STUDIES OF FOLIAR PENETRATION .V. FACTORS CONTROLLING PENETRATION OF 2,2-DICHLOROPROPIONIC ACID (DALAPON) INTO LEAVES OF PHASEOLUS-VULGARIS

The factors which control the penetation of 2,2-dichloropropionic acid (dalapon), containing 38Cl, into leaf disks of Phaseolus vulgris have been investigated. In many respects the pattern of penctration resembles that already reported for 2,4-dichlorophenoxyacetic acid (2,4-D) but in others the results dispaprate.In darkness the rate of penetration is proportional to the external concentration, remains constant over at least 24 h, is unaffected by 3-(3,4-dichlorophenyl)-1,1-dimethlyrea (DCMU), and has a temperature coefficient ranging from 1.6 to 2.3. Light intensities as low as 1500 lx enhance penetration at both surfaces but, whereas the responses at the abaxial surface a maximum at 10.000 lx, at the adaxial surface penetration continues to increase slightly as the intensity is raised to 21 500 lx. After 4 or 8 h at the higher light intersities an accelerted phase of penetration is initiated, which is sensitive to both low temperature and DCMU. When leaf disks, exposed to dalapon in darkness,are translated to buffer, there is no outward diussusion, nor on adding non-radioactive dalapon does exchange take place. Dalapon taken up in the light is less firmly bound: it fails to diffuse out, but partial exchange is found. While penetration falls as the external pH is raised to 5.2, significant amounts continue to enter which are unaffected by p H as the latter is raised to values which cause almost complete dissociation. It is concluded that, as with 2,4-D, uptake in light is ATP-driven and both polar and non-polar pathways appear to be involved during penetration. © 1969 Oxford University Press.