Ribonuclease Levels in the Mesocotyl Tissue of Zea mays as a Function of 2,4-Dichlorophenoxyacetic Acid Application

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Abstract
Ribonuclease (RNase) levels in young (2.5 - 4 days) etiolated corn seedlings were studied. The application of 2,4-dichlorophenoxy-aceticacid(2,4-D) to intact tissue promoted or inhibited growth depending upon concentration; but ribonuclease, protein, and nucleic acids increased with increases in 2,4-D even into the herbicidal range (8000 mg/liter). With excised tissue, low concentrations (0.1 - 50 mg/ liter) of 2,4-D accelerated growth and RNase activity in parallel, but there was about a 30% RNase increase independent of growth. High concentrations (500 mg/liter) of 2,4-D inhibited both growth and RNase increases. The time course of these events showed RNase continuing to increase after growth rates declined. Incubation of tissue in favorable temperatures increased RNase even under conditions where growth was limited by lack of auxin. During incubation of excised tissue there was a loss of protein, but studies with the inhibitors actinomycin D and puromycin suggest that protein synthesis is essential for both growth and RNase increase. RNase synthesis appears to be associated with cell maturation, and parallels growth only through that phase of the cell''s ontogeny involving expansion.