云南松居群遗传学研究的等位酶分析方法

针对１５个云南松Ｐｉｎｕｓｙｕｎｎａｎｅｎｓｉｓ居群,开展了１４种酶系统的水平切片淀粉凝胶电泳实验,在谱带遗传分析的基础上确定了３３个等位酶位点及其等位基因。其中有３２个等位酶位点是多态的（有２个以上的等位基因）,只有一个单态位点Ｄｉａ－４。有３个等位基因的位点有Ｌａｐ－１、Ｌａｐ－２、Ａａ－３、Ｓｋｄ－１、Ｓｋｄ－２、Ａｄｈ－１、Ａｄｈ－３、Ｇｄｈ、Ｐｇｄ－１、Ｐｇｍ－１、Ｐｇｍ－３、Ｐｇｉ－１、Ｐｇｉ－３、Ｍｄｈ－１、Ｍｅ、Ｇ６ｐｄ、Ｄｉａ－１、Ｔｐｉ－１、Ｔｐｉ－２、Ｔｐｉ－３和Ｔｐｉ－４,有４个等位基因的位点有Ｓｋｄ－３、Ａｄｈ－２、Ｐｇｄ－２、Ｍｄｈ－２、Ｍｄｈ－３、Ｍｄｈ－４和Ｄｉａ－２,有５个等位基因的位点有Ａａｔ－１和Ｄｉａ－３。云南松居群的等位基因平均数Ａ＝２１,在松属中居于中上水平。本研究揭示了云南松居群酶位点及其等位基因带谱的变异式样,为松属植物的遗传多样性研究提供了一批酶位点及其等位基因的参考图谱     

印楝种子提取物对荔枝蝽的毒性及与其等位酶基因型之间的关系

用5.2 mg/mL（LC₅₀）的印楝种子提取物对荔枝蝽1龄若虫进行急性毒性处理,24 h死亡率为51.8%。通过等位酶分析检测了死亡与存活试虫两种酶（PGI和MDH）,两个基因座（Pgi和Mdh）上各基因型及等位基因与印楝种子提取物毒性之间的关系,进行致死性差异比较研究。结果表明,印楝种子提取物对具有不同基因型及等位基因个体的致死性存在差异。在Pgi基因座上,Pgi-bb基因型死亡率最高,为84%,Pgi-aa 和Pgi-cc基因型死亡率较低,分别为0和7%,且与死亡率最高的Pgi-bb基因型存在显著差异（P<0.05）。在基因座Mdh上,Mdh-aa基因型个体死亡率最高（93%）,而具有Mdh-cc基因型的个体全部存活了下来, 另外3个基因型Mdh-ab、Mdh-bb与Mdh-bc死亡率居中,都与Mdh-aa、Mdh-cc基因型死亡率之间存在显著差异。在等位基因上,Pgi-a和Mdh-c个体的死亡率都最低,与各自其他两个等位基因的死亡率之间存在显著差异。结果说明不同基因型个体对印楝提取物具有不同的反应,印楝种子提取物对荔枝蝽等位酶基因型及等位基因存在选择性致死作用。这种荔枝蝽对印楝种子提取物的敏感性与其等位酶基因型及等位基因之间显明的相关关系提示我们,可将荔枝蝽种群中对印楝种子提取物敏感性低的基因型及等位基因作为遗传标记去监测荔枝蝽对印楝种子提取物的抗性状况。     

Relationship between seed and clonal growth in the reproduction of Carex rugulosa Kük. in riverside meadows

Carex rugulosa Kük. develops riverside vegetation in brackish marshes along the lower parts of rivers. Because the rhizomatous ramets grow densely (590–950/m²) in its developed population, it is expected that seedlings cannot get enough light to grow if seeds germinate in crowded ramets. We studied the reproductive contribution of seed in a marshy meadow of the Ohashi River, Japan. The number of seeds produced was 6900–14 200/m² in 2002. The number of buried seeds in the following germination season differed among sites from 1190 to 2690/m². No seedlings were observed at plots where the ramets from rhizomes grew densely. In contrast, seedlings appeared in plots where all rhizomatous ramets were artificially cut. The number of seedlings corresponded to 17.5–39.5% of that of buried seeds. All these seedlings were submerged and died when it rained heavily. In the genotype analysis using allozyme detection, one of the phosphoglucoisomerase loci ( Pgi-2 ) indicated a pair of alleles. Among eight plots (each plot was 50 or 60-cm square), four showed an excess of heterozygotes and two showed homozygote domination in the Pgi-2 genotype. These results suggest that: (i) seed germination is suppressed in crowded ramets; (ii) seedling survival is severely reduced by inundation; and (iii) the population is usually maintained by clonal growth. As germination is induced in open areas, it is hypothesized that the main role of seed is recovery after vegetation decline caused by environmental stresses or colonization to other areas without dense vegetation.     

