dois estádios fenológico (V2-primeiro trifólio aberto e V4-terceiro trifólio aberto) de duas cultivares de soja: MG/BR 46 Conquista (convencional) e BRS Valiosa (RR), sob três condições hídricas no solo (-0,03; -0,07 e - 0,5 MPa). Avaliou-se a fitointoxicação e altura de plantas aos 3, 7, 14 e 21 dias após a aplicação do herbicida. Ao final do estudo, determinou-se a massa seca da parte aérea, massa seca das raízes e nodulação do sistema radicular por meio do número e massa seca de nódulos. Constatou-se que, em condição de déficit hídrico as plantas de soja apresentaram uma menor fitotoxicidade visual quando submetida à pulverização do herbicida chlorimuron-ethyl. Além disso, o uso do herbicida chlorimuron-ethyl reduziu o crescimento e a biomassa das plantas de soja, afetando também a nodulação da cultura. A cultivar transgênica BRS Valiosa RR mostrou um melhor desempenho quando submetida a uma condição de escassez hídrica moderada (-0,07 MPa) para sustentar a fixação biológica de nitrogênio.
Knowing genotype response to waterstress – deficit, or excess – is important for cultivar selection and recommendation, besides determining well- adapted techniques to grow soybeanin hydromorphic soils, with the aim to express productivity potential (Thomas & Lange, 2014). If, on the one hand, rotating soybean crops with irrigated rice have increased recently, on the other hand, there are few studies on the development and productivity of the used soybeancultivarsin hydromorphic soils in Brazil (Zanon et al., 2015, 2016; Sartori et al., 2016), Uruguay (Chebataroff et al., 2002; Castillo et al., 2013), and Argentina (Caride et al., 2011). These few studies do not completely explain the differences of the ecophysiological processes (photosynthetic rate, dry matter partition), and the development of soybean cultivated in hydromorphic and nonhydromorphic soils in an integrated way. This approach may help soybean breeding programs to develop cultivars for cultivation in hydromorphic soils, and to improve management practices to reduce waterstressinsoybeancultivars currently used in rotation with irrigated rice, in order to assist extensionists, consultants, and farmers in decision-making.
lular damage response (Shinozaki and Yamaguchi- Shinozaki, 2007). The expressed genes have been shown to belong to many classes of genes (Figure 3). However, the largest class of genes expressed understress remains unknown, partly because there is no similarity in data- bases available to date, and partly due to the gene func- tions are not understood yet (Reddy et al., 2008; Nelson and Shoemaker, 2006). Many genes expressed under wa- ter deficit conditions are present in the contrasting cultivars Embrapa 48 and BR 16 (Figure 5A). Among oth- ers, common processes affected by the stress are those re- lated to transport, protein folding and assembling as well as protein degradation and ubiquitination. Some proteins are synthesized in requirement of defense pathways trig- gered by the stress whereas other proteins are degraded because its aggregation or denaturation events are pre- dominant inwaterstress conditions. The transport cate- gory involves the translocation of ions, lipids, sugar and others molecules. Also included in this category are the genes for aquaporins, which are proteins that might be di- rectly involved inwaterdeficit acclimation by facilitating water movement across the membranes (Zhao et al., 2008). We have identified several transcripts encoding the tonoplast and plasma membrane intrinsic proteins that were more frequently found in roots rather than in leaves, especially in the BR 16 plants (Figure 5B). Roles played by aquaporins in plants can be regulated in different com- plex ways, but the expression of aquaporins throughout the plant would most likely be regulated by water poten- tial gradient (Zhao et al., 2008). However, there are differ- ences between the mRNA changes and its respective pro- tein level. The changes expressed here by soybean plants in response to waterstress are only at the transcriptional
GmaxRD20A-like showed a similar expression pro- file in the sensitive and tolerant cultivars. However, GmaxRD20A-like was more expressed in the tolerant culti- var under severe stress (Yw -3.0 MPa) in PSys (Figure 2A). In Arabidopsis, the RD20A gene is regulated by the AREB1/ABF2 transcription factor, which is also involved in the regulation of the RD29B gene (Fujita et al., 2005; Shinozaki and Yamaguchi-Shinozaki, 2007). Even after exhaustive searches in the soybean genome, the most simi- lar gene we found to Arabidopsis RD29B, Glyma16g31330, showed low similarity (e-value 10 -18 ). Furthermore, this putative RD29B soybean homolog is not regulated by the waterdeficitstress according to our exper- iments (data not shown). These results indicate that RD29B homologs are absent in the soybean genome. Recently, it was shown that Arabidopsis RD29B is unlikely to perform any protective effects during drought stress (Msanne et al., 2011). Therefore, the lack of RD29B homologs in the soy- bean genome should not interfere in the tolerance of this species to drought.
