Differences in sensitivity of the photosynthetic apparatus in Cd-stressed runner bean plants in relation to their age

Abstract

Cadmium effects depending on the time of its action and growth stage/age of Phaseolus coccineus were investigated. Three groups of plants at different growth stages of their primary leaves were treated with 25 μM CdSO 4. The photosynthetic activities and selected growth parameters of these plants were measured on days 4, 8 and 12 of the metal action and compared with their age-adequate controls. The responses of plants depended on the age of plants and time of Cd action. The younger the Cd-treated plants the bigger the changes in growth parameters observed but photosynthetic activity was almost unchanged during Cd action. With the age of plants their sensitivity to Cd increased and it was more related to the functioning of the photosynthetic apparatus than to the growth parameters. In the oldest Cd-treated plants the lowest activity of photosystem II was accompanied by disruption of the thylakoid membranes in comparison with control. A sensitivity of the photosynthetic apparatus in young Cd-treated plants is discussed with regard to the metal action causing free fatty acids or feedback inhibition of electron flow, while in older plants with regard to changes resembling plant senescence.