Lilian Beatriz Penteado Zaidan

Seed germination in Cerrado species

O objetivo desta revisao e comentar dados disponiveis sobre a germinacao de sementes de especies herbaceas, arbustivas e arboreas do Cerrado, desde a publicacao da revisao feita por Felippe e Silva na decada de 1980. Estudos de germinacao de sementes de especies herbaceas do Cerrado enfatizam as respostas das sementes a luz, temperatura e armazenamento no solo. A maioria dessas sementes germina entre 20oC e 30oC e sao fotoblasticas. Temperaturas alternadas nem sempre favoreceram a germinacao das sementes, no entanto, alteraram a sensibilidade a luz em aquenios de Bidens gardneri. A maioria das sementes das especies arbustivas de Melastomataceae estudadas apresentaram fotoblastismo positivo; entre as Velloziaceae, foi observada germinacao no escuro em algumas especies. Sementes de algumas especies arbustivas possuem dormencia causada pela impermeabilidade do tegumento, quebrada com imersao em acido sulfurico, como no genero Bauhinia. Sementes de Heteropterys pteropetala sao sensiveis a temperaturas altas, similares aquelas registradas durante as queimadas. Plantas de algumas especies tem efeitos alelopaticos e podem inibir a germinacao de sementes de outras especies e o estabelecimento de plântulas. A maioria das sementes de especies arboreas nao requer luz para germinar e grande parte dos estudos teve como objetivo testar metodos de quebra de dormencia. Os metodos mais eficazes para a quebra dos diferentes tipos de dormencia foram passagem por acido sulfurico e incisoes no tegumento das sementes. Em termos gerais, os estudos realizados limitaram-se a tres aspectos: fotoblastismo, temperatura e quebra de dormencia. Ainda ha grande falta de dados para o entendimento dos aspectos fisiologicos e bioquimicos da composicao e mobilizacao das reservas das sementes e do efeito do fogo na germinacao dessas sementes.

Elevated CO2 atmosphere promotes plant growth and inulin production in the cerrado species Vernonia herbacea

Carbon allocation in biomass is an important response of plants to the increasing atmospheric [CO2]. The effects of elevated [CO2] are scarcely reported in fructan-accumulating plants and even less in tropical wild species storing this type of carbohydrate. In the present study, the effects of high [CO2] atmosphere was evaluated on growth, biomass allocation and fructan metabolism in Vernonia herbacea (Vell.) Rusby, an Asteraceae from the Brazilian cerrado, which accumulates inulin-type fructans in the underground organs (rhizophores). Plants were cultivated for 120 days in open-top chambers (OTCs) under ambient (~380 μmol mol–1), and elevated (~760 μmol mol–1) [CO2]. Plant growth, photosynthesis, fructan contents, and the activities of fructan metabolising enzymes were analysed in the rhizophores at Time 0 and 15, 30, 60, 90 and 120 days. Plants under elevated [CO2] presented increases in height (40%), photosynthesis (63%) and biomass of aerial (32%) and underground (47%) organs when compared with control plants. Under elevated [CO2] plants also presented higher 1-SST, 1-FFT and invertase activities and lower 1-FEH activity. Although fructan concentration remained unchanged, fructan productivity was higher in plants maintained under elevated [CO2], due to their higher rhizophore biomass. This is the first report on the effects of elevated [CO2] on a plant species bearing underground organs that accumulate fructans. Our results indicate that plants of V. herbacea can benefit from elevated atmospheric [CO2] by increasing growth and carbon allocation for the production of inulin, and may contribute to predict a future scenario for the impact of this atmospheric condition on the herbaceous vegetation of the cerrado.

Germinação de sementes de espécies de Melastomataceae de Cerrado sob condições controladas de luz e temperatura

The aim of this study was to investigate the germination of seeds of Miconia albicans, M. langosdorffii, M. rubiginosa, M. stenostachya, Schizocetron elegans and Tibouchina gracilis that occur in Cerrado areas. The seeds were exposed daily to light during 0, 10 min, 15 min, 30 min, 60 min, 90 min, 180 min, 360 min, 720 min and 1.440 min at 25 oC. Five gradients of phytochrome photoequilibrium (j) were tested in seeds of M. albicans and M. rubiginosa. The effect of temperature was observed at constant 15, 20, 25, 30 and 35 oC, and alternated temperatures of 30/20 oC, under continuous light and darkness. Germinability and speed of germination were analyzed. Seeds of all the species are photoblastic. Seeds of M. albicans, M. langsdorffii, S. elegans and T. gracilis need at least 60 to 90 min of light to start germination. M. stenostachya (15 min) and M. rubiginosa (360 min) showed the extreme responses to light treatment. The germinability of the seeds of M. albicans increased under higher gradients of R:FR photoequilibrium. Germination was low inM. rubiginosa, so the response of the seeds to R:FR photoequilibrium was inconclusive. In relation to temperature, germination occurred mainly between constant 20 oC and 30 oC and at 30/20 oC. Germination under light and with temperatures between 20 oC and 30 oC are characteristics that may contribute to the establishment of plantlets of the Melastomataceae in the cerrado. The seeds remain in the soil seed bank and may germinate when light is available even for short periods and despite the daily variation in temperature.

