AbstractPlant growth regulators (PGR) have potential to increase grain yield and may also alter grain protein levels of cereal crops. A 3‐yr field experiment with spring barley (Hordeum vulgareL.) and wheat (Triticum aestivumL.) cultivars was conducted to determine whether ethephon treatment increased protein concentration, protein yield, and grain yield. A greenhouse experiment was also conducted to evaluate the response of barley grain protein concentration to gradual addition of ethephon (2.2 × 10‐3mM) or chlormequat (5.8 × 10‐3mM) solution after an thesis. Under field conditions, ethephon treatment increased barley and wheat grain protein concentrations by as much as 16 but decreased grain yield so that protein yield increases were small or did not occur. ForLaurierbarley, total gram N content was increased by up to 20 in one year of this study. However, over the 3 years, an inverse relation existed between grain protein and yield. Greenhouse data showed that i) the gradient in grain size and protein concentration among spikelets of a spike, which is established before anthesis, was not affected by either chlormequat or ethephon; and ii) chlormequat increased grain protein by 7 to 11 whereas ethephon increased protein concentration by up to 13 in one of the two experiments. Our data indicate that PGR can alter protein accumulation in the grain, and thus, the quality of bread wheat and feed barley crops can be increased m regions with a short crop‐growing season. However, a portion of the increase in gram protein concentration is due to decreased starch deposition, which is associated with yield reductions. The greenhouse data confirmed that a portion of the increase in grain protein concentration due to PGR application is caused by increased protein accumulation in the bar
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