哺乳动物的受精

受精是单倍体配子（精子和卵子）融合产生新生命的过程,是有性生殖个体发育的起点。根据动物种类的不同,受精可以发生在体内,也可以发生在体外。它一方面恢复了染色体双倍体数目,保证了双亲的遗传作用;另一方面,受精可以把生殖细胞通过减数分裂同源重组获得遗传物质变化和个体发生过程中产生的变异遗传下去,保证了物种的遗传多样性,在生物进化上具有重要意义。     

Environmental friendly nitrogen fertilization

With the huge intensification of agriculture and the increasing awareness to human health and natural resources sustainability, there was a shift towards the development of environmental friendly N application approaches that support sustainable use of land and sustain food production.The effectiveness of such approaches depends on their ability to synchronize plant nitrogen demand with its supply and the ability to apply favored compositions and dosages of N-species.They are also influenced by farming scale and its sophistication, and include the following key concepts: (i) Improved application modes such as split or localized ("depot") application; (ii) use of bio-amendments like nitrification and urease inhibitors and combinations of (i) and (ii); (iii) use of controlled and slow release fertilizers; (iv) Fertigation-fertilization via irrigation systems including fully automated and controlled systems; and (v) precision fertilization in large scale farming systems. The paper describes the approaches and their action mechanisms and examines their agronomic and environmental significance. The relevance of the approaches for different farming scales, levels of agronomic intensification and agro-technical sophistication is examined as well.     

Imaging motility during fertilization

Studying reproduction in domestic species is now possible at the cellular and molecular level due to advances in the production of large numbers of zygotes and embryos in these species. In this paper we review the microtubule patterns during fertilization in domestic species. These results indicate that domestic species accomplish fertilization in a similar fashion to one another but in a far different fashion from rodents. Recent results indicate that human fertilization is similar to that of domestic species. We discuss the significance this has on the use of domestic species as a model system for human studies and possible consequences for the alleviation of human infertility.     

Environmental friendly nitrogen fertilization

With the huge intensification of agriculture and the increasing awareness to human health and natural resources sustainability, there was a shift towards the development of environmental friendly N application approaches that support sustainable use of land and sustain food production.

The effectiveness of such approaches depends on their ability to synchronize plant nitrogen demand with its supply and the ability to apply favored compositions and dosages of N-species. They are also influenced by farming scale and its sophistication, and include the following key concepts: (i) Improved application modes such as split or localized (“depot”) application; (ii) use of bio-amendments like nitrification and urease inhibitors and combinations of (i) and (ii); (iii) use of controlled and slow release fertilizers; (iv) Fertigation-fertilization via irrigation systems including fully automated and controlled systems; and (v) precision fertilization in large scale farming systems. The paper describes the approaches and their action mechanisms and examines their agronomic and environmental significance. The relevance of the approaches for different farming scales, levels of agronomic intensification and agro-technical sophistication is examined as well.

     

Single fertilization inSpiranthes sinensis

The reproduction system inSpiranthes sinensis (Orchidaceae), collected at various localities in Japan, was revealed to be of a peculiar new type which is not to be found in other angiosperms. None of generative cell nuclei has been observed to dividede novo throughout the progamic phase, although they do participate in fertilization. Neither fertilization of the generative cell nucleus with the central nucleus nor formation of endosperm occurred in this plant. Although the chromosome number in the developing proembryonic cells numbered 2n=30, exhibiting diploidy, the number of marker chromosomes was equal to the sum of half the number of marker chromosomes of the parental clones. From the results described above, we may conclude that the reproduction system of this species represents a new type of single fertilization (non-double fertilization) between egg cell and sperm cell nuclei caused by the omission of generative cell division and the formation of only one sperm cell nucleus.     

Environmental friendly nitrogen fertilization

With the huge intensification of agriculture and the increasing awareness to human health and natural resources sustainability, there was a shift towards the development of environmental friendly N application approaches that support sustainable use of land and sustain food production. The effectiveness of such approaches depends on their ability to synchronize plant nitrogen demand with its supply and the ability to apply favored compositions and dosages of N-species. They are also influenced by farming scale and its sophistication, and include the following key concepts: (i) Improved application modes such as split or localized ("depot") application; (ii) use of bio-amendments like nitrification and urease inhibitors and combinations of (i) and (ii); (iii) use of controlled and slow release fertilizers; (iv) Fertigation-fertilization via irrigation systems including fully automated and controlled systems; and (v) precision fertilization in large scale farming systems. The paper describes the approaches and their action mechanisms and examines their agronomic and environmental significance. The relevance of the approaches for different farming scales, levels of agronomic intensification and agro-technical sophistication is examined as well.     

Nitrogen fertilization in citrus orchards

Summary The purpose of this review was to evaluate critically the results obtained in citrus nitrogen fertilization experiments in Israel and in other parts of the world, in order to increase our understanding of the processes involved and to improve the recommendations to growers. Mature citrus trees contain 1–2 kg N/tree, 30–60% of which is in the annual parts (leaves and fruits). 30g N is deposited annually in the tree skeleton. Based on these results and on a review of long-term fertilization experiments with citrus from various parts of the world, it was concluded that 200 kg N/ha applied annually is sufficient to sustain good citrus yields and tree development, about half of which is incorporated in the fruits and one-tenth deposited in the tree, the balance being made up by leaching and gaseous losses. Experiments with¹⁵N labeled fertilizer applications showed that the highest N-uptake rate occurred during fruit set and that in winter the uptake was very low. N reserves in the older tissues played an important part in the development of new leaves and flowers in the spring, when the uptake from the soil was still low. It was concluded that the nitrogen contained in the soil organic matter (2 Mg/ha) and in the mature trees (1 Mg/ha) plays an important part in the regulation of N supply to the growing parts of the tree. More N is derived from these parts with low N fertilization than with an abundant supply. The purpose of fertilization is to ensure proper development of the tree, not the current fruit yield. Contribution from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel. No. 1770-E. 1986 series.     

Carbohydrates and fertilization in animals

A frequently used mechanism for sperm-egg recognition in many species involves complementary protein-carbohydrate interaction. The usual paradigm includes complex glycoconjugates in reproductive tract fluids or on the eggs which are recognized by carbohydrate-binding proteins on the sperm surface. Various glycoconjugates are utilized in the steps of sperm capacitation, sperm binding to the egg extracellular matrix and vitelline membrane and induction of the acrosome reaction. Several types of complex glycoconjugates are involved in these processes, including proteoglycans, lactosaminoglycans, sulfated fucose-containing glycoconjugates, and glycoproteins. There appear to be some structural similarities between active glycoconjugates; they are large in molecular weight and complex, and they are often sulfated, fucosylated, and attached to a protein through serine or threonine residues. In some species, the protein core of the glycoconjugates also participates in the interaction by limiting the binding of carbohydrates to sperm only of the relevant species, likely by providing the proper steric arrangement for the interaction. In other cases the protein core seems to serve more as a crosslinker of the carbohydrate moieties. This review discusses the types of glycoconjugates implicated in fertilization and the complementary lectin-like proteins found on sperm.     

Induced single fertilization in maize

 Bicellular pollen with one vegetative nucleus and one diploid arrested generative cell (”monospermic” pollen) was induced by trifluralin treatment of diploid maize plants at 7–9 days before flowering. The arrested generative cell (seemingly a diploid sperm cell) fused with the central cell of diploid plants and produced shriveled endosperm resembling that of a 2n×4n cross in maize. Dual pollination experiments with a purple embryo marker revealed single fertilization events in which the union of one sperm cell with the egg occurs but there is no union of a second sperm cell with the central cell. Singly fertilized ovules survived at least 4 days. Furthermore, many viable triploid plants were obtained. This technique therefore appears to have the potential for manipulating ploidy level in crops and may become useful in investigating fertilization mechanisms of angiosperms. Received: 1 October 1996 / Revision accepted: 8 January 1997