Estudo de desenvolvimento de Viguiera robusta Gardn., uma Asteraceae do cerrado

ABSTRACT - (Developmental studies in Viguiera robusta Gardn., an Asteraceae from the cerrado). The purpose of this study was to add new information about physiological aspects of herbaceous plants from the cerrado. Plants of Viguiera robusta grown from seeds (achenes) were maintained under controlled photoperiodic conditions, and vegetative growth and flowering were observed during the first life cycle; sprouting was also quantified after senescence and during the subsequent growth period. The achenes germinated better under continuous light at 30oC and 20/30oC, and the viability was maintained during 12 months with the seeds kept at 5oC in glass flasks. The growth parameters used, shoot length, leaf number, dry and fresh mass were not significantly different among the photoperiods tested, the least growth response appearing under 8 h photoperiod. Flowering was first induced in shorter photoperiods but occurred also in the longer ones; flowering plants were also observed when long-short day were given. Plants under 8 h - photoperiod presented a higher number of developed capituli. Young plants show opposite leaves which are alterned to alternate leaves during plant growth. This change in phyllotaxis could not be related to flower induction. When flowering occurs, liberation of lateral buds is observed. These buds form new shoots, specially under short-days. Senescence of the aerial parts is followed by sprouting, which is independent of the photoperiodic treatment applied to the plants but is probably better related to the biochemical/physiological conditions of the reserve underground organ.

Soluções nutritivas para cultivo e produção de frutanos em plantas de Vernonia herbacea

The limited growth of rhizophores of Vernonia herbacea in Hoagland solution demanded the definition of a nutrient solution for plants of V. herbacea, aiming at the increase of the rhizophore biomass and fructan production. This solution, named Vernonia, is comprised of Ca(NO 3 ) 2 .4H 2 O 2.5 mmol L -1 , KNO 3 2.3 mmol L -1 , KH 2 PO 4 0.52 mmol L -1 , Mg(NO 3 ) 2 .6H 2 O 1.7 mmol L -1 and Na 2 SO 4 1.3 mmol L -1 . Its effect on plants was compared to that of Hoagland solution, both with different ionic strengths, 50%, 100% and 200%. The effect of the solutions on plant growth and fructan content was evaluated twice in a six-month period. Plants did not survive up to two months, when cultivated in 200% Hoagland solution. The 50% Vernonia solution was the most effective for rhizophore biomass increase and fructan production per plant. Growth of aerial organs was promoted in 100% Hoagland and Vernonia solutions. Compared to Hoagland, Vernonia solution contains less macronutrients, which confirms the hypothesis that plants adapted to the oligotrophic soils of the cerrado, as V. herbacea, demand less mineral nutrients to achieve full growth.

Growth, photosynthate partitioning and fructan accumulation in plants of Vernonia herbacea (Vell.) Rusby under two nitrogen levels

The effect of two nitrogen concentrations on fructan accumulation and plant growth was analysed in plants of Vernonia herbacea during a year period. Plants of this species accumulate inulin-type fructans in the underground reserve organs (rhizophores). The plants were cultivated in glasshouse conditions and received weekly nutrient solutions containing 1.3 mmol.L-1 NO3- (N-limited) or 10.7 mmol.L-1 NO3- (N-sufficient). Plants treated with N-sufficient solution presented an increase in total growth with higher biomass, more but smaller leaves resulting in higher total leaf area, higher net assimilation rate, specific leaf mass and higher biomass allocation to aerial organs. In addition, these plants presented higher contents of reducing sugars and lower fructan contents. In contrast, N-limited plants showed reduced total growth with lower biomass, higher biomass allocation to underground organs and higher fructan contents. Therefore, although N-limited plants presented a higher fructan concentration, the amount of fructan produced per plant was similar in both N treatments.

Effect of storage of achenes of Bidens gardneri Baker on light sensitivity during germination

Bidens gardneri e uma planta herbacea muito frequente nos cerrados do estado de Sao Paulo, cujas sementes so germinam em luz na temperatura de 25°C. Aquenios foram armazenados a 4°C e enterrados em solo de cerrado e solo de mata. Os experimentos de campo foram realizados no cerrado na Reserva Biologica e Estacao Experimental de Moji Guacu, em Moji Guacu e na floresta do Instituto de Botânica de Sao Paulo, em Sao Paulo, Brasil. Os aquenios de B. gardneri variam em tamanho e aquenios de 7 a 12 mm de comprimento foram usados. Os aquenios armazenados ate 6 meses a 4°C apresentaram sensibilidade a luz, que foi perdida depois de 9 meses de armazenamento, tanto para os menores como para os maiores aquenios usados nos experimentos. Aquenios da especie germinaram durante o periodo de armazenamento no solo; o numero de aquenios germinados aumentou com o tempo de armazenamento e o numero de aquenios intactos diminuiu com o periodo de armazenamento; estes resultados foram independentes do fato de o experimento ter sido feito em cerrado ou na floresta. Isto mostra que aquenios germinaram no escuro quando armazenados em solo. Os aquenios intactos perderam a sensibilidade a luz apos armazenamento no solo por tres meses.

