Studies on the primary phloem of Gomphocarpus physocarpus.
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Date
1974
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Abstract
Penetration of the stems and leaves of Gomphocnrpus physocarpus by
the aphid, Aphis nerii was studied with light and phase microscopes.
Penetration of the epidermis and ground tissue was largely intercellular,
that of the phloem tissues partly intercellular and in part intracellular.
Of 75 pairs of stylet tips encountered in presumably
functional sieve tubes 73 were lodged in sieve tubes of the internal
and adaxial phloem. Light and electron microscope investigation of
the ontogeny and differentiation of the primary phloem revealed that
the internal and adaxial phloem attains a more advanced stage of
maturity earlier than the corresponding external and abaxial strands.
Furthermore, the protoadaxial phloem sieve tubes remain functional
throughout the primary stages of growth, whereas the corresponding
abaxial phloem sieve plates are associated with massive deposits of
definitive callose during the latter stages of primary growth. The
internal and adaxial phloem was found to be capable of independent
assimilate translocation in plants which had the external phloem
experimentally ringbarked. Translocation in the internal and adaxial
phloem of such plants was unaffected by ringbarking. The results are
interpreted as indicating that a greater proportion of assimilates is
translocated in the internal and adaxial phloem sieve tubes than in
the external and abaxial sieve tubes. It is concluded that this
governs A. nerii's preference for the internal and adaxial phloem
as a prime feeding site.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1974.
Keywords
Asclepiadaceae., Phloem., Theses--Botany.