumulated in the pericarps of plants cultured in 400 mM NaCl than in 1 mM NaCl. Pericarps accumulated much higher ion concentrations in the intertidal zone population than in the saline inland population, while the opposite trend occurred for ion accumulation in the embryos. Seeds of plants from the intertidal zone population germinated more rapidly than those from plants of the saline inland population, regardless of the NaCl concentration during seed germination. However, seedling emergence under high salinity was lower with seeds from the intertidal zone population than with seeds from the saline inland population. In conclusion, S. salsa in the intertidal zone employs superior control of ion compartmentalization in the pericarps to tolerate salinity but requires a minimal level of ions in embryos to ensure seedling establishment in highly saline environments. This indicates that euhalophytes require salts during the mature seed stage to maintain seed viability and to ensure seedling emergence and population establishment.     

Developmental and Hormonal Regulation of Gibberellin Biosynthesis and Catabolism in Pea Fruit

In pea (Pisum sativum), normal fruit growth requires the presence of the seeds. The coordination of growth between the seed and ovary tissues involves phytohormones; however, the specific mechanisms remain speculative. This study further explores the roles of the gibberellin (GA) biosynthesis and catabolism genes during pollination and fruit development and in seed and auxin regulation of pericarp growth. Pollination and fertilization events not only increase pericarp PsGA3ox1 message levels (codes for GA 3-oxidase that converts GA₂₀ to bioactive GA₁) but also reduce pericarp PsGA2ox1 mRNA levels (codes for GA 2-oxidase that mainly catabolizes GA₂₀ to GA₂₉), suggesting a concerted regulation to increase levels of bioactive GA₁ following these events. 4-Chloroindole-3-acetic acid (4-Cl-IAA) was found to mimic the seeds in the stimulation of PsGA3ox1 and the repression of PsGA2ox1 mRNA levels as well as the stimulation of PsGA2ox2 mRNA levels (codes for GA 2-oxidase that mainly catabolizes GA₁ to GA₈) in pericarp at 2 to 3 d after anthesis, while the other endogenous pea auxin, IAA, did not. This GA gene expression profile suggests that both seeds and 4-Cl-IAA can stimulate the production, as well as modulate the half-life, of bioactive GA₁, leading to initial fruit set and subsequent growth and development of the ovary. Consistent with these gene expression profiles, deseeded pericarps converted [¹⁴C]GA₁₂ to [¹⁴C]GA₁ only if treated with 4-Cl-IAA. These data further support the hypothesis that 4-Cl-IAA produced in the seeds is transported to the pericarp, where it differentially regulates the expression of pericarp GA biosynthesis and catabolism genes to modulate the level of bioactive GA₁ required for initial fruit set and growth.     

Frugivory by introduced black rats (Rattus rattus) promotes dispersal of invasive plant seeds

Oceanic islands have been colonized by numerous non-native and invasive plants and animals. An understanding of the degree to which introduced rats (Rattus spp.) may be spreading or destroying seeds of invasive plants can improve our knowledge of plant-animal interactions, and assist efforts to control invasive species. Feeding trials in which fruits and seeds were offered to wild-caught rats were used to assess the effects of the most common rat, the black rat (R. rattus), on 25 of the most problematic invasive plant species in the Hawaiian Islands. Rats ate pericarps (fruit tissues) and seeds of most species, and the impacts on these plants ranged from potential dispersal of small-seeded (≤1.5 mm length) species via gut passage (e.g., Clidemia hirta, Buddleia asiatica, Ficus microcarpa, Miconia calvescens, Rubus rosifolius) to predation where <15% of the seeds survived (e.g., Bischofia javanica, Casuarina equisetifolia, Prosopis pallida, Setaria palmifolia). Rats consumed proportionally more seed mass of the smaller fruits and seeds than the larger ones, but fruit and seed size did not predict seed survival following rat interactions. Although invasive rat control efforts focus on native species protection, non-native plant species, especially those with small seeds that may pass internally through rats, also deserve rat control in order to help limit the spread of such seeds. Black rats may be facilitating the spread of many of the most problematic invasive plants through frugivory and seed dispersal in Hawaii and in other ecosystems where rats and plants have been introduced.     

