Physiological Responses Involved in Tolerance of Citrus Plants to Soil Waterlogging

摘要

Soil waterlogging exerts several disturbances to citrus physiology leading to a reduced plant performance and, if flooding conditions persist, to plant death. It is not known which physiological parameters regulate the differential tolerance of different citrus genotypes to waterlogging stress. Three citrus rootstocks, Cleopatra mandarin, CPB4475 citrumelo and Carrizo citrange were subjected to continuous waterlogging. Leaf gas exchange, oxidative damage, antioxidant activity, proline and plant hormones were measured. Cleopatra plants (the most sensitive to soil flooding) experienced a marked reduction in photosynthetic performance together with a significant down-regulation of antioxidant defenses, whereas Carrizo plants (the most tolerant to this stress) exhibited significantly improved parameters,and CPB4475 had an intermediate behaviour. Moreover,our data showed increased levels of proline in flooding-sensitive genotypes whereas no change was recorded in Carrizo which indicates that higher proline ratios might be related to sensitivity. Results from hormonal analyses suggested that jasmonic acid could be the signal that mediates stress perception and subsequent down-stream regulatory processes whereas abscisic acid could modulate physiological responses. In addition, the putative protective role of polyamines under flooding stress seems to be marginal. Overall, the maintenance of an adequate photosynthetic activity together with an active antioxidant machinery seem to be reliable markers of tolerance to soil flooding.