Leaf gas exchange and multiple enzymatic and non-enzymatic antioxidant strategies related to drought tolerance in two oil palm hybrids

Drought is a major environmental constraint limiting growth and yield of oil palm trees. In this study, two oil palm hybrids (BRS Manicore and BRS C 2501) were grown in large containers and subjected to a water deficit during 57 days. Leaf gas exchange analysis was combined with an in-depth assessment of the antioxidant system over the drought imposition. Under drought, leaf water potential at predawn (Psi(pd)) decreased similarly in both hybrids. In parallel, there were decreases in the net CO2 assimilation rate (A), chlorophyll concentrations and Rubisco total activity. Overall, these decreases were more pronounced in BRS C 2501 than in BRS Manicore. BRS C 2501 plants triggered more markedly its enzymatic antioxidant system earlier (Psi(pd) = -2.1 MPa) than did BRS Manicore, but these responses were accompanied by higher concentrations of H2O2 and malondialdehyde in BRS C 2510 than in BRS Manicore. With the progress of drought stress (Psi(pd) = -2.9 MPa and below), BRS Manicore was better able to cope with oxidative stress through a more robust antioxidant system. In addition, significant decreases in drought-induced NAD(+)-malate dehydrogenase activities were only observed in stressed BRS C 2501 plants. Regardless of watering regimes, the total carotenoid, ascorbate and glutathione concentrations were higher in BRS Manicore than in BRS C 2501. In conclusion, BRS Manicore is better able to tolerate drought than BRS C 2501 by triggering multiple antioxidant strategies involved both in reactive oxygen species scavenging and dissipation of excess energy and/or reducing equivalents particularly under severe drought stress.