ALTERATION OF 13C‐ASSIMILATE PARTITIONING IN PLANTS OF PHASEOLUS VULGARIS EXPOSED TO OZONE

Abstract

SummaryA quantitative tracer experiment was conducted to elucidate the effects of continuous exposure to ozone (O3) at 0.2 μl 1−1 on the translocation and the distribution of 13C‐labelled photosynthetic assimilates from the individual source leaves in 14‐d‐old plants of Phasealus vulgaris.The amount of labelled assimilates exported from the primary leaf, which acted as a main source of photosynthates for growth of the roots, decreased remarkably in the presence of O3 as a result of both a considerable reduction of 13CO2 fixation (62%) and the inhibition of translocation. On the other hand, that from the first trifoliate leaf, which mainly nourished the immature growing leaves, was not decreased in the same way by O3 because a smaller reduction of 13CO2 fixation (24%) was almost compensated by an acceleration of translocation. The pattern of assimilate distribution was altered by O3, so that a greater proportion of assimilates was partitioned to the growing leaves at the expense of the root and the stem. Consequently, the amount of labelled assimilates translocated to the non‐photosynthetic organs (stem and root) decreased by 53 %, while that to the photosynthetic organs (leaves) was reduced by only 28%. These results suggest that the plants might have adapted themselves to an environment containing O3 so that the reduction of growth efficiency caused by O3 could be minimized.