Developments in scientific research follow improvements in analysis and deduction—improvements in analytical techniques allowing the detection of trace amounts of substances has led to advances in the understanding of plant hormones and their effect on gene expression.
In this case, the NOS statement is referring to the use of genomics to analyse gene expression in plants. Some of the earliest experiments into tropisms were conducted by none other than Charles Darwin, whose 1880 book The power of movement in plants represented the first attempt to synthesise available evidence on tropisms and included many of his own experiments in this field. As developments in technology increased, the role of hormones became increasingly important and better understood.
Hormones influence gene expression; by detecting changes in gene expression, we can determine the role of hormones in this process. DNA sequences have been analysed to determine how these change in response to hormone exposure and mRNA levels (evidence of transcription and hence gene expression) can also be detected, pinpointing the cells that are responding to these hormones. Scientists have detected a range of common short sequences of nucleotides, from four to twelve bases in length. Different combinations of these appear to be linked to specific hormones and allow the genes to be affected by different classes of hormones. Details on some of these nucleotide sequences can be seen in the table below (Plants in Action). Experiments have revealed that plant hormones can act extremely fast – with mRNA changes detected as quickly as 2-5 minutes from exposure.
The advances in microarray analysis of DNA and mRNA was thus critical to our improved understanding of how plant hormones work.
Jennifer J. Holland, Diana Roberts, Emmanuel Liscum; Understanding phototropism: from Darwin to today, Journal of Experimental Botany, Volume 60, Issue 7, 1 May 2009, Pages 1969–1978, https://doi.org/10.1093/jxb/erp113 Web. Accessed 6 Feb, 2018.
“Modiﬁed Gene Expression.” Plants in Action, 1st ed., Australian Society of Plant Physiologists, 1998, plantsinaction.science.uq.edu.au/edition1/?q=content/9-2-4-modi-ed-gene-expression. Web. Accessed 6 Feb, 2018.