Postanthesis temperatures influence cytokinin accumulation and wheat kernel weight

High temperatures during reproductive development alter kernel development and reduce yield and quality in wheat (Triticum aestivum L.). Understanding how temperature alters kernel formation will help the development of genet ic approaches to enhance heat tolerance in this cereal, A relationship betw een kernel development and postanthesis cytokinin accumulation is well docu mented, but the effect of temperature on this relationship is not known. Th is study quantified the effects of a postanthesis temperature treatment (7 d at 35/25 degrees C day/night) on kernel development and cytokinin accumul ation in a soft white winter wheat (c.v. Stephens). Kernels from control pl ants maintained at 25/15 degrees C accumulated zeatin, dihydrozeatin and th eir corresponding 9-ribosides from 1 to 4 d postanthesis, Postanthesis kern el cytokinin accumulation was reduced by 50-80% by the temperature treatmen t. Kernel cytokinin content in control plants declined to baseline by 5 d p ostanthesis and remained at that level. Kernels from treated plants had a s econdary peak of cytokinin accumulation 6-8 d after anthesis, This treatmen t significantly reduced kernel weight. The magnitude of the effect on kerne l number was smaller than on kernel weight, but was statistically significa nt. Reduced kernel weight was accompanied by reduced cytokinin accumulation . Exogenous cytokinins did not mitigate the temperature effects on kernel w eight, but at the highest concentrations, did reduce the effect on kernel n umber.