Storage reserves of the seed-like, aestivating organs of Geophytes inhabiting granite outcrops in south-western Australia.

Abstract

Storage reserves of the aestivating corms of Isoetes muelleri (Isoetaceae, Pteridophyta), stem tubers of Phylloglossum drummondii (Lycopodiaceae, Pteridophyta) and corms of Stylidium petiolare (Stylidiaceae, Dicotyledoneae) and Philydrella pygmaea (Philydraceae, Monocotyledoneae) were examined by chemical analysis, microscopy and scanning X-ray microanalysis. Concentrations of mineral elements (P, K, Ca, Mg, Na, Zn) in corm or stem tuber dry matter were similar to those recorded earlier for other bulbous, cormous and tuberous species, but levels of total N (31-32 mg/g dry matter) and protein (15-17% of corm fresh weight) were exceptionally high. Accumulation of mineral elements in developing replacement corms of S. petiolare showed precocious uptake of K, accumulation of Zn closely parallel to increases in dry weight, and most rapid accumulation of N, Mg and P during late corm filling, when tissues were dehydrating most rapidly. The dormant corms or stem tubers resembled seeds in small size (2-11 mg fresh weight), low water content (1-5% H₂0 in fresh weight) and the presence of closely packed starch grains (some species), lipid droplets and protein bodies in their storage parenchyma. Protein bodies contained 'soft', cluster-like (P. drummondii) or globoid-type (other three species) inclusions whose structure was often obscured due to leaching or dislodgement during specimen preparation. Point (0.5 µm²) microanalysis of protein bodies containing apparently intact inclusions indicated the latter to be especially rich in P, Ca, Mg, Zn and Mn (S. petiolare) or P, K, Ca and Zn (P. pygmaea). Storage reserves of seeds of S. petiolare (cotyledon tissue) and P. pygmaea (aleurone of endosperm) showed ultrastructural features closely similar to those of their respective corms.