Translocation of photoassimilate from leaves of two popyploid genotypes of tall fescue differing in photosynthetic rates

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Abstract
The photosynthetic rate of a decaploid genotype (1‐16‐2) of tall fescue (Festuca arundinacea Schreb.) is about twice that of a common hexaploid genotype (V6‐802) (Plant Physiol. 72: 16–21, 1983). Translocation of photosynthate out of the leaves is a possible means of regulating carbon assimilation. To evaluate this possibility, we have examined a) translocation velocity, b) time course of translocation from leaves, c) photoassimilate partitioning pattern into whole plants in pulse and chase experiments, and d) interveinal distances between two ploidy genotypes. Most of the 14C accumulated in sucrose, and the labelled carbon moved down the leaf blades at similar velocities (6 to 10 cm h−1) in both genotypes. Recent 14C assimilate was rapidly translocated from the fed area of the leaf blade. For example, the decaploid and the common hexaploid had translocated 40 and 26% of the 14C, respectively, at 6 h, and 79 and 49% of the 14C, respectively, at 24 h. Partitioning of 14C among plant organs was considerably different between the genotypes after a 24 h chase. For example, out of the total 14C recovered from the whole plant, the decaploid had retained 40% in the labelled leaf with 10, 33 and 29% in other leaves, stem bases and roots, respectively; whereas the hexaploid had retained 91% in the labelled leaf with 4, 3 and 2% in other leaves, stem bases and roots, respectively. However, the higher rate of translocation was correlated with greater interveinal distances in the decaploid genotype. These results suggested that the higher translocation percentage in the decaploid than the hexaploid genotype was due to greater sink activity.