As part of a project to identify nove1 maize (Zea mays 1. cv B73) genes functionally, we have partially sequenced 130 randomly selected clones from a maize leaf cDNA library. Data base comparisons revealed seven previously sequenced maize cDNAs and 18 cDNAs with sequence similarity to related maize genes or to genes from other organisms. One hundred five cDNAs show little or no similarity to previously sequenced genes. Our results also establish the suitability of this library for large-scale sequencing in terms of its large insert size, proper insert orientation, and low duplication rate.
As one component of a maize genome project, we report the analysis of a number of randomly selected cDNAs, by a combination of measuring mRNA expression, 'single-pass' sequencing (SPS), and genome mapping. Etiolated seedling (490) and membrane-free polysomal endosperm cDNA clones (576) were evaluated for their transcription levels by hybridizing with a probe prepared from total mRNA and categorized as corresponding to abundantly or rarely expressed mRNAs and as either constitutive or tissue-specific. A total 313 clones from the two libraries were submitted to 'single-pass' sequencing from the presumed 5' end of the mRNA and the nucleotide sequence compared with the GenBank database. About 61% of the clones showed no significant similarities within GenBank, 14% of the clones exhibited a high degree of similarity, while the remaining 25% exhibited a lesser degree of similarity. The chromosomal location of more than 300 clones was determined by RFLP mapping using standard populations. The results demonstrate that a combination of analyses provides synergistic information in eventually deducing the actual function of these types of clones.
ABSTRAC1The flow of carbon into sucrose and starch was investipted in fully expanded primary leaves of spinach using the long to short day transition and partial defoliation as tools to manipulate sucrose/starch synthesis. Transfer from 12 hour to 7 hour photosynthetic periods resulted in a 4-fold increase in the initial rate of starch synthesis, a 50% increase in the initial rate of sucrose synthesis, a 30% increase in leaf sucrose, and a 40% decrease in fructose, 2,6-biphosphate. In addition, sucrose synthesis rates in cells isolated from shortened daylength plants are 80% higher than in cells isolated from control plants. These results show that, in spinach, an increase in the rates of both sucrose and starch synthesis can occur under short day conditions. In contrast, when short day plants are partially defoliated, starch levels remain high, fructose 2,6-biphosphate levels remain low, but the level of leaf sucrose drops by 50%. Thus, when demand exceeds supply, starch synthesis has priority over filling of leaf sucrose pools in the short day plant.Sucrose and starch biosynthetic pathways are major consumers of fixed CO2 in the photosynthetic cell. The regulation of these pathways, therefore, should be tightly coupled to the requirement for photosynthate by the rest of the plant. Previous work demonstrated that transfer of plants from long to shortened photosynthetic periods resulted in an increased rate of starch synthesis (2-5, 13, 14, 16, 19) and that this increased rate is maintained in chloroplasts isolated from SD' plants (16). These results show that starch synthesis rates can increase under conditions where daily assimilate production is reduced (SD) and that cytoplasmic metabolite regulation is not the only mechanism available for adjusting the rates of synthesis. Thus, starch synthesis is tightly coupled to the diurnal demand for assimilate and the process is not simply the result of an 'excess' supply of assimilate.The effect of SD conditions on the rate of sucrose synthesis is not as well defined. As sucrose and starch synthesis are often inversely related (13,24), it would be reasonable to conclude that in the SD plant, sucrose synthesis rates should decline. Such a decline has, in fact, been observed in cells isolated from SD soybean leaves (13). Yet under SD conditions, in
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.