Identification of potentially embryogenic microspores in Brassica napus

Studies were undertaken with Brassica napus L. cv. Topas to identify buds containing microspores predisposed to embryogenesis in vitro and to investigate bud and microspore development in relation to this process. No significant correlation was found between the final embryo number and bud components. There appears to be a developmental window of less than 8 h duration during which microspores are very likely to form embryos: over 70% of the microspores can undergo division and up to 70% of these can form embryos. Embryos were mainly obtained from late uninuucleate to early binucleate microspores: the former contained mainly a G2 or M phase nucleus located at the microspore periphery and the latter a generative nucleus (associated with the intine) and a vegetative nucleus. Observations indicated that only the vegetative nucleus contributed to embryo formation. The first embryogenic division occurred between 8 and 16 h for uninucleate- and between 8 and 48 h for binucleate-derived embryos.     

Detection of linkage between marker loci and loci affecting quantitative traits in crosses between segregating populations

Summary By making use of pedigree information and information on marker-genotypes of the parent and F-1 individuals crossed to form an F-2 population, it is possible to carry out a linkage analysis between marker loci and loci affecting quantitative traits in a cross between segregating parent populations that are at fixation for alternative alleles at the QTL, but share the same alleles at the marker loci. For two-allele systems, depending on marker allele frequencies in the parent populations, 2–4 times as many F-2 offspring will have to be raised and scored for markers and quantitative traits in order to provide power equivalent to that obtained in a cross between fully inbred lines. Major savings in number of F-2 offspring raised can be achieved by scoring each parent pair for a large number of markers in each chromosomal region and scoring F-1 and F-2 offspring only for those markers for which the parents were homozygous for alternative alleles. For multiple allele systems, particularly when dealing with hypervariable loci, only 10%–20% additional F-2 offspring will have to be raised and scored to provide power equivalent to that obtained in a cross between inbred lines. When a resource population contains novel favorable alleles at quantitative trait loci that are not present (or rare) in a commercial population, analyses of this sort will enable the loci of interest to be identified, mapped and manipulated effectively in breeding programs.Contribution no. 2124-E, 1987 series from The Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel     

Natural selection of allozyme polymorphisms: a microgeographic climatic differentiation in wild emmer wheat (Triticum dicoccoides)

Summary Allozymic variation in proteins encoded by 48 loci was analyzed electrophoretically in 1984 and 1985 in 137 individual plants of wild emmer wheat, Triticum dicoccoides, from a microsite in Yehudiyya, northeast of the Lake of Galilee, Israel. The test involved two climatic microniches in the open Tabor oak forest (1) sunny between trees and (2) shady under trees' canopies. Significant genetic differentiation at single-, two- and multilocus structures was found between neighboring climatic niches, which were only separated by a few meters. Our results suggest that allozyme polymorphisms in wild emmer wheat are partly adaptive, and differentiate primarily at the multilocus level by climatic factors presumably related to aridity stress.     

Structure of the Bombyx mori fibroin light-chain-encoding gene: upstream sequence elements common to the light and heavy chain.

Two overlapping genomic clones containing the fibroin light-chain (Fib-L)-encoding gene (Fib-L) were obtained from the cosmid library of the silkworm, Bombyx mori J-139, by hybridization with the Fib-L cDNA clone. Sequencing of the 14.6-kb region revealed that Fib-L was 13472 bp long containing seven exons, and that the gene contained a large first intron which occupied about 60% of the gene. Comparison of restriction patterns of the J-139 Fib-L with those of eight other B. mori breeds producing normal-level fibroin demonstrated that considerable restriction-fragment length polymorphisms were present in regions containing the first intron and the 3′-flanking sequence. However, sizes of the Fib-L mRNA and the Fib-L polypeptide were very similar among the nine breeds tested, suggesting that the exon sequences and the splice signals were all well conserved. 5′-Flanking regions of Fib-L and the fibroin heavy-chain (Fib-H)-encoding gene (Fib-H) compared in this study contained three 18-30-bp sequences of high similarity and many 8-10-bp common elements, six of which coincided with the binding sites of homeodomain proteins. Gel retardation assays with the nuclear extracts of the posterior and middle silk glands suggested that protein factors present in the posterior silk-gland nuclei could bind to a set of those common upstream elements.     

Floral scent in dioeciousSalix (Salicaceae)—a cue determining the pollination system?

Floral scents of male and female inflorescences of three dioeciousSalix species were collected by head-space adsorption, and analysed by GC-MS. InSalix caprea andS. cinerea 1,4-dimethoxy benzene was the main compound, and male and female scents showed a high degree of resemblance. No dominant compound was found inS. repens and malefemale scent similarity was low. Floral scent inSalix is likely a strong orientation cue, guiding pollinators between male and female plants ensuring pollen transfer and pollination. We suggest that a high degree of male-female floral scent resemblance is coupled to a high degree of insect pollination. Floral scent does not promote reproductive isolation betweenS. caprea andS. cinerea.     

Reproductive and Pollination Biology of Magnolia and its Allied Genera (Magnoliaceae). I. Floral Volatiles of Several Magnolia and Michelia Species and their Roles in Attracting Insects

Abstract Volatile substances emitted from the flowers of eight Magnolia taxa ( M. sieboldii ssp. japonica, M. praecocissima var. praecocissima and var. borealis, M. tomentosa, M. salicifolia, M. obovata, M. denudata, and M. grandiflora ) and one Michelia species ( M. compressa ) (Magnoliaceae) were examined and identified using GC-MS. Volatile substances of these Magnolia and Michelia species consist primarily of monoterpenoids and sesquiterpenoids produced by the mevalonate pathway, acetogenins by the acetate-malonate pathway, and phenyl-propanoids by the shikimate pathway. These Magnolia and Michelia species all possessed various combinations of volatile monoterpenoids, acetogenins, and phenylpropanoids, except for Magnolia obovata , which emitted primarily sesquiterpenoids. Free amino acids in pollen of 12 Magnolia and one Liriodendron species were also analyzed, and their value as food sources for pollinators evaluated.
Pollinators visiting the flowers of five Magnolia species were collected in their native sites and identified. Their behaviors and roles as pollinating agents were assessed.     

