Patterns of wing size variation in seeds of the lily Cardiocrinum cordatum (Liliaceae)

We examined the patterns of variation in wing-loading and its related characteristics in Cardiocrinum cordatum to clarify the factors that determine the variation in seed dispersal ability in this species. The square root of wing-loading of a seed of a plant was not significantly correlated with basal stem diameter of a plant, indicating that large plants did not necessarily produce seeds with high dispersal ability. This result was inconsistent with the hypothesis that large plants produce seeds with high dispersal ability to avoid high mortality of seeds and seedlings in the vicinity of the parents. On the other hand, the square root of wing-loading of a seed of a fruit was negatively dependent on seed number of a fruit. Thus, many-seeded fruits produced seeds with high dispersal ability. This was because the projected surface area per seed was large in large fruits and large fruits contained large numbers of seeds. The cost per seed of producing fruit structures was small for many-seeded fruits. Thus, high dispersal ability of seeds in many-seeded fruits may be a result of an effective resource allocation pattern in which a high proportion of resources are allocated to those many-seeded fruits, enabling seeds to develop large wings and thus reducing the structural cost of fruits per seed.     

Seed output and the seed bank in Vallisneria americana (Hydrocharitaceae)

Seed banks and sexual reproduction are known to be significant in colonization and re-establishment of some aquatic macrophyte communities. For highly clonal aquatic macrophytes, however, there is a lack of information on seed production and seed fate as compared with annual sexual species. The seed bank for three populations of Vallisneria americana in the Huron-Erie corridor of the Great Lakes was sampled and quantified in the spring of 1994, and related to seed production in the previous season at these sites. Seed deposition rates during 1994 were also assessed. Sites varied in the proportion of plants flowering and in their tertiary sex ratios, but did not differ in seed numbers produced per unit area. The size of the seed bank was not significantly related to the previous season's seed output, and estimates of seed deposition in the following year tended to be approximately tenfold greater than seed densities found in the seed bank. The stages between seed production and subsequent seed germination are generally very dynamic, with dispersal, mortality, and predation as likely regulating factors. The potential for seedling establishment in V. americana needs to be assessed more fully before the role of seeds in population processes can be determined.     

Preferential exclusion of hybrids in mixed pollinations between oilseed rape (Brassica napus) and weedy B. campestris (Brassicaceae)

In most experimental hybridizations between oilseed rape (Brassica napus) and weedy B. campestris, either intra- or interspecific pollen has been applied to individual flowers. Under field conditions, however, stigmas will often receive a mixture of the two types of pollen, thereby allowing for competition between male gametophytes and/or seeds within pods. To test whether competition influences the success of hybridization, pollen from the two species was mixed in different proportions and applied to stigmas of both species. The resulting seeds were scored for paternity by isozyme and randomly amplified polymorphic DNA analysis. Using data on the proportion of fully developed seeds and the proportion of these seeds that were hybrids, a statistical model was constructed to estimate the fitness of conspecific and heterospecific pollen and the survival of conspecific and heterospecific zygotes to seeds. B. campestris pollen in B. napus styles had a significantly lower fitness than the conspecific pollen, whereas no difference between pollen types was found in B. campestris styles. Hybrid zygotes survived to significantly lower proportions than conspecific zygotes in both species, with the lowest survival of hybrid zygotes in B. napus pods. This is in contrast to the higher survival of hybrid seeds in B. napus than in B. campestris pods when pollinations are made with pure pollen. Altogether, the likelihood of a foreign pollen grain producing a seed was much lower on B. napus than on B. campestris. In addition, pods on B. napus developed to a lower extent the more heterospecific pollen was in the mix, whereas this had no effect on B. campestris.     

Substrate water potential constraints on germination of the strangler fig Ficus aurea (Moraceae)

Palms are the most common support hosts for strangler fig (Ficus aurea) in the tropical dry forest. At Hummingbird Cay Tropical Field Station in the Bahamas, viable F. aurea seeds scattered on open soil germinate within 6 d in the laboratory at 27C in light or darkness. To test the hypothesis that water relations between seed and substrate can restrict the site of F. aurea establishment, fig seeds were imbibed in mannitol solutions with water potential (psi) from 0 MPa to -2.0 MPa. At psi > -1.0 MPa, germination ranges from 70 to 90%. Below -1.0 MPa, germination drops under 4%. Seedling growth rate slows linearly with decreasing psi, due to reduced cell enlargement in the radicle. Sensitivity of F. aurea seeds to psi stress is similar to that of mesophytic crops with "threshold' psi of -1.2 to -1.5 MPa, below which germination and/or seedling growth stops. F. aurea shows no evidence of xerophytic adaptation in germination physiology. In the field, psi of humus in palm leaf bases does not drop below -1.0 to -1.1 MPa, while humus in terrestrial sites reaches psi F. aurea germination and seedling growth is met by humus in palm leaf bases, not by terrestrial sites. In dry forests, this restricts F. aurea establishment to the crown of palm trees.     

