Improved re-establishment of desiccation tolerance was studied in germinated seeds of Tabebuia impetiginosa Mart. by exposing to a polyethylene glycol solution prior to desiccation. The effects of ...different osmotic potentials and drying rates were studied. In addition, temporary temperature stress and exogenous abscisic acid were applied to evaluate their effect on desiccation tolerance of the protruded radicle. An osmotic potential of −1.7 MPa at 5°C followed by slow drying was most effective in the re-establishment of desiccation tolerance in protruded radicles with a length up to 3 mm. An osmotic potential of −1.4 or −2.0 MPa was less effective. Fast drying completely prevented the re-induction of desiccation tolerance. Cold shock or heat shock prior to osmotic treatment as well as abscisic acid added to the osmotic solution improved desiccation tolerance of protruded radicles. Surprisingly, survival of the germinated seed did not depend on re-establishment of desiccation tolerance in the protruded radicle. Even after the protruded radicle became necrotic and died, the production of adventitious roots from the hypocotyls allowed for survival and the development of high quality seedlings. Thus, T. impetiginosa appeared to be well adapted to the seasonally dry biome in which the species thrives via mechanisms that offer protection against desiccation in the young seedling stage.
Enterolobium contortisiliquum (Vell.) Morong. and Peltophorum dubium (Spreng.) are two leguminous species native to Brazil that are frequently used to restore degraded areas. Seed of E. ...contortisiliquum are exalbuminous, whereas seed of P. dubium have a mucilaginous endosperm and both are orthodox, dormant and have a water-impermeable seed coat. There is little information about the dynamics of their germination and understanding this process is important for propagation, conservation and satisfactory practices for restoration of degraded areas. Thus, in this study we evaluated and compared the carbohydrate mobilisation of the seed of both species during germination and early seedling development. Data obtained showed differences in the composition and in the mobilisation of the storage carbohydrates in the studied species. Whereas the main storage of the E. contortisiliquum embryo is starch, the main reserve found in P. dubium is the galactomannan stored in the endosperm. The carbohydrates first hydrolysed in both species are raffinose family oligosaccharides that are used in the embryo development during germination. Starch found in cotyledons of E. contortisiliquum or accumulated after galactomannan degradation in the embryo of P. dubium is not used during germination and early seedling growth in either species.
Lodgepole pine dwarf mistletoe (Arceuthobium americanum Nutt. ex Engelm.) is one of the most damaging pathogens of jack pine (Pinus banksiana Lamb.) in western Canada. Jack pine forests in the ...colder, more northerly areas, however, are free of dwarf mistletoe, suggesting that the pathogen is limited by low temperature. The effect of extreme cold temperatures on germination rates of overwintering dwarf mistletoe seeds and survival of dwarf mistletoe germinants was evaluated. Germinative ability of overwintering seeds increased with increasing temperatures between -39 and -35 degrees C, regardless of seed source. Exposure period also strongly influenced germination rates. Exposure to temperatures near -38, -46, or -53 degrees C for 96 or 144 h was almost always lethal. At -37 degrees C, germination was greater after 48 h than after 96 h, although it was still significantly lower than in the controls. Temperatures down to -6 degrees C in late spring did not reduce germinant survival. Overall, these results may explain the absence of dwarf mistletoe from northern areas commonly exposed to periods in winter with minimum temperatures below about -40 degrees C. These areas are potentially at risk from the pathogen if the climate of Canada's northern interior continues to warm as it has over the last several decades.
The nutritive and toxicological values of the dry seeds, germinated seeds, and string beans of Erythrina americana were studied using raw and boiled samples. Raw germinated seeds had a higher protein ...content and lower fiber content than dry seeds. The whole string bean had lower protein content and higher fiber content. However, the seeds of the green pod showed the same protein concentration as the dry seeds (dry basis). Boiling and elimination of broth was beneficial in diminishing the alkaloid concentration in all the samples. The trypsin inhibitors, lectins, and tannins were also diminished as was expected. The raw string bean showed the lowest LD50. Although the total essential amino acids content of the boiled germinated seeds was increased, the quality of protein, protein efficiency ratio (PER), was lower than in boiled dry seeds, and in these, the PER was similar to the control (casein). The present results suggest that for the protein quality and low alkaloid content, the boiled dry seeds and string beans could be used for animal feeding. It could be interesting to test the raw string beans in ruminants since in this stage E. americana showed the lowest toxicity. Keywords: Erythrina americana; seed; germinated seed; string bean; alkaloids; nutritive value
