ABSTRACT Drought stress is the main abiotic factor limiting soybean yield. The memory of recurrent water stress can provide greater efficiency in minimizing the negative effects of drought. Thus, the aim of this work was to understand the temporal adjustments in photosynthesis presented by soybeans when exposed to recurrent drought at the beginning of the flowering and grain filling stages. The experiment was carried out in a randomized block design with five replications, consisting of four treatments: i) WS-R1 (moderate water deficit at the beginning of flowering), ii) WS-R5 (severe water deficit during grain filling), iii) WS-R1+R5 (moderate water deficit at early flowering and severe water deficit during grain filling), and iv) WW (well-watered condition). Severe stress caused reductions in gas exchange parameters and the relative water content, with increased initial fluorescence and water use efficiency. The plants from the WS-R5 and WS-R1+R5 treatments showed a reduction in the apparent rate of electron transport in photosystem II (PSII), photochemical quenching, and effective quantum yield of PSII, as well as increased nonphotochemical quenching values. Furthermore, the proline concentration in the leaves was higher in plants from the WS-R1+R5 treatment, contributing to the greater ability to maintain turgid cells compared to the WS-R5 plants. The photosynthetic adjustments related to faster isohydric responses and photoprotective mechanisms in soybean plants subjected to recurrent drought allowed the maintenance in the weight or number of grains compared to plants without water restriction, demonstrating the activation of efficient memory mechanisms of response to water stress.

RESUMO O estresse hídrico é o principal fator abiótico que limita a produtividade da soja. A memória ao estresse hídrico recorrente pode proporcionar maior eficiência na minimização dos efeitos negativos da seca. Assim, o objetivo deste trabalho foi compreender os ajustes temporais na fotossíntese apresentados pela soja quando exposta à ciclos recorrentes de seca, no início da floração e enchimento de grãos. O experimento foi conduzido em blocos casualizados com cinco repetições, composto por quatro tratamentos: i) WS-R1 (déficit hídrico moderado no início da floração), ii) WS-R5 (deficiência hídrica severa durante o enchimento de grãos), iii ) WS-R1+R5 (déficit hídrico moderado no início da floração e déficit hídrico severo durante o enchimento de grãos) e iv) WW (condição bem irrigada ao longo de todo ciclo). O estresse severo causou reduções nos parâmetros de trocas gasosas e no teor relativo de água, aumento da fluorescência inicial e eficiência do uso da água. As plantas dos tratamentos WS-R5 e WS-R1+R5 apresentaram redução na taxa aparente de transporte de elétrons no fotossistema II (PSII), extinção fotoquímica e rendimento quântico efetivo de PSII, além de aumento nos valores de extinção não fotoquímica. Além disso, a concentração de prolina nas folhas foi maior nas plantas do tratamento WS-R1+R5, contribuindo para a maior capacidade de manter as células túrgidas em relação às plantas WS-R5. Os ajustes fotossintéticos relacionados a respostas isoídricas mais rápidas e mecanismos fotoprotetores em plantas de soja submetidas a seca recorrente permitiram a manutenção no peso ou número de grãos em comparação com plantas sem restrição hídrica, demonstrando a ativação de mecanismos eficientes de memória de resposta ao estresse hídrico.

ABSTRACT Water availability is the main factor that explains current patterns of palm abundance. However, the interaction between water stress and increasing atmospheric CO2 concentrations caused by climatic change and its effects on palm physiology remain poorly known. Macauba palm is a widespread Neotropical species commonly found in ecosystems subjected to seasonal drought and has potential use in oil production. The present work investigated the influence of increased CO2 concentrations on photosynthetic responses to drought in macauba palm plants. Exposure to increased CO2 concentrations led to up-regulation of photosynthesis through higher stomatal conductance and improved light and water use efficiency. Macauba palm plants under water stress, irrespective of CO2 concentration, were able to maintain constant levels of proline and chlorophyll, while preventing oxidative damage. Plants grown at higher CO2 concentrations were more capable of recovering from drought due to higher Rubisco carboxylation rate (Vc max) and electron transport rate (J max), which prevented a reduction in total dry mass at the end of the stress period. Stomatal control of photosynthesis, coupled with the prevention of severe damage under stress, would allow efficient biomass production by the macauba palm under future scenarios of climate change.

RESUMO Foram avaliados os teores de sólidos solúveis (SS), acidez titulável (AT), relação SS/AT, pH, teor de umidade, açúcares solúveis (AS), açúcares redutores (AR) e açúcares não redutores (ANR) em polpa de frutos de pequi coletados na planta, coletados no chão após a queda natural e coletados no chão três dias após a queda natural (caracterizando três estágios de maturação), e mantidos por seis meses em freezer após submetidos a congelamento rápido (nitrogênio líquido seguido de freezer) e lento (diretamente em freezer). As variáveis avaliadas não foram influenciadas pelo método de congelamento. Os teores de SS, AT, e AR foram crescentes com o avanço no estágio de maturação dos frutos, indicando que frutos coletados na planta encontram-se imaturos e apresentam qualidade inferior aos coletados após a queda natural. Embora considerados maduros quando caem da planta, um intervalo de três dias entre a coleta após a queda natural e o consumo favorece a qualidade dos frutos.