Seed mass,genotype, and density effects on growth and yield of Oenothera biennis L.

Summary Seed mass and genotypic effects on the growth and reproduction of Oenothera biennis L. over a gradient of intraspecific density were examined in a greenhouse experiment. By using genetically identical seeds from five parental genotypes we were able to examine independently the effects of seed mass and genotype on seedling and adult performance. Seedling size was significantly correlated with seed mass for the first five weeks but had no effect on adult size or reproductive output. In contrast, genotype differences became increasingly apparent with time. In particular, there were striking differences in reproductive output among genotypes. Plants grown from two of the genotypes consistently produced more, but lighter, seeds and a greater proportion flowered at high density than the other three genotypes. In all five genotypes, seed number was much more variable than seed mass across the density gradient. Initial seed mass accounted for a significant proportion of the variation in progeny seed mass, and mean seed mass produced in the greenhouse was positively correlated with mean seed mass of the parent (in the field). This result, together with the observed constancy of seed mass within a genotype across the density gradient, indicates the differences in reproductive output among these genotypes are genetically determined.     

Allele frequency shifts in response to climate change and physiological consequences of allozyme variation in a montane insect

Rapid changes in climate may impose strong selective pressures on organisms. Evolutionary responses to climate change have been observed in natural populations, yet no example has been documented for a metabolic enzyme locus. Furthermore, few studies have linked physiological responses to stress with allozyme genotypic variation. We quantified changes in allele frequency between 1988 and 1996 at three allozyme loci (isocitrate dehydrogenase, Idh; phosphoglucose isomerase, Pgi; and phosphoglucomutase, Pgm) for the leaf beetle Chrysomela aeneicollis in the Bishop Creek region of the Sierra Nevada of California (2900-3300 m). Beetles often experience high daytime (> 32 degrees C) and extremely low nighttime (< -5 degrees C) temperatures during summer. Bishop Creek weather station data indicated that conditions were unusually dry before 1988, and that conditions were cool and wet during the years preceding the 1996 collection. We found directional changes in allele frequency at Pgi (11% increase in the Pgi-1 allele), but not at Idh or Pgm. We also found that physiological response to thermal extremes depended on Pgi genotype. Pgi 1-1 individuals induced expression of a 70-kD heat shock protein (HSP) at lower temperatures than 1-4 or 4-4 individuals, and 1-1 individuals expressed higher levels of HSP70 after laboratory exposure to temperatures routinely experienced in nature. Survival after nighttime laboratory exposure to subzero temperatures depended on gender, previous exposure to cold, and Pgi genotype. Females expressed higher levels of HSP70 than males after exposure to heat, and recovery by female Pgi 1-1 homozygotes after exposure to cold (-5 degrees C) was significantly better than 1-4 or 4-4 genotypes. These data suggest that the cooler climate of the mid-1990s may have caused an increase in frequency of the Pgi-1 allele, due to a more robust physiological response to cold by Pgi 1-1 and 1-4 genotypes.     

Seed dispersal by animals: exact identification of source trees with endocarp DNA microsatellites

