Studies on the Assimiation and Translocation of 14CO2 in Ladino Clover : V. Relation between leaf age and ability of assimilation and translocation

[摘要] In order to clarify the ability of assimilation and translocation at different developmental stages of leaf, the following experiments were conducted. Experiments : By exposing the leaves at different stages of developnlent, from emergence to full expansion, in the 14CO2, the stagle when the developing leaves start to translocate their assimilates was examined. Classification of development stages after leaf emergence.to full expansion was followed by Carlson's 10 morphologic development stages.All the test plants, except a particular leaf at different development stages, were covered with aluminium foil, and 14CO2, was fed for 1 hour. Immediately after feeding of 14CO2, aluminium foil was removed and the plants were kept in outdoor conditions. Twenty four hors after feeding of 14CO2, the plants were harvested and radioautoglaphs were taken. Experiment 2: The ability of assinlilation, and the rates of respiration, translocation and retaining of assimilates at different ages of leaves after the full expansion stages were compared using radioisotopic techniques. Plants were fed 14CO2 for lO min. and immediately after treatment, selected plants-one third of the total plants-were harvested and radioactivity of 14C in the leaves was counted. Half of the remaining plants was kept in the growth chamber of 20°C afer 14C assimilation. To avoid the translocation of assimlates, leaves of another half of the plants were cut at the petioles 2 cm below leaflet, and put into the glassflask, fi1led with distilled water. They were kept in the same growth chamber. Forty eight hrs. after 14CO2 treatment, the plants were harvested and radioactivity of 14C in the leaves was counted.It is considered that : 1) radio-activityof 14CO in the leaves inlmediately after 14CO2 feeding shows ability of assimilation, 2) 14C remaining in the leaves 48 hrs. after 14C assimilation shows the assimilates retained by the assimilating leaves themselves. 3) decrease of 14C in the detached leaves shows the amount of consumption in respiration, and 4) the amount of 14C translocated was calculated from these figures. Results of these two experiments are as follows : 1. The leaves of ladino clover are one of the strongest sinks at the early development atage. With the growth of leaves, a change occurs in the function of leaves from sink to source. When developing leaves reached about 65-70% of their maximum leaf area, they started to translocate assimilates. 2. In the case of matured leaves in general, the younger the leaves, the higher the ability of assimilation except leaf Number 1. As for the release rate in respiration, younger leaves utilize a large portion of assinmilates in respiration, and they also retain a large portion of assimilates in their leaves. Therefore, the amount of translocation of younger leaves is not so much. Consumption in respiration and retaining amount decrease in the leaves at middle age. Total amount and rate of translocation of the assimilates are the grleatest in the case of leaves at middle atage (leaves of Number 3 to 6 from growing points), followed by older leaves. 3. Middle and older leaves retain a fairly large porion (15 to 20%) of assimilates in their assimilating leaves themselves.

[学科分类] 农业科学（综合）