David W Galbraith
Work Summary
I examine the molecular functions of the different cells found in the tissues and organs of plants and animals and how they combine these functions to optimize the health and vigor of the organism.
I examine the molecular functions of the different cells found in the tissues and organs of plants and animals and how they combine these functions to optimize the health and vigor of the organism.
PMID: 19675157;PMCID: PMC2754645;Abstract:
A great number of plants synchronize flowering with day length. In rice (Oryza sativa), photoperiod is the primary environmental cue that triggers flowering. Here, we show that the s73 mutant, identified in a g-irradiated Bahia collection, displays early flowering and photoperiodic insensitivity due to a null mutation in the PHOTOPERIOD SENSITIVITY5 (SE5) gene, which encodes an enzyme implicated in phytochrome chromophore biosynthesis. s73 mutant plants show a number of alterations in the characteristic diurnal expression patterns of master genes involved in photoperiodic control of flowering, resulting in up-regulation of the floral integrator Heading date3a (Hd3a). Early heading date1 (Ehd1), an additional rice floral activator, was also highly expressed in the s73 mutant, suggesting that SE5 represses Ehd1 in wild-type plants. Silencing of Ehd1 in both Bahia and s73 backgrounds indicated that SE5 regulates Ehd1 expression. The data also indicate that SE5 confers photoperiodic sensitivity through regulation of Hd1. These results provide direct evidence that phytochromes inhibit flowering by affecting both Hd1 and Ehd1 flowering pathways. © 2009 American Society of Plant Biologists.
Flow cytometry provides a rapid, accurate, and simple means to determine nuclear DNA contents (C-value) within plant homogenates. This parameter is extremely useful in a number of applications in basic and applied plant biology; for example, it provides an important starting point for projects involving whole genome sequencing, it facilitates characterization of plant species within natural and agricultural settings, it allows facile identification of engineered plants that are euploid or that represent desired ploidy classes, it points toward studies concerning the role of C-value in plant growth and development and in response to the environment and in terms of evolutionary fitness, and, in uncovering new and unexpected phenomena (for example endoreduplication), it uncovers new avenues of scientific enquiry. Despite the ease of the method, C-values have been determined for only around 2% of the described angiosperm (flowering plant) species. Within this small subset, one of the most remarkable observations is the range of 2C values, which spans at least two orders of magnitude. In determining C-values for new species, technical issues are encountered which relate both to requirement for a method that can provide accurate measurements across this extended dynamic range, and that can accommodate the large amounts of debris which accompanies flow measurements of plant homogenates. In this study, the use of the Accuri C6 flow cytometer for the analysis of plant C-values is described. This work indicates that the unusually large dynamic range of the C6, a design feature, coupled to the linearity of fluorescence emission conferred by staining of nuclei using propidium iodide, allows simultaneous analysis of species whose C-values span that of almost the entire described angiosperms.
Cytometric instruments and the associated measurement methodologies were generally developed to enable examination of the properties of mammalian cells, tissues, and organs, with a major concern being that of human health. This general statement is particularly applicable to flow cytometric measurements, which were originally used for the study of blood cells, and analysis of these cells and their subsets remains a major fraction of the activities in flow cytometry and cell sorting. Although this statement is less applicable to image cytometry, including microscopy in its various forms, both flow and image cytometry encounter technical difficulties when they are applied outside the field of mammalian biology. Part of this relates to structural issues: cells of non-mammalian origin are often of sizes very different to those of mammals, and may come in the form of tissues and organs that are difficult to convert into single cell suspensions. Cell suspensions obtained from natural non-mammalian ecosystems may also comprise mixtures of cells of very different sizes. Part of this also relates to the functional activities of non-mammalian cells in producing secondary products, or other polymeric components that can interfere with cytometric measurements. This special section describes four recent articles that demonstrate ways in which cytometric methodologies can be improved to ameliorate systematic errors in measurement that are a consequence of the unconventional properties of the cells being studied.