Ethylene and the responses of roots of maize (Zea mays L.) to physical impedance

Abstract

. SUMMARYThe response of the roots of maize seedlings to physical impedance was studied in glass chambers that enabled roots to be grown either unimpeded or in loosely packed small glass spheres (ballotini) and flushed with humidified air or other gas mixtures. Impedance decreased root length when measured after approxmiately 40 h by 30-60 "" and increased root diameter 10 cm behind the tip hy a similar percentage. Fresh weight was reduced by up to 28-40%, while ethylene evolution from roots was increased 2-to 2-S-fold. Supplying ethylene (5-13 //I 1 ') in the air flow to unimpeded roots simulated closely the effects of impedance.The volatile inhibitor of ethylene action, 2,5-norbornadiene (approx. 900//I 1 '), overcame the effects of ethylene (5 4//I 1 ') completely, but the growth of impeded roots was unchanged by norbornadiene. Smiilarly, aminoethoxyvinylglycinc (O-5-O-75 mmol m •') inhibited endogenous ethylene formation, but did not modify the growth responses of roots to impedance, even though ethylene production was suppressed to rates well below those of unimpeded roots. The concentration of ahscisic acid was not affected by impedance.It is concluded that despite a widespread view to the contrary, ethylene is not the cause of the morphological response of roots to physical impedance. Abscisic acid is also unlikely to be involved.

Interaction with ethylene: changing views on the role of abscisic acid in root and shoot growth responses to water stress

“…3). Exogenous ethylene inhibits elongation and causes a similar pattern of swelling in maize primary roots at high water potential (Moss, Hall & Jackson 1988;Whalen & Feldman 1988). Second, it was shown that under water stress, ethylene production of ABA-deficient seedlings was substantially greater than in control plants (Figs 4 & 5), and this effect was completely prevented when the root ABA content was restored with exogenous ABA, together with restoration of root elongation .…”

Ethylene Evolution from Maize (Zea mays L.) Seedling Roots and Shoots in Response to Mechanical Impedance

“…Moss et al. (20) reported observations of ethylene production made 40 h after inhibitor treatment but did not record the status before the initiation of the impedance treatment or the shortterm responses. We applied inhibitors and monitored ethylene production even before pressure was applied.…”

“…However, the technique used to measure length (see "Materials and Methods") minimized the opportunity for overestimation; therefore, any potential error would shift all treatment curves in Fig. 3 (20) in which it was concluded that ethylene did not play an important role in tissue response to mechanical impedance. We believe the discrepancy between our results and this report may be explained by the differences in the way mechanical impedance was simulated in each case, the way inhibitors were applied, and the manner and timing of ethylene production measurements.…”

“…The higher the ethylene concentration, the shorter the elapsed time before elongation rates deviated from pretreatment rates and the longer the time required to recover upon removal of the gas (26). However, whether ethylene regulates the changes in growth observed under physical impedance remains controversial (20,27).…”

“…One uses either beds of glass beads of small diameter as growth medium (10,20) or hollow containers in which tissue is brought in contact with a solid barrier (15,27). However, these systems do not simulate actual soil conditions.…”