ABSTRACT Soluble solids (SS), titratable acidity (TA), SS/TA ratio, pH, moisture, soluble sugars (SSU), total reducing sugars (RSU), and non-reducing sugars (NRS) were assessed in the pulp of pequi fruits collected at three ripening stages: from the plant, from the ground after naturally falling off, and collected from the ground three days after naturally falling off. The evaluation was performed after six months of freezer storage both for fruits subjected to quick freezing (liquid nitrogen followed by freezer) and slow freezing (straight into the freezer). The variables assessed were not influenced by the freezing method. The SS, TA, and RSU contents increased with the ripening stage, suggesting that the fruits collected from the plant are still immature and have lower quality than those collected after naturally falling off. Although considered mature when they fall off, fruits consumed three days after naturally falling off have better quality.

ABSTRACT Fire is an abiotic disturbance that regulates vegetation structure and biodiversity. Some plant species have adapted to fire prone environments by evolving protective structures. Acrocomia aculeata (macaw palm) is widely distributed throughout tropical America, and is found in environments continuously influenced by anthropogenic fire. We aimed to determine whether the fruit characteristics of A. aculeata enable seeds to resist the effects of fire and also the consequent effects of fire on fruit biometric traits and embryo viability. After a fire event in a region of pasture-forest transition, we marked 30 individuals of A. aculeata. The trees were separated by UPGMA analysis into 5 groups according to fire exposure, ranging from trees with no exposure to trees with fruit completely exposed to fire. Fruit exposure to high temperatures led to lower values in fruit fresh weight, length, density, and processable mass.Fire had no significant effect on seed biometric variables, because of the structures of the fruit, including its lignified endocarp and its insulating and mucilaginous mesocarp. These structures helped to maintain the embryos viability by preventing oxidative damage. In conclusion, the fruit structure of the macaw palm may facilitate seed persistence, even when subject to increasingly frequent fire events.

ABSTRACT Iron plays a pivotal role in the redox reactions of photosynthesis and metabolic processes such as chlorophyll synthesis. Iron availability in waterlogged soils can reach toxic levels and promote oxidative stress. Fe toxicity is the most concerning of stresses for rice in many lowland environments around the world and may cause severe impairments in rice photosynthesis. This study aimed to investigate the extension of oxidative stress after excess Fe exposure and its effects on the photosynthesis of rice cultivars with differential sensitivity. Three Brazilian rice cultivars (EPAGRI 107, BRSMG SELETA and BR IRGA 409) were grown in Hoagland nutrient solution (pH 4.0) with two Fe-EDTA doses corresponding to excess Fe (7 mM) and control (0.009 mM) treatments. After just three days of excess Fe exposure, there was a significant increase in iron concentration in the shoots. The BR IRGA 409 cultivar exhibited higher Fe accumulation in its shoots, and the EPAGRI 107 cultivar recorded the lowest values, which were below the critical toxicity level, as a resistance strategy. Impairment in light energy partitioning and oxidative damage became evident before changes in stomatal resistance, chlorophyll content, maximal PSII quantum yield or visual symptoms for the most sensitive cultivar (BR IRGA 409). The photosynthesis limitations, in addition to the impairment of excess energy dissipation in rice from iron toxicity, are the results of oxidative damage.

Jatropha curcas (physic nut) is a plant with economic and pharmaceutical uses. Basic studies on the influence of environmental factors on the early development of J. curcas are important for improving farming techniques and increasing productivity. This study investigated the adjustments of J. curcas to the environmental factors of drought and light stress in order to determine which factors most strongly affect the allocation of biomass during early growth. Leaves, stems, and roots of young plants were sampled and leaf area was measured during January and June in 2011. Plants of J. curcas that were grown in shade and subjected to water stress showed higher biomass allocation to aerial parts (mainly stems), which can be explained as a strategy for maximizing carbon assimilation. The pattern of biomass allocation between aerial components and the root system changed in plants grown in shade. During June 2011, biomass in shade-grown J. curcas was preferentially allocated to stems, indicating long-term adjustment. The lower biomass allocation to the root system suggests reduced exploitation of soil water even when this resource is scarce. Thus, over the long term, growth of J. curcas may be compromised by the combined effects of light stress and water deficit.

