. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. IONIC CURRENTS AROUND PEA ROOT TIPS Table I Effects of ion-substitutions and ion-channel Mockers on pea root wound currents 59 Alterations to Vj Hoaglands Trial Test solution Control solution % of initial current1 -Na+ -NaH:PO4(34X 10~'A/) +K Isethionate (34 x 10~5 A/) 96 ± 2(11) +KH:PO4(34X 10~SA/) -K+ (1 X 10~3A/) +Nalsethionate(l X 10~JA/) 106 ± 2(7) +NaNO3(lX 10'3A/) -Ca2+ +EGTA: ( 1 x 10"4 A/) ml 59 ± 12(9) +Cr +KCK3X 10~4A/) nil 107 ± 4(15) +Gd3+ +GdCl3(5x \Q--.\fi +KCK3 x 10'5A/) 73± 3(10) +La3+ +LaCl3(l x
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. IONIC CURRENTS AROUND PEA ROOT TIPS Table I Effects of ion-substitutions and ion-channel Mockers on pea root wound currents 59 Alterations to Vj Hoaglands Trial Test solution Control solution % of initial current1 -Na+ -NaH:PO4(34X 10~'A/) +K Isethionate (34 x 10~5 A/) 96 ± 2(11) +KH:PO4(34X 10~SA/) -K+ (1 X 10~3A/) +Nalsethionate(l X 10~JA/) 106 ± 2(7) +NaNO3(lX 10'3A/) -Ca2+ +EGTA: ( 1 x 10"4 A/) ml 59 ± 12(9) +Cr +KCK3X 10~4A/) nil 107 ± 4(15) +Gd3+ +GdCl3(5x \Q--.\fi +KCK3 x 10'5A/) 73± 3(10) +La3+ +LaCl3(l x 10"4A/) +KCl(3x 10~5A/) 50 ± 10(11) +verapamil +verapamil (8 x 10~7 A/) nil 97 ± 5(9) +verapamil(l X 10~5A/) ml 92 ± 4(11) -H+3 +HEPES4(5x 10~3A/) +MES5(5X 10~3A/) 108 ± 5(11) 1 Mean percentages ± SEM (parentheses indicate number of cases studied). See Figure 6 for method of calculation. : EGTA: '.N'.-tetraacetic acid. 3 pH of solutions was adjusted with 5 A/ 4 HEPES: N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid. 5 MES: [2-(N-Morpholino)ethanesulfonicacid]. nA cm 2 was measured at the wound site (Fig. 4a). A consistent feature of this wound current is that the cur- rent density peak is not centered directly over the wound site, but slightly shifted acropetally by about 150 //m. To- wards the basipetal end of the root, 500 ^m from the wound center, the current changes direction and out- ward currents of the order of 1-2 ^A cm"2 are found. By h, this initial large inward current drops off, giving rise to outward currents of 1-2 //A cm 2, and a shifted peak over the wound is still visible (Fig. 4b). Six h after wounding these secondary outward currents have dimin- ished to nA cm"2, although the peak value is still markedly higher at fiA cm"2 (Fig. 4c). Also at this stage, inwardly directed currents of ^A cm"2 appear about 300 urn from the wound center, on the basipetal side of the w
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