Castor (Ricinus communis L.) is one of the oldest cultivated crops, but currently it represents only 0.15% of the vegetable oil produced in the world. Castor oil is of continuing importance to the global specialty chemical industry because it is the only commercial source of a hydroxylated fatty acid. Castor also has tremendous future potential as an industrial oilseed crop because of its high seed oil content (more than 480 g kg−1), unique fatty acid composition (900 g kg−1 of ricinoleic acid), potentially high oil yields (1250–2500 L ha−1), and ability to be grown under drought and saline conditions. The scientific literature on castor has been generated by a relatively small global community of researchers over the past century. Much of this work was published in dozens of languages in journals that are not easily accessible to the scientific community. This review was conducted to provide a compilation of the most relevant historic research information and define the tremendous future potential of castor. The article was prepared by a group of 22 scientists from 16 institutions and eight countries. Topics discussed in this review include: (i) germplasm, genetics, breeding, biotic stresses, genome sequencing, and biotechnology; (ii) agronomic production practices, diseases, and abiotic stresses; (iii) management and reduction of toxins for the use of castor meal as both an animal feed and an organic fertilizer; (iv) future industrial uses of castor including renewable fuels; (v) world production, consumption, and prices; and (vi) potential and challenges for increased castor production.
Using an in vitro culture system, we observed the migration of malaria ookinetes on the surface of the mosquito midgut and invasion of the midgut epithelium. Ookinetes display constrictions during migration to the midgut surface and a gliding motion once on the luminal midgut surface. Invasion of a midgut cell always occurs at its lateral apical surface. Invasion is rapid and is often followed by invasion of a neighboring midgut cell by the ookinete. The morphology of the invaded cells changes dramatically after invasion, and invaded cells die rapidly. Midgut cell death is accompanied by activation of a caspase-3-like protease, suggesting cell death is apoptotic. The events occurring during invasion were identical for two different species of Plasmodium and two different genera of mosquitoes; they probably represent a universal mechanism of mosquito midgut penetration by the malaria parasite.T he transmission of malaria to a new vertebrate host depends on the successful passage of the malaria ookinete through the mosquito midgut, transformation to an oocyst on the external midgut wall, and the multiplication and migration of sporozoites into the lumen of the insect's salivary gland. After ingestion by its vector mosquito in a blood meal taken from an infected vertebrate host, male and female gametes form a zygote, which transforms into an ookinete in the lumen of the midgut. Before it can develop into an oocyst, however, the ookinete must escape from the blood meal and traverse the midgut epithelium to reach the midgut's basement membrane (1). Although several studies by light and transmission electron microscopy (TEM) have been directed at the ookinete's invasion of midgut cells (2-8), none have succeeded in producing a mechanistic description of the invasion process.The development in the past of methods to culture various stages of Plasmodium or to observe their behavior in vitro has been of great importance in our ability to study the malaria parasite (9-15). With this history in mind, we developed an in vitro system to observe ookinete migration on the mosquito midgut surface and penetration of midgut cells. We here report the mechanism and kinetics of midgut cell invasion by the malaria ookinete. Materials and MethodsParasite and Mosquito Cultivation. The 8A strain of the avian malaria parasite Plasmodium gallinaceum and the Liverpool͞ black eye strain of Aedes aegypti were used throughout this study. Parasites were maintained in white Leghorn chickens by serial blood passages. In addition, a standard laboratory strain of Anopheles stephensi was used, as well as the ANKA strain of Plasmodium berghei, which was maintained in BALB͞c mice by serial blood passages. Mosquitoes were raised and fed by using standard techniques (16, 17).Invasion Assay. The midgut was removed from bloodfed A. aegypti mosquitoes and was cut longitudinally into two halves (18). The midgut epithelia were cleaned of the blood meal and gently spread out on a glass slide in M199 medium supplemented with 2 mM L-glutamine͞100 units͞ml peni...
Autonomous chromosomes are generated in yeast (yeast artificial chromosomes) and human fibrosarcoma cells (human artificial chromosomes) by introducing purified DNA fragments that nucleate a kinetochore, replicate, and segregate to daughter cells. These autonomous minichromosomes are convenient for manipulating and delivering DNA segments containing multiple genes. In contrast, commercial production of transgenic crops relies on methods that integrate one or a few genes into host chromosomes; extensive screening to identify insertions with the desired expression level, copy number, structure, and genomic location; and long breeding programs to produce varieties that carry multiple transgenes. As a step toward improving transgenic crop production, we report the development of autonomous maize minichromosomes (MMCs). We constructed circular MMCs by combining DsRed and nptII marker genes with 7–190 kb of genomic maize DNA fragments containing satellites, retroelements, and/or other repeats commonly found in centromeres and using particle bombardment to deliver these constructs into embryogenic maize tissue. We selected transformed cells, regenerated plants, and propagated their progeny for multiple generations in the absence of selection. Fluorescent in situ hybridization and segregation analysis demonstrated that autonomous MMCs can be mitotically and meiotically maintained. The MMC described here showed meiotic segregation ratios approaching Mendelian inheritance: 93% transmission as a disome (100% expected), 39% transmission as a monosome crossed to wild type (50% expected), and 59% transmission in self crosses (75% expected). The fluorescent DsRed reporter gene on the MMC was expressed through four generations, and Southern blot analysis indicated the encoded genes were intact. This novel approach for plant transformation can facilitate crop biotechnology by (i) combining several trait genes on a single DNA fragment, (ii) arranging genes in a defined sequence context for more consistent gene expression, and (iii) providing an independent linkage group that can be rapidly introgressed into various germplasms.
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