Applications & Publications

An Improved Method for Extracting, Sorting, and AMS Dating of Pollen Concentrates From Lake Sediment

High-resolution chronologies are crucial for paleoenvironmental reconstructions, and are particularly challenging for lacustrine records of terrestrial paleoclimate. Accelerator Mass Spectrometry (AMS) radiocarbon measurement of terrestrial macrofossils is the most common technique for building age models for lake sediment cores, but relies on the presence of terrestrial macrofossils in sediments. In the absence of sufficient macrofossils, pollen concentrates represent a valuable source of dates for building high-resolution chronologies. However, pollen isolation and dating may present several challenges, as has been reported by different authors in previous work over the last few decades. Here we present an improved method for extracting, purifying and radiocarbon-dating pollen concentrates using flow cytometry to improve the extraction efficiency and the purity of the pollen concentrates. Overall, the nature of the sediments and the abundance of the pollen represent major considerations in obtaining enough pollen grains and, consequently, enough carbon to be dated. Further, the complete separation of pollen from other forms of organic matter is required to ensure the accuracy of the dates. We apply the method to surface samples and sediment cores recovered from two contrasting lake basins on the eastern side of the Sierra Nevada (California), and describe the variations that may be used to optimize pollen preparation from a variety of sediments.

Testing Pollen Sorted by Flow Cytometry as the Basis for High-Resolution Lacustrine Chronologies

A new seed-based assay for meiotic recombination in Arabidopsis thaliana

Meiotic recombination is a fundamental biological process that plays a central role in the evolution and breeding of plants. We have developed a new seed-based assay for meiotic recombination in Arabidopsis. The assay is based on the transformation of green and red fluorescent markers expressed under a seed-specific promoter. A total of 74 T-DNA markers were isolated, sequenced and mapped both physically and genetically. Lines containing red and green markers that map 1–20 cM apart were crossed to produce tester lines with the two markers linked in cis yielding seeds that fluoresced both in red and green. We show that these lines can be used for efficient scoring of recombinant types (red only or green only fluorescing seeds) in a seed population derived from a test cross (backcross) or self-pollination. Two tester lines that were characterized during several generations of backcross and self-pollination, one in the background of ecotype Landsberg and one in the ecotype Columbia, are described. We discuss the number of plants and seeds to be scored in order to obtain reliable and reproducible crossing over rate values. This assay offers a relatively high-throughput method, with the benefit of seed markers (similar to the maize classical genetic markers) combined with the advantages of Arabidopsis. It advances the prospect to better understand the factors that affect the rate of meiotic crossover in plants and to stimulate this process for more efficient breeding and mapping.

(1) Department of Plant Sciences, Weizmann Institute of Science, Rehovot 76100, Israel, and (2) Department of Genetics, Institute for Molecular Cell Biology, Vrije Universiteit, de Boelelaan 1087,1081 HV, Amsterdam, The Netherlands

DOI:10.1111/j.1365-313X.2005.02466.x

Cytometric Sorting of Pinaceae Pollen and its Implications for Radiocarbon Dating and Stable Isotope Analyses.

(1) Department of Geography, UC Berkeley, Berkeley CA, (2) Department of Earth and Planetary Science, UC Berkeley, Berkeley CA, (3) Union Biometrica, Holliston, MA.