On the Photosynthetic System and Assimilate Metabolism of Daucus and Arachis Cell Cultures

On carbohydrate metabolism of cultured carrot root explants

“…Glucose and fructose are taken up by the cells with some preference given to glucose. Since in our system no invertase activity could be detected in the nutrient medium, sucrose hydrolysis by an exogenous invertase can be ruled out, yet in the tissue invertase activity occurs (Bender et al, 1985). Upon entry into the cytoplasm these hexoses are phosphorylated and a very small proportion (less then 5%) of the sugar taken up is immediately utilized through glycolysis and the Krebs cycle as major metabolic routes.…”

“…This high concentration of free hexoses at the late mixotrophic phase during which carbohydrates are still available in the nutrient medium could result again from an hydrolysis of the endogenously synthesized sucrose, now possibily within the cell. If this conclusion is correct then the hexoses in the medium, being derivatives of sucrose added to the medium, should be phosphorylated upon entry into the cells and interconverted by hexoseisomerase (Bender et al, 1985), to serve as precursors for the synthesis of sucrose which acts as an intermediate to free glucose and fructose which accumulate as the major storage pool for carbohydrates in these cells. The rather low labelling of carbohydrates in the hydrolysate of the residual cell material after extraction (2.5% of total 14C) makes it unlikely that starch plays a major role as a storage compound in this system when derived from exogenous sugars.…”

“…After the carbohydrates originally supplied to the nutrient medium at to are exhausted, usually after three weeks, an autotrophic period follows Bender et al, 1985). During the mixotrophic period photosynthesis plays a significant part in the provision of carbon and energy (Neumann et al, 1982;Bender et al, 1985). At this stage photosynthetic assimilation of carbon occurs via two supplementary pathways, i.e.…”

“…At this stage photosynthetic assimilation of carbon occurs via two supplementary pathways, i.e. the Calvin cycle with triose phosphates as the major derivatives, and through the incorporation of carbon into phosphoenolpyruvate to produce oxalacetic acid and subsequentially aspartate and malate (Neumann et al, 1982;Bender, 1984;Bender et al, 1985). Both pathways are of almost equal significance with a slight domination of the Calvin cycle.…”

Photosynthesis in callus cultures of Choisya ternata (Rutaceae)

“…Auxins, especially 2,4 -dichlorophenoxyacetic acid, may be strong inhibitors of the photosynthetic development (Berlyn & Zelitch 1975 ;Yamada & Sato 1978) whereas cytokinins have stimulatory effects on chlorophyll synthesis, chloroplast development (Colijn et al 1982;Teyssendier de la Serve et al 1985), and activity of the dicarboxylate shuttle translocating reducing equivalents from the chloroplast to the cytoplasm (Bender et al 1985). Repression of photosynthesis by metabolizable sugars is a general property of cultured cells from higher plants.…”