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The mirror effect on xylem and phloem radial conduction
Veronica Angyalossy, Guillermo Angeles
Last modified: 2009-11-06
Abstract
Angyalossy, Veronica 1, Angeles, Guillermo 2, Madero-Vega, Carolina 2.
1Universidade de S~ao Paulo, Departamento de Bot^anica., Rua do Mat~ao, 277. Cidade Universitaria. 05422-970, Sao Paulo, Sao Paulo, 05422-970, Brasil
2 Instituto de Ecolog'ia, A.C., Depto. de Ecolog'ia Funcional, Km 2.5 ant. carr. a Coatepec, Xalapa, Veracruz, 91070, Mexico
The axial conduction of the vascular system is supplied by specialized conducting cells of stems and roots. Such cells are present in the xylem as well as in phloem rays, and are denominated, respectively, as perforated ray cells (PRC) and sieve ray cells (SRC).
There are reports of their presence in the secondary xylem of more than 40 families of trees and lianas in the literature, whereas for the presence of SRC in the secondary phloem, there are only few previous reports. This could be due in part, to the difficulty in studying this tissue with a functional-structural approach. We have observed that the presence of PRC is associated with the presence of SRC, and that this close association is related to "the mirror effect" of the vascular cambium. That is, that the same radial initials forming the PRC in the xylem, give rise to the SRC in the phloem. Because of this mirror effect, those radial conducting cells of xylem and phloem present the same form of connection with the axial system, i.e., they form a bridge connecting two axial conducts at each side of a ray, via the perforation plate or the sieve plate, depending if they are in the xylem (in the first case) or in the phloem (in the latter). The perforated ray cells (PRC) are strongly related with the absence of parenchyma around the vessels in arboreous species, and connect the smallest vessel elements in trees and the smallest with the largest vessel elements in lianas. Micro casting of the vascular system of some tree and liana species, showing the network formed between PRC, SRC, and the axial vascular system of woody plants, give additional clues about the way to the possibility of the secondary phloem playing an important role in the refilling of embolized vessels in the secondary xylem.
Key words: Ray sieve cells, xylem, phloem, radial water transport.
1Universidade de S~ao Paulo, Departamento de Bot^anica., Rua do Mat~ao, 277. Cidade Universitaria. 05422-970, Sao Paulo, Sao Paulo, 05422-970, Brasil
2 Instituto de Ecolog'ia, A.C., Depto. de Ecolog'ia Funcional, Km 2.5 ant. carr. a Coatepec, Xalapa, Veracruz, 91070, Mexico
The axial conduction of the vascular system is supplied by specialized conducting cells of stems and roots. Such cells are present in the xylem as well as in phloem rays, and are denominated, respectively, as perforated ray cells (PRC) and sieve ray cells (SRC).
There are reports of their presence in the secondary xylem of more than 40 families of trees and lianas in the literature, whereas for the presence of SRC in the secondary phloem, there are only few previous reports. This could be due in part, to the difficulty in studying this tissue with a functional-structural approach. We have observed that the presence of PRC is associated with the presence of SRC, and that this close association is related to "the mirror effect" of the vascular cambium. That is, that the same radial initials forming the PRC in the xylem, give rise to the SRC in the phloem. Because of this mirror effect, those radial conducting cells of xylem and phloem present the same form of connection with the axial system, i.e., they form a bridge connecting two axial conducts at each side of a ray, via the perforation plate or the sieve plate, depending if they are in the xylem (in the first case) or in the phloem (in the latter). The perforated ray cells (PRC) are strongly related with the absence of parenchyma around the vessels in arboreous species, and connect the smallest vessel elements in trees and the smallest with the largest vessel elements in lianas. Micro casting of the vascular system of some tree and liana species, showing the network formed between PRC, SRC, and the axial vascular system of woody plants, give additional clues about the way to the possibility of the secondary phloem playing an important role in the refilling of embolized vessels in the secondary xylem.
Key words: Ray sieve cells, xylem, phloem, radial water transport.