K. Ojanpera et al., EFFECTS OF LOW OZONE EXPOSURE OF SPRING WHEAT ON NET CO2 UPTAKE, RUBISCO, LEAF SENESCENCE AND GRAIN FILLING, New phytologist, 138(3), 1998, pp. 451-460
Effects of ozone on spring wheat (Triticum aestivum L. cv. Satu) were
studied in an open-top chamber experiment during two growing seasons (
1992-1993) at Jokioinen in south-west Finland. The wheat was exposed t
o filtered air (CF), non-filtered air (NF), non-filtered air+35 nl l(-
1) ozone for 8 h d(-1) (NF+) and ambient air (AA). Each treatment was
replicated five times. Two wk after anthesis, after 4 wk of ozone trea
tment (NF+, 45 nl l(-1) 1000-1800 hours, seasonal mean) the net CO2 up
take of wheat flag leaves was decreased by c. 40% relative to CF and N
F treatments, both initial and total activity of Rubisco and the quant
ity of protein-bound SH groups were decreased significantly. Added ozo
ne also significantly accelerated flag leaf senescence recorded as a d
ecrease in chloroplast size. The effect was significant 2 wk after ant
hesis, and senescence was complete after 4 wk. In the CF and NF treatm
ents senescence was complete 5 wk after anthesis. The significant effe
ct of ozone on the chloroplasts and net CO2 uptake 2 wk after anthesis
did not affect the grain filling rate. However, since the grain filli
ng period was shorter for ozone fumigated plants, kernels were smaller
. The decrease in 1000-grain weight explained most of the yield reduct
ion in the plants under NF+ treatment. The results indicate that wheat
plants are well buffered against substantial decrease in source activ
ity, and that shortened flag leaf duration is the major factor causing
ozone-induced yield loss.