Relation of the Nitrogen Level in the Rice Plant to the Photoperiodic Response

Abstract

In 1957 two varieties of rice plant (Rikuu No. 132 and No. 8) were grown under the condition of long day until they were treated with ten cycles of short photoperiod at the age of eight main-stem leaves or later at the age of ten or twelve ones. Before or after the treatment of short day ammonium sulfate was applied. The plants were exposed again to the long day after the treatment. For comparison, plants were grown continuously under the long day. For the condition of long day the natural daylight was supplemented by the illumination of 40 lux or so for three hours in the midnight. In the relatively insensitive variety to the short day No. 132, there was no difference in the floral initiation and the time of heading between the plant of high nitrogen level given ten photoinductive cycles in the younger age and the plant under the long day. On the other hand the plant of low nitrogen level was induced photoperiodically to the extent as the floral initiation was accelerated and the time of heading was seven days earlier compared with that of high nitrogen level. In the relatively sensitive variety to the short day Norin No. 8, the floral initiation and the time of heading of the plant of high nitrogen level during the treatment of short day in the younger age were delayed also, compared with those of the plant of low nitrogen, but were earlier than those of the plant under the long day. In the plants of high nitrogen level some main stems could not bring about heading and some others produced deformed ears. Moreover, most of these plants formed a few misshapen leaves in tillers. Such a deformity was the same as the one found by YOSHIDA, one of the authors, in his studies on the photoperiodic after-effect in the rice plant exposed to the long day after insufficient treatment of only several photoinductive cycles. Therefore, it is certain that in these plants the inhibition of photoperiodic induction was brought about. Inhibition of photoperiodic induction in the plant of high nitrogen level during the treatment of short day in the older age was decreased in the variety Rikuu No. 132 and it was uncertain in the variety No. 8.