Avaliou-se o potencial prognóstico de parâmetros microscópicos de folhas assintomáticas de . Clusia hilariana Schltdl. expostas à deposição particulada de ferro (2.14 mg cm² dia-1), por 45 dias consecutivos. Amostras de folhas jovens e expandidas sem sintomas foram coletadas e submetidas a técnicas usuais em microscopia de luz e eletrônica de varredura. Foram mensurados a altura das células epidérmicas de ambas as faces da folha e a espessura da hipoderme, do parênquima clorofiliano e da lâmina foliar. Danos micromorfológicos ocorreram na superfície abaxial de folhas jovens e em ambas as faces de folhas expandidas. Erosão da cera epicuticular e ruptura cuticular foram frequentes na face adaxial, enquanto na face abaxial, de ambas as folhas, houve perda da sinuosidade da parede anticlinal das células epidérmicas, deformação e obstrução estomática. Alterações micromorfométricas foram observadas em todos os tecidos foliares, exceto na altura das células epidérmicas em razão, provavelmente, da espessa cutícula e flanges cuticulares proeminentes. A maior diferença na espessura da lâmina foliar foi verificada nas folhas jovens de plantas expostas à SPM Fe, indicando maior sensibilidade ao ferro particulado em comparação com as folhas expandidas. As alterações micromorfológicas e micromorfométricas observadas na lâmina foliar de . Clusia hilariana Schltdl. demonstraram o potencial prognóstico dessas ferramentas na avaliação de impactos causados pela deposição de particulados, em especial na vegetação natural de restinga, onde a exposição é crescente diante da expansão de usinas mineradoras implantadas em sua vizinhança.

This study aims to evaluate the prognostic value of microscopic parameters of asymptomatic leaves of Clusia hilariana Schltdl. subjected to particulate deposition of iron (2.14 mg cm-2 day-1) for 45 consecutive days. Samples of young and expanded leaves without symptoms were collected and subjected to light and scanning electron microscopy techniques. The height of the epidermal cells on both surfaces of the leaf and the thickness of the hypodermis, the chlorophyll parenchyma, and the leaf blade were measured. Micromorphological injury occurred in the abaxial surface of young leaves and on both surfaces of expanded leaves. Erosion of the epicuticular wax and cuticle rupture were frequent on the adaxial surface, while on the abaxial surface of both leaves there was a loss of sinuosity on the anticlinal wall of the epidermal cells, stomatal deformity and obstruction. Micromorphometric alterations were seen in all leaf tissues except in the height of epidermic cells, probably due to the thick cuticle and prominent cuticular flanges. The highest difference in thickness of the leaf blade was seen in young leaves of plants subjected to SPMFe, indicating greater sensibility to particulate iron in comparison to the expanded leaves. The micromorphological and micromorphometric alterations in the leaf blade of Clusia hilariana Schltdl. showed the prognostic potential of these tools on the evaluation of impacts caused by the deposition of particulate matter, especially in the 'Restinga' natural vegetation, where the exposure is increasing due to the presence of iron ore industry in their surroundings.

O presente estudo foi realizado com o objetivo de se avaliar diferentes métodos para o cálculo de graus-dia (GD). Foram comparados quatro métodos de soma térmica, frequentemente usados no cálculo de GD: Ometto, Snyder, Dufault e método residual de Arnold. Esses métodos foram aplicados às culturas do milho e do feijão. As simulações foram feitas com as temperaturas observadas em Viçosa, MG no ano de 2011, e temperaturas simuladas (com acréscimo aleatório entre 0 a 5ºC em cada dia do período). As respostas dos quatro métodos de cálculo dos GD foram similares para as temperaturas observadas (reais). Para as temperaturas elevadas, os métodosnão apresentaram respostas similares. Fixando os graus-dia em 1.600 ºC dia para a cultura do milho e 1.300 ºC dia para o feijão, os métodos estudados reduziram de forma diferente o ciclo das culturas. As maiores reduções foram obtidas pelo método Arnold e Snyder, reduzindo igualmente o ciclo em 28 e 17 dias para as culturas do milho e do feijão, respectivamente. No método de Ometto, foram observadas as menores reduções, de 12 (milho) e 11 (feijão) dias, pois, nesse caso utilizam-se as temperaturas basais superior e inferior e considera-se uma penalização maior em dias em que a temperatura máxima ultrapassa a temperatura basal.

The present study was performed in order to compare different methods for calculating degree-days. Four methods of thermal sum, often used in calculation of degree-days, were compared: Ometto, Snyder, Dufault and Arnold residual methods. These methods were applied to corn and beans crops. The simulations have been done considering the actual temperatures on Viçosa, MG, Brazil, in 2011, and simulated temperatures (random additions between 0 and 5ºC for each day). The responses of the four methods on calculating the degree-days were similar for the observed temperatures in both studied crops. However, for the higher temperatures (simulated), the methods did not show similar responses. Fixing the degree days in 1,600 ºC day for corn crop and 1,300 ºC day for beans, the studied methods showed different reduction on the crop cycle. The largest reductions were obtained by Arnold and Snyder methods which have reduced equally the cycles by 28 and 17 days for corn and beans, respectively. The Ometto method resulted in the lowest reductions: 12 (corn) and 11 (beans) days, because it uses the upper and lower baseline temperatures, and it considers a greater penalty in days when the temperature exceeds the maximum baseline temperature.