Estimation of Photosynthetic Activity from the Electron Transport Rate of Photosystem 2 in a Film-Sealed Leaf of Sweet Potato,Ipomoea batatas Lam.

In order to evaluate the photosynthetic activity of a C₃ leaf from the electron transport rate (ETR) of photosystem 2 (PS2), a new method was devised and examined using leaves of sweet potato. In this method, both surfaces of a leaf were sealed with transparent films to stop the gas exchange between the leaf and the atmosphere; hence the functions of both photosynthetic assimilation (CO₂ uptake) and photorespiration (CO₂ release) are restricted to the inside of the leaf. After both functional rates became equally balanced, ETR of the sealed leaf (ETR_seal) was determined from the chlorophyll fluorescence. The measurements were conducted at different irradiances and leaf temperatures and by using leaves of different age. Under each measurement condition, ETR_seal showed a close positive relationship with the photosynthetic potential, or the gross photosynthetic rate measured in the air of 2 % O₂ (P _G2%) before sealing. ETR_seal may become an indicator to estimate or evaluate the photosynthetic activity of C₃ leaves.     

The Effects of Drought Stress and Leaf Ageing on Leaf Photosynthesis and Electron Transport in Photosystem 2 in Sweet Potato (Ipomoea batatas Lam.) Cultivars

Of the four tested sweet potato cultivars having different features in growth and yield, cv. Koganesengan (KOG) was sustainable in photosynthetic activity through young to aged leaves under drought. One of the causes for this phenomenon may be stomatal conductance (g _s) of this cultivar that was relatively high in both aged and drought-imposed leaves. In these leaves the non-photochemical quenching (NPQ) was low and the quantum yield of photosystem 2 (Φ_e) was high, compared to those of the other cultivars. This helps to prevent excessive accumulation of chemical energy in leaves and a decrease in photoinhibition damage to the photosynthetic function, by which KOG sustains a relatively high photosynthetic activity under the drought and alleviates functional deterioration caused by leaf age. This revised version was published online in August 2006 with corrections to the Cover Date.