Cadmium injury to water-cultured mulberry tree

Abstract

Mulberry trees precultured by water culture method were tested on the growth disorder caused by Cd toxicity and Cd distribution in tissues.
1. When the Cd concentration in culture solution was less than 5μM/l (0.56ppm), any growth disorder did not appear. With increasing Cd concentration above 10μM/l (1.12ppm) the petioles became drooping and the leavees at lower position shoot fell down. In addition to this, the Cd concentration higher than 25μM (2.8ppm) resulted in browning of roots and barbed wire like shape of secondary roots, then graduall rotting out.
2. Most fallen leaves kept fresh green color. The specific symptoms did not appear, like necrosis developed on midrib and veinlets of leaves as so-called Cd excess symptom.
3. The greatest Cd accumulation was observed in shoot, with stock and petiole with midrid showing lesser amounts. Mesophyll accumulation was slight. With increasing Cd concentration in solution Cd accumulation increased in shoot, stock and petiole with midrib. The older the age of shoot and petiole with midrib, the more accumulation, But the content in leaf was little affected by increasing concentration and ageing.
4. Cd content in fallen leaves was comparatively constant in about 13ppm in spite of leaf order.
5. From the above-mentioned facts, it was supposed that when Cd concentration in vascular tissues was raised to a certain level absciss layers may be formed and this may result in little fluctuation of Cd content in surviving leaf with more increasing concentration in culture solution.