The Effects of Mechanical Impedance to Growth on the Levels of ABA and IAA in Root Tips ofZea maysL.

Abstract

Extraction and analytical methods have been refined and new ones devised to allow precise determinations by GC-EC of the levels of abscisic acid (ABA) and indol-3ylacetic acid (IAA) in samples of maize root tips as small as 1.0 g fr. wt. Seminal roots of 5-d-old maize seedlings grown in normal (bulk density 1200 kg m⁻³) and compacted (bulk density 1600 kg m⁻³) sand/garden loam mixtures have been examined. Seminal roots from compacted soil had an average length of about 40% of that of control roots and were much thicker. The ABA levels in 10 mm tips of impeded roots (c. 25–35 ng g⁻¹ fr.wt.) did not differ significantly from those of normal root tips on both a fresh and dry weight basis. The levels in 0–1 mm tips were approximately double those in the remaining 1–10 mm zones. IAA levels were increased by about 3½ times in impeded roots (176.3 as compared with 52.4 ng g⁻¹ fr.wt) and it is concluded that this response is likely to be the main cause of the morphological and growth changes brought about by soil compaction.