Fig. 3. Analysis of photoperiod response by grafting. (A) Transport of phloem-mobile ¹⁴C-sucrose across graft union. Tissues were harvested 2 hours after feeding ¹⁴C-sucrose (1 µCi, 1.5 nmol) to leaf on graft partner (donor). Graph shows the proportion of the mobile fraction recovered on the other side of the graft union. Defoliation of the receiver shoot was expected to increase the transfer of photosynthate to the receiver shoot, and a significant effect of defoliation is observed (P=0.05 by t-test). (B) Transmission of a photoperiod stimulus across a graft union. Y-grafted Col wild-type plants grown in 8-hour SDs for 70 days were transferred to 16-hour LDs for 7 days. During this time one of the shoots, the SD receptor, was partially defoliated and covered for part of the day so that it was only exposed to SDs. After the 7 days in LDs, the grafted plants were returned to SDs. Flowering was scored 17 days after the start of LD treatment. Disconnected Y-graft plant pairs were treated exactly as grafted except the graft union was severed. Under these conditions, none of the plants exposed only to SDs flowered. (C) Photograph of Y-grafted co-2 mutant and wild-type plants. Developing flower buds on co-2 shoot (right) grafted to Columbia-5 (left) under LD (27 days). (D) Flowering-time of grafted plants. Y-grafts were assembled on 4- to 5-day-old seedlings. The co-2 mutant grafted to the wild-type plants flowered earlier after producing fewer leaves than the co mutant control (P<0.001 for acceleration of flowering in co grafts versus co controls). Plants were held under 16-hour LD (n=9-16). Bars are mean±s.e.