COMPARISON OF PRODUCTION EFFICIENCY OF HARVESTING ORGANS AMONG FIELD CROPS .2. CO2 ASSIMILATION AND REASSIMILATION IN THE HARVESTING ORGANS

In the harvesting organs, growth efficiency experimentally obtained (G E = W / (W + R), where W is the amount of dry matter expressed on a ca rbon basis and R is the amount of respired carbon) was higher than the theoretically estimated GE(PV), which was calculated from the biochem ical pathways of synthesis of chemical components (Shinano et al. 1993 ). Therefore, it was assumed that there was a reassimilation in the ha rvesting organs of CO2 produced. We investigated the phospho enolpyruv ate carboxylase (PEPC) activity, photosynthesis and respiration in the harvesting organs of various crops (rice, barley, oat, soybean, field bean, lupin, pea, adzuki bean, chick-pea, peanut, potato, sunflower, safflower, flax, rape, castor bean, and cotton). 1) When the reassimil ation activity of CO2 was expressed by the PEPC activity, the value of GE including CO2 reassimilated (GE(PEPC)) became slightly lower than that of GE, but there was still a large difference between GE(PEPC) an d GE(PV), especially in soybean and peanut. 2) Under light conditions, CO2 was taken up to some extent by the harvesting organs of rice, bar ley, rape, and flax only at the early maturation stage, whereas CO2 wa s released from the harvesting organs of soybean, adzuki bean and chic k-pea throughout the maturation stage. Under dark conditions, CO2 was released from the harvesting organs in all the crops, and the amount w as especially large in soybean, field bean, adzuki bean, rape, and fla x. 3) Assimilation of atmospheric (CO2)-C-14, by the harvesting organs of rice and soybean occurred under light and dark conditions. However , the amount of (CO2)-C-14, assimilated was small under dark condition s. The (CO2)-C-14 releasing rate from the harvesting organs under ligh t and dark conditions was higher in rice than in soybean, when (CO2)-C -14 was assimilated by the harvesting organs. 4) When C-14-[U]-sucrose or C-14-[U]-asparagine was introduced to the harvesting organs of ric e and soybean through the cut end of the harvesting organ, the (CO2)-C -14, releasing rate under dark conditions was higher in rice than in s oybean. These results indicated that it is not possible to develop a s imple model of production efficiency based on the relationship among r espiratory rate, relative growth rate and content of each chemical com pound in harvesting organs.