Observing germination and elongation of eight soybeancultivars exposed to water potentials of 0, -0.5, -1.1 and -1.5MPa, and at 15 or 30ºC, Seong et al. (1988) reported that the moisture content and the seedling length decreased when the mannitol concentration increased, concluding that germination in mannitol was useful for the selection of soybean cultivar for emergency capacity under conditions of waterdeficit. Induced waterdeficit by polyethylene glycol showed similar values to that observed in the fields (Thill et al., 1979), permitting also vigour evaluation (Santos et al., 1996). In similar potential ranges, germination patterns may be different between species or even between varieties of the same species (McWilliam and Phillips, 1971; Therios, 1982). However, some species, as soybean are very sensitive to sodium chloride during germination (Bourgeais-Chaillov et al., 1992; Santos et al., 1992).
Regarding the decrease in the cortex:central cylinder ratio observed in both the cultivarsunderwaterdeficit Vasellati et al. (2001) showed that drought increased the number of root hairs and decreased the diameter of the metaxylem bundle in Paspalum dilatatum, a common characteristic of plants submitted to drought that could cause a reduction in the cortex:central cylinder ratio. Trichomes observed on the leaves of both soybean genotypes, were barriers to air movement, consequently decreasing water loss from the leaf surface (Mauseth, 1988). In the present work was observed stomata in the epidermis on both surfaces of the leaf. According to Mott et al. (1982), amphistomatic leaves have a potentially higher capacity for carbon dioxide capture and could achieve elevated levels of photosynthesis, if conditions were suitable.
variation in germination, plant height, plant dry matter, seedling growth, relative saturation deficitandwater contents grown under 0 and -0.06 Mpa. However, not all these parameters proved to be equally effective for screening wheat varieties for their tolerance to stress. It was claimed by Fernan- dez (1992) that selection based on STI (stress to- lerance index) would help to evaluate the higher stress tolerance genotypes with good yield poten- tial. Bouslama and Schapaugh (1984) reported same findings insoybean. Ashraf et al. (1992) concluded that under moisture deficit, germination is not the standard for predicting plant’s drought tolerance. However there are other reports (Ri- chards, 1978) indicating germination as a useful criterion in screening for waterstress tolerance. Several factors disproved seed quality such as the age of the seed, abiotic factors during plant life, growth and development, harvest and post harvest conditions etc. The response of genotypes may be different to different factors, which could be re- flected in their respective seed performances. Thus, for identifying healthy and vigorous seed lots capable of establishing appropriate popula- tions underdeficit soil moisture conditions or un- der abiotic stress (Ibrahim et al., 2007), the germi- nation test of seed may be useful, but these genetic differences may not be related to subsequent growth of seedling and seed yield.
The dynamic of carbon assimilation in plants is functionally controlled by a source-sink relationship (Ainsworth et al. 2004; Ribeiro et al. 2012). Sources are the sites where net assimilation of CO 2 occurs while sinks are tissues where photoassimilates are allocated for growth or storage. Although the CO 2 assimilation rate is genetically determined, exogenous factors, such as waterdeficit, exerts substantial control over it (Liu et al. 2004a). Endogenous factors can also reduce the CO 2 assimilation rate by a negative feedback effect on photosynthesis due to high leaf carbohydrate content (Mondal et al. 1978; Ribeiro et al. 2012). Insoybean, the pods and seeds are the major sink tissues and their size and number per plant determine grain yield (Declaux et al. 2000; Egli and Bruening, 2004). Effects of waterdeficit on soybean productivity have been attributed to impairment of yield components mainly when waterstress occurs during reproductive stages (Egli et al. 1976, 1983; Chaves et al. 2002).
