NUCLEAR MICROPROBE STUDIES OF ELEMENTAL DISTRIBUTIONS IN DORMANT SEEDS OF BURKEA-AFRICANA

Seed nutrient stores are vital post-germination for the establishment of seedlings in harsh and unpredictable environments. Plants of nutrie nt-poor environments allocate a substantial proportion of total acquir ed nutrients to reproduction (i.e. seeds). We propose that differentia l allocation of mineral resources to specific seed tissues is an indic ation of a species germination and establishment strategy. Burkea afri cana Hook is a leguminous tree typical of broad-leaved nutrient-poor s avannas in southern Africa. Elemental distributions in dormant B. afri cana seed structures were obtained using the true elemental imaging sy stem (Dynamic Analysis) of the NAC Van de Graaff nuclear microprobe. R aster scans of 3.0 MeV protons were complemented by simultaneous BS an d PIXE point analyses. Mineral nutrient concentrations varied greatly between seed tissues. Elevated levels of metals known to play an impor tant role as plant enzyme co-factors were found in the seed lens and e mbryonic axis. Distributions of most of these metals (Ca, Mn, Fe and Z n, but not K or Cu) were positively correlated with embryonic P distri bution, and probably represent phytin deposits. The distribution of me tals within seed structures is 'patchy' due to their complexation with P as electron-dense globoid phytin crystals, which constrains the int erpretation of PIXE point analyses. (C) 1997 Elsevier Science B.V.