Drought tolerance in relation to protection against oxidative stress in clones of Coffea canephora subjected to long-term drought

Four clones of Coffea canephora (Robusta coffee) representing drought-tolerant (14 and 120) and drought-sensitive (46 and 109A) genotypes were submitted to slowly imposed water deficit, until predawn leaf water potential approximately -3.0MPa was reached. Drought-tolerant clones were better able to maintain their leaf water status than drought-sensitive clones after withholding irrigation. Regardless of the clones investigated, the net carbon assimilation rate decreased under drought stress, but little or no effect of drought on the quantum yield of electron transport was observed. The photosynthetic apparatus of clone 120 was more tolerant to both drought and paraquat-mediated oxidative stress, with no clear distinction amongst the other clones in this regard. Drought triggered increases in superoxide dismutase (clones 109A and 120), ascorbate peroxidase (clones 14, 46 and 109A), catalase and guaiacol peroxidase (clones 46 and 109A), and also in glutathione reductase (clone 46) and dehydroascorbate reductase (clone 109A). Activity of monodehydroascorbate reductase was not induced in drought-stressed plants. Maximal catalytic activities of the two last enzymes were much lower than that of ascorbate peroxidase, irrespective of the clone investigated. No drought-induced decrease in enzyme activity was found, except for glutathione reductase in clone 120. In any case, oxidative damage appeared to be evident only in clone 109A. A general link between protection against oxidative stress with differences in clonal tolerance to drought was not observed. (C) 2004 Elsevier Ireland Ltd. All rights reserved.