Molecular identification of individual oak and fir trees from maternal tissues of their fruits or seeds

The applicability of DNA markers to purely maternal tissues has been scarcely addressed in trees. We have focused on non-parenchymatic maternal tissues of the fruits and seeds of pedunculate oak (Quercus robur L.) and silver fir (Abies alba Mill.) and investigated whether they can be used for a direct molecular identification of the mother trees. Total DNA with sufficient quantity and quality was extracted from single woody pericarps of acorns as well as from single dry wings of silver fir seeds. The DNA was analysed by PCR at highly polymorphic microsatellite loci. A comparison of the multi-locus genotypes from pericarps and wings with those of the respective mother trees revealed absolute identity. Thus, mother trees could be identified by genotyping their fruits or seeds. The results demonstrate the applicability of DNA fingerprinting to woody and/or dry seed tissues without the destruction of embryos and endosperm or a significant contamination. Progress is now expected in dispersal biology as well as in forensics and forest management.     

Physical and chemical properties of fruit and seeds eaten byPithecia andChiropotes in Surinam and Venezuela

Pithecia pithecia andChiropotes satanas are seed predators that eat fruits with hard pericarps. We measured resistance to puncturing and crushing of fruit and seeds eaten by these two pitheciins at two localities: in evergreen rain forest at Raleighvallen-Voltzberg, Surinam, and in tropical dry/transitional moist forest on islands in Guri Lake, Venezuela. Average measurements of pericarp hardness were similar at both sites for fruit eaten byChiropotes, but a higher maximum value was obtained at the rainforest site.Chiropotes andPithecia both ate fruits that had harder pericarps than did fruits eaten byAteles paniscus, but crushing resistances of seeds eaten were lower than values forAteles. Thus, both pitheciins selected fruits with hard pericarps and soft seeds, although there were notable intergeneric differences in hardness of fruit ingested. When fruit became scarce,Pithecia ate more flowers, whileChiropotes continued to eat fruits with hard seed coverings. Chemical analysis of species of seeds eaten byPithecia suggests that they avoided seeds with extremely high tannin levels, though they tolerated moderate tannin levels in combination with high levels of lipids. We propose that sclerocarpic harvesting (the preparation and ingestion of fruit with a hard pericarp) allows pitheciin monkeys to obtain nutritious seeds, with reduced tannins, that are softer than those ingested by other frugivores.Presented at XIIIth Congress, International Primatological Society, July 27, 1990.     

Hsp104 Overexpression Cures Saccharomyces cerevisiae [PSI+] by Causing Dissolution of the Prion Seeds

The [PSI⁺] yeast prion is formed when Sup35 misfolds into amyloid aggregates. [PSI⁺], like other yeast prions, is dependent on the molecular chaperone Hsp104, which severs the prion seeds so that they pass on as the yeast cells divide. Surprisingly, however, overexpression of Hsp104 also cures [PSI⁺]. Several models have been proposed to explain this effect: inhibition of severing, asymmetric segregation of the seeds between mother and daughter cells, and dissolution of the prion seeds. First, we found that neither the kinetics of curing nor the heterogeneity in the distribution of the green fluorescent protein (GFP)-labeled Sup35 foci in partially cured yeast cells is compatible with Hsp104 overexpression curing [PSI⁺] by inhibiting severing. Second, we ruled out the asymmetric segregation model by showing that the extent of curing was essentially the same in mother and daughter cells and that the fluorescent foci did not distribute asymmetrically, but rather, there was marked loss of foci in both mother and daughter cells. These results suggest that Hsp104 overexpression cures [PSI⁺] by dissolution of the prion seeds in a two-step process. First, trimming of the prion seeds by Hsp104 reduces their size, and second, their amyloid core is eliminated, most likely by proteolysis.     

Nuclear replication activities during imbibition of abscisic acid- and gibberellin-deficient tomato (Lycopersicon esculentum Mill.) seeds