A long-standing challenge in studies of seed dispersal by animal frugivores has been the characterization of the spatial relationships between dispersed seeds and the maternal plants, i.e. the seed shadow. The difficulties to track unambiguously the origin of frugivore-dispersed seeds in natural communities has been considered an unavoidable limitation of the research field and precluded a robust analysis of the direct consequences of zoochory. Here we report that the multilocus genotype at simple sequence repeat (SSR; microsatellite) loci of the woody endocarp, a tissue of maternal origin, provides an unequivocal genetic fingerprint of the source tree. By comparing the endocarp genotype against the complete set of genotypes of reproductive trees in the population, we could unambiguously identify the source tree for 82.1% of the seeds collected in seed traps and hypothesize that the remaining 17.9% of sampled seeds come from other populations. Identification of the source tree for Prunus mahaleb seeds dispersed by frugivores revealed a marked heterogeneity in the genetic composition of the seed rain in different microhabitats, with a range of 1-5 distinct maternal trees contributing seeds to a particular landscape patch. Within-population dispersal distances ranged between 0 and 316 m, with up to 62% of the seeds delivered within 15 m of the source trees. Long distance dispersal events, detected by the exclusion of all reproductive trees in the population, accounted for up to 17.9% of the seeds sampled. Our results indicate strong distance limitation of seed delivery combined with infrequent long-distance dispersal events, extreme heterogeneity in the landscape pattern of genetic makeup, and a marked mosaic of multiple parentage for the seeds delivered to a particular patch.     

Developmental changes in the germinability, desiccation tolerance, hardseededness, and longevity of individual seeds of Trifolium ambiguum

Background and Aims

Using two parental clones of outcrossing Trifolium ambiguum as a potential model system, we examined how during seed development the maternal parent, number of seeds per pod, seed position within the pod, and pod position within the inflorescence influenced individual seed fresh weight, dry weight, water content, germinability, desiccation tolerance, hardseededness, and subsequent longevity of individual seeds.

Methods

Near simultaneous, manual reciprocal crosses were carried out between clonal lines for two experiments. Infructescences were harvested at intervals during seed development. Each individual seed was weighed and then used to determine dry weight or one of the physiological behaviour traits.

Key Results

Whilst population mass maturity was reached at 33–36 days after pollination (DAP), seed-to-seed variation in maximum seed dry weight, when it was achieved, and when maturation drying commenced, was considerable. Individual seeds acquired germinability between 14 and 44 DAP, desiccation tolerance between 30 and 40 DAP, and the capability to become hardseeded between 30 and 47 DAP. The time for viability to fall to 50 % (p₅₀) at 60 % relative humidity and 45 °C increased between 36 and 56 DAP, when the seed coats of most individuals had become dark orange, but declined thereafter. Individual seed f. wt at harvest did not correlate with air-dry storage survival period. Analysing survival data for cohorts of seeds reduced the standard deviation of the normal distribution of seed deaths in time, but no sub-population showed complete uniformity of survival period.

Conclusions

Variation in individual seed behaviours within a developing population is inherent and inevitable. In this outbreeder, there is significant variation in seed longevity which appears dependent on embryo genotype with little effect of maternal genotype or architectural factors.     

Maternal environment affects the genetic basis of seed dormancy in Arabidopsis thaliana

The genetic basis of seed dormancy, a key life history trait important for adaptive evolution in plant populations, has yet been studied only using seeds produced under controlled conditions in greenhouse environments. However, dormancy is strongly affected by maternal environmental conditions, and interactions between seed genotype and maternal environment have been reported. Consequently, the genetic basis of dormancy of seeds produced under natural field conditions remains unclear. We examined the effect of maternal environment on the genetic architecture of seed dormancy using a recombinant inbred line (RIL) population derived from a cross between two locally adapted populations of Arabidopsis thaliana from Italy and Sweden. We mapped quantitative trait loci (QTL) for dormancy of seeds produced in the greenhouse and at the native field sites of the parental genotypes. The Italian genotype produced seeds with stronger dormancy at fruit maturation than did the Swedish genotype in all three environments, and the maternal field environments induced higher dormancy levels compared to the greenhouse environment in both genotypes. Across the three maternal environments, a total of nine dormancy QTL were detected, three of which were only detected among seeds matured in the field, and six of which showed significant QTL × maternal environment interactions. One QTL had a large effect on dormancy across all three environments and colocalized with the candidate gene DOG1. Our results demonstrate the importance of studying the genetic basis of putatively adaptive traits under relevant conditions.     