The results derived from the PV curves (Table 2) showed that, in general, the turgor loss point (TLP) was reduced in all treatments underwater deficiency, without significant difference between both cultivars. On the other hand, Ws % and RWC at TLP values remains stable among treatments, except by an increase in RWC at TLP in the conventional cultivar underwaterdeficit. The water deficiency tended to increase e (volumetric elasticity module), mainly in the conventional cultivar (Table 2). Changes in the cell wall elasticity play an important role in the plant’s ability to respond to waterdeficit. Water loss in plant tissues controls the turgor pressure, affecting the elasticity of cell wall. However, water deficiency can result both in the increase and reduction of cell wall elasticity, and this can be a species-specific characteristic. The loss of elasticity (higher values of e) is related to a higher lignification of tissues, phenolic cross-linking and a reduction of extensin synthesis, while the loosening of the wall is associated with regions of growth, mediated by complex physiological and biochemical processes (MOORE et al., 2008). Our results indicate a loss of cell wall elasticity in response to the water deficiency in both cultivars, which, overall, led to a reduction in TLP values. Thus, plants undergoing water deficiency increased their tolerance to dehydration, losing cellular turgor at lower water potentials. According to DICHIO et al. (2003) high values of e
The percentage of emergence (PE) and the speed of emergence (SE) of corn were not affected by the electrical conductivity of the irrigation water (EC i ), while for soybean, EC i responded to both vari- ables (Table 1). Effects of EC i on PE and SE for soy- bean were practically the same and they were reduced for the second growing season for all levels of EC i due to the higher salinity of the soil solution as a result of salt accumulation in the soil profile with the succes- sive irrigations (Figure 2). Mean EC i threshold (c t ) for relative values of PE and SE for soybean was about 2.7 dS m -1 , with a reduction of 20% for each unitary
consequence, the destructuring of the membrane systems at a cellular level with the lipid oxidation being the direct cause of the seed deterioration during storage. Furthermore, within the lipid fraction, the polyunsaturated fatty acids such as linoleic and linolenic are the most important and susceptible to oxidative degradation by enzymatic and non- enzymatic reactions. Jeng & Sung (1994) observed that the increase in the peroxidation of lipids and the accumulation of hydroperoxides were observed in embryonic axis and cotyledon of aged peanut seeds. The deterioration process has been associated with the loss of integrity of the endomembrane system and with cellular solution leakage because of the lipid oxidation process, including the phospholipides in the plasmatic membrane. Powell & Matthews (1979) showed that a reduction in the phospholipid content of the membranes, especially of phosphatidilocoline, was a prime event during pea seed aging.
such as water can affect the plant growth is influencing physiological processes (Koslowski & Pallardy 1997). Due to the increase of carbon dioxide in atmosphere, which leads to an increase in air temperature, it is considered that there will raise the atmospheric demand for waterand, on many regions, with higher occurrence, frequency, intensity and distribution of droughts. The climate change models show an high frequency of rainfall separated by long dry periods (Dore 2005). In this scenario, the projected climate changes for the coming years due to global warming, make studies on water use by native species critical, not only to preserve ecosystems, but also to define strategies for recovery of degraded areas, since the establishment of the species is a critical step to the recovery of these areas. Thus, among the environmental factors, water deficiency stands out as an adverse factor to the growth and crop production making it essential for studies to address the issue.
