Rodrigo Danielowski

Development of rice seedlings grown from pre-hydrated seeds and irradiated with gamma rays

Tecnicas como radiacoes ionizantes, utilizadas para induzir mutacoes constituem ferramenta eficaz no aumento de variabilidade genetica em programas de melhoramento de especies de interesse economico. Neste trabalho, objetivou-se verificar o efeito de diferentes doses de radiacao gama Co60 em sementes previamente embebidas sobre a emergencia e o crescimento inicial de plântulas de duas cultivares de arroz. Lotes de sementes com 25% de umidade das cultivares BRS Querencia e BRS Fronteira foram irradiados com doses de zero (controle), 50, 100, 150 e 200 Gy, sendo, em seguida, semeadas em bandejas contendo solo e mantidas em casa de vegetacao. Os resultados mostraram que a radiacao gama afetou o desenvolvimento das plântulas, sendo que a maior dose testada (200 Gy) reduziu, significativamente, a emergencia e o indice de velocidade de emergencia. Os parâmetros de crescimento apresentaram maior reducao na cv. BRS Querencia. Na atividade das enzimas antioxidantes, a superoxido dismutase expressou pouca variacao para os periodos avaliados. Ja, a ascorbato peroxidase e catalase mostraram expressivo aumento na cv. BRS Fronteira aos 14 DAS, seguidas de incremento para as duas cultivares na atividade da ascorbato peroxidase aos 28 DAS. A maior capacidade antioxidante observada na cv. BRS Fronteira conferiu uma maior tolerância ao estresse causado pela radiacao gama.

Transcriptome profiling of rice seedlings under cold stress

Rice (Oryza sativa L.) is one of the most important species for food production worldwide, besides being an excellent genetic model among the grasses. Cold is one of the major abiotic factors reducing rice yield, primarily affecting germination and reproduction phases. Currently, the RNAseq technique allows the identification of differential expressed genes in response to a given treatment, such as cold stress. In the present work, a transcriptome (RNAseq) analysis was performed in the V3 phase for contrasting genotypes Oro (tolerant) and Tio Taka (sensitive), in response to cold (13°C). A total of 241 and 244M readings were obtained, resulting in the alignment of 25.703 and 26.963 genes in genotypes Oro and Tio Taka respectively. The analyses revealed 259 and 5579 differential expressed genes in response to cold in the genotypes Oro and Tio Taka respectively. Ontology classes with larger changes were metabolic process ~27%, cellular process ~21%, binding ~30% and catalytic activity ~22%. In the genotype Oro, 141 unique genes were identified, 118 were common between Oro and Tio Taka and 5461 were unique to Tio Taka. Genes involved in metabolic routes of signal transduction, phytohormones, antioxidant system and biotic stress were identified. These results provide an understanding that breeding for a quantitative trait, such as cold tolerance at germination, several gene loci must be simultaneously selected. In general, few genes were identified, but it was not possible to associate only one gene function as responsible for the cultivar tolerance; since different genes from different metabolic routes were identified. The genes described in the present work will be useful for future investigations and for the detailed validation in marker assisted selection projects for cold tolerance in the germination of rice.

Regeneração in vitro de melão, cv. 'Gaúcho'

The aim of the present study was to optimize a cv. Gaucho melon cotyledon explant regeneration protocol, evaluating the germination media composition and the explant exposition period in these media. For this purpose, seeds were germinated in semi-solid MS medium containing either BAP or ANA, and without growth regulators. The seeds were kept in these media for one, two, three or four days; afterwards, their cotyledons were inoculated in MS medium containing different BAP concentrations (0.5; 0.9; 1.5 and 2.0mg L-1). The highest regeneration rates occurred with cotyledons from seeds which had been kept for one or two days in media containing 0.5 and 0.9mg L-1 BAP. Both the increase in the explant exposition time in germination media and high BAP concentrations in regeneration media decreased explant organogenic capacity, and increased callus formation.

In vitro regeneration of ‘carrick’ pear from leaf explants

The aim of the present study was to investigate a two-step protocol as well as the effect of two types of cytokinins in the pretreatment and shoot induction media on in vitro adventitious shoot regeneration of pear leaf explants of ‘Carrick’ pear. Fully expanded healthy leaves were explanted onto shoot induction medium (SIM) following a pretreatment in liquid medium (PLM). Both media were supplemented with thidiazuron (TDZ) or 6-benzyladenine (BA) (PLM: 2 mg dm -3 ; SIM: 3 mg dm -3 ). The two-step protocol PLM [BA] + SIM [TDZ] is efficient for in vitro adventitious shoot regeneration from leaves of ‘Carrick’ pear.