Hormonal conditioning of plants in order to increase photosynthetic performance and reduce oxidative stress may improve plants' tolerance to stress. This study aims to elucidate the effects of ABA pretreatment on the photosynthetic apparatus and antioxidant battery of Ulmus minor plants under well watered (WW) and drought stress (DS) conditions. Leaves were sprayed with ABA (50 and 100??M). After 25 days of treatment DS was initiated by withholding water for 6 days. Water deficit decreased the RWC, induced stomatal closure and impaired net CO2 assimilation rate (A). However, independently of the water regime, ABA pretreatment increased plant DW accumulation, A, carotenoids and Chl a contents and reduced water loss. DS induced oxidative stress, but ABA application increased DS tolerance by the enhancement of the antioxidant system. Under WW conditions, the benefits of ABA application in reducing the cell membrane damages were noticeable. ABA pretreatment and DS induced changes in U. minor cell cycle of leaf cells, with a delay in S phase and an increase of FPCV coefficient. We propose that ABA pretreatment improves plant performance by increasing plant DW accumulation and augmenting the antioxidant system of U. minor plants, not only under DS conditions, but also under WW conditions. The use of ABA as pretreatment to alleviate the negative effects of DS seems to be a promising strategy to reduce plant's water loss and improve plant productivity in drought prone habitats.

We compared the metabolic responses of leaves and roots of two Eucalyptus globulus Labill. clones differing in drought sensitivity to a slowly imposed water deficit. Responses measured included changes in concentrations of soluble and insoluble sugars, proline, total protein and several antioxidant enzymes. In addition to the general decrease in growth caused by water deficit, we observed a decrease in osmotic potential when drought stress became severe. In both clones, the decrease was greater in roots than in leaves, consistent with the observed increases in concentrations of soluble sugars and proline in these organs. In roots of both clones, glutathione reductase activity increased significantly in response towater deficit, suggesting that this enzyme plays a protective role in roots during drought stress by catalyzing the catabolism of reactive oxygen species. Clone CN5 has stress avoidance mechanisms that account for its lower sensitivity to drought compared with Clone ST51.

Water deficit represents a serious limitation for agriculture and both genetic and chemical approaches are being used to cope with this stress and maintain plant yield. Next-generation agrochemicals that control stomatal aperture are promising for controlling water use efficiency. For example, chemical control of abscisic acid (ABA) signaling through ABA-receptor agonists is a powerful method to activate plant adaptation to water deficit. Such agonists are molecules able to bind and activate ABA receptors and, although their development has experienced significant advances in the last decade, few translational studies have been performed in crops. Here, we describe protection by the ABA mimic fluorine derivative 4 (AMF4) agonist of the vegetative growth in tomato plants subjected to water restriction. Photosynthesis in mock-treated plants is markedly impaired under water deficit conditions, whereas AMF4 treatment notably improves CO2 assimilation, the relative plant water content and growth. As expected for an antitranspirant molecule, AMF4 treatment diminishes stomatal conductance and transpiration in the first phase of the experiment; however, when photosynthesis declines in mock-treated plants as stress persists, higher photosynthetic and transpiration parameters are recorded in agonist-treated plants. Additionally, AMF4 increases proline levels over those achieved in mock treated plants in response to water deficit. Thus water deficit and AMF4 cooperate to upregulate P5CS1 through both ABA-independent and ABA dependent pathways, and therefore, higher proline levels are produced Finally, analysis of macronutrients reveals higher levels of Ca, K and Mg in AMF4-compared to mock-treated plants subjected to water deficit. Overall, these physiological analyses reveal a protective effect of AMF4 over photosynthesis under water deficit and enhanced water use efficiency after agonist treatment. In summary, AMF4 treatment is a promising approach for farmers to protect the vegetative growth of tomatoes under water deficit stress.

Seedlings of two forage sorghum genotypes (Sorghum bicolor (L.) Moench) differing in salt tolerance were subjected to 0 and 100 mM NaCl and shoot development, leaf elongation, and organic and inorganic solutes contents in leaves were measured. Salt stress reduced both shoot development and leaf elongation and enhanced leaf senescence and injury. It also led to accumulation of toxic ions (Na+ and Cl−), organic solutes (carbohydrates, amino acids and proline), and reduction of K+ content in leaf blades. Toxic ion accumulation was higher in the basal zone of the leaf blade and occurred during the period of intense leaf growth while organic solutes accumulation, mainly proline, was higher in the apical zone and occurred when the leaves practically had reached their final size. All these changes were more conspicuous in the sensitive than in the tolerant genotype. The latter also retained more toxic ions in leaf sheath tissue than the former. It is suggested that the reduction in shoot development and leaf elongation were related to toxic ion accumulation and depletion of K+ ions in the leaf blades. The accumulation of organic solutes in leaves did not appear to be related to salt tolerance. Proline accumulation appears to be a reaction to salt stress damage and not a plant response associated with salt tolerance.

