Ozone-responsive proteins in a tolerant and sensitive clone of white clover (Trifolium repens)

Two clones of white clover (Trifolium repens L. cv. Regal), NC-R (O-3-resis tant) and NC-S (O-3-sensitive), were used to investigate biochemical respon ses associated with O-3 tolerance. Plants were exposed in CSTR chambers to a step-function O-3 profile (minimum concentration of 50 nl liter(-1), maxi mum concentration of 150 nl liter(-1)) for 3 days, 8 h day(-1). No visible foliar symptoms were apparent on the sensitive genotype after fumigation. T otal soluble leaf protein and the activity of superoxide dismutase isoenzym es either declined or was not affected by O-3 in both NC-S and NC-R. Catala se activity increased by 15-20% in the clones. Two-dimensional gel electrop horesis demonstrated the differential, exposure-dependent accumulation of a small group (two to four) of O-3-responsive proteins (ORPs). These polypep tides were not present at detectable levels in control plants. During the 3 -day fumigation with O-3, the ORPs progressively accumulated in both clones ; however, the increase in NC-S was delayed and protein content never attai ned comparable levels to those observed in NC-R. The proteins have apparent molecular masses of 21.5-23 kD and pIs in the range of 4.2-4.5. The identi ty of these polypeptides is not known. (C) 1999 Elsevier Science Ltd. All r ights reserved.