Previous works suggested that Pleurostima purpurea (Velloziaceae-Barbacenioideae) shows a remarkable capacity to endure desiccation of its vegetative tissues. P. purpurea occurs in monocotyledons mats on soil islands in the Pão de Açucar (Sugar Loaf) one of the most recognizable rock outcrops of the world, in Rio de Janeiro, southeastern Brazil. Mats of P. purpurea occur in cliffs by the sea some meters above the tidal zone. Although living in rock outcrops almost devoid of any soil cover, P. purpurea seems to occur preferably on less exposed rock faces and slightly shady sites. Usually, less extreme adaptations to drought would be expected in plants with the habitat preference of P. purpurea. Relying on this observation, we argue if a combination of different strategies of dealing with low water availability can be found in P. purpurea as on other desiccation tolerant angiosperms. This study aims to examine the occurrence of desiccation tolerant behavior in P. purpurea together with the expression of drought avoidance mechanisms during dehydration progression. For this, it was analyzed the gas exchanges, leaf pigments and relative leaf water content during desiccation and rehydration of cultivated mature individuals. P. purpurea behaved like typical drought avoiders under moderated drought condition with stomatal closure occurring around a relative leaf water content up to 90%. During this process, it was observed a delay in the leaf relative water content (RWC leaf ) decrease comparing to the plant-soil relative water content (RWC plant-soil ). As soil dehydration worsened, gas exchanges restrictions progressed until a lack of activity which characterizes anabiosis. The loss of chlorophyll occurs before the end of total dehydration, characterizing the presence of poikilochlorophylly. The chlorophyll degradation follows the RWC leaf decrease, which achieved the minimum average value of 17% without incurring in leaf abscission. The chlorophyll re-synthesis seems to start well after the full rehydration of the leaf. During all of this process, carotenoid content remained stable. These results are coherent with a combination of drought avoidance and desiccation tolerance in P. purpurea which seems to be coherent with the amplitude of water availability in the rock outcrop habitat where it occurs, suggesting that the periods of water availability are sufficiently long for the success of the costly desiccation tolerant behavior but too short to make a typical drought avoider species win the competition for exploring the rock outcrop substrate where P. purpurea occurs.
Recursos Genéticos Vegetais. Instituto Agronômico (IAC). Caixa Postal 28, Brasil * mortiz@iac.sp. gov.br RESUMO: Entre as plantas nativas de uso medicinal no Brasil, encontra-se Ocimum selloi Benth., planta anual herbácea da família Lamiaceae que ocorre nas regiões Sudeste e Sul do país. Este trabalho avaliou os aspectos da biologia floral (estrutura floral, floração e frutificação) e mecanismos reprodutivos de Ocimum selloi em quatro populações oriundas das regiões de Piquete e Apiaí, Estado de São Paulo, Camanducaia, Estado de Minas Gerais, e Colombo, Estado do Paraná. O período de antese teve início às 11 horas e término às 15 horas, com o clímax de floração às 13 horas, sendo a temperatura pouco importante neste processo. A viabilidade do pólen foi alta nas quatro populações. A espécie é autocompatível, formando frutos e sementes tanto em polinização livre quanto em autopolinização espontânea, o que mostra uma grande versatilidade reprodutiva da espécie, garantindo a variabilidade genética. A germinação das sementes também foi alta nas quatro populações. Palavras-chave: Ocimum selloi, biologia reprodutiva, biologia floral, plantas medicinaisABSTRACT: Reproductive biology of Ocimum selloi Benth. populations. Among the medicinal plants native to Brazil, Ocimum selloi Benth., an herbaceous annual plant of the Lamiaceae family, occurs in the southeastern and south regions of the country. This work evaluated flower biology aspects (flower structure, flowering and fructification) and reproductive mechanisms of four O. selloi populations from Piquete and Apiaí regions, São Paulo State; Camanducaia, Minas Gerais State; and Colombo, Paraná State. Anthesis started at 11:00 a.m. and finished at 3:00 p.m., with flowering climax at 1:00 p.m., and temperature was slightly important in this process. Pollen viability was high in all four studied populations. This species is self-compatible, forming fruits and seeds under both free pollination and spontaneous self-pollination, which indicates it has a great reproductive versatility, assuring genetic variability. Seed germination was also high in all four populations.
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