Environmental, developmental, and genetic factors differentially affect rapid ethylene growth response kinetics in dark-grown Arabidopsis thaliana hypocotyls.

Studies on dark-grown wild-type Arabidopsis thaliana seedlings have demonstrated that the hypocotyls respond to the application and removal of the hormone ethylene with stereotypical growth kinetics. This includes a rapid decrease in growth rate when ethylene is applied that stabilizes at a low growth rate approximately 75 min after the addition of saturating levels of ethylene. Hypocotyl growth rate recovers to pre-treatment levels approximately 80 minutes after removal of ethylene. The growth of plants is influenced by environmental conditions that can vary between laboratories as well as genetic backgrounds and developmental factors. To address the importance of these variables on ethylene responses, experiments were conducted to determine the effects of composition of growth medium, seed size, seedling age, and accession on ethylene growth response kinetics. These variables led to only minor alterations in growth inhibition kinetics when ethylene was added with the largest effect being an acceleration in growth inhibition when nutrients were excluded from the medium. By contrast, growth recovery kinetics upon ethylene removal showed more plasticity. Sucrose accelerated growth recovery, whereas other environmental variables delayed recovery compared to controls. Other variables that are often overlooked, such as seed size and seedling age, also affected growth recovery where older seedlings recovered more slowly and plants from larger seeds recovered faster than plants from smaller seeds. Accessions from more northern latitudes tended to recover faster than those from more southern latitudes. Our data indicate that these factors need to be carefully controlled for optimal reproducibility of responses to ensure accurate interpretation of data and make sure important traits are not masked.