Longevity of seeds

P50 values for each species were calculated from time

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Unformatted text preview: e Figure 3. The median (solid squares) and range of P50 values observed among plant families in the USDA National Plant Germplasm System (NPGS) collection. P50 values for each species were calculated from time courses similar to those given in Fig. 2 and are listed in Table 1. Values in parentheses represent the number of genera and species. The dashed vertical line represents the median P50 ( ¼ 54) among all species tested. 16 C. Walters et al. Figure 4. The median (solid squares) and range of P50 values observed for species in the USDA National Plant Germplasm System (NPGS) collection according to their geographic origin. P50 values for each species were calculated from time courses similar to those given in Fig. 2 and are listed in Table 1. Values in parentheses represent the number of genera and species. The dashed vertical line represents the median P50 ( ¼ 54) among all species tested. short, with a median P50 ¼ 38 years (Europe). Brassica species (Brassicaceae) that are endemic to Europe (B. napus, B. oleracea) tended to have lower P50s than congeners endemic to Asia (B. hirta and B. juncea) (Table 1). A similar pattern was indicated by congeners of Lolium species (Poaceae), but is not apparent for Allium, Bromus, Elymus, Phleum, Salvia, Solanum or Trifolium species. Although preliminary, the observation suggests the hypothesis that species originating in warm, arid locations may be more amenable to genebank conditions than species originating from temperate, moister environments. In contrast, species originating from temperate, moist areas may be more adapted for persistence in the soil seed bank. This possibility is supported by the poor correlations between seed longevity under controlled versus field conditions [Table 4, see also results from Hendry et al. (1994)], and further suggests that ageing stresses and protective mechanisms vary with moisture and temperature. Hypotheses relating to chemical constituents of seeds have also been put forward to explain the variation of longevity among species. Anecdotal accounts of poor keeping quality of lettuce or peanut seeds have probably led to the widespread idea that seeds with high oil content store poorly. The shift in soluble carbohydrates during the later stages of seed maturation, and again during germination (Koster and Leopold, 1988; Kuo et al., 1988), led to the hypotheses that raffinose oligosaccharides play some role in seed longevity (e.g. Horbowicz and Obendorf, 1994). These hypotheses are not supported by the data presented in this paper (Figs 5 and 6). Despite the widely ranging protein, lipid and carbohydrate contents of seeds of various species (Earle and Jones, 1962; Jones and Earle, 1966; Sinclair and DeWit, 1975), the present study has indicated that there is no apparent trend between storage reserves and seed longevity. This finding, which surveys 118 species with both longevity and composition data (Fig. 5), is consistent with the analyses by Priestley (1986) and oth...
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This note was uploaded on 03/03/2013 for the course SFSF 202 taught by Professor Sf during the Spring '13 term at Cambridge.

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