PLANT-GROWTH AND CELL-DIVISION IN PISUM-SATIVUM L AND PICEA-SITCHENSIS (BONG) CARR EXPOSED TO OZONE

Pea (Pisum sativum L. cv. Feltham First) and clonal Sitka spruce plants (Picea sitchensis (Pong.) Carr.) were exposed to ozone concentrations of 0-90 ppb to investigate effects on both shoot and root growth and also cell division in the apical mm of roots. P. sativum plants were maintained under these conditions for 3 wk whilst P. sitchensis were left for 3 months. After 3 wk in the presence of 90 ppb ozone the mitotic index in the root apical mm of P. sativum was reduced compared with control plants (0 ppb ozone), whereas the number of primordia along the length of the main root in P. sativum plants increased at 90 ppb ozone. The smallest concentration of ozone (30 ppb) had no effect on leaf area, shoot dry weight and number of leaves of P. sativum. However, the number of second order lateral roots and total root dry weight were reduced at concentrations of 60 ppb and above, while leaf size, plant height and shoot dry weight were only reduced in the presence of 90 ppb ozone. Cell doubling time in the root apical mm of P. sitchensis increased in plants which had been grown in the presence of 30 ppb ozone and decreased in those plants grown in chambers containing 90 ppb ozone. Ozone did not appear to have any other effects on those aspects of the cell cycle examined in either P. sativum or P. sitchensis.