DNA repair capacity of Gunnera magellanica, a native plant of Tierra del Fuego (southern Argentina), in its natural environment

GIORDANO C. V.; ZIMA A. M.; HERRERA M. V.; ROUSSEAUX M. C.; SCOPEL A. L.; BALLARÉ C. L.; CALDWELL M. M.

San Diego, USA

Congreso; Annual Meeting of the American Society of Plant Physiologists; 2000

UV-B (280-315 nm) radiation produces two major forms of  DNA damage: cyclobutane pyrimidine dimers (CPDs), and  pyrimidine (6-4) pyrimidone dimers. These photoproducts are repaired by two different mechanisms: excision repair and photorepair. We studied the effect of solar UV-B on Gunnera magellanica, a native plant of Tierra del Fuego (55oS), a region that is subjected to seasonal increments in UV-B doses due to the passage of the “ozone hole” during the spring. The expansion of G. magellanica leaves is reduced by solar UV-B, and this growth inhibition is accompanied by increased DNA damage, measured as CPDs. The steady state level of CPDs at midday correlates with the pre-middday dose of solar UV-B. The level of photoproducts in the DNA of a plant is a function of  UV-B penetration to the mesophyl and the capacity to repair the lesions. During 1998 and 1999 we carried out field and laboratory experiments designed to asses the repair capacity of G. magellanica. Our results show that leaves of this plant are capable of  repairing in a light-dependent manner c. 50% of the initial content of CPD in one hour, at 25 oC. This photorepair rate is in the lower end of the range of values reported for plants of temperate species such as soybean, alfalfa, cucumber, rice, sorghum and wheat. A low photorepair rate might be one of the factors that explains why there is a high correlation between UV-B doses and DNA damage in G. magellanica, in spite of the fact that the leaves of this plant are loaded with high quantities of UV-absorbing phenolic sunscreens.