Passive Components in the Ion Absorption of the Plant. I. The Zonal Ion and Water Absorption in Brouwer's Experiments

Abstract

The ion ahsorption of the plant from the medium has lon^ heen re as an active process associated with the metaholi.sm in the root. Dnriny the most recent years, however, strong evidence has been presented from different quarters that the ion ahsorpliou of the plant is of a cotnplex nature. Thus it has been established that ion diffiisioti from the medium to the root with suh-.sequent adsorption to the cell walls and plasma together with mass flow of ions with Ihe transpiration stream accounts for a considerahle part of the ion ttplake of the platit. Some of the ions which hy diffusion or mass flow from the medium penetrate into the root are actively accumulated in Ihe root tissues, ahove all in the vacuoles, while the other ions are carried passively further to the shoot with Ihe transpiration stream or are pressed actively to the shoot hy the bleeding' mechanism. A valuahle resume of the more recent stndies on the mechanism and different components of ion uptake has been made by Burslrotn (1954).Diffusion witfi adsorption. It has frequetitly heen detnonslrated that when excised roots are transferred to a more eoneentrated medium a rapid uptake of ions takes place immediately after the transfer. This phenomenon is currently interpreted as a diffusion of ious to the parts of ibe root which are freely accessible lo ion diffusion from the medium. This first c-ompunent of ion uptake includes also the subsequent adsorption of ions to electrically charged points in the cell walls and ahove all in tlie cytoplasm within the root. Here positive ious exhihit a hif.;her adsorption than nej^ative ones. If the root is placed in a weaker medinm, on the other hand, ions from the root dif- [433]

Iron Transport in Pea Plants

“…Similar results were observed by Butler (8) and Brouwer (4) in their studies of chloride uptake in wheat and broad bean plants. However, Hylmo (18) claimed that DNP eliminated only the active component ("active bleeding") of transport and that the salt uptake in the presence of DNP was still proportional to water uptake. He further suggested that transport of the active component also is partly dependent upon water movement.…”

“…Ion uptake from a nutrient solution into the roots and to the shoots of a plant has been described as an active process, dependent upon the metabolic activity of the root cells (4,7,34), and as a passive process dependent upon mass flow in the transpiration stream (11,17,18,19,22). The opposing viewpoints were recently reviewed by Russell and Barber (33).…”

Diurnal Variation in Root Respiration

“…Arisz, Helder, and van Nie (2), van Andel (1), and Vaadia (25) have extended these observations to implicate the transfer of salt to the xylem elements as the process primarily concerned. Hanson and Biddulph (11) demonstrated a diurnal variation in ion transfer to the shoot of intact bean plants grown at constant temperature and humidity under artificial light, which Hylm6 (16) believes may be associated with increased transpiration during the period of illumination. Went (26) observed that the accumulation of p32 in the shoots of tomato plants was more rapid during the day.…”

Kinetics of rubidium absorption & translocation by barley

“…The transport of ions from a bathing solution to the top of a plant has been described as a passive (7,8,18,19,22,23,28) and active (2,3,17,26,27) process. Brouwer (3) states that at least 70 to 85 % of the ions appearing in the tops of plants go through an active process, i.e., "owing to a mechanism controlled or started by metabolism lands into the transpiration stream".…”