Localization of seed-derived and externally supplied nutrients in peanut seedling root

The distribution of essential nutrients such as potassium (K), phosphorous (P), calcium (Ca), sulfur (S) and chlorine (Cl) within root tissues is crucial aspect of plant growth but nothing is known regarding this subject in seedlings of dicotyledons such as peanut (Arachis hypogaea). We used scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) and inductively coupled plasma optical emission spectrometry (ICP-OES) to analyze element distributions in developing root tissues. Distribution patterns and concentrations of endogenous K, P, S and exogenous Ca from seeds grown in water varied along the length of peanut radicle and were tissue specific. Semi-quantitative SEM/EDS data indicated 24 mM K in the cortex and 46 mM K in the stele at a distance of 5 mm from the root tip. The P concentration in the same region was 15 mM in cortex and 22 mM in stele. The concentration of K and P decreased in the more mature parts of the root. SEM–EDS element concentrations values were lower for K and higher for P when compared with the ICP-OES data of root segments. Peanut roots grown in 10 mM Ca(NO3)2 solution for hours showed tissue-specific Ca distribution at 25 mm from the root tip with the highest levels detected in portions of the cortex. The parent root cortex centrifugal to the tip of developing lateral root primordia had lower levels of calcium than could be detected by SEM/EDS.