RESUMOForam estudados o crescimento, a partição de assimilados e a produção de grãos nas cultivares de arroz BRS Pelota (maior produtividade) e BRS Firmeza (menor produtividade). O experimento foi realizado em casa de vegetação, com plantas cultivadas em vaso. Utilizou-se o delineamento experimental inteiramente casualizado, com duas cultivares, nove coletas e quatro repetições por tratamento. Com a cultivar BRS Pelota houve maior acúmulo de matéria seca total (W t ), principalmente no fim do ciclo, bem como maior área foliar (A f ). A matéria seca alocada para o colmo + bainha e às panículas também foi maior em BRS Pelota. Porém, a porcentagem de W t destinada às panículas aos 125 DAE foi semelhante entre as cultivares. Em BRS Firmeza, o aumento em W t nas raízes pode ter influenciado o direcionamento de fotoassimilados para os grãos e contribuído para o atraso na senescência das plantas. A produtividade de BRS Pelota foi maior que a de BRS Firmeza (17,4 contra 11,8 g por vaso) e seu número de panículas por planta por vaso foi três vezes superior em relação à cultivar BRS Firmeza. O componente de produção de maior expressão no rendimento foi o número de panículas. A maior produtividade da cultivar BRS Pelota pode estar relacionada à maior área foliar e sua duração, o que permite o fornecimento de elevada quantidade de fotoassimilados por um período maior.Palavras-chave: matéria seca, análise de crescimento, área foliar, BRS Firmeza, BRS Pelota. ABSTRACT GROWTH AND ASSIMILATES PARTITIONING IN RICE CULTIVARS DIFERING IN GRAIN YIELD POTENTIALThe growth, assimilate partitioning and grain yield in BRS Pelota (high yield) and BRS Firmeza (low yield) rice cultivars were evaluated. The experiment was conducted in greenhouse (Department of Botany, Federal University of Pelotas) with complete randomized design composed by two cultivars, nine plant sampling times and four replicates. BRS Pelota rice cultivar exhibited higher accumulation of total dry matter (W t ), mainly at the end of life cicle, as well as higher leaf area (A f ). The dry matter allocated toward culm + sheath and panicles was higher in BRS Pelota. However, the W t percentage accumulated in panicles at 125 DAE was the same between cultivars. In BRS Firmeza the increase in W t in the roots may had influenced photoassimilates partitioning toward grains, and also contributed to delay of in plant senescence. Grain yield was higher in BRS Pelota than in BRS Firmeza (17.4 versus 11.8 g vaso), and also panicle number was three times greater in relation to BRS Firmeza. The yield component which exhibited higher relevance for productivity was the panicle number. The higher grain yield of BRS Pelota could be related to higher leaf area and leaf area duration, which allows the provision of elevated quantity of photoassimilates during longer period time.

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The portable chlorophyll (Chl) meter (CL-01, Hansatech) has been successfully used for a rapid and direct estimation of total Chl content in the leaves of some crops. We compared CL-01 meter readings (Chl value) and Chl contents in leaves of Zea mays, Cucumis sativus, Raphanus sativus, and Ceiba speciosa. Chl index was linearly and positively correlated to Chl content in all the species.Additional key words: Ceiba; Cucumis; Raphanus; Zea.---Plants contain chlorophylls (Chls) a and b. The two compounds have different solubilities in organic solvents, and somewhat different, though overlapping, electronic spectra in the visible region. Traditionally, chemical methods of determination have required Chl extraction by a solvent, followed by the spectrophotometric determination of absorbance by the Chl solution, and conversion from absorbance to concentration using standard equations (Arnon 1949, Lichtenthaler 1987, Ritchie 2008. In the standard method of Chl determination, extraction requires destructive sampling and is relatively time consuming (Richardson et al. 2002). More recently, non-destructive optical methods, based on the absorbance and/or reflectance of radiation by the intact leaf have been developed. Optical methods yield a 'Chl index' value that expresses relative Chl content but not absolute Chl content per unit leaf area or per mass of leaf tissue. These newer methods are non-destructive, very quick, and can be used in the field (Markwell et al. 1995, Hawkins et al. 2007.Many papers show the application of "Chl value" to the estimation of leaf Chl content (Richardson et al. 2002, Uddling et al. 2007), but some have failed to show the applicability of the index across different studies, plant species, or stresses. Neufeld et al. (2006) working with ozone-affected leaves of cutleaf coneflower (Rudbeckia laciniata var. digitata) observed that when relatively uninjured leaves were measured, SPAD meter readings were linearly related to total Chl content. However, when leaves with foliar injury were added, it was no longer possible to use the same equation to obtain Chl estimations for both classes of leaves.The objective of this work was to evaluate the existence of relation between the Chl content and "Chl value" measured by hand-held Chl meter CL-01 in maize (Zea mays), cucumber (Cucumis sativus), radish (Raphanus sativus), and floss-silk tree (Ceiba speciosa). Plants were grown from seed in a glasshouse. Approximately 50 leaf samples of the each species, spanning as wide a range of Chl contents as possible, from very pale yellow to very dark green leaves, were used. One hand-held Chl meter, the CL-01 (Hansatech, King's Lynn, Norfolk, England) was used. This equipment provides a convenient, low cost method of measuring the relative Chl content of a leaf sample using dual wavelength optical absorbance (620 and 940 nm) measurements from leaf samples. Five separate measurements were made on each leaf and we used the arithmetic mean of these measurements for all subsequent analyses, and the results were expres...