Seed Weight inLolium perenneas Affected by Interactions among Seeds within the Inflorescence

Little is known about interactions between seeds within theinflorescence of perennial ryegrass (Lolium perenneL.) and theireffect on final seed weight. These relations were investigatedin two glasshouse experiments using two genotypes, by reducingthe number of seeds in an inflorescence at anthesis. In thefirst experiment, entire spikelets were removed to study therelations between seeds in different spikelets. The effectson seed dry weight were not proportional to the number of spikeletsremoved. In one genotype, removal of two-thirds of the spikeletsincreased seed dry weight of the remaining seeds by 15%. Inthe other genotype, such treatment did not increase seed dryweight. In the second experiment, investigating seed interactionswithin a spikelet, either two proximal seeds or two centralseeds were maintained in a spikelet by removing the other ovulesin combination with no or 75% shading. Shading by 75% reducedseed dry weight by about 10%. In the unshaded treatment, seeddry weight was not affected by ovule removal. Under shading,the central seeds in a spikelet were about 12% heavier if theygrew alone, in contrast to the proximal seeds. The effects ofa reduction in seed number on seed dry weight were not relatedto the final nitrogen concentration of seeds. These experimentsshow that assimilate partitioning and the relationship betweenseeds in the inflorescence of perennial ryegrass are alreadylargely determined at anthesis; increasing seed yield by manipulationsafter anthesis is not feasible.Copyright 1998 Annals of BotanyCompany. Lolium perenne, perennial ryegrass, seed growth, seed interactions, shading, spikelet removal.     

Differential siring success of Pgi genotypes in Clarkia Unguiculata (Onagraceae)

Competition among pollen grains for the fertilization of ovules can play an important role in determining the male and female reproductive success of flowering plants. To examine the influence of pollen-donor genotype on male reproductive success, hand-pollinations were conducted on Clarkia unguiculata and the siring success of pollen-donor plants was compared between donors homozygous for different allelomorphs of the allozyme PGI (phosphoglucoisomerase). Donors homozygous for the B allele sired more seeds than C-allele donors. Single-donor crosses indicated that C-donor-sired seeds are aborted more often than are B-donor-sired seeds, suggesting that the B-allele donor's advantage in mixed pollinations was a result of differential abortion. A negative relationship between pollen load and the siring success of B-allele donors implies that pollen from B-allele donors has reduced performance relative to C-allele donors when pollen loads are high. These data demonstrate consistent differences in siring success between individuals homozygous for different alleles at a single locus and suggest that variation at the Pgi locus may be maintained by a post-pollination trade-off.     

Influence of insect pollinators and harvesting time on the quality of Stevia rebaudiana (Bert.) Bertoni seeds

Stevia rebaudiana (Bert.) Bertoni has sporophytic self-incompatibility and this may lead to poor seed yield and quality, which are obstacles to large-scale crop establishment. This research investigated the influence of insect pollinators and the harvesting time on the qualitative and quantitative characteristics of the ripe seeds. A pot trial under open field conditions was established to evaluate the abundance of insect pollinators and three harvesting times on the production of ripe seeds, germination percentage, mean germination time and thousand seed weight (TSW) in 36 F1 open-pollinated genotypes. Large variability in the number of corymbs of capitula, flowering time, reproductive period and seed yield was observed among the genotypes. Genotypes with promising phenological and reproductive properties were identified. The worst germination percentage and TSW were recorded in the latest harvest. Significant linear regressions were found among the investigated parameters (insect number, germination percentage, TSW, seeds yield per plant and cycle length), confirming complex interactions on the yield and quality of stevia seeds. Results indicate that earlier flowering genotypes produced higher seed quantity, due to favourable weather conditions during the reproductive phase. Moreover, cross-pollination and the insect abundance, as Apidae and Syrphidae, play a crucial role for enhancing the stevia seed yield and quality.     

Seed zinc content influences early vegetative growth and zinc uptake in oilseed rape (Brassica napus and Brassica juncea) genotypes on zinc-deficient soil