The role of cis-abscisic acid (ABA) and gibberellins (GAs) in the induction of cell-cycle activities has been studied during imbibition and subsequent germination of tomato seeds. Using flow cytometry, nuclear replication activity was investigated in embryo root tips isolated from seeds of the ABA-deficient mutant sit ^w , the GA-deficient mutant gib-1, and the wild-type (MM) tomato (Lycopersicon esculentum Mill. cv. Moneymaker) upon imbibition in water, 10 μM GA₄₊₇, 5 μM ABA or 5 μM ABA+10 μM GA₄₊₇. The nuclei of fully matured dry MM, sit ^w and gib-1 seeds predominantly showed 2C DNA signals, indicating that the cell-cycle activity of most root-tip cells had been arrested at the G₁ phase of nuclear division. However, ABA-deficient sit ^w seeds contained a significantly higher amount of G₂ cells (4C DNA) compared with the other genotypes, suggesting that, during maturation, cell-cycle activity in sit ^w seeds is less efficiently arrested in G₁. Upon imbibition in water, an induction of the 4C signal, indicating nuclear replication, was observed in the root tip cells of both MM and sit ^w embroys. The augmentation in the 4C signal occurred before visible germination. Gib-1 seeds did not show cell-cycle activity and did not germinate in water. Upon imbibition in GA₄₊₇, both cell-cycle activity and subsequent germination were enhanced in MM and sit ^w seeds, and were induced in gib-1. In ABA, the germination of MM and sit ^w seeds was inhibited while nuclear replication of these seeds was not affected. It is concluded that GA influences germination by acting upon processes that precede cell-cycle activation, while ABA affects growth by acting upon processes that follow cell-cycle activation.     

Silique burst ofCardamine scutata (Cruciferae) as a physical inducible defense against seed predatory caterpillars

Matured seeds of bitter cress,Cardamine scutata Thumb, are scattered by the bursting of siliques. They also burst in response to chewing by seed predatory caterpillars even when seeds are immature. In this case, the caterpillars are frequently expelled, or killed when their bodies become enswathed by the released pericarps. Consequently, many seeds escape from the attack. The plant trait is explained as an immediate induction of a physical defense against seed predators. The germination rate of scattered immature seeds was significantly lower than that of mature ones, which is a direct demonstration of trade-off between anti-herbivore defense and reproduction of the plant.     

Composition and seasonal dynamics of seed rain in broad-leaved Korean pine (Pinus koraiensis) mixed forest in Changbai Mountain, China

To explore the composition and spatio-temporal dynamics of seed rain in broad-leaved Korean pine (Pinus koraiensis) mixed forest, 150 seed traps were set up in a 25 hm2 plot in Changbai Mountain. Seeds, fruits, anthotaxy and others in seed traps were collected, identified and divided into 4 types. From 2005 to 2006, we collected 47 different types. Total number of seeds and fruits was 121291, including 23147 mature seeds and fruits (19.1% of the total). Tilia amurensis and Fraxinus mandshurica, with the most seeds and fruits, accounted for 90% of the total. The analysis on seasonal dynamics of seed rain showed that there were the largest number of seeds and fruits between July and October, which were composed of immature seeds and fruits. In mid-October, mature seeds and fruits reached their peak, but immature seeds and fruits still accounted for high proportion. There were 91 traps that contained 100–200 mature seeds and fruits, and one trap without any mature seed or fruit. The largest number of species found in a trap was 7, and usually 3 or 4 species were found in most of the traps. There were obvious relationships between spatial patterns of mature seeds and fruits and their parent trees, indicating that their mature seeds and fruits were not dispersed far from their parent trees.     

Separation of Light-Induced [C]ent-Kaurene Metabolism and Light-Induced Germination in Grand Rapids Lettuce Seeds

The effect of light on the metabolism of [¹⁴C]kaurene in light-requiring lettuce seeds (Lactuca sativa L. cv Grand Rapids) was investigated. Seeds were soaked in a solution of [¹⁴C]ent-kaurene in methylene chloride with 0.01% Tween-20, dried, and incubated in 20% polyethylene glycol (PEG) to prevent seedling development. Labeled metabolites were extracted and analyzed by high performance liquid chromatography and gas chromatography-radio counting. [¹⁴C]ent-Kaurenol and [¹⁴C]ent-kaurenal were identified in seeds incubated in constant white light, while no ethyl acetate-soluble metabolites were found in seeds incubated in the dark. In time course experiments using acid scarified seeds, metabolism began after 18 hours of incubation and greatly increased after 24 hours of incubation in 20% PEG. By 48 hours, several unidentified, more polar metabolites were found. Germination was induced in seeds imbibed in 20% PEG by 4 hours of red or 4 hours of white light following 20 hours in the dark, and was fully reversed by 2 hours of far red light. However, in metabolism experiments, [¹⁴C]ent-kaurene oxidation was observed only with constant white light. These results indicate that although ent-kaurene oxidation is a light sensitive step in the biosynthesis of gibberellins in Grand Rapids lettuce seeds, ent-kaurene metabolism is not required for light-induced germination.     

