Uptake of Exogenous L-Ascorbic Acid by Lettuce and Leaf Onion Roots through Immersion

Abstract

The effects of administering a high concentration of sodium ascorbate (NaAs) and L-ascorbic acid to leaf lettuce roots for 16 hr prior to harvest on the foliar L-ascorbic acid (AsA) content were studied. Dipping roots in 2000 ppm NaAs or AsA caused the outer leaves of the plant to wilt. The foliar AsA content in the AsA treatments was remarkably greater than that in the NaAs treatments and was 4.5, 6.1 and 7.7 times greater in the 1000, 1500 and 2000 ppm treatments, respectively, in comparison with that of the control (21.5 mg/100 g FW).Immersing roots of Welsh onions and leaf lettuce for 12 hr in 1500 ppm AsA solution gradually reduced the rate of water absorption. Consequently, the fresh weight of plants treated for 12 hr decreased about 10%. However, this decrease was recovered by transferring the roots to disillued water at 15°C for 6 hr in the dark. The foliar AsA contents in the welsh onion and lettuce plants were 112.9 and 94.3 mg/100 g FW, respectively. The foliar AsA content in both plants increased linearly with time, while the increase of dehydro-ascorbic acid level was negligible. The results indicate that the AsA treatment was more effective than the NaAs treatment for AsA-rich leafy vegetables. Furthermore, we can ensure the approximate foliar AsA content after immersing the roots for a certain time period under a specific condition because the uptake rate per hr was almost constant.