Este trabalho objetivou avaliar a contribuição da prolina, do metabolismo oxidativo e dos pigmentos fotossintéticos na propagação in vitro e aclimatização de Pitcairnia encholirioides, uma bromélia criticamente ameaçada de extinção. As análises foram realizadas após 150 dias de cultivo in vitro em meio MS suplementado com 10 µM de GA3 ou 0,2 µM de ANA, 15 ou 30 g L–1 de sacarose, em tubos de ensaio que permitiam trocas gasosas ou em sistema hermeticamente vedado, e também 180 dias após aclimatização. A manutenção in vitro em frascos hermeticamente fechados, com GA3 e 15 g L–1 de sacarose apresentou efeito metabólico adverso, demonstrado pelo menor acúmulo de prolina e pigmentos fotossintéticos e também pelo aumento das atividades de enzimas antioxidantes. Após aclimatização, as diferenças para prolina e pigmentos fotossintéticos não foram mais encontradas e as atividades enzimáticas variaram de maneira desuniforme. Os resultados sugerem que o cultivo in vitro em meio com 0,2 µM de ANA e 30 g L–1 de sacarose, em tubos fechados com tampas que permitem trocas gasosas, é mais adequado para a micropropagação de P. encholirioides, proporcionando uma manutenção prolongada das culturas in vitro e plântulas com qualidade superior para o desenvolvimento ex vitro.

In this study we investigated the effects of the high endogenous proline level on water relations, gas exchange and antioxidant enzymatic activity in leaves of transgenic ?Swingle? citrumelo rootstocks transformed with the P5CSF129A gene coding for the key-enzyme for proline synthesis, under water deficit. Leaf total water, osmotic and pressure potentials, stomatal conductance, photosynthetic rates and xylem sapflowwere evaluated in non-transformed control and transgenic plants during water deficit treatment. Malondialdehyde (MDA) content, catalase (CAT; EC 1.11.1.6), superoxide dismutase (SOD; EC 1.15.1.1) and ascorbate peroxidase (APX; EC 1.11.1.11) activities were quantified in leaves collected based on their total water potential, representing the following conditions: irrigated (w =−1.3 MPa), moderate stress (w =−2.3 to −2.5 MPa), severe stress (w =−3.8 to −3.9 MPa) and recovery (24 h after re-irrigation: w =−1.3 to −1.9 MPa). Osmotic adjustment was observed in transgenic plants until 11 days after withholding water, while pressure potential in non-transformed controls was close to zero after nine days of water deprivation. This superior maintenance of turgor pressure in leaves of transgenic plants led to higher stomatal conductance, photosynthetic and transpiration rates when compared to non-transgenic plants. Drought caused a significant decrease in APX and SOD activities in control plants, followed by an increase after re-watering. On the other hand, CAT was more active in control than in transgenic plants under irrigated condition and both stress levels. Our results suggest that transgenic plants were able to cope with water deficit better than non-transformed controls since the high endogenous proline level acted not only by mediating osmotic adjustment, but also by contributing to gas exchange parameters and ameliorating deleterious effects of drought-induced oxidative stress.

Drought is the most limiting environmental factor to crop productivity and presents a great variability in the degree of tolerance among and within species, among varieties. The aim of this study was to characterize sugarcane accessions regarding tolerance to water stress during in vitro cultivation based on changes in biometric, physiological and biochemical characteristics, within species and among species, to support future breeding programs. Adventitious shoots of five sugarcane accessions: Saccharum robustum, Saccharum spontaneum and Saccharum officinarum species, cultivated in Murashige and Skoog medium supplemented with 2% sucrose and 4 g/l Phytagel were used in five water potentials, 0, -0.3, -0.6, -0.9, -1.2 MPa, induced by mannitol. Survival, length of shoots and roots, number of shoots and roots, biomass, proline content in leaves and activity of antioxidant enzymes were analyzed. There is difference among species, and also, within the same sugarcane species when submitted to in vitro drought stress, and S. officinarum was shown to be the most tolerant. Proline can be used as a biochemical indicator of response to drought in sugarcane accessions and its accumulation was intensified in S. robustum and S. spontaneum accessions. Catalase activity remained unchanged with increased drought in sugarcane accessions evaluated.

ABSTRACT Silicon (Si) has beneficial effects on many crops, mainly under biotic and abiotic stress. Silicon can affect biochemical, physiological, and photosynthetic processes and, consequently, reduce drought stress. However, the effects of Si on rice (Oryza sativa L.) plants under drought stress are not well known. The objective of this study was to evaluate the effects of supplemental Si on proline content and peroxidase activity in upland rice plants in the presence and absence of drought stress. The experiment was conducted under greenhouse conditions and was arranged in completely randomized blocks in a 2 x 2 x 2 factorial scheme. Treatments comprised combinations of (1) presence or absence of Si supply (0 or 350 kg ha-1 of Si), (2) presence or absence of a water deficit (-0.050 MPa or -0.025 MPa soil water potential values, respectively), and (3) two upland rice cultivars: Caiapo (traditional type) and Maravilha (modern type), with eight replications. Under water stress conditions, silicon fertilization reduced the proline content in the vegetative and reproductive phases of upland rice plants and increased peroxidase activity in the plants' reproductive phase, which could be indicative of stress tolerance.