Polyamines in chloride-stressed Citrus plants: Alleviation of stress by nitrate supplementation via irrigation water

A study was conducted to elucidate the effects of chloride in the irrigation water on growth and development of two citrus rootstocks. 'Cleopatra' mandarin (Citrus ershni Hort, ex Tan) is salt tolerant and 'Troyer' citrange (Poncirus ×Citrus sinensis) is salt sensitive. Increasing chloride from 2 to 48 mM in the irrigation water resulted in increased leaf chloride levels, more severe damage of the leaves, and reduced branch growth. High chloride in the irrigation water also caused increased putrescine (PUT) and decreased spermine (SPM) contents of the leaves. These effects were slight in 'Cleopatra' but highly apparent in 'Troyer'. The symptoms caused by high chloride were associated with high PUT and low SPM levels in the leaves. PUT may be involved in the development of chloride toxic symptoms, and SPM may protect or have no effect on chloride plant injury. The leaf polyamine profiles of 'Troyer' and 'Cleopatra' under nonstress chloride conditions were different. In 'Troyer' leaves, PUT level was 9-fold higher than in 'Cleopatra'; in 'Cleopatra' leaves, SPM level was 25-fold higher than in 'Troyer'. Nitrate supplement to saline water reduced chloride accumulation in the leaves and reduced the increase in PUT. The possible connection between ethylene production and PUT and SPM levels in the leaves of stressed plants is discussed.