Low-Zn seed (around 80 ng Zn per seed) and high-Zn seed (around 160 ng Zn per seed) of Zhongyou 821 (a traditional Brassica napus genotype from China found to be Zn-inefficient in our previous experiments), Narendra (Zn-efficient B. napus genotype from Australia) and CSIRO-1 (a Zn-efficient B. juncea genotype from Australia) oilseed rape genotypes were sown in pots containing Zn-deficient siliceous sand fertilized with low Zn supply (0.05 mg Zn kg^–1 soil) or high Zn supply (2.0 mg Zn kg^–1 soil) in a controlled environment. After six weeks, plants derived from the high-Zn seed had better seedling vigour, increased root and shoot growth, more leaf area and chlorophyll concentration in fresh leaf, and higher Zn uptake in shoot compared to those from low-Zn seed at low Zn supply; the impact of high-Zn seed was more marked in Zhongyou 821 compared with CSIRO-1 and Narendra. The influence of high-Zn seed was dissipated at high Zn supply. CSIRO-1 was superior in terms of shoot dry matter production and Zn uptake in shoots at low Zn supply. The results demonstrate that although oilseed rape has very small seeds (about 3 mg per seed weight) compared with wheat (30 mg per seed weight), Zn reserves present in this very small seed still have a strong impact on early vegetative growth as well as on Zn uptake of plants in Zn-deficient soils. The results suggest that sowing high-Zn seed coupled with growing Zn-efficient genotypes may help in sustaining the production of oilseed rape in Zn-deficient soils, and this has implications for improved seed technology.     

Isozyme analysis of progeny derived from (Allium fistulosum ×Allium cepa) ×Allium cepa

Summary Relatively large quantities of seed were obtained from the interspecific backcross (A. fistulosum xA. cepa) ×A. cepa allowing, for the first time, an extensive study of the heritable traits exhibited by backcross progeny. Two backcross populations, BC1034 and BC1040, distinguished by differentA. fistulosum parents, were characterized for the isozyme markersIdh-1, Adh-1, andPgi-1. Statistical methods are described to calculate cell probabilities for a mixed population of F₂ and BC₁ progeny, using an estimate of the fraction of F₂ progeny in the population derived from the isozyme data. Cell probability distributions were calculated for a mixed population with independent pairs of loci and a mixed population with nonindependent pairs of loci. The isozyme lociIdh-1 andPgi-1 appear to be linked, with a map distance estimated at 33 centimorgans (cM) in BC1034 and 42 cM in BC1040. The probability distribution model for linked loci did not account for all of the distorted segregation ratios inIdh-1 ×Adh-1 orPgi-1 ×Adh-1. The cytological literature does not support linkage betweenIdh-1 ×Adh-1 orPgi-1 ×Adh-1. The distorted segregation ratios for these pairs of loci are likely the result of genetic incompatibilities between the two species.Journal Article No. 1578, Agricultural Experiment Station, New Mexico State University, Las Cruces, NM, USA     

Central cell nuclear-cytoplasmic incongruity:a mechanism for segregation distortion in advanced backcross and selfed generations of (Allium cepa L. x Allium fistulosum L.) x A. cepa interspecific hybrid derivatives

A model is presented as an explanation for an anomaly observed in germination and establishment and isozyme segregation patterns in Allium cepa x A. fistulosum F2BC3 populations generated in an introgression-breeding program. The F1BC3 parent of these populations was selected for its heterozygous PGI phenotype, Pgi-1(2/3); Pgi-1(2) was inherited from an A. cepa (Ac) seed parent and Pgi-1(3) from an A. fistulosum (Af) pollen parent. Germination and establishment was recorded for the F2BC3 progeny population. Segregation of Ac and Af Pgi-1 alleles was investigated in F2BC3 seeds and embryo and endosperm tissue was isolated and tested for isozyme expression. A pooled goodness-of-fit test of the segregation of Pgi-1 alleles in the populations to the expected Mendelian 1:2:1 ratio using the chi-square statistic gave a chi2 = 185.9, well beyond the accepted limits at 2 degrees of freedom. The 1:2:1 ratio expected for simple Mendelian inheritance was rejected, while a pooled chi-square goodness-of-fit test of the segregation of Pgi-1 alleles in the populations fit a 1:1 ratio with a chi2 = 0.203, based on the incongruity model. We present here the central cell nuclear-cytoplasmic incongruity hypothesis to explain the observed anomalies.     

