| Abstract: | The pattern of penetration of chloride ions into the abaxialsurfaces of the primary leaves of Phaseolus vulgaris has severalfeatures in common with those previously recorded for 2,4-dichlorophenoxyaceticacid (2,4-D), 2,2-dichloropropionic acid (dalapon), and 4-amino-3,5,6-trichloropicolinicacid (picloram). In the dark the rate of entry of chloride ionsup to 24 h is constant, but in the light entry is at first slowand then more rapid. This acceleration does not occur at lowtemperature or when the tissue is treated with 3-(3,4-dichlorophenyl)-l,l-dimethylureaor phenylmercuric chloride. Neither does it take place at theadaxial surface or when the leaves are more mature. The most distinguishing feature of the pattern of penetrationof chloride ions is its dependence on external pH. In darknessentry is unaffected by changes in pH but in the light the rateof entry is increased as the pH falls, but this response isrestricted to young leaves. No binding of chloride seems tooccur within the tissue. These findings support the view that penetration of the abaxialsurface in young leaves of Phaseolus is largely determined bya membrane system. This system decreases in importance as theleaf matures and the overlying cuticle thickens. At the adaxialsurface the thicker cuticle is seemingly a major barrier topenetration even in very young leaves. |
