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,

The objective of this research was to assess the manner in which the presence of green soybean seeds affects their physiological quality. In this study, six lots of soybean seeds of cultivar 5958RSF IPRO with 0, 0, 7, 8, 16 and 18% of green seeds were examined. The tests done included the first germination count, germination, electrical conductivity, field emergence, accelerated aging, emergence speed index, Tetrazolium, length, dry mass and seedling growth curve. Results were tested employing the normality test and analysis of variance, and the means were compared by the Tukey test at 5% probability level, employing the Rbio statistical program. Growth data were analyzed by the nonlinear regression analytical method, using the SigmaPlot 12.0 software. The viability and vigor of the greenish seeds were confirmed to reveal higher deterioration, proportional to the percentage of seeds in which the cotyledons had green pigmentation, indicating that the presence of chlorophyll caused the physiological quality of the soybean seeds to decrease.

Non-structural carbohydrates (NSC) accumulation and photosynthesis traits were studied in two rice (Oryza sativa L.) genotypes maintained under control (22/30 °C -night/day) and at high night temperatures (HNT) (28/30 °C) conditions from heading to milk stage. Rice cultivars were Nagina22 -N22 and BRS Querência -Quer, which are tolerant and sensitive to high temperatures, respectively. The source-sink flow related attributes were tested to understand the nature of NSC accumulation and translocation. Compared to N22, Quer maintained higher stem starch in glucose on seventh day after heading and at milk stage independently of imposed temperatures. However, the levels of starch in glucose were lower for N22 meanwhile their total sugar concentration (TSC) were higher at control and at HNT at milk stage as compared to Quer. N22 maintained unaltered the spikelet sterility and 1000-grain weight across environments showing a consistent trend with its stem NSC translocation. Both genotypes showed similarity in some gas exchange and chlorophyll fluorescence performance suggesting unaffected photosystem II photochemistry, linear electron flux, and CO 2 assimilation. Beyond indicating that source functioning was not the limiting factor for low TSC and starch in glucose levels found in N22 on seventh day after heading stage. Moreover, our data suggest that the higher translocation capacity shown by N22 can be involved in their lower spikelet sterility and 1000-grain weight stability across the environments. These results indicate that selecting genotypes with higher capacity to stem NSC translocation at HNT could lead to more grain yield stability in future climate scenarios.

Aluminum (Al) toxicity is one of the main aspects restricting the development of fabaceous plants grown in soils with spontaneous vegetation prevalence in temperate climate zones. Salicylic acid (SA) minimizes the effects of stress on plants. Therefore, the aim of the current study was to evaluate the ability of SA seed priming to mitigate the effects of Al on seed germination and seedling performance in two Trifolium species. Trifolium vesiculosum (annual) and Trifolium repens (perennial) seeds were primed in solution added, or not, with SA (25 μM) and placed on germination paper moistened with aluminum sulfate (Al 2 (SO 4) 3) solutions at three different doses: 0 mM (control), 0.25 mM (moderate dose), and 1.25 mM (high dose). Seed priming with SA has mitigated the global toxicity effects of Al on T. vesiculosum and T. repens seedlings. Inferior damages were observed in T. vesiculosum root length and dry mass and in T. repens shoot dry mass, after SA pretreatment. T. vesiculosum seed priming with SA in the presence of Al has significantly reduced the osmotic potential of seedling sap. Salicylic acid (SA) has also enabled increased antioxidant activity of enzymes such as superoxide dismutase (SOD) in the two investigated plant species and ascorbate peroxidase (APX) in T. repens. In addition to the increased antioxidant activity, SA-primed seeds reduced the malondialdehyde content in T. vesiculosum seedlings exposed to Al. Overall, seed priming with SA mitigates oxidative effects of Al and improves T. vesiculosum and T. repens seedling performance in the presence of this element.

Rice is a crop that presents sensitivity to cold, especially in the germination phase, which leads to high economic losses. Alternative management forms are essential to increase tolerance to low temperatures, and seed priming represents a promising tool. The objective of this study was to investigate the priming effect of the aqueous extract of carrot roots on rice seeds to increase tolerance to low temperatures during germination. Seeds from cultivars BRS Querência (cold-susceptible) and Brilhante (cold-tolerant) were soaked for 24 h in concentrations of 0, 25, 50, and 100% carrot extract, sown on germitest paper and conditioned in BOD for 21 days at 15 °C. As a control, the seeds soaked in water were also germinated at 25 °C. They were evaluated for germination, first germination count, and germination speed index to calculate the stress indices: tolerance index, susceptibility index, and harmonic mean. They were also evaluated for the length and dry mass of shoot and root. The results showed that the rice seeds conditioning in carrot extract effectively reduces the damage caused by cold, significantly increasing the germination speed and the percentage of final germination and the growth evaluations, more expressive at 100% concentration. The stress indexes are efficient in estimating the tolerance of the cultivars and the effect of the different conditions in low-temperature conditions, highlighting the superiority of the Brilhante cultivar.