Vegetative responses to temperature and photoperiod in saplings of brazilwood (Caesalpinia echinata Lam., Leguminosae)

Caesalpinia echinata Lam. (pau-brasil) e uma especie arborea ameacada, que ocorre na costa leste do Brasil, em latitudes de 5°56´S a 22°56´S. Em tal faixa de distribuicao espera-se que a temperatura e o comprimento do dia possam afetar o desenvolvimento da planta, o que foi investigado no presente estudo. Plantas jovens com um e cinco anos de idade foram cultivadas sob fotoperiodos controlados de 8 h, 12 h e 20 h e em casa de vegetacao, sob luz natural, durante 16 meses. Em outro experimento, plantas jovens com um ano de idade foram cultivadas por seis meses em câmara de crescimento, onde a temperatura maxima foi reduzida, e em casa de vegetacao. O numero de folhas, a altura do caule e o diâmetro do caule a superficie do solo foram avaliados a cada dois meses (experimento 1), ou mensalmente (experimento 2). No experimento 1, nao foi encontrada alteracao de crescimento nas plantas crescendo sob os diferentes tratamentos fotoperiodicos. Foi possivel ajustar regressao polinomial para o aumento do numero de folhas, em funcao do tempo, com diferenca significativa na inclinacao da curva para as plantas das duas idades. A altura do caule aumentou linearmente nas plantas mais jovens e, nas mais velhas, tal parâmetro ajustou-se a regressao polinomial. As medidas de crescimento relacionaram-se significativamente com as medias das temperaturas maximas diarias registradas. No experimento 2, tambem foram encontradas regressoes significativas entre o crescimento das plantas e as temperaturas maximas para aumento do numero de folhas e da altura do caule. Os resultados mostraram que o crescimento vegetativo dessa especie tropical e afetado pela temperatura e nao pelo fotoperiodo.

Efeito do fotoperíodo no crescimento e no padrão de acúmulo de frutanos em plantas aclimatizadas de Gomphrena macrocephala St.-Hil. (Amaranthaceae)

Gomphrena macrocephala is a perennial herb, native to the Brazilian cerrado, with medicinal properties and ornamental potential. As with other plants of the cerrado, it is characterized by well defined phenological phases. This species has been studied because of its particular fructan accumulation in the tuberous root, the variation of these carbohydrates being related with phenological phases. Micropropagated and acclimatized plants were used in the present study to investigate the presence of fructans in tuberous roots and to verify if the photoperiodic conditions interfere on growth, phenological behavior and on fructan accumulation. Short days (8 h) provided lower shoot growth, and induce the appearance of senescence characteristics and accumulation of polysaccharides, as already reported to plants in early dormancy. Long days (12 and 16 h), however, increased shoot growth and resulted in lower fructan contents, similar to what is observed in the vegetative growth phase of this plant.

Fructan production in Vernonia herbacea (Vell.) Rusby is related to adequate nitrogen supply and period of cultivation

Estudos realizados anteriormente mostraram que plantas de Vernonia herbacea cultivadas durante um ano sob uma condicao limitante de nitrogenio tiveram seu crescimento reduzido e apresentaram maiores teores de frutanos em comparacao a plantas que receberam suprimento adequado de nitrogenio. Entretanto, a producao total de frutanos foi similar nos dois grupos de plantas devido a maior biomassa dos orgaos subterrâneos de reserva das plantas N-suficientes. O objetivo do presente estudo foi avaliar se o cultivo sob uma condicao adequada de nitrogenio, que promove o crescimento das plantas, seguido de uma condicao estressante de crescimento imposta por suprimento limitante de nitrogenio, promoveria a producao de frutanos. As plantas receberam durante um ano solucao N-suficiente (10,7 mmol L1 N-NO3). Nos seis meses subsequentes, metade das plantas passou a receber solucao N-limitante (1,3 mmol L1 N-NO3), permanecendo as demais no tratamento N-suficiente. O crescimento, a fotossintese e os carboidratos soluveis foram analisados no dia da transferencia (dia 0) e aos 30, 60, 90 e 180 dias. Aos 30 dias as plantas transferidas para N-limitado mostraram aumento significativo do crescimento e diminuicao da concentracao de frutanos, em resposta a condicao nutricional estressante. No entanto, no periodo seguinte (60 dias) o crescimento foi reduzido e a concentracao de frutanos aumentou em relacao as plantas mantidas em N-suficiente, confirmando a relacao inversa entre suprimento de nitrogenio e conteudo de frutanos. Apos 180 dias, embora a concentracao de frutanos em N-limitado tenha sido significativamente mais elevada, com uma producao de frutanos de 6,0 g planta-1, o maior ganho de biomassa de rizoforos observado nas plantas mantidas sob N-suficiente durante 18 meses, levou a uma producao de frutanos de 8,3 g planta1, compensando assim a menor concentracao de frutanos observada nessas plantas.