Ethylene association with chloride stress in citrus plants

Under non-chloride stress conditions, the chloride-sensitive citrus plant rootstock 'Troyer' citrange (Poncirus trifoliata [L.] Rafinesque x Citrus sinensis [L.] Osbeck) accumulated 5-fold more chloride in their leaves [Bar, Y., Apelbaum, A., Kafkafi, U., Goren, R., 1996. Polyamines in chloride-stressed Citrus plants: alleviation of stress by nitrate supplementation via the irrigation water. J. Am. Sec. Horti. Sci., 121. 507-513.] and produced ethylene at a higher rate than the chloride-tolerant rootstock 'Cleopatra' mandarin (Citrus reshni Hort. ex Tan). Increasing chloride concentrations in the nutrient solution(2, 16 and 48 mM), which caused a marked increase in leaf chloride content of 'Troyer', increased the level of 1-aminocyclopropane-1-carboxylic acid (ACC) in the leaves which increased the rate of ethylene production, leaf and branch scorching, but decreased growth. 'Cleopatra' responded only by exhibiting moderate inhibition of branch growth and by a slight leaf chlorosis at the higher chloride concentrations, Application of silver thiosulfate, an inhibitor of ethylene action, revealed that in citrus plants under chloride-induced stress, ethylene is responsible for leaf abscission, but not for the scorching symptoms. A possible link between the increased rate of ethylene production and putrescine accumulation in leaves of stressed plants [Bar et al., 1996] is suggested. Addition of nitrate to nutrient solution with high chloride concentration reduced chloride level in the leaves, reduced ethylene production and the intensity of toxic symptoms in 'Troyer'. In 'Cleopatra' mandarin and 'Trifoliata' orange (P, trifoliata [L.] Rafinesque), a chloride-sensitive rootstock, the response of the detached leaves to chloride was similar to that of the intact plants with respect to scorching, ACC synthesis, ethylene production and abscission, but the response in leaves was apparent within a shorter period of time. (C) 1998 Elsevier Science B.V.