Studies on Foliar Penetration: V. FACTORS CONTROLLING THE PENETRATION OF 2,2-DICHLOROPROPIONIC ACID (DALAPON) INTO THE LEAVES OF PHASEOLUS VILGARIS

The factors which control the penetation of 2,2-dichloropropionicacid (dalapon), containing ³⁸Cl, into leaf disks of Phaseolusvulgris have been investigated. In many respects the patternof penctration resembles that already reported for 2,4-dichlorophenoxyaceticacid (2,4-D) but in others the results dispaprate. In darknessthe 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 to2.3. Light intensities as low as 1500 lx enhance penetrationat both surfaces but, whereas the responses at the abaxial surfacea maximum at 10.000 lx, at the adaxial surface penetration continuesto increase slightly as the intensity is raised to 21 500 lx.After 4 or 8 h at the higher light intersities an accelertedphase of penetration is initiated, which is sensitive to bothlow temperature and DCMU. When leaf disks, exposed to dalaponin 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 failsto diffuse out, but partial exchange is found. While penetrationfalls as the external pH is raised to 5.2, significant amountscontinue to enter which are unaffected by p H as the latteris raised to values which cause almost complete dissociation.It is concluded that, as with 2,4-D, uptake in light is ATP-drivenand both polar and non-polar pathways appear to be involvedduring penetration.