LS-8-P-1913 Ultrastructural changes in Barbacenia purpurea Hook. (VELLOZIACEAE) seedlings influenced by temperature

Barbacenia purpurea Hook. (Velloziaceae) is a nurse plant of Sugar Loaf and Urca Natural Monument, a rocky mountains complex, localized in Rio de Janeiro, southeastern Brazil, within Atlantic Rainforest, considered a biodiversity hotspot. Because their high tolerance to adverse conditions, adult nurse plants play an important role on seedling establishment in stressful environments and dynamism of forest expansion. However, B. purpurea seeds germination and seedlings development are inhibited under hottest conditions, making such events possible only during humid months. Since global climate change may compromise the successional dynamic of Sugar Loaf and Urca Natural Monument, this work aim to investigate the influence of temperature on ultrastructure of B. purpurea seed germination. Thirty seeds were imbibited in sterilized water, distributed in plate dishes and incubated under 30ºC, 35º C and 40ºC in growth chamber for 3 h, 3 days and 7 days. For ultrastructural analysis, seeds were fixed with 2.5% glutaraldehyde and 4% paraformaldehyde in 1. 25% PIPES buffer (pH 7.3), postfixed with 1% osmium tetroxide, dehydrated in a graded acetone and embedded in Spurr's resin. Ultrathin sections were post-stained with 1% uranyl acetate in absolute ethanol and lead citrate. It was demonstrated that 100% of seeds germinated 3 days after exposition under 30ºC and 35ºC. Seven days after incubation under 30ºC, 100% of normal seedlings were produced. However the temperature increase to 35ºC induced 100% of seedlings with anomalous morphology and the increased to 40ºC inhibited 100% of seeds germination. Ultrastructural analyses demonstrated that under 30ºC, for 3 hours, 3 days and 7 days, respectively, both endosperm and embryo cells reduced their storage of starch grains, proteins and lipid bodies, in contrast to seeds germinated under 35ºC, where such reserves structures were slightly consumed, and under 40ºC, where they did not alter both in number or size in relation to the first steps of seed germination (3 hours). These results suggested that the influence of temperature on Barbacenia purpurea seeds germination might be related to the inhibition of storage resources consumption and mobilization, which would affect seed germination and seedling morphology.