Relationship of endogenous abscisic Acid to sucrose level and seed growth rate of soybeans

It has been proposed that abscisic acid (ABA) may stimulate sucrose transport into filling seeds of legumes, potentially regulating seed growth rate. The objective of this study was to determine whether the rate of dry matter accumulation in seeds of soybeans (Glycine max L.) is correlated with the endogenous levels of ABA and sucrose in those sinks. The levels of ABA and sucrose in seed tissues were compared in nine diverse Plant Introduction lines having seed growth rates ranging from 2.5 to 10.0 milligrams dry weight per seed per day. At 14 days after anthesis (DAA), seeds of all genotypes contained less than 2 micrograms of ABA per gram fresh weight. Levels of ABA increased rapidly, however, reaching maxima at 20 to 30 DAA, depending upon tissue type and genotype. ABA accumulated first in seed coats and then in embryos, and ABA maxima were higher in seed coats (8 to 20 micrograms per gram fresh weight) than in embryos (4 to 9 micrograms per gram fresh weight. From 30 to 50 DAA, ABA levels in both tissues decreased to less than 2 micrograms per gram fresh weight. Levels of sucrose were also low early in development, less than 10 milligrams per gram fresh weight at 14 DAA. However, by 30 DAA, sucrose levels in seed coats had increased to 20 milligrams per gram fresh weight and remained fairly constant for the remainder of the filling period. In contrast, sucrose accumulated in embryos throughout the filling period, reaching levels greater than 40 milligrams per gram fresh weight by 50 DAA. Correlation analyses indicated that the level of ABA in seed coats and embryos was not directly correlated to the level of sucrose measured in those tissues or to the rate of seed dry matter accumulation during the linear filling period. Rather, the ubiquitous pattern of ABA accumulation early in development appeared to coincide with water uptake and the rapid expansion of cotyledons occurring at that time. Whole tissue sucrose levels in embryos and seed coats, as well as sucrose levels in the embryo apoplast, were generally not correlated with the rate of dry matter accumulation. Thus, it appears that, in this set of diverse soybean genotypes, seed growth rate was not limited by endogenous concentrations of ABA or sucrose in reproductive tissues.     

GENETIC EFFECTS OF GERMINATION TIMING AND ENVIRONMENT: AN EXPERIMENTAL INVESTIGATION

Seeds of many species do not germinate immediately after dispersal, but instead may remain indefinitely in a dormant but viable state. Although it is well established that seeds often exhibit diversified patterns of dormancy and germination, the causes and consequences of this variation remain poorly understood. In this study, we investigate the extent to which seed genotypes of the desert mustard Lesquerella fendleri differentially germinate and establish under experimental conditions in a greenhouse. We used a two-way factorial design to compare genotypes of Lesquerella plants derived from seeds that germinated and established at different times and under different soil water regimes. Overall allozyme allele frequencies of Lesquerella plants varied significantly with both germination time and initial soil water availability. Single-locus heterozygosity analyses revealed that seeds sown into initially low water conditions produced plants that were significantly more heterozygous than plants derived from seeds experiencing constantly high water conditions, but heterozygosity did not differ significantly among plants originating from early- and late-germinating seeds. This is the first study to experimentally demonstrate that germination timing and environment can significantly affect the genetic structure of emerging plant populations. The study suggests that germination and survival behavior may (1) play an important role in generating and maintaining the genetic structure of natural plant populations and (2) set the stage for subsequent evolution.     

Seed storage at elevated partial pressure of oxygen, a fast method for analysing seed ageing under dry conditions

Background and Aims

Despite differences in physiology between dry and relative moist seeds, seed ageing tests most often use a temperature and seed moisture level that are higher than during dry storage used in commercial practice and gene banks. This study aimed to test whether seed ageing under dry conditions can be accelerated by storing under high-pressure oxygen.

Methods

Dry barley (Hordeum vulgare), cabbage (Brassica oleracea), lettuce (Lactuca sativa) and soybean (Glycine max) seeds were stored between 2 and 7 weeks in steel tanks under 18 MPa partial pressure of oxygen. Storage under high-pressure nitrogen gas or under ambient air pressure served as controls. The method was compared with storage at 45 °C after equilibration at 85 % relative humidity and long-term storage at the laboratory bench. Germination behaviour, seedling morphology and tocopherol levels were assessed.

Key Results

The ageing of the dry seeds was indeed accelerated by storing under high-pressure oxygen. The morphological ageing symptoms of the stored seeds resembled those observed after ageing under long-term dry storage conditions. Barley appeared more tolerant of this storage treatment compared with lettuce and soybean. Less-mature harvested cabbage seeds were more sensitive, as was the case for primed compared with non-primed lettuce seeds. Under high-pressure oxygen storage the tocopherol levels of dry seeds decreased, in a linear way with the decline in seed germination, but remained unchanged in seeds deteriorated during storage at 45 °C after equilibration at 85 % RH.