Nutrient levels in malformed and healthy tissues of mango (Mangifera indica L.)

Samples of malformed and healthy panicles of mango (Mangifera indica L.) as well as leaves and shoots bearing them were collected at different stages of development (fully swollen buds, bud inception, fully grown panicles prior to full bloom and at full bloom) over two consecutive years and were analysed for their macro- and micronutrient status. In addition, malformed and healthy seedlings were collected and analysed. Malformed panicles were found to be significantly higher in N at all the developmental stages except at bud inception. Phosphorus and K also tended to accumulate in malformed panicles at later stages of their development. In general, malformed panicles exhibited lower levels of P, K and Ca than healthy panicles. The differences in levels of Mg and S in malformed and healthy panicles were not significant. All micronutrients were in much lower concentrations in malformed panicles except for Mn which appears to accumulate in malformed panicles particularly at the early stages of development. The leaves on the shoots bearing malformed panicles also showed a tendency to accumulate N, while P, Mg and S were always higher in leaves on shoots bearing healthy panicles. The leaves on shoots bearing healthy panicles had lower levels of Fe, Cu and Mn, whereas levels of Zn and B tended to be higher in leaves on shoots bearing malformed panicles. The nutrient concentration differences between the two kinds of shoots were generally nonsignificant (P=0.05), except for K and S which were significantly lower in shoots bearing malformed panicles. The shoots bearing malformed panicles showed significantly (P=0.05) higher levels of almost all nutrients compared with shoots bearing healthy panicles. Vegetative malformation was found to be associated significantly (p=0.05) with higher amounts of all nutrients except Ca which was significantly higher in healthy seedlings. The present study, therefore, seems to point to lower Ca as one of the pre-disposing factors causing malformation in mango.A part of Ph.D. thesis of the senior author.A part of Ph.D. thesis of the senior author.     

Parentage determination in maize hybrids using the arbitrarily primed polymerase chain reaction (AP-PCR)

Summary Using a novel procedure based on the polymerase chain reaction, we have developed a rapid, efficient, and economical method for identifying plant genotypes. The arbitrarily primed polymerase chain reaction (AP-PCR) generates reproducible fingerprints from any organism, without the need for DNA sequence information. These fingerprints include DNA fragment polymorphisms that can be (1) used for varietal identification and parentage determination, (2) followed in segregating populations produced by crosses, (3) used as markers for the construction of genetic maps, and (4) used to generate dendograms of phylogenetic relationships, especially at the intraspecific level. AP-PCR requires only minute quantities of DNA (10–25 ng per reaction) and therefore can be used in situations in which DNA is limiting. We demonstrate the use of AP-PCR to identify inbred parents of hybrid maize plants in double-blind experiments.     

Paradise lost: Mitochondrial eve refuted

Being based solely on neontological data, all «unique parent» evolutionary hypotheses, of which «Mitochondrial Eve» is one, fall into the category ofscala naturae. Mathematical treatment of neontological data bases, using cladistic approaches does not confer the status of scientific hypotheses onto such scenarios. Apart from these fundamental problems, such hypotheses are flawed on a number of other bases, including the fact that there is a proportion of parental contribution to mitochondrial lineages, despite widely publicised statements that mithocondrial DNA in mammals is «strictly» maternally inherited. Other weaknesses of «unique mother» hypotheses on that their proponents endeavour to describe the evolution of diploid organisms on the basis of variability in extant haploid organelles, the evolution of which is delinked from that of the diploid organism. A further difficulty is that it is not possible to reconstruct interspecific relationships on the basis of intraspecific variability. There is a general ignorance among proponents of «unique mother» hypotheses regarding the distribution of biological variability on the surface of the globe, a fact which renders the molecular clock inaccurate, and which upsets the simplistic proposal that molecular diversity equates with time. «Unique mother» scenarios are also invalidated by the presence of shared chromosome and other polymorphisms in african great apes and humans at similar percentages in the different lineages, a fact which indicates that these evolving populations did not experience «bottlenecks». These and other difficulties effectively refute the «Mitochondrial Eve» hypothesis, which in any case much resembles creationism of a special kind, in which the offspring of a breeding pair are visualised as belonging to a species different from its parents. Such extreme examples of the punctuational mode of evolution are highly likely to be incorrect.     

Resumption of cellular activity induced by cytokinin and gibberellin treatments in tomato flowers targeted for abortion in unfavorable light conditions

Mitotic activity and nuclear DNA synthesis in tomato ( Lycopersicon esculentum Mill., cv. King plus) flowers targeted for abortion under unfavorable light conditions are completely stopped 6 days after macroscopic appearance of the inflorescence. Ovular cells are arrested at the G₁ (80%) and G₂ (20%) stages of the cell cycle. Exogenous applications of a mixture of N⁶-benzyladenine (BA) and gibberellins A₄₊₇ (GA) directly on the inflorescence may prevent its failure. Nuclear DNA synthesis and mitoses resume in ovules of the flower 16 to 20 h after the BA+GA treatment. When applied alone, BA and GA are able to mimic the effect of the mixture upon the progression of ovular cells through their cycle. Sporogenesis processes are also set in motion by the exogenous plant growth regulators. The mechanism of action of cytokinins and gibberellins in the control of floral development is discussed.