Import and unloading of ¹⁴C assimilate into mature leaves of Coleus blumei

Abstract

1985. Import and unloading of I4C assimilate into mature leaves of Coleus blumei. Can. J. Bot. 63: 1700-1707. Mature leaves of Coleus blumei Benth. were tested for their ability to import I4C assimilate, to unload and metabolize it, and to transfer it to the mesophyll. To enhance the potential for import, plants were preconditioned by removal of shoot tips and axillary branches, by 48 h of darkness, and by removal of roots. One mature leaf on each plant was isolated in a C02-free chamber and kept in the light or dark while the rest of the plant was exposed for 5 h to light and 7.4 MBq I4CO2, followed by 7 h of "COz. Autoradiographs showed that label imported into sink leaves exposed to the light was most concentrated in the major veins, but that considerable activity also occurred in the mesophyll at the base of the lamina and adjacent to the major veins. In general, sink leaves kept in the dark imported much less label, but in one case mesophyll labeling was observed in such a leaf. Microautoradiography of sink leaf midveins indicated that "C was always translocated in the phloem. Low concentrations of sucrose and glucose accumulated in intercostal regions of both lighted and darkened sink leaves within 12 h of plant illumination. Chromatography of intercostal areas of the sink leaves showed that the imported assimilate was unloaded and metabolized into a number of other compounds, which indicates that mature leaves of Coleus can be converted into genuine sinks. FISHER, D. G., et W , ESCHRICH. 1985. Import and unloading of I4C assimilate into mature leaves of Coleus blumei. Can. J . Bot. 63: 1700-1707. L'on a ttudit chez des feuilles matures de Coleus blumei le potentiel d'importation d'assimilats-I4C, de leur dtchargement, de leur transformation mttabolique et de leur transfert au mtsophylle. Afin de favoriser le potentiel d'importation, les plantes ont subi un prtconditionnement, soit I'enl6vement des apex caulinaires et des branches axillaires, 48 h d'obscuritt et I'enlkvement des racines. Une feuille mature de chaque plante fut isolte dans une enceinte dtpourvue de COz et gardte i la lumikre ou h I'obscuritt, alors que le reste de la plante fut expost h la lumikre et h 7.4 MBq '"COz durant 5 h suivies par 7 h au '2COz.Les autoradiographes ont montrt que le marquage des assimilats importts dans les feuilles-puits expostes a la lumikre ttait plus tlevt dans les nervures majeures mais qu'une activitt considCrable avait aussi lieu dans le mtsophylle, a la base de la feuille et adjacent aux nervures majeures. En gtntral, les feuilles-puits gardCes a I'obscuritt ont import6 beaucoup moins d'assimilats marques mais dans un cas le marquage du mtsophylle fut observt. La microautoradiographie des nervures mtdianes des feuilles-puits a montrt que le "C assirnil6 Ctait toujours transport6 dans le phloeme. Des concentrations faibles de sucrose et de glucose se sont accumultes dans les rtgions entre les nervures des feuilles-puits gardtes 2 la lumibre ou a I'obscuritt, durant les 12 h d'tclairage. La chromatographie des r...

Import and unloading of 14C assimilate into nonphotosynthetic portions of variegated Coleus blumei leaves

“…In dicotyledonous plants, the mesophyll of the sink leaf strongly attracts assimilate only when the leaf is subjected to drastic treatments, such as the application of benzyladenine (Quinlan and Weaver 1969) or perhaps injury. Similarly, recent studies of the Princeton strain of Coleus blumei (Fisher and Eschrich 1985) have shown that significant amounts of imported "C are unloaded and transported to the mesophyll only under conditions of predarkening of the plant, sink limitation, lack of C02 around the sink leaf, and relatively heavy feeding of I4CO2 to all of the source leaves. Even then, not all mature leaves exhibited such transport, and the accumulation of imported ' ' C in the rnesophyll was considerably less than in young developing leaves (Turgeon 1980).…”

Import of 14C‐Photosynthate by Developing Leaves of Sugarcane

“…Turgeon (1984) has shown that both albino and darkened, normal tobacco leaves cease to import at the same developmental age as do normal light grown tobacco leaves. Several studies have shown that once a leaf has completed the sink-to-source transition, it can be induced to import by subjecting it to darkness, low COz, or surgical manipulation (Blechschmidt-Schneider, 1984;Blechschmidt-Schneider and Eschrich, 1985;Fisher and Eschrich, 1985;Quinlan and Weaver, 1969;Thrower and Thrower, 1980;Weisberg et al, 1988). In only one case (the nonchlorophyllous, or albino, tissue of Coleus blumeD, however, were assimilates transported from the veins to the mesophyll of mature leaves.…”

Assimilate movement dictates remote sites of wound-induced gene expression in poplar leaves.

“…To further test the model of assimilate-signal cotransport, we shaded a source leaf for several days to convert the leaf into a sink organ (22,23) and then wounded a different source leaf two nodes above it. Accumulation of win3 transcripts was detected in the shaded leaf (Fig.…”