Search

Drought is considered the main abiotic stress because it influences the distribution of plant species and limits the productivity of ecosystems. The aim of this study was to evaluate the effects of drought on physiological and biochemical parameters during the initial development of Vatairea macrocarpa, a native cerrado species. Plants were subjected to daily watering (control); suppression of watering during 90 days with field capacity (fc) 50% and 25% and then followed by rewatering. Relative leaf water content (RWC), gas exchange, photosynthetic pigments content, carbohydrate and amino acids content, antioxidant activities and growth were recorded. The RWC decreased according to the soil water restriction, causing reduction in stomatal conductance and decrease of 76.4% in net photosynthesis in plants submitted to 25% fc. Water restriction decreased the chlorophyll content, however increased carotenoid content and also improved the antioxidant activities of superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT). In addition, high levels of sugars (sucrose, raffinose) and amino acids (proline, tryptophan, valine, glutamine and GABA) were detected in drought stressed plants, contributing to osmoregulation and as sources of carbon and nitrogen after rehydration. Decreases in carbon assimilation promoted a reduction of the leaf area, however an increase in the root surface area was observed. After rewatering, the analized parameters became similar to the control plants indicating that the severe water stress did not impair the survival of young plants. Instead, adjustments were made to protect them against drought such as the maintenance of the assimilatory metabolism at minimal levels. Made available in DSpace on 2017-11-14T23:19:58Z (GMT). No. of bitstreams: 1 Physiologicalandbiochemicalchanges.pdf: 1766127 bytes, checksum: 80711c8791f68e18ffe54688d0ba7d4c (MD5) Previous issue date: 2017-11-14

Climatic change forecasts suggest an increase in the frequency and severity of droughts that would affect the plant water relations and the characteristics of terrestrial ecosystems. We examined how juvenile plants of D. alata use physiological and metabolic changes to resist the drought effects in the natural environment. This study was conducted in a remnant area of Cerrado, and the effect of seasonality was assessed by the end of the dry season, at the beginning of the rainy season and during the rainy season. The decrease in rainfall resulted in changes in the plant water status, with a significant decrease in the leaf RWC, Ψs, and Fv/Fm ratio, with a concomitant increase in the VPD. The increase in the carbohydrate content resulted from starch degradation contributed to osmotic adjustment, whereas increases in proline, tryptophan, aspartate, and other derived amino acids also promoted the balance in the C/N metabolism and the maintenance of energy homeostasis during dry season. The efficiency of ROS cleaning by the antioxidant enzymes related to the AsA-GSH cycle minimized the negative impact of dehydration and prevented oxidative and nitrosative damage to the leaves of D. alata, improving its performance to cope with water deficit.

Invasive grasses inhibit the growth of other plant species, and water deficit is one of the major competition problems for native vegetation. We evaluated whether the presence of Brachiaria brizantha cv. Piata has a negative influence on the competition for water and nutrients between Anadenanthera macrocarpa and Anadenanthera colubrina (Angico species). The interspecific competition was evaluated using a randomized experimental design with the following treatments: 1) free competition (FC), in which the native species were cultivated without the grass presence and 2) under competition (UC), in which the native species grew together with the invasive grass for 120 days. We analysed the water relationships in the two species, the effect of water limitation on the antioxidant stress, the nutritional content of shoots and roots, the relative competition intensity (RCI) and growth. The presence of Piata grass reduced the soil moisture causing a decrease of 21.9% and 29.5% in the relative water content (RWC) of leaves for A. macrocarpa and A. colubrina, respectively. For the two Angico species, the quantum efficiency of Photosystem II (ΦPSII) decreased with reduction of RWC leaf, resulting in the H2O2 increase (57.5% at day 30 for A. colubrina and 38.8% at day 120 for A. macrocarpa). The oxidative stress was evidenced by the increase in the superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) activities in leaves and roots of both young native trees. In the UC treatment, reductions in water uptake also led to a decrease in root absorption of N, P, K, a Mg and low transport of these nutrients to the leaves of both Angico species. A. macrocarpa and A. colubrina showed less growth caused by limitation of water uptake, but the joint activity of the physiological and biochemical adjustments provided competitive ability.

Made available in DSpace on 2018-11-26T17:44:33Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-12-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Rocky outcrops represent the diversity center of vascular desiccation tolerant (DT) plants. Vegetation in this environment is exposed to an extended dry season and extreme conditions due to rocky soils and high sun exposure. In this study, we demonstrated that Pitcairnia burchellii, a bromeliad from rocky outcrops, tolerates intense desiccation for about 90 days due to strategies as accumulation of compatible osmolytes and antioxidant substances together with leaf morphological changes. In dehydrated plants, an increase in antioxidant activity was observed and the vacuolization of parenchyma cells was accompanied by proline accumulation in leaves and rhizomes. Precursors related to phenylpropanoid pathway increased significantly during plant dehydration. Accordingly, increases in anthocyanin and phenolic contents as well as lignin deposition were observed in leaves of dehydrated plants. Cell divisions and a decrease in stored starch were observed in the rhizomes indicating starch mobilization. Anatