Fertility in Crosses Involving Diploid and Autotetraploid Raspberries: I. The Embryo

Crosses between diploid raspberry cultivars (Rubus idaeus L.)and their autotetraploid forms have shown that embryo shapedepends on three main factors—the variety, the stage ofdevelopment reached before growth ceases, and the ploidy ofthe embryo itself. Embryo growth, however, depends on the abilityof the endosperm to nourish the embryo and so on the harmoniousco-existence of derivatives of the gametes which formed theendosperm. Crosses between plants of unequal ploidy produceendosperms which are unbalanced. In general, the order of fertilityof the crosses is 2n selfed, 4n selfed, 4n X 2n, 2n X 4n, andthis can be partly explained if the effect of chromosome doublingis to increase the genetic strength of the male gametes morethan that of the female. Variations in the embryo growth inthe 2n X 4n and 4n x 2n crosses are ascribed to smaller differencesin genetic strength between varieties and between the male andfemale gametes within a variety. Embryos derived from crosseswithin a single variety grew less well than those derived fromcrosses between varieties, other factors being equal, and thisis considered to be an early expression of inbreeding depressionin the embryo.     

The Histology of Seed Development following Crosses between Diploid and Autotetraploid Raspberries (Rubus idaeus L.)

Seed development was studied in crosses made between the diploidforms and autotetraploid mutants of two raspberry (Rubus idaeusL.) cultivars. Drupelet abortion did not appear to be causedby failure of fertilization; it occurred mainly between thefourth and eighth day after pollination, and manifested itselfas simultaneous cessation of growth in all tissues. In healthydrupelets at eight days after pollination, growth appeared tobe proceeding at similar rates in all the tissues except thatthe embryo seemed to be growing faster than the endosperm inthe most advanced crosses. Both diploid and tetraploid ovulesappeared to be more stimulated by pollen from tetraploid plants.Embryo differentiation differed according to the direction ofcross, especially in stunted embryos. Radicles tended to beabnormally large when diploid pollen was used and smaller thanusual with haploid pollen.     

The Histology of Seed Development in Diploid and Tetraploid Raspberries (Rubus idaeus L.)

Ovules of the raspberry, Rubus idaeus L., resembled those ofother Rubus species in being unitegmic, crassinucellate, andanatropous. In one cultivar, ‘M. 69/139’, both eggcell and embryo were inserted slightly laterally to the micropyle.Of the tetraploid forms, 4n M. 69/139 showed a proportion ofembryo sacs with delayed differentiation, and 4n ‘M. Jewel’some with four antipodal cells. Embryo development showed littleuniformity in timing, but followed the Asterad type. Occasional delayed endosperm development seemed to be a varietalpeculiarity of M. 69/139. At maturity, the ergastic materialin healthy endosperms consisted of oil globules and aleurongrains. The hypostase formed a projecting pedestal below theendosperm at 8 days. The inner epidermal layer of the testaappeared specialized, both in the early stages of seed growth,when it is suggested that it functioned as an endodermis, andat maturity, when it appeared to form an osmotic barrier.     

Physiology of Polyploid Plants: Water Balance in Autotetraploid and Diploid Tomato under Low and High Salinity

Diploid and autotetraploid plants of the cultivated tomato Lycopersicon esculentum cv. Lukullus (Luk) were studied under low and high salinity. Polyploids had a higher water content than diploid plants. Water content in both plant types decreased under salinity, the decrease being smaller in the polyploid plants. Dry weight of whole young plants decreased in both diploid and polyploid plants under salinity, the decrease being smaller in the latter. Transpiration of whole plants, grown in control solution, was lower in polyploid than in diploid plants and decreased more under salinity in the latter. Rate of change of water loss of detached drying leaves was similar in diploid and polyploid plants. Leaves of control diploid plants, however, lost more water per unit leaf area during the phase of stomatal closure apparently due to higher stomatal density. Polyploid plants had fewer but more open stomata per unit leaf area, under both control and saline conditions. Root pressure, determined only under control conditions, seemed to be higher in polyploid plants. No difference in Cl^? concentration per unit leaf dry weight was found between diploid and polyploid plants grown in either control or NaCl solution.     

Microsatellite Analysis of Genetic Variation and Population Genetic Differentiation in Autotetraploid and Diploid Rice

Genetic diversity and population genetic structure of autotetraploid and diploid populations of rice collected from Chengdu Institute of Biology, Chinese Academy of Sciences, were studied based on 36 microsatellite loci. Among 50 varieties, a moderate to high level of genetic diversity was observed at the population level, with the number of alleles per locus (A _e) ranging from 2 to 6 (mean 3.028) and polymorphism information content ranging from 0.04 to 0.76 (mean 0.366). The expected heterozygosity (H _e) varied from 0.04 to 0.76 (mean 0.370) and Shannon’s index (I) from 0.098 to 1.613 (mean 0.649). The autotetraploid populations showed slightly higher levels of A _e, H _e, and I than the diploid populations. Rare alleles were observed at most of the simple sequence repeat loci in one or more of the 50 accessions, and a core fingerprint database of the autotetraploid and diploid rice was constructed. The F-statistics showed genetic variability mainly among autotetraploid populations rather than diploid populations (F _st = 0.066). Cluster analysis of the 50 accessions showed four major groups. Group I contained all of the autotetraploid and diploid indica maintainer lines and an autotetraploid and its original diploid indica male sterile lines. Group II contained only the original IR accessions. Group III was more diverse than either Group II or Group IV, comprising both autotetraploid and diploid indica restoring lines. Group IV included a japonica cluster of the autotetraploid and diploid rices. Furthermore, genetic differences at the single-locus and two-locus levels, as well as components due to allelic and gametic differentiation, were revealed between autotetraploid and diploid varieties. This analysis indicated that the gene pools of diploid and autotetraploid rice were somewhat dissimilar, as variation exists that distinguishes autotetraploid from diploid rices. Using this variation, we can breed new autotetraploid varieties with some important agricultural characters that were not found in the original diploid rice varieties.     

