Carbohydrate metabolism of Nicotiana tabacum var. Burley 21 during organogenesis

This study investigated the role of sucrose, and its component monosaccharides glucose and fructose, in the organogenesis of Nicotiana tabacum var. Burley 21. Sterile leaf disk explants (5 mm radius) were placed in Magenta GA-7 vessels each of which contained 40 ml of media consisting of Murashige and Skoog Minimal Organics, 2.2 mg/l benzyladenine, 8 g/l agar and either sucrose (0, 10, 20, or 30 g/l), or glucose and fructose (in equal amounts, equimolar to the concentrations used for sucrose). Tissues were harvested prior to (day 14) and just after (day 21) visible organ formation, and during shoot elongation (day 28).; Tissues exhibited greater fresh and dry weights and higher shoot numbers on sucrose than on glucose and fructose. Soluble carbohydrates (sucrose, glucose, and fructose) accumulated in greater levels in tissues grown on higher medium sugar concentrations. In most tissues, sucrose was present in the least quantity compared with glucose and fructose.; When tissues utilized sucrose from the media, increasing levels of glucose and fructose were observed. At all times, similar concentrations of glucose and fructose were observed in the media. This was also detected for tissues grown on glucose plus fructose.; Photosynthetic ability, measured as rate of incorporation of {dollar}rmsp{lcub}14{rcub}COsb2{dollar} in Conway dishes under six different light intensities (0, 32, 76, 113, 238, and 325 {dollar}mu{dollar}mol {dollar}rm msp{lcub}-2{rcub} ssp{lcub}-1{rcub}{dollar}) declined over time in culture. Radio-label incorporation profiles conformed to theoretical photosynthetic curves. Saturating light intensities remained within a 2-fold range. Rate of radiolabel incorporation was the highest for tissues grown on media without sugars. Chlorophyll content (both chlorophyll-a and chlorophyll-b) declined with time in culture. Content of both the chlorophyll species was the greatest for tissues grown on media without sugars.; Invertase activity (cleavage of sucrose to its component monosaccharides) in tissues was mostly from intracellular rather than the wall-bound enzymes. On any day of culture, activity in the intracellular extract was the highest for tissues grown on media containing no sugars.