REVERSAL OF CAESIUM INHIBITION OF GROWTH BY POTASSIUM IN HYPOCOTYLS OF TOMATO SEEDLINGS (LYCOPERSICON ESCULENTUM L.).

Stunted, misshapen, necrotic hypocotyls of tomato seedlings (Lycopersicon esculentum L.) germinated on caesium cations in continuous red or white light indicated caesium-associated hypocotyl photo-injury. Continuous, far red irradiation inhibited seedling germination in control and caesium treatments but was reversed by continuous white light. Hypocotyl photo-injury also occurred in far red pretreated seedlings germinated on caesium in continuous white light. Except for suppressed elongation, hypocotyls of caesium-treated seedlings were normal in appearance. Etiolated caesium-treated seedlings placed in continuous white light also exhibited hypocotyl photo-injury. The effects of caesium cations were reversed by potassium cations but not by cations of other alkali metals.