Protein Synthesis during Natural and Precocious Soybean Seed (Glycine max [L.] Merr.) Maturation

Protein synthesis was studied during precocious and natural soybean seed (Glycine max [L.] Merr.) maturation. Developing seeds harvested 35 days after flowering were precociously matured through controlled dehydration. Total soluble proteins and proteins labeled with [³⁵S]methionine were extracted from control, developing seeds and from precociously and naturally matured seeds and were analyzed by one-dimensional PAGE and fluorography. The results demonstrated that several polypeptides which were designated “mature polypeptides,” were synthesized de novo during precocious and natural seed maturation. Two of these polypeptides, 31 and 128 kilodalton in mass, also stained intensely with Coomassie blue, suggesting their abundant accumulation during seed maturation. Results from in vitro translation experiments showed that the mRNAs corresponding to these “maturation polypeptides” accumulated during precocious maturation and in naturally matured seeds, but not in seeds freshly harvested 35 days after flowering (control). The role of the “maturation polypeptides” is currently unknown; however, their presence and that of their corresponding mRNAs was coincident with the ability of matured seeds to establish seedling growth. This study has demonstrated that precocious seed maturation treatments may be extremely useful for investigations of metabolic events and molecular control mechanisms affecting soybean seed maturation.     

Global 5-methylcytosine alterations in DNA during ageing of Quercus robur seeds

Background and Aims Epigenetic regulation plays an important role in the management of plant growth, development and response to stress factors, and several reports have indicated that DNA methylation plays a critical role in seed development and viability. This study examines changes in 5-methylcytosine (m⁵C) levels in the DNA of seeds during ageing, a process that has important implications for plant conservation and agriculture.Methods Changes in the global level of m⁵C were measured in mature seeds of oak, Quercus robur. The extent of DNA methylation was measured using a protocol based on two-dimensional thin-layer chromatography. Viability of seeds was determined by germination and seedling emergence tests.Key Results An ageing-related decrease in total m⁵C during storage of recalcitrant seeds was highly and significantly correlated with a decrease in seed viability, as reflected by a reduction in germination (r = 0·8880) and seedling emergence (r = 0·8269).Conclusions The decrease in viability during ageing of Q. robur seeds is highly correlated with a global decline in the amount of m⁵C in genomic DNA, and it is possible that this may represent a typical response to ageing and senescence in recalcitrant seeds. Potential mechanisms that drive changes in genomic DNA methylation during ageing are discussed, together with their implications for seed viability.     

The occurrence and activity of epithiospecifier protein in some cruciferae seeds

Epithiospecifier protein (ESP) activity was determined in the seeds of two cultivars of Brassica napus, in B. campestris and in Lepidium sativum. All four types of seeds contained susceptible substrates for ESP (that is, glucosinolates with terminal unsaturation in their side-chain), although L. sativum contained only a very small amount of one. Results suggest that Fe²⁺ is essential for ESP activity, but its presence certainly promoted the effects of ESP to a considerable extent, and even at a very low level (e.g. 6 × 10^?11 mol Fe²⁺. Further evidence was gained for the intramolecular nature of the reaction which results in cyanoepithioalkane formation.     

Seed Removal Rates Under Isolated Trees and Continuous Vegetation in Semiarid Thornscrub

Clearing native vegetation to increase the amount of land available for agriculture in northeastern Mexico has left remnants ranging in size from fragments of continuous vegetation to isolated individual trees. These provide valuable opportunities for restoring larger areas of native vegetation. We explored whether fragmentation of Tamaulipan thornscrub affects the removal of seeds from 12 woody species that encompass a range of sizes and dispersal mechanisms. We tested whether (1) seed removal rates under isolated trees were higher than under continuous vegetation; (2) dispersal structures, such as fleshy pericarps, made some seeds more attractive to seed removers; and (3) microenvironmental variation affected seed removal rates. Seeds were placed under canopies of Texas ebony (Ebenopsis ebano) and Mesquite trees (Prosopis laevigata). Seed removal trials were conducted three times, each trial lasting 30 days. Most seeds were removed in all trials by the end of one month. Seed removal rate was slower under isolated trees. In general, fleshy fruits were removed faster than other fruits; whole fruits and fleshy tissue were removed faster than depulped seeds. In species with fleshy pericarps, acid washing of seeds, to simulate seeds processed in the digestive tract of dispersers, reduced the seed removal rates, suggesting that it would be a good pre‐treatment for restoration efforts.