A comparison of NH₄⁺ and NO₃^– net fluxes along roots of rice and maize

Abstract

Net fluxes of NH 4+ and NO 3 -along adventitious roots of rice (Oryza sativa L.) and the primary seminal root of maize (Zea mays L.) were investigated under nonperturbing conditions using ion-selective microelectrodes. The roots of rice contained a layer of sclerenchymatous fibres on the external side of the cortex, whereas this structure was absent in maize. Net uptake of NH 4 + was faster than that of NO 3 -at 1 mm behind the apex of both rice and maize roots when these ions were supplied together, each at 0·1 mol m -3 . In rice, NH 4 + net uptake declined in the more basal regions, whereas NO 3 -net uptake increased to a maximum at 21 mm behind the apex and then it also declined. Similar patterns of net uptake were observed when NH 4 + or NO 3 -was the sole nitrogen source, although the rates of NO 3 -net uptake were faster in the absence of NH 4 + . In contrast to rice, rates of NH 4 + and NO 3 -net uptake in the more basal regions of maize roots were similar to those near the root apex. Hence, the layer of sclerenchymatous fibres may have limited ion absorption in the older regions of rice roots.

Biochemical Background and Compartmentalized Functions of Cytosolic Glutamine Synthetase for Active Ammonium Assimilation in Rice Roots

“…Rice plants are usually cultivated in paddy fields and utilize ammonium as a major nitrogen source. Absorption of ammonium by rice roots occurs in the root tip region in the presence of ammonium (Tatsumi 1982, Colmer andBloom 1998). Transporters involved in the uptake of ammonium are regulated by a complex mechanism.…”

Short-term effects of coumarin along the maize primary root axis

“…As cells mature along the developing root axis, differential changes in gene expression may explain these differences. 33 The presence of lignified sclerenchymatous fibers 32 and suberized endo-and exodermal cells 34 in the more mature root regions of maize may limit the coumarin-plasma membrane interactions.…”

Changes in growth, porosity, and radial oxygen loss from adventitious roots of selected mono‐ and dicotyledonous wetland species with contrasting types of aerenchyma

“…Littorella, Luronium and Isoetes) from sandy substrates, which are low in organic matter, that do not become highly reduced in redox potential when flooded, have large aerenchyma cavities but also appear to be relatively permeable to ROL (Smits et al 1990). The ecological advantage of not forming a 'strong barrier' to ROL may be prolonged uptake of water and nutrients by the basal root zones (Colmer & Bloom 1998). In addition, nitrifying micro-organisms (Both, Gerards & Laanbroek 1992) and even other plant species (Hacker & Bertness 1995) may benefit from high ROL along the root.…”