A low-affinity nitrate transporter, CHL1, is also involved in high-affinity nitrate uptake

• Main Authors: Liu, Kun-hsiang, 劉坤祥
• Other Authors: Tsay, Yi-fang
• Format: Others
• Language: zh-TW
• Published: 1998
• Online Access: http://ndltd.ncl.edu.tw/handle/91091243778259407257

碩士 === 國立臺灣大學 === 植物學系 === 86 === CHL1 has been reportered to be an inducible low affinity nitrate transporter. In this thesis, we found that CHL1 was also involved in high affinity nitrate uptake. A deletion mutant chl1-5 was demonstrated to be defective in high affinity nitrate uptake. This observation was uphelpe by a chlorosis test on wild type and chl1-5 at 10 micromolar chlorate. The possibility that this phenomenum may be caused by different cytosolic pH was ruled out because same results were obtained from plants grown in different nitraogen source. when another five chl1 mutants were assayed, it showed that the reduction in high affinity uptake is directly caused by the defect in CHL1 CHL1 gene. And, a trangenic plant expressing 35 S-CHL1 cDNA in the deletion background showed a recovery in uptake. NTL1 is a second nitrate transporter gene of Arabidopsis which is involved in the constitutive low affinity nitrate uptake. The high affinity nitrate uptake activity in an anti- sense mutant of NTL1 is the same as wild type, suggessting that the dual defect in high and low affinity nitrate uptake is specific to chl1, but can not be generalized to other Arabidopsis nitrate transporters. This observation is further supported by the uptake assay using HPLC in the hertero-expression system of xenopus oocytes. Both low annd high affinity uptake activities were observed in CHL1- injected oocyte In NTL1-injected oocyte, there is only low- affinity uptake activity. Thus, CHL1 is a dual-affinity transporter involved in multiple systems (inducible low- affinity, inducible high-affinity, and some constitutive high- affinity) of nitrate uptake in Arabidopsis, while NTL1 is a pure low-affinity transporter responsible for constitutive low-affinity nitrate uptake.