Effects of abscisic acid on growth and metabolism of protein and ribonucleic acid in Lemna minor L

The objective of this work was to arrive at a better understanding of the processes that cause abscisic acid (ABA; a natural growth inhibitor) to inhibit the growth of individual plants of Lemna minor L. Growth rates as measured by frond area and by root length were 60% inhibited by ABA with a concentration of 2 mg/1. Application of ABA for 24 hr inhibited both cell division and cell elongation in roots. The latent-period of the root growth inhibition was 1 hr. Abscisic acid inhibited the rate of uridine incorporation into roots by 55% within 2 to 4 hr after application; the decreased rates of incorporation were not attributable to effects of ABA on uptake. Abscisic acid had no effect on root uptake or incorporation of DL-leucine over a 4 hr period. Incubation in ABA for 24 hr stimulated the accumulation of starch in the peripheral, differentiated cell layer of the root cortex. It was concluded that the mechanism(s) by which ABA induces changes in RNA and starch metabolism are separate and indirect from those mechanism(s) which cause the growth inhibition. Preliminary root absorption studies showed uridine and DLleucine to be actively transported across the plasmalemna. The absorption curves for DL-leucine and uridine in the roots followed a dual pattern with Michaelis constants for the lower concentration mechanism of 0.03 mM for DL-leucine and 0.4 mM for uridine. Anatomical investigations showed starch accumulation in the two cortical cell layers which surround 8 air lacunae. It was concluded that the air lacunae are located within the cortical tissue