Pre-replication recovery from methyl methanesulphonate induced chromosomal damage in Vicia faba seeds

Vicia faba seeds were treated with methyl methanesulphonate (MMS) and stored at 50 % water content for 0, 14 and 28 d. This water content prolongs the period between the mutagenic treatment and the onset of DNA synthesis. Storage of seeds after mutagen treatment at the selected water content led to a significant decrease in DNA damage, manifested as a reduction in the frequency of chromosomal aberrations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Water and sucrose regulate canola embryo development

The effect of water and sucrose on the growth and development of zygotic, 30-day-old canola ( Brassica napus L. cv. Bounty) embryos was examined in vitro by manipulating the levels of sucrose and/or sorbitol present in the culture medium. In some experiments, the medium water potential was allowed to vary with sucrose concentration, while in other experiments, the medium water potential was held constant by adding sorbitol to varying amounts of sucrose. Our results showed that embryos cultured on sorbitol alone exhibited two developmental patterns: embryos germinated precociously on media containing up to 0.70 M sorbitol, whereas embryos became yellow and quiescent on media with higher concentrations of sorbitol. For embryos cultured on media containing sucrose alone, three distinct developmental patterns were noted: at low sucrose concentrations, embryos germinated precociously; at intermediate concentrations, embryos continued to grow in an embryonic mode; and, at high concentrations, embryos became yellow and quiescent. Continued embryonic growth was never observed in embryos cultured on media containing sorbitol alone. Embryos never germinated precociously when cultured on media maintained at a constant water potential of -1.4 MPa, rather dry weight increased in these embryos with an increase in sucrose concentration. We envision the effect of sucrose on embryo growth and development to be nested within the effect of water availability. When water availability is restricted, embryos become quiescent. When water is available, embryos have the potential to grow, but the developmental growth pattern depends on the availability of sucrose. In the absence of sucrose, embryos germinate and initiate the transition to autotrophy. If sufficient sucrose is available, embryos remain photohet-erotrophic and continue to grow in an embryonic mode.     

Oleosins prevent oil-body coalescence during seed imbibition as suggested by a low-temperature scanning electron microscope study of desiccation-tolerant and -sensitive oilseeds

In order to clarify further the physiological role of oleosins in seed development, we characterized the oil-body proteins of several oilseeds exhibiting a range of desiccation sensitivities from the recalcitrant (Theobroma cacao L., Quercus rubra L.), intermediate (Coffea arabica L., Azadirachta indica A. Juss.) and orthodox categories (Sterculia setigera Del., Brassica napus L.). The estimated ratio of putative oleosins to lipid in oil bodies of Q. rubra was less than 5% of the equivalent values for rapeseed oil bodies. No oleosin was detected in T. cacao oil bodies. In A. indica cotyledons, oil bodies contained very low amounts of putative oleosins. Oil bodies both from C. arabica and S. setigera exhibited a similar ratio of putative oleosins to lipid as found in rapeseed. In C. arabica seeds, the central domain of an oleosin was partially sequenced. Using a low temperature field-emission scanning electron microscope, the structural stability of oil bodies was investigated in seeds after drying, storage in cold conditions and rehydration. Despite the absence or relative dearth of oleosins in desiccation-sensitive, recalcitrant oilseeds, oil bodies remained relatively stable after slow or fast drying. In A. indica seeds exposed to a lethal cold storage treatment, no significant change in oil-body sizes was observed. In contrast, during imbibition of artificially dried seeds containing low amounts of putative oleosins, the oil bodies fused to form large droplets, resulting in the loss of cellular integrity. No damage to the oil bodies occurred in imbibed seeds of Q. rubra, C. arabica and S. setigera. Thus the rehydration phase appears to be detrimental to the stability of oil bodies when these are present in large amounts and are lacking oleosins. We therefore suggest that one of the functions of oleosins in oilseed development may be to stabilize oil bodies during seed imbibition prior to germination. Received: 22 April 1997 / Accepted: 5 June 1997     

Free and bound amino acids and proteins in developing grains of rice with enhanced lysine/proteins

 Free amino acids were determined in developing seed of a rice mutant with enhanced grain lysine. This phenotype frequently has enhanced protein. Some free amino acids of developing seed are inversely related to the level of total amino acids in proteins of the mature grain. Amino acids that were enhanced in protein, including aspartic acid, threonine, methionine and lysine, were notably lower in the free amino-acid pool. Our conclusion is that mutant-developing grains process aspartate amino acids more rapidly than the controls. Conversely, arginine, valine and glutamic acid/glutamine accumulate as free amino acids with mutant/control ratios of 1.39, 1.29 and 1.12, respectively. Glutamic acid/glutamine in proteins of mature seeds is lower in the mutant than the control. ³H-lysine incorporation showed enhanced isotope incorporation into at least four proteins. One mutant protein was less actively labelled than analogous controls. The ³Hlysine pattern indicates processing modifications in this useful rice mutant. Received: 14 October 1996/Accepted: 8 November 1996