Ethylene regulators influence germination and root growth of globe artichoke seedlings exposed to heat stress conditions

Abstract

High seed germination and root vigour are important traits to improve post-transplant performance of artichoke (Cynara cardunculus var. scolymus) under heat stress conditions. The effects of exogenous applications of five ethylene regulators each at different concentrations were evaluated on germination and early root growth of artichoke at 23°C in two incubation assays. The ethylene precursors or promoters were DL-methionine (DL-MET), 1-aminocyclopropane-l-carboxylic acid (ACC) and 2-chloroethylphosphonic acid (ethephon, ETH); and ethylene inhibitors were aminoethoxyvinylglycine (AVG) and 1-methylcyclopropene (1-MCP). A subsequent study examined the effects of ETH concentrations on seeds exposed at 23 vs. 30°C (stress). Seed thermodormancy was significantly improved by the application of 30 μM L-1 ETH. At optimal temperature (23°C), early root growth was enhanced by ACC and ETH (range of 1-100 μM L-1) with increasing root hair density, root area and lateral roots (except with ETH at 30 μM L-1). Conversely, AVG induced primary root elongation but decreased root hair formation. At higher temperature (30°C), inhibition of early root growth was alleviated when seedlings were incubated at 30 μM L-1 ETH. Our results suggest that exogenous ethylene could be useful to alleviate heat stress on artichoke seeds and seedlings, which in turn may improve early growth during stand establishment.