ETHYLENE ASSOCIATION WITH CHLORIDE STRESS IN CITRUS PLANTS

Under non-chloride stress conditions, the chloride-sensitive citrus pl ant rootstock 'Troyer' citrange (Poncirus trifoliata [L.] Rafinesque x Citrus sinensis [L.] Osbeck) accumulated 5-fold more chloride in thei r leaves [Bar, Y., Apelbaum, A., Kafkafi, U., Goren, R., 1996. Polyami nes in chloride-stressed Citrus plants: alleviation of stress by nitra te supplementation via the irrigation water. J. Am. Sec. Horti. Sci., 121. 507-513.] and produced ethylene at a higher rate than the chlorid e-tolerant rootstock 'Cleopatra' mandarin (Citrus reshni Hort. ex Tan) . Increasing chloride concentrations in the nutrient solution(2, 16 an d 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, l eaf and branch scorching, but decreased growth. 'Cleopatra' responded only by exhibiting moderate inhibition of branch growth and by a sligh t 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 li nk between the increased rate of ethylene production and putrescine ac cumulation in leaves of stressed plants [Bar et al., 1996] is suggeste d. Addition of nitrate to nutrient solution with high chloride concent ration reduced chloride level in the leaves, reduced ethylene producti on and the intensity of toxic symptoms in 'Troyer'. In 'Cleopatra' man darin and 'Trifoliata' orange (P, trifoliata [L.] Rafinesque), a chlor ide-sensitive rootstock, the response of the detached leaves to chlori de was similar to that of the intact plants with respect to scorching, ACC synthesis, ethylene production and abscission, but the response i n leaves was apparent within a shorter period of time. (C) 1998 Elsevi er Science B.V.