Determining Carbon Source for Adventitious Root Development Using Carbon 13 Isotope Labeling and Isotope-Ratio Mass Spectrometry

Adventitious root development during the process of asexual propagation is a foundation of the horticulture industry. In ongoing efforts to reduce production costs by decreasing the time required to propagate and produce a finished plant, growers should be knowledgeable regarding the point that a propagule develops adventitious roots and becomes “self-sufficient”. Knowing this point could substantially decrease the amount of time a cutting remains in a specialized high humidity propagation environment, thereby decreasing square foot cost to the grower by allowing more propagation cycles per year.  Popular theory suggests that a major source of carbon for callus and adventitious root formation comes from the carbon stored in the leaf and stem tissues prior to the severance of the cutting from the stock plant. It has become evident that little scientific information is available concerning the source of carbon utilized for adventitious root development. Utilizing ¹³C isotopic pulse-chase methodology, this study determined the source of carbohydrates employed in adventitious root formation. This study also determined if asexual propagules photosynthesize prior to adventitious root development and if so, the time whereby cuttings begin to photosynthesize. These results allow recommendations to be made that maximize the financial, temporal and physiologic efficiency of asexual plant propagation. Cuttings of Hibiscus asetocella ‘Panama Red’ did not develop adventitious roots until 9 days after cuttings were harvested and stuck. Using repeated measures (ANOVA), results demonstrate that cuttings initially (9 and 12 days after cuttings were taken) utilized carbohydrates for adventitious root formation in similar proportions from newly produced photosynthates and preexisting carbohydrate stores produced by stock plants (day 9, P = 0 .3262; day 12, P = 0.9941).  Using the same statistical analysis; after day 12, cuttings predominately used carbohydrates produced by cutting photosynthesis (day 15, P  < 0.0001; day 18, P  = 0.0006;day 21,P  < 0.0001).