The effect of 2,4-D on the photosynthetic apparatus in cotyledons of spruce (Picea abies L. Karst.) seedlings grown in the dark

Growth regulating substance, 2,4-dichlorophenoxyacetic acid (2,4-D) is widely used in plant cell cultures and also in agriculture as a herbicide. The effect of 2,4-D on photo­ synthetic pigment content and chloroplast ultrastructure in spruce seedlings grown in the dark was studied. Seedlings were grown for 16 days in the dark at room temperature in Petri dishes moistened either with tap water (control) or 4.5, 45 and 450 uM 2,4-D. The lowest concentration (4.5 pM) of 2,4-D induced both chlorophyll and carotenoid bio­ synthesis as compared to the control treatment. There were no statistically significant dif­ ferences in any of the measured parameters between the control and the 45 pM 2,4-D treatment. A herbicidal concentration of 2,4-D (450 pM) induced a decline in chlorophyll content, while carotenoids were not significantly influenced. In contrast to the low con­ centration treatments, a herbicidal concentration of 2,4-D caused extensive changes in chloroplast shape and ultrastructure.