Cytogenetics and the Fate of Trees


Aspens at sunset in Purgatory, Colorado. Photo by John Fowler, courtesy of Wikimedia Commons.

Nurul Islam-Faridi, research geneticist with the Southern Research Station (SRS) Forest Tree Molecular Cytogenetics Laboratory on the Texas A&M campus at College Station, TX, and adjunct professor in the university’s Department of Ecosystem Science and Management, is one of a handful of scientists in the world who can literally count the chromosomes inside the living cells of any plant species. Faridi uses high-powered microscopes equipped with chromosome analysis software and fluorescent probes to look directly at the chromosomes and genes of forest trees.

Faridi played a crucial role in a recent study on the genetics of aspen in the western United States that may have implications for the tree’s future under the more arid conditions predicted by climate change models.

In an article published in the October 31 edition of the online journal PLOS ONE, a team of researchers led by Karen Mock, Associate Professor in the Quinney College of Natural Resources at Utah State University, report finding triploidy—three sets of chromosomes—in large numbers of clonal colonies of quaking aspen (Populus tremuloides) in forest areas in Utah and Colorado.

“Most organisms have two sets of chromosomes, one from each parent. In many plants, triploidy isnt unusual, but this kind of frequency is rare, especially in trees,” says Mock. “When we tied the results of genetic studies to forest inventory data on aspen, we found a striking pattern. Aspen triploids are especially common in dry western landscapes.”

Faridi provided evidence that the patterns the researchers were seeing were indeed due to triploidy. “We sought out Nurul for this task because of his reputation as an expert in conventional and molecular cytology,” says Mock. “He was able to get photographs of the chromosomes, which is very difficult because aspen chromosomes are so tiny.”

“Trees are notoriously difficult to do this work with compared to most crop plant species,” says Dana Nelson, Project Leader of the SRS Southern Institute of Forest Genetics. “The cytological analysis Nurul conducted is the only option to check whether the genome had a duplicated segment of a chromosome, an extra chromosome, or indeed three complete sets of chromosomes, confirming triploidy.”

Aspen grow in clonal colonies, groups or stands of genetically identical trunks that reproduce asexually from roots. Though aspen also reproduces sexually, the seeds are very tiny and depend on moisture to germinate. 

A usual trait of plants with triploidy is sterility or reduced fertility; aspen with triploidy would be unlikely to produce viable seed. Triploid plants also often have larger cells, which may affect how they absorb water. The high incidence of aspen triploidy the researchers mapped in Utah and Colorado caused them to wonder what advantages triploids might have in the western landscapes—and whether this makes them more or less susceptible to climate changes.

One of the few broad-leaved trees growing at high altitudes in western U.S. mountains, aspen trees are seen as an emblem of the Rockies. Over the last decade they’ve suffered from large-scale die-offs in some western landscapes, affecting hundreds of thousands of acres.

Faridi’s expertise provides the ability to investigate the relationships among genetics of forest trees and local and regional environmental conditions, ultimately helping land managers develop approaches needed to manage and restore forest landscapes during times of climate change and accelerating stresses from drought, fire, insects and disease.

For more information, email Nurul Islam-Faridi at .

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