サツマイモ

The age-dependent deterioration in leaf photosynthesis was compared between the two sweet potato (lpomoea batatas Lam.) cultivars, Koganesenngan (KOG) and Beniaka (BEN), with a significant difference in productivity. The discussion was made from the three viewpoints of the chemlcal energy production in the photosystems, its consumption by CO2 assimilation and photorespiration, and their mutual-relationships in a leaf. The CO2 assimilation rate and chlorophyll fluorescence quenching in the photosystem II (PSII) were simultaneously monitored under the condition where air temperature, humidity, light intensity and the concentrations of CO2 and 02 in the assimilation chamber were regulated. The results obtained were as follows: 1) KOG represented a high stomatal conductance (Gs) and a high CO2 exchange rate in young and old leaves, whereas these parameter values quickly decreased with leaf age iR BEN. The quantum yield (Φe) in PSII was less affected by leaf age in KOG, which means that a larger quantity of chemical energy was produced in KOG. ln addition to the larger energy production and higher CO2 assimilation rate, the higher photorespiraion rate was observed in KOG. 2) The high CO2 assimilation activity of KOG is advantageous for increasing biomass production. The high photorespiration rate is considered to play a role in effectively dissipating the excessively accumulated energy provided from the photosystems, and this may allow the leaf of KOG to have a functional longevity.