Conclusions

Seed storage under high-pressure oxygen offers a novel and relatively fast method to study the physiology and biochemistry of seed ageing at different seed moisture levels and temperatures, including those that are representative of the dry storage conditions as used in gene banks and commercial practice.     

Trade-off between seed number and weight: Influence of a grass–endophyte symbiosis

Plant fitness is enhanced by resource allocation to seed number (offspring number) or weight (offspring survival). Besides, there is a well known trade-off in resource allocation between both traits. Symbiotic interactions can influence plant resource allocation to reproduction, yet little research has been performed in this direction. We studied the consequences of a grass–fungus symbiosis on the trade-off between seed number and weight, using Lolium multiflorum and the endophyte Neotyphodium occultans as our study system. In ecological terms, we experimentally removed N. occultans from L. multiflorum plants, and compared reproductive allocation to seed number and weight in endophyte-symbiotic vs. non-symbiotic plants at different levels of nutrient availability (small pots vs. large pots). In evolutionary terms, we compared reproductive allocation between symbiotic vs. non-symbiotic plants for different host genotypes. All plants showed a negative association between seed number and weight, once standardized for total reproductive biomass. Under high nutrient availability, endophyte-symbiotic plants showed higher seed weight than non-symbiotic plants for any seed number. However, no differences were observed under low nutrient availability. Endophyte influence also varied according to L. multiflorum genotype; specifically, endophyte-symbiotic plants showed a lower slope in the relationship between seed number and weight than non-symbiotic plants for the ‘Marshall’ genotype but no endophyte influence was found for the “Pampean” genotype. The results implied a higher plasticity in seed weight and lower plasticity in seed number for symbiotic plants. Indeed, endophyte-symbiotic plants showed an overall lower slope in the association between seed number and total reproductive biomass than non-symbiotic plants. Our results suggest that N. occultans induces heavier seeds in L. multiflorum plants under environmental conditions favorable to plant growth or for certain plant genotypes. We propose that symbiotic interactions may influence the evolution of seed number and weight trade-off.     

Trade-offs between male and female reproduction associated with allozyme variation in phosphoglucoisomerase in an annual plant (Clarkia unguiculata: Onagraceae)

The genotype of an individual for allozymes such as phosphoglucoisomerase (Pgi) is often not neutral with regard to fitness. Studies of several taxa have found consistent fitness differences among Pgi genotypes expressing different allozymes. We conducted a greenhouse experiment with Clarkia unguiculata to determine whether allelic variation at the Pgi-C1 locus may affect components of male and female function. We found significant differences in siring success between pollen donors homozygous for different Pgi alleles. When a mixture of pollen was applied to stigmas under conditions of gametophytic competition (more pollen deposited on stigmas than there are ovules available to fertilize), donors homozygous for the C allele of Pgi sired more seeds per fruit than B-allele donors. Differences between genotypes with respect to female fertility per fruit contrasted with the male advantage associated with the C allele. Recipients homozygous for the C allele produced fruits with more aborted seeds and fewer viable seeds than recipients homozygous for the B allele. These results suggest that allelic variation at a single locus may have opposing effects on male and female reproductive success in C. unguiculata, and that trade-offs between the two types of reproductive success could contribute to the maintenance of variation at the Pgi-C1 locus.     

Biochemical genetics of some seed proteins of Pinus radiata

In a high-salt soluble fraction of the total protein from single seeds of Pinus radiata, up to 45 polypeptides were resolved on SDS-polyacrylamide gels. At least one-fifth of these polypeptides showed variation between seeds. In the 27,000–29,000 dalton region, two polypeptides were inherited as codominant alleles at a single locus and were shown to assort independently of another seed protein locus and three allozyme loci. A survey of 120 individuals from the five known native populations of P. radiata in California detected only the 27K and 29K alleles at the locus. In all populations, the 29K allele predominated, and the two island populations were monomorphic for the 29K allele. The 27 and 29 kdalton polypeptides were shown to have very similar amino acid sequences, and the allelic difference at this locus is most probably in the gene sequence for the polypeptide.