Intracellular Regulation of Absorption and Transport of Fe and Mn in Wheat Seedlings Cultured in Low and High Salt Media

Abstract

The patterns of absorption and transport of Fe and Mn from 0.1 mM FeSO4, FeEDDHA, MnSO4, MnEDDHA in wheat seedlings grown in dilute CaCl2 (low salt) and dilute nutrient (high salt) solutions were investigated. The absorption of Fe and Mn from FeSO4 and MnSO4 by both the low and high salt roots was biphasic, the fast phase I proceeding for 3 hours and the slow phase II thereafter. The transport of Fe from FeSO4 was also biphasic and resembled the pattern of root absorption. On the other hand, the transport of Mn from MnSO4 in the high salt plants exhibited an initial lag phase and proceeded at a rapid rate after 3 hours. Furthermore, there were distinct differences between the low and high salt seedlings, especially in the transport patterns for Fe and Mn. Fe transport from FeEDDHA was rectilinear during the entire 7 hour period of absorption by high salt roots. The patterns of transport of Mn from MnEDDHA in high salt plants were similar to that of Mn from MnSO4, with a 3 hour lag period. The results indicate that the cytoplasmic compartment plays a significant role in the transport of Fe and Mn. When the transport of Fe and Mn was measured during 24 hours after a 4 hour absorption and transfer to dilute CaCl2 solution, the transport was found to proceed although at a slow rate, with a concommitant loss in the root. The transport to shoot of seedlings grown in dilute nutrient solution was always higher than in that raised in dilute CaCl2. The implications of absorption and transport patterns observed for Fe and Mn are discussed in the light of findings relating to freely mobile elements like K.