In order to evaluate growth, plants within the working area of each experimental plot were collected at 75 DAS and taken to the Chemistry Laboratory on the Umirim Campus of IFCE, where the following were analyzed: main stem length (MSL), determined by measuring the stem with the aid of a graduated tape; total dry matter (TDM), by drying the shoots of the plant in a closed air circulation oven at a temperature of 65°C to constant weight, the weight later being determined with the aid of a semi-analytic balance; and leaf area (LA), each foliole of the plant was separated and the length and width measured. After this procedure, the values obtained were applied to Equation 3, obtained by Lima et al. (2008): AF= ∑[0,9915×(C×L) 0,9134 ] (3)
Singh et al. (2001) registered the line SEA 5 as a drought tolerant cultivar, derived from interracial crosses between the races Mesoamerican and Durango, and one of the parents originating the line was the cultivar BAT 477, also described by the authors as drought tolerant. Later, Terán & Singh (2002) also observed productive superiority of the genotype SEA 5 in both waterdeficitandunder irrigated condition, using BAT 477 and San Cristobal 83 as tolerant controls. Studying the root system by means of a screening using soil tube system to evaluate the impact of drought on different genotypes of beans, Rao et al. (2006) found that SEA 5 and BAT 477 remained among the genotypes with deeper roots.
In the present study, a significant increase in leaf SOD activity was observed in both tomato cultivars treated with Ca and His treatments during different levels of nickel (Table 4), suggesting that SOD may function as a ROS scavenger (Alscher et al., 2002). Recent studies have demonstrated that over expression of chloroplastic Cu/Zn-SOD intransgenic Nicotiana tabacum (Badawi et al., 2004) can provide enhanced ion toxicity tolerance. Even though a high SOD activity (compared in equal total protein content of tissue) protects plants against the superoxide radical, it cannot be considered solely responsible for membrane protection against peroxidation. This ROS should be then scavenged by other enzymes such as catalase and peroxidases.
A deficiência hídrica é o principal fator limitante para o crescimento e desenvolvimento das culturas. Para sobreviver nessas condições adversas, várias modificações bioquímicas e fisiológicas são desencadeadas pelas plantas. Em geral, os efeitos da seca em plantas são diminuição do status hídrico, reduções da condutância estomática, fotossíntese e crescimentos e aumentos nos níveis de carboidratos. Os açúcares solúveis desempenham papéis chave no metabolismo das plantas, atuando como substratos e moduladores da atividade enzimática em vias relacionadas com o carbono. Além disso, os açúcares controlam a expressão de genes associados com as rotas do metabolismo do carbono, lipídios e nitrogênio. Entretanto, os mecanismos envolvidos com a regulação negativa da fotossíntese por deficiência hídrica e açúcares em plantas C4 não estão totalmente entendidos. O objetivo deste estudo foi investigar como a deficiência hídrica e perturbações na relação fonte-dreno regulam a fotossíntese em plantas de cana-de-açúcar. Dois estudos foram conduzidos com plantas de cana-de-açúcar com quatro meses de idade cultivadas sob condições de casa de vegetação. No primeiro estudo, plantas de cana-de-açúcar (cv. IACSP94-2094) foram submetidas a deficiência hídrica por 5 dias (WD) com subsequente aplicação de sacarose exógena 50 mM (WD + Suc). Enquanto que no segundo estudo a relação fonte-dreno foi perturbada em duas cultivares de cana-de-açúcar (cv. IACSP94-2094 and cv. IACSP95-5000) pela imposição parcial de sombreamento, aplicação de sacarose exógena 50 mM e por suas combinações por 5 dias. Os efeitos negativos de WD nos parâmetros de trocas gasosas e fotoquímicos foram agravados por sacarose exógena. As reduções na fotossíntese foram relacionadas com limitações estomáticas e bioquímicas, porém a sacarose exógena intensificou as restrições bioquímicas principalmente por reduções na atividade inicial de Rubisco e eficiência quântica do PSII em plantas sob seca. Além disso, o estado de ativação de Rubisco foi inibido por WD + Suc, sugerindo que a atividade inicial dessa enzima foi possivelmente reduzida por inibidores que se ligam fortemente em seu sitio ativo, tais como açúcares fosfato. As enzimas do metabolismo de sacarose e a concentração de açúcares foram modificados diferentemente por WD e WD + Suc em folhas, bainha e colmo. Interessantemente, a relação sacarose/hexose decresceu em folhas e bainha, enquanto que no colmo essa relação aumentou, sugerindo que sacarose e outros açúcares relacionados foram intensamente metabolizados e transportados. Em condições irrigadas a fotossíntese foi inibida pela aplicação de sacarose nos dois genótipos, através de decréscimos da taxa máxima de carboxilação de Rubisco (V cmax ), inclinação inicial da curva A-C i (k), condutância estomática
Damage to plants in response to abiotic and biotic stresses is a worldwide ecologic and economic concern. Recent and predicted climate changes exacerbate this concern (Lobell & Gourdji, 2012). Environmental stresses not only have adverse effects on plant growth and productivity but also are expected to become more variable, severe, and widespread in decades to come. Prolonged and repeated severe environmental stresses affecting plant growth and development would bring down long-lasting effects in woody plants as a result of its long-term growth period. Plant tolerance to stress englobes a variation in the detail network and cascade of events or reactions leading to alleviation of potential stress-induced cellular injuries depending on the plant species that have evolved through environmental changes. The development of lignin biosynthesis has been considered to be one key factor that allowed plants to flourish in terrestrial ecosystems. Therefore, to understand and improve waterstress tolerance in plants by manipulating lignin in wood plant tissues becomes a necessity if tree survival and biomass production are to be increased and profitable in face of future climate changes. Plasticity in lignin biosynthesis may be an important feature in understanding future species distribution as impacted by changing waterstress patterns.
