Adenine Nucleotide Content of Corn Roots as Affected by Injury and Subsequent Washing

Abstract

The adenine nucleotide content of the 2-centimeter segments excised from tray-grown corn (Zea mays L., WF9 x MoI7) roots declines for the first hour after excision. Concomitant with the loss of adenine nucleotides is a decline in respiration and a leakage of K+. With continued washing, these parameters partially or completely recover and increased phosphate influx develops. Increasing the wound effect by cutting 0.5-centimeter segments gives a more rapid and pronounced degradation of adenine nucleotides and slower recovery. Conversely, the mild injury caused by submerging intact roots induces less degradation and produces greater net adenine nucleotide synthesis during recovery, adding auxin to the washing medium produces a similar result. With all treatments, there is stabilization of energy charge at about 0.85.Brief submersion or rubbing of intact roots, as well as recutting washed and recovered root segments, will initiate the transient loss of adenine nucleotides but will not induce increased phosphate influx.It is suggested that the loss in adenine nucleotides may reflect homeostasis in energy charge via catabolism arising from membrane permeablity changes.Washing (or 'aging') of excised root tissue leads to increased ion influx (9, 10, 13, 16, 24), H+ efflux (13, 14), and electrogenic cell potential (14,20). To a large extent these changes reflect recovery from injury inflicted by cutting, cold shock, or handling the tissue (10, 13, 14). There are two phases to the washing response: an initial phase lasting about I h during which there is rapid (no lag) reinitiation of the H+ and K+ fluxes and cell potential, much as with fusicoccin but slower, followed by a general augmentation of solute transport, typified by increase in phosphate influx and microsomal K+-ATPase activity (14,16,17). These phases have been termed 'inductive ' and 'developmental' (14, 16).During the inductive phase, there is a decline in the level of ATP which recovers if washing is continued for 3 to 4 h (19). Similar changes in adenine nucleotides (and other metabolites) during washing or aging of excised plant tissue have been reported by other investigators (7,21,23,25). The phenomenon must reflect some important metabolic change in the cells which is linked to wounding or other injury, and in corn roots may have a role in inducing the developmental phase.In the study reported here, we have examined the changes in A preliminary report on part of this work has been given (12). MATERIALS AND METHODSPlant Material and Treatments. Corn seeds (Zea mays L., WF9 x Mol7) were germinated for 3 d in the dark at 28°C on paper towels saturated with 0.1 mm CaCl2, and 2-cm segments were excised 0.5 to 2.5 cm from the tip of the primary root as described (16). Segments were assayed for AdN or phosphate influx immediately after cutting, and after various periods of washing in aerated 0.2 mm CaC12 + 0.2 mm KH2PO4 (adjusted to pH 6.0) at 30°C (16). In some experiments, the 2-cm segment was additionally wounded by cutting into four 0.5-cm segme...

Linking root traits to potential growth rate in six temperate tree species

“…Cleaning order of species was rotated between the 2 days. For each plant, approximately three roots of each root class were placed in each of two Histoprep tissue cassettes (Fisher Scientific, Pittsburgh, Pa., USA); one cassette was used for P uptake measurements at 2 µM P and the other at 20 µM P. Cassettes were stored in a calcium-MES buffer solution (1 mM CaSO 4 , 5 mM MES, adjusted with KOH to pH 5.5) in the dark until all plants of that day's harvest were cleaned; about 9 h. Excised roots of corn have been found to require 4 h after excision for their P uptake to recover from disturbance and wounding (Gronewald and Hanson 1982). As well, P uptake in eucalyptus roots was similar up to 3 days after excision (Keith 1998).…”

Shoot excision has no effect on net flux of protons, ammonium or nitrate in seedling roots of a conifer and three crop species

“…Excision effectively isolates the root from endogenous sources of carbohydrates produced in the shoot during photosynthesis. This could potentially affect ions such as NO 3 − that are actively taken up but stored or transported in ionic form, compared to NH 4 + which is less costly to acquire but must be assimilated in the roots (Bloom et al, 1992;Macduff and Jackson, 1992), or HPO 4 2− that is acquired passively and stored in ionic form (Gronewald and Hanson, 1982). The exogenous addition of glucose or sucrose in the uptake medium can ameliorate the effects of carbohydrate depletion, however results may be compromised because excised roots can readily absorb and metabolize soluble sugars (BassiriRad et al, 1999).…”

Metabolic Acclimation to Hypoxia in Winter Cereals

“…Extension of this flooding period to 3 h does not further decrease the level of total adenylates suggesting that the initial rapid decline in adenylates is due to a flooding shock (9,27).…”