Plants growing in temperate regions are often exposed to stress conditions caused by high temperatures. Photosynthesis is one of the metabolic processes most sensitive to high temperature stress, and it is often inhibited before other cellular functions. Using peach leaf disks, we studied the transient chlorophyll a fluorescence along with the gas exchanges at temperatures of 25 (control)

In order to analyse the effect of salt (0, 25, 50, 75 and 100 mM) concentration on chlorophylls, total carotenoids and proline contents, an experiment was carried out in greenhouse conditions with cultivars BRS Bojurú, IAS 12-9 Formosa and BRS Agrisul. Total contents were determined 30 days after soil salinization. The salinity strongly reduced chlorophylls and total carotenoids contents on Agrisul genotype, but pigments were not quite affected on Bojuru and Formosa. Proline contents were ligher in Agrisul than in the Bujuru and Formosa genotypes, and the proline accumulation was accentuated with increase in salt concentration. A threshhold of salt concentration that starts the process of proline accumulation in leaves was verified, being 50 mM to cultivar BRS Agrisul (sensitive) and 75 mM to cultivars BRS Bojuru and IAS 12-9 Formosa (tolerants).

-The objective of this work was to evaluate the physiological changes that occur in different leaves during the early and late grain-fi lling stages of two rice genotypes (Oryza sativa subsp. indica, BRS Pelota cultivar, and O. sativa subsp. japonica, BRS Firmeza cultivar), which present differences in grain yield potential. The plants were cultivated in greenhouse. Pigment content, chlorophyll fl uorescence, electron transport and oxygen evolution rate were determined in the grain-fi lling stage, from the fi rst to the forth leaf (top to bottom). Pigment content, photochemical effi ciency of photosystem II and electron transport decreased signifi cantly according to the position of leaves in 'BRS Pelota'. The BRS Firmeza cultivar shows higher pigment content and higher activity of the photosynthetic apparatus in comparison to 'BRS Pelota' during the grain-fi lling stage.Index terms: Oryza sativa, oxygen evolution rate, photochemical quenching, photosystem II, photochemicol effi ciency, stay green. Análise fi siológica da senescência foliar de duas cultivares de arroz com diferentes potenciais de produtividadeResumo -O objetivo deste trabalho foi avaliar as mudanças fi siológicas que ocorrem em diferentes folhas durante o início e o fi nal do estádio de enchimento de grãos em dois genótipos de arroz (Oryza sativa subsp. indica cultivar BRS Pelota e O. sativa subsp. japonica cultivar BRS Firmeza) que apresentam diferenças no potencial de produção de grãos. As plantas foram cultivadas em casa de vegetação. Os teores de pigmentos, a fl uorescência da clorofi la e a taxa de liberação de oxigênio foram determinados no estádio de enchimento de grão da primeira à quarta folha (do topo à base). O teor de pigmentos, a efi ciência fotoquímica do fotossistema II e o transporte de elétrons decresceram signifi cativamente de acordo com a posição das folhas na cultivar BRS Pelota. A cultivar BRS Firmeza apresentou maior teor de pigmentos e maior atividade do aparato fotossintético em comparação à 'BRS Pelota' durante o estádio de enchimento de grão.Termos para indexação: Oryza sativa, taxa de evolução de oxigênio, extinção fotoquímica, fotossistema II, efi ciência fotoquímica, senescência retardada.