Water Relations of Seed Development and Germination in Muskmelon (Cucumis melo L.) : I. Water Relations of Seed and Fruit Development

Total water potential (ψ), solute potential, and turgor potential of field-grown muskmelon (Cucumis melo L.) fruit tissue (pericarp) and seeds were determined by thermocouple psychrometry at 5-day intervals from 10 to 65 days after anthesis (DAA). Fruit maturity occurred between 44 and 49 DAA, and seed germination ability developed between 35 and 45 DAA. Pericarp ψ was essentially constant at approximately −0.75 megapascal (MPa) from 10 to 25 DAA, then decreased to a minimum value of −1.89 MPa at 50 DAA before increasing to −1.58 MPa at 65 DAA. Seed ψ remained relatively constant at approximately −0.5 MPa from 10 to 30 DAA then decreased to −2.26 MPa at 50 to 60 DAA before increasing to −2.01 MPa at 65 DAA. After a rapid increase to 20 DAA, seed fresh weight declined until 30 DAA due to net water loss, despite continuing dry weight gain. As fruit and seed growth rates decreased, turgor potential initially increased, then declined to small values when growth ceased. A disequilibrium in ψ was measured between seeds and pericarp both early and late in development. From 20 to 40 DAA, the ψ gradient was from the seed to the tissue, coinciding with water loss from the seeds. From 50 to 65 DAA, seed ψ decreased, causing a reversal of the ψ gradient and a slight increase in seed water content. The partitioning of solutes between symplast and apoplast may create and maintain ψ gradients between the pericarp and seed. The low solute potential within the pericarp due to solute accumulation and loss of cellular compartmentation during ripening and sensecence may be involved in prevention of precocious germination of mature seeds.     

细胞分裂素在果实及种子发育中的作用

就最近几年来细胞分裂素与果实及种子发育的研究进展作简要介绍。     

The Influence of Seed Size Variation on Seed Germination and Seedling Vigour in Diploid and Tetraploid Dactylis glomerata L.

In this study the effects of seed size variation on germinationand seedling vigour have been investigated within and betweenploidy levels of diploid and related autotetraploid Dactylixglomerata. Rates of seed germination and seedling growth werecompared in two contrasting environments using diploid and tetraploidseeds of equal and also different biomass. Within each ploidylevel, seed biomass had no effect on either the overall percentagenor the rate of germination. In contrast, the comparison ofseeds of equal biomass but differing in ploidy level showedthat seeds from tetraploid plants germinated faster and to ahigher percentage than those from diploid plants. With respectto seedling growth, heavier seeds from the tetraploid genotypesgave seedlings of significantly higher biomass than those fromlighter tetraploid and diploid seeds throughout the 2 monthsof study. Interestingly, seeds of equal biomass but from differentploidy levels produced seedlings more similar than those fromthe extreme seed weight categories. These differences were maintainedin two different environmental conditions. These results suggestthat there is a complex interdependance of seed size and ploidyon seed germination and seedling growth but is not a simpleconsequence of differences in seed size between diploids andtheir related tetraploids.Copyright 1995, 1999 Academic Press Dactylis glomerata, polyploidy, seed size, germination, seedling     

Seed Development in Phaseolus vulgaris L. cv Seminole: II. Precocious Germination in Late Maturation

Seeds of Phaseolus vulgaris L. cv Seminole in late maturation phase germinated precociously in vitro. Germination occurred in the absence of free water after 5 days but within 24 to 48 hours in contact with water. Excised axes germinated within 12 hours and embryos by 48 hours only if supplied with water. Ethylene accelerated the germination of seeds and embryos irrespective of water availability. There was no effect of ethylene on the rate of axis germination. Ethylene was equally effective within the range 0.5 to 1000 parts per million and 1 hour exposure was fully effective. Induction of precocious germination in vivo was observed by manipulating water content inside pods or by ethylene injection, whether pods were attached to the parent plant or not. These results demonstrate the importance of endogenous regulation of water supply in suppressing precocious germination. Ethylene is identified as a powerful antagonist to the natural control.     

An Analysis of Seed Development in Pisum sativum II. The Effect of the r-Locus on the Growth and Development of the Seed

The r-locus is one of the few genetic loci known to affect thestorage product composition and the morphology of pea (Pisumsativum) seeds. Lines which are near-isogenic except for ther-locus have been developed to study the effects of this locuson seed development. The plant phenotypes of these lines werevery similar except for those characteristics previously attributedto the r-locus. The seed development of the two lines followedsimilar patterns until the endosperm was absorbed by the embryo.The fresh weight of the rr line then increased more rapidlydue to the overall effect of a higher rate of water uptake anda lower rate of dry weight increase of the rr embryos comparedwith embryos homozygous for the R-allele. The effect of the r-locus on the relationship between embryofresh weight and dry weight suggests that the alleles may beaffecting the osmotic regulation of the developing embryo. Pisum sativum, pea, seed development, r-locus, genetic variation, growth analysis