The presence of a compact soil layer detected at the 0.07-0.10 m (Munareto et al., 2010) and 0.10-0.20 m (Sartori et al., 2015; Sartori et al., 2016b) is another problem for those intending to rotate crops in lowland areas cultivated with irrigated rice. The presence of this less permeable layer intensifies OD by keeping the soil moist during rainfall periods and intensifies WD by confining the roots in the surface layer of the soil, which increases the risk of waterstress during periods of low rainfall. To reduce the risk of soybean yield loss in lowland soils, tolerant cultivars, the seeding period, and soil management strategies must be selected in a combined manner to minimize stress. The effectiveness of these actions, however, depends on rainfall, which controls the water table (Ronen et al., 2000; Gomes et al., 2012), the key factor in the occurrence of OD. Several studies indicate that chiseling (Sartori et al., 2015; Sartori et al., 2016b) and the use of ridge tillage are effective management strategies in lowland soils for increasing soybean yield (Silva et al., 2007). Chiseling favors internal drainage of the profile (Sartori et al., 2016a), whereas the ridge promotes a more aerated zone, which is also elevated in relation to the groundwater level (Sartori et al., 2015). Studies have not yet evaluated the combination of these two approaches. The expectation is that together they can provide greater aeration in the root zone of plants, though intensify waterstress during periods of drought.
Control of charcoal rot by different methods, such as crop rotation (Francl et al., 1988) and irrigation (Kendig et al., 2000), has been tried. However, since M. phaseolina is a soil-borne pathogen and is able to infect several plant species, crop rotation may not be very beneficial. According to Dhingra& Sinclair (1978), susceptible crops such as corn and soybeans cropped for three years increased the number of sclerotia. On the other hand, Chattopadhayay & Mustafe (1977) reported the reduction of M. phaseolina inoculum when crop rotation was conducted with pea (Pisum sativum L.) or rice (Oryza sativa L.) between two soybean seasons. Short et al. (1980) observed that M. phaseolina survived well insoybean residue. There was a rapid increase in the number of sclerotia in the soil after susceptible crops, such as corn andsoybean, were planted. They suggested that the control of this fungus should be achieved by techniques other than crop rotation.
Low GCA values usually do not differ between them, which can be explained by the masking presence of small effect complementary genes in the parental genotypes involved in the crosses (Barbieri et al. 2001). For the character MPW, it can be observed that the cultivar UPF 18 showed a high individual mean, much higher than the general mean for the environment without stress. However, its GCA value (0.53) was not very high (Table 3). Regarding the environment with waterstress, all parents showed a performance inferior to the general mean for the character. The correct selection of parental genotypes to form the crossing blocks is essential to the success of plant breeding programs, and the combining ability, with the presence of complementary genes, the major player in this process. Parents presenting higher GCA must be preferred to be part of crossing blocks, favoring the selection of promising homozygous lines in self crossing species (Miranda et al. 1988). A very low g i estimate indicates that