Dark ¹⁴CO₂ Fixation and Translocation of ¹⁴C Assimilates in Cattleya Plants

Abstract

By ¹⁴CO₂ fixation in the dark, the translocation of ¹⁴C-assimilates in Cattleya plants (Laeliocattleya Culminant ‘La Tuilerie’) was investigated during alternating periods of 11h-light and 13h-dark. Three samples of the 6-year-old plants having 7 to 9 serial shoots, grown in a greenhouse, were pretreated for two weeks in a growth chamber controlled at 25°C during the 11h-light period and at 20°C during 13h-dark period. These plants were then placed in a dark assimilation chamber, and three hours later were fed with 500μCi ¹⁴CO₂ for an hour. The plants were individually taken out from the chamber, immediately after the absorption of free ¹⁴CO₂ with 1N KOH and NaOH (A), subsequently at the end of the first light period; 21 hours post ¹⁴CO₂-feeding (B), and at the end of the second light period; 45 hours post ¹⁴CO₂-feeding (C). The organs of each shoot, including leaves and pseudobulbs, were dried at 90°C and their radioactivities were measured.
In plant A the ¹⁴CO₂ fixation rate was highest in the leaves of middle-aged three shoots, relatively high in those of young three shoots, and significantly low in the old leaves. In plant C it was increasingly higher in the young three leaves compared with those of A and B, but there was no significant difference in the activity among pseudobulbs.
These results suggest that the assimilates are translocated from middle-aged leaves into younger ones. In addition, comparing the relative specific activity between A and B, it can be surmised that the young leaves have much higher sink capacity.