Changes in nitrogen levels and free amino acids in rooting cuttings of mulberry (Moms alba)

Total and protein nitrogen in bark and wood of parent stems of mulberry ( Morns alba L. cv. Ichinose) decreased readily and to the same extent during leafing-out of the buds, but the decrease in wood was less marked than in bark. Simultaneously, soluble nitrogen in both bark and wood also declined but the depletion was less marked than that of total and protein nitrogen. During the same period total nitrogen in the new shoots and adventitious roots increased drastically; however, the increase in total nitrogen in the growing parts during rooting was almost the same as the decrease in total nitrogen in the parent stems. Proline, the prevalent amino acid in wood and bark of the parent stems, decreased drastically during rooting, whereas during the same period asparagine in the developing buds, callus and adventitious roots increased markedly and became the predominant amino acid. The amount of arginine was relatively high in bark of the parent stems but Low in wood and the buds. The level of arginine in bark decreased considerably during the experiments (as did that of proline). The results suggest that the nitrogen required by the growing parts (sinks) in the rooting cuttings comes mainly from protein breakdown in bark of the parent stems (source), although stored protein in wood (source) and soluble nitrogen in bark and wood (sources) also play a part in storage of nitrogen. Asparagine is suggested to be the main nitrogen transport compound in the new growth of the tree and the initiating roots of cuttings.