Effects of the Environment on the Symptom Pattern of Nickel Toxicity in the Oat Plant

Under conditions of nickel toxicity in oats (Avena byzantina), a predisposing condition for the development of chlorosis is induced in areas of the leaf before emergence from the coleoptile or the enclosing leaf sheath. These areas give rise to chlorotic bands which develop on the emerged leaf a little over 24 h after emergence of the tissue. Alternating light and dark are essential for the development of chlorotic bands. The evidence indicates that the potentially green tissue is that which is developing under the coleoptile during the day and emerges later in the day or early in the night, while the potentially chlorotic tissue is that which develops under the coleoptile during the night and emerges from the top of the coleoptile later in the night or during the following daylight hours before midday. Plants containing high levels of nickel contain higher levels of protochlorophyll and lower levels of of chlorophyll than control plants. The visual symptom of nickel toxicity is influenced by the length of the light and dark periods. The nature of these effects is discussed.