ABSTRACT
Discs cut from plant storage organs have long been favourite material for experiments upon salt absorption. A recent series of papers (Steward, 1932 a–c, 1933 ; Steward, Wright and Berry, 1932) which refers especially to potato tissue indicates that in the past the attention directed to the respiration of these tissues was far too scanty. With the development of an adequate technique (Steward, 1932 b) the general principles operating in the case of potato tissue became increasingly apparent, and the occasion thus arose to extend the investigations to other storage organs. A survey of several storage organs (Berry and Steward, 1934) revealed that discs cut from artichoke tubers combined a conspicuous ability to absorb the salt studied (KBr) with a characteristic respiratory behaviour which presented features somewhat different from those of potato. The present paper records an attempt to ascertain whether the observed behaviour in respiration is reflected in salt absorption in the manner anticipated and to determine further details of the absorption process, with particular reference to potassium bromide and artichoke tissue. A matter which received some special attention was to ascertain whether the absorbed salt replaces ions already within the cell, or accumulates, against a concentration gradient, in the vacuole where it exists in true solution without displacing other ions. Since they were obtained, the results here presented have gained added interest in the light of the results published by Briggs and Petrie (1931) and, more particularly, in view of a theoretical interpretation of absorption by cells (Briggs, 1932) based upon ionic exchange.
After the customary procedure of rinsing, blotting and weighing (Steward, 1932 b).
Initial tissue = tissue cut and washed for a brief period in running tap water.
For methods see Steward (1932 b).
The inulin (total carbohydrate) content of artichoke tissue is of the order of 70 per cent, dry weight or 18·5 per cent, fresh weight (Tincker, 1928) or 160 gm. per litre of expressed sap (Tanret, 1893). For further information on the nature of the polysaccharide see Schlubach and Knoop (1932).
Reducing and total sugar estimations (after add hydrolysis) showed that loss of sugar to the external solution was quite negligible.
There is some indication that the absolute increase of respiration due to addition of bromide is smaller the later the addition is made.
In relatively strong solutions (o·1N NaCl) the preliminary loss was not observed by Stiles (1924). It was presumably masked by absorption.
Unpublished results of Rosenfels (University of California) show an almost identical behaviour for the respiration and bromide absorption of Elodea.
Periods 1 and 2 overlap by 6 hours—so that the concentration obtained in period 1 should for this purpose be taken as 4·86 approx.
The percentage water content of similar discs to those in question was 88·57 pct cent.
Any effects of the salts already present in the sap upon the conductivity due to the added bromide or effects upon the conductivity due to metabolism are of course neglected in these calculations.
Initial sap: K content = 92·82 × 10−3 equivalent per litre. Final sap: K content= 114·5 × 10−3 equivalent per litre.
The writers are aware that Stiles found (1924) that artichoke tissue absorbed from 0·1 NaCl about three times as much Na as Cl, due, perhaps, to base exchange in the wall.
Compare the case of Nitella (Hoagland, Hibbard and Davis, 1926) in which previous accumulation of chloride causes subsequent absorption of bromide to depend on exchange to a greater degree.
Observations by Miss E. Chamberlain (unpublished).
This may be due to differing magnitude and extent of the surface effects in absorption and respiration. Perhaps one ought to compare the salt absorption only to “surface respiration.” (See Steward, 1932 c.)
The writers cannot see in the results in this paper, in others (Steward, 1932 a–c, 1933 ; Steward, Wright and Berry, 1932), or in their unpublished results any evidence of impermeability to cations in dilute solution.
