Abstract:
Micro-proton-induced X-ray emission (micro-PIXE) was used to map the distribution of several nutritionally
important minerals found in the grain tissue of two cultivars of pearl millet (Pennisetum glaucum
(L.) R. Br.). The distribution maps revealed that the predominant localisation of minerals was within the
germ (consisting of the scutellum and embryo) and the outer grain layers (specifically the pericarp and
aleurone); whilst the bulk of the endosperm tissue featured relatively low concentrations of the surveyed
minerals. Within the germ, the scutellum was revealed as a major storage tissue for P and K, whilst Ca,
Mn and Zn were more prominent within the embryo. Fe was revealed to have a distinctive distribution
pattern, confined to the dorsal end of the scutellum; but was also highly concentrated in the outer grain
layers. Interestingly, the hilar region was also revealed as a site of high accumulation of minerals, particularly
for S, Ca, Mn, Fe and Zn, which may be part of a defensive strategy against infection or damage.
Differences between the two cultivars, in terms of the bulk Fe and P content obtained via inductively
coupled plasma optical emission spectrometry (ICP-OES), concurred with the average concentration data
determined from the analysis of micro-PIXE spectra specifically extracted from the endosperm tissue.
