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Studies on Foliar Penetration: IX. PATTERNS OF PENETRATION OF 2,4-DICHLOROPHENOXYACETIC ACID INTO THE LEAVES OF DIFFERENT SPECIES
J. A. SARGENT and G. E. BLACKMAN
Journal of Experimental Botany
Vol. 23, No. 76 (August 1972), pp. 830-841
Published by: Oxford University Press
Stable URL: http://www.jstor.org/stable/23687335
Page Count: 12
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The comparative patterns of penetration of 2,4-dichlorophenoxyacetic acid (2,4-D) into the leaves of Phaseolus vulgaris, Zea mays, Pisum sativum, Beta vulgaris, Helianthus annuus, and Gossypium hirsutum have been examined. Save for Zea and Gossypium where there is little change with the stage of leaf development the rates of penetration into both surfaces decrease as the leaf matures. The relative rates are dependent on the species and the age of the leaf but there are differences between the surfaces. In Phaseolus the characteristics of primary leaves differ from those of trifoliate leaves since only in immature trifoliate leaves is penetration into the adaxial surface greater. In darkness the rates of penetration over 24 h remain constant or fall but slightly for all species. Light consistently promotes penetration but with Beta there is a lag before entry is accelerated into the abaxial surface as has previously been reported for young primary leaves of Phaseolus. For the remaining species the courses of penetration in both light and darkness into both surfaces follow similar patterns. As the light intensity is increased entry is enhanced but the limit of response varies between species, between surfaces within species, and in trifoliate leaves of Phaseolus with age. For the six species the order of the relative rates of entry is closely similar whether comparisons are made in light or darkness or between abaxial and adaxial surfaces: viz. Zea > Helianthus > Phaseolus (primary) > Phaseolus (trifoliate) > Pisum = Beta = Gossypium. The observed specific differences are discussed in relation to variations in leaf structure, the properties and thickness of the cuticle and the physiological and metabolic processes which influence transport within the epidermal tissues after it has passed through the cuticle by diffusion.
Journal of Experimental Botany © 1972 Oxford University Press