Development tuberization

So much for the theory, in practice this approach led to a significant reduction in the starch yield rather than the expected increase.25 Measurements of the intermediates revealed that at the first approximation the approach was working as intended there was in excess of a 90% reduction in the sucrose content, while the hexose phosphate levels increased by a factor of 7. However, detailed measurements of both starch levels in developing tubers and density measurements on tubers following large scale greenhouse trials confirmed that there was in fact a 30% reduction in the yield of starch. 

Timing during the development cycle is also a critical factor. For example, during the first half of the developmental cycle, photosynthate is partitioned predominantly into stem storage sites (Incoll and Neales, 1970 McLaurin et al., 1999). However, with the onset of tuber bulking, allocation within the plant shifts dramatically. Now a major portion of new assimilate preferentially moves into the rapidly developing tubers, and assimilate previously stored in the stems begins to be recycled to the tubers. 

Approximately 20 weeks after planting, tuber bulking accelerated, with stored carbon redistributed from other organs into the developing tubers (Somda et al., 1999). The tubers continued to accumulate carbon until the final harvest, at which time they contained 93.3 mg g 1 dwt or 437.8 mgg fwt (Table 10.5). By the end of the developmental cycle the tubers accounted for approximately 68% of the total plant carbon content, compared to 28% for the stems and less than 2% for each of the other plant parts. Approximately 61.2, 65.3, and 42.7% of carbon in the leaves, stems/branches, and rhizomes, respectively, were redistributed to the tubers (or lost via respiratory or other processes). The stems/branches contributed the greatest percentage of carbon to the mature tubers (77.2%), followed by the leaves (14.7%) and rhizomes (1.7%). 

Viola, R., Davies, H. V., and Chudeck, A. R. 1991. Pathways of starch and sucrose biosynthesis in developing tubers of potato (Solanum tuberosum L.) and seeds of faba bean (Vicia faba L.) Elucidation by 13C-nuclear magnetic-resonance spectroscopy. Planta 183, 202-208. 

Gardner A., Davies H.V., and Burch L.R. 1992. Purification and properties of fructokinase from developing tubers of potato (Solamtm tuberosum L.). Plant Physiol 100 178-183. 

Another plant hormone with important function in growth and development as well as in environmental responses is a group called cytokinins (CKs). CKs are involved in processes such as seed development, tuber formation, shoot and meristem... 

Nufrifional bars confaining cold-extruded whey have been developed (Joseph et ah, 1995). Extrusion was conducted at 37 °C to produce a low-calorie product with high nutrient value. A weaning food was obfained by extending WPC, WPI, or a-LA with taro flour, which is derived from a tropical root tuber (Onwulata et ah, 2002). The extrudates were pulverized, made into powders, and rehydrated into pastes. WPI coblended extrudates produced the best consistency. 

In a replacement-series study, Elmore et al. (27) have shown that purple nutsedge is a stronger competitor than four other species, including cotton. The data are insufficient to document allelopathy, but nutsedge tuber residue has been shown to affect cotton seedling development (31). 

The unique suberin components that are not found as significant components of cutin are the very long chain molecules and the dicarboxylic acids. Therefore, chain elongation and conversion of co-hydroxy acids to the corresponding dicarboxylic acids constitute two unique biochemical processes involved in the synthesis of suberin. Incorporation of labeled acetate into the very long chain components of suberin was demonstrated and this ability developed during suberization in potato tuber disks [73]. The enzymes involved... 

Norwalk virus (NV) capsid protein Potato tuber tobacco leaf Mice and humans developed serum IgG and secretory IgA specific for recombinant NV. Immunogenic in mice and humans when administered orally. 45,57... 

Transmissible gastroenteritis coronavirus N-terminal domain of the spike glycoprotein (S) Potato tuber Mice developed serum antibodies specific for gS. Immunogenic in mice when delivered parenter-ally or orally. 115, 116... 

Enterotoxigenic E. coli epitope and rotavirus epitope fused to CTB Potato tuber Mice developed detectable levels of serum and intestinal antibodies. Immunogenic in mice against ETEC, rotavirus, and V. cholerae when delivered orally. Symptoms reduced in passively immunized mouse neonates following rotavirus challenge. 63... 

The development of a by-production system could further minimize the cost of such plant-derived products. For example, potatoes are the raw material for the production of technical grade starch. During this process, soluble proteins are separated by heat treatment and sold as animal fodder. Recombinant proteins could be produced in transgenic potato tubers as a by-product of starch extraction, and this would be useful for proteins produced in large amounts with a low commercial impact, like structural fiber proteins. 

Kolomiets MV, Hannapel DJ, Chen H, Tymeson M and Gladon RJ. 2001. Lipoxygenase is involved in the control of potato tuber development. Plant Cell 13 613-626. 

The introduction of the invertase from yeast alone was not sufficient. Invertase cleaves sucrose to release the two component sugars, glucose and fructose. While fructose can be readily metabolized by fructokinase in potato tubers, there is insufficient hexokinase activity in developing potato tubers to bring the glucose into intermediary metabolism. Therefore, it was necessary to introduce a second transgene, a bacterial glucokinase, in order to ensure that the hexoses became available for subsequent metabolism.25... 

GEIGENBERGER, P., STITT, M., Sucrose synthase catalyses a readily reversible reaction in vivo in developing potato tubers and other plant systems, Planta, 1991,189, 329-339. 

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