The effects of salinity stress on chlorophyll fluorescence and the growth of Brassica napus L were investigated. The chlorophyll a fluorescence transient were recorded and analyzed according to the JIP-test which can quantify PSII performance. Salt stress resulted in decreased leaf area and dry matter compared with the control treatment (0 mM NaCl). The most pronounced effects of salt stress were observed with 200 mM NaCl, and the hybrids displayed different levels of sensitivity to stress. The Performance Index (PI ABS ) was the most sensitive parameter to salt stress, which suggests that this parameter can be used to screen genotypes for salt tolerance.Keywords: Canola; growth; JIP-Test, salt stress; spring rapessed oil.Abbreviations: ABS, absorption of light energy; Chl, chlorophyll; ET, conversion of excitation energy to electron transport (ET); ET o /ABS, electron transport activity; F 0 , F V , and F M -minimal, variable and maximum Chl fluorescence of PSII in the dark adapted state; F V /F M = φ Po = TR 0 /ABS, maximum efficiency of PSII photochemistry; F 0 ', F V ' and F M ' -minimal, variable and maximum Chl fluorescence in the light adapted state; F V '/F M ', efficiency of excitation capture by open PSII reaction centers; FW, fresh weight; PI ABS , Performance Index; PSII, photosystem II; Q A , electron acceptor of PSII; qP, photochemical quenching coefficient; RC/ABS, ratio of reaction centers and the absorbance; TR, trapping of excitation energy; φ PSII , actual PSII efficiency; φ Eo = ET 0 /ABS, quantum yield of electron transport; φ Do , quantum yield of dissipation; Ψ o = ET 0 /TR 0 , yield of electron transport per trapped exciton; PAR, photosynthetic active radiation.

RESUMO -A presente pesquisa teve por objetivo avaliar o efeito de agentes indutores de estresse hídrico e salino na germinação, crescimento e resposta antioxidante de plântulas de girassol. Sementes da cv. M735 foram germinadas em papel umedecido com soluções osmóticas nos potenciais de 0,0; -0,2; -0,4 e -0,8 MPa, induzidos com PEG 6000 e NaCl. O teste de germinação foi conduzido com quatro subamostras de 100 sementes e quatro repetições por tratamento, em câmara de germinação sob temperatura média de 25 ºC, na ausência de luz. Foram avaliados a porcentagem final e índice de velocidade de germinação das sementes, além do crescimento inicial e atividade de enzimas antioxidantes das plântulas. O estresse hídrico induzido por PEG 6000 aumentou a porcentagem de sementes germinadas no potencial de -0,2 MPa, por outro lado, para o NaCl no potencial de -0,8 MPa, houve significativa redução. Para este mesmo potencial, também houve redução no índice de velocidade de germinação das sementes para ambos os agentes condicionantes. Para os parâmetros de crescimento, o comprimento da parte aérea reduziu linearmente com o aumento das concentrações de PEG 6000 e NaCl. Já para a massa seca de folhas e raízes e o comprimento das raízes, este efeito foi mais expressivo somente no potencial de -0,8 MPa. As enzimas SOD, APX e CAT apresentaram tendência de menor atividade nas plântulas oriundas de sementes acondicionadas em PEG 6000. Na presença do NaCl, a atividade da SOD nas folhas aumentou significativamente nos três potenciais testados em relação a testemunha. Para a APX e CAT este aumento foi observado nos potenciais de -0,2 e -0,4 MPa. Nas raízes não foi observada diferença significativa. A análise conjunta dos parâmetros avaliados indica que a cv de girassol M735, nas condições testadas, apresenta tolerância ao estresse hídrico e salino até o potencial de -0,4 MPa.Termos para indexação: Helianthus annuus L., germinação, crescimento e estresse oxidativo. ANTIOXIDANT ACTIVITY AND THE VIABILITY OF SUNFLOWER SEEDS AFTER SALINE AND WATER STRESSABSTRACT -This study aimed to evaluate the effect of agents inducing water and saline stress on the seed germination and early growth and antioxidant activity in sunflower seedlings. Sunflower seeds, cv. M735, were germinated on moistened paper in solutions with osmotic potentials of 0.0,