subject: The Carbon Skeleton [print this page] The (+)-Discodermolide is a polyketide discovered recently, it has been found to be a potent inhibitor of cell growth tumor . The carbon skeleton of the molecule is made ??up of eight units of poly propionate and four acetate with 13 stereocenters .
In the area of genetic resources , a seed bank or seed bank is a place for the conservation of genetic diversity of one or more crops and their wild relatives. In many cases, but not retained seeds other propagules such as tubers or roots because the crop in question is multiplied only asexually. The conservation of the seeds is performed at low temperatures, so as to maintain adequate for many years viability thereof. Physically, genebanks consist of large deposits on seed stored at low temperatures.
The reasons for storing seeds in genebanks can be varied. In the case of crops for food, many useful plants that have evolved over centuries and is not used for commercial agricultural production and are increasingly rare, so it is essential to preserve them before their complete disappearance. Storing seeds also guards against catastrophic events like natural disasters, outbreaks of disease or war.
There are about 6 million accessions or samples of a particular plant population, stored as seeds in about 1,300 seed banks around the world since 2006. This represents only a small fraction of the world's biodiversity, since many parts of the world have not been fully explored to collect genetic resources.
The seeds to be preserved in the genebank are harvested and dried to a moisture content of less than 5%. The seeds are then stored in freezers at -18 C or less. Because the seed loses its viabiliad with time, the seeds have to be periodically reseeded so fresh seed to harvest which initiate another round of long-term storage.
The self-incompatibility (AI) is the inability of a plant hermaphrodite to produce seeds by self-pollination although this gamete viable. It is a reproductive strategy to promote fertilization among unrelated individuals and, therefore, is a creative mechanism of new genetic variability . 1
During the evolution of angiosperms the AI has arisen on several occasions, totally different lineages. More than 100 families of plants, among which include the Solanaceae , Poaceae , Asteraceae , Brassicaceae , Rosaceae and Fabaceae , have self-incompatible species. In fact, it is estimated that 39% of angiosperm species are AI. 2 As widely distributed taxonomy is consistent with the existence of several different genetic mechanisms that regulate the LA, depending on the family considered.
However, in all cases the same phenomenon is observed: the grains of pollen reaching the stigma of the same plant (or plants genetically related) are incapable of effecting the impregnation because stop developing in some stage of the process (germination of pollen grains, pollen tube development in pistils and fertilization of the oosphere). As a result of this impediment is not set seed after self-pollination. 1 This arrest of growth or development of pollen tubes within the pistils involves, first, the recognition by the pistil of pollen tubes which are the same individual and which are the other plants. On the other hand, occur after this recognition, the development of pollen tubes themselves (or of genetically related) should be discontinued. Both phenomena, the recognition and cessation of growth, have been studied extensively both cytological , physiological , genetic and molecular .
As stated previously, the AI systems in higher plants have evolved several times in independent lineages. At the molecular level, there are three systems properly characterized by: the self-incompatibility system of the Solanaceae and Rosaceae , that of the poppy ( Papaver ) and the Brassica . In two such systems are currently known genes encoding the recognition component pollen-pistil which has clearly demonstrated that proteins of the pistil and pollen involved in recognition are different from each other and that the AI is a mechanism of "key lock" at the molecular level.When the flowers of the species that has self-incompatibility are morphologically identical, it is said that self-incompatibility is homomorphic . Conversely, when the species are two or three different morphological types of flowers, it is said that the self-incompatibility is heteromrfica and the mechanism is called heterostyly . The best studied of AI mechanism in plants acts through the inhibition of germination or growth of pollen tubes in the stigma or the like. This mechanism is based on interactions between proteins produced by a single locus called S (English Self-incompatibility , or self-incompatibility). The S locus contains two genes actually basic, one of which is expressed in the pistil and the other in the anther or pollen grains. Reference is made ??to such genes as determinants of female and male, respectively. These genes are physically close in the genome , genetically linked and are considered as a single allele . The protein produced by male and female determinants of the same allele interact with each other at the time of germination of pollen on the stigma and lead to the arrest of pollen tube growth. In other words, the identity of the proteins from the pollen grain and stigma AI generates a response that stops the process of fertilization since the beginning of it. When, by contrast, a female determinant interacting with a male determinant from a different allele of AI, no response to AI and fertilization occurs. This brief description of the AI response in plants is usually more complicated and, often involving more than one locus of AI. Thus, in the grass , there are two loci that govern the reaction of AI-called S and Z . 6 Two types of incompatibility homomorphic, the IA and IIA gametophytic sporophytic, which are described below.http://www.prairiefloristsaskatoon.ca/by: Plumstech
