Elevated ozone (O 3) alters carbohydrate metabolism during grain filling in wheat ( Triticum aestivum L.)

Abstract

In Swedish open-top chamber experiment, field-grown spring wheat ( Triticum aestivum L. cv. Dragon) was exposed to ozone in 1995 and 1997 to determine the effect of ozone on non-structural carbohydrate concentrations in different plant organs. In both 1995 and 1997, the plants were exposed to an ozone AOT40 dose of approximately 2500 nmol mol −1 h during and after anthesis (NF1+), with non-filtered air (NF) alone as a control. In 1995, there was also a treatment with a similar AOT40 dose (2500 nmol mol −1 h) administered before (NF1+ pre-treatment) anthesis. In 1997, treatments with AOT40 doses of 0 (CF), 6321 (NF2+) and 10 900 nmol mol −1 h (NF3+) during and after anthesis were additionally used. In both years, the concentrations of non-structural carbohydrates were determined several times during plant development to detect ozone-induced changes in carbohydrate metabolism. In 1995, ozone exposure during and after anthesis (NF1+) reduced significantly post-anthesis leaf and stem carbohydrate concentrations, indicating accelerated senescence of the plants. In 1997, the flag leaves of plants of the NF3+ treatment contained significantly more water soluble carbohydrates (WSC) and total non-structural carbohydrates (TNC) than the flag leaves of the other treatments at anthesis and 2 weeks after anthesis. Evidently, this indicates disturbed export of assimilates from the flag leaves of the NF3+ treatment. Lower ozone doses (NF2+ and NF1+) had a non-significant effect on leaf carbohydrates. The stems of wheat plants exposed to elevated ozone contained significantly less carbohydrates than the stems of CF and NF plants 2 and 4 weeks after anthesis. Ear/grain starch and TNC concentrations (i.e. grain quality in terms of carbohydrates) were less affected by ozone exposure compared with the parameters related directly to grain growth and yield, such as the TNC amount in 1000 grains. It is concluded that most of the ozone-induced changes in carbohydrate concentrations were associated with accelerated leaf and plant senescence.