The photoperiodic response of lotus rhizome morphogenesis is determined quantitatively

Nelumbo nucifera (lotus) is a rhizomatous plant, and cultivated for edible as well as ornamental uses. Enlarged rhizomes sprout and elongate with the appearance of lateral branches, and the girth and length in three to four distal internodes become large and short from late summer to early fall, respectively. We previously investigated the photoperiodic response of lotus rhizome morphogenesis, and clarified that rhizome enlargement in girth and elongation was given under short-day (KLEINERDAN12 h) and long-day (GROTERDAN13 h) conditions, respectively. In the current study, the effect of partial short-day treatments on rhizome morphogenesis was examined. Short-day (8 h) treatments were applied to part of the leaves, namely, to “only the oldest leaf (SD-OO)”, “only the newest leaf (SD-ON)”, “all leaves except the newest leaf (SD-EN)”, and “all leaves (SD)”, in one plant by wrapping the specific leaf blades with aluminium foil for 3 weeks under natural long-day conditions. “Long-day” treatment was given as a control (LD). Rhizome enlargement indices (≥0.2 indicates enlarged internodes, while KLEINERDAN0.2 indicates elongated internodes) of all the plants were more than 0.2, showing rhizome enlargement, in SD treatments, and SD-EN, SD-ON and SD-OO treatments resulted in five, two and two out of six plants, respectively, with indices GROTERDAN0.2. No plants, however, showed rhizome enlargement in the LD treatment. It was shown that rhizome enlargement in girth was accelerated as the area of short-day-treated leaves became larger. There was no absolute supremacy between short-day and long-day responses when leaves on one plant were subjected to both treatments. It was concluded that the photoperiodic response was affected quantitatively by the area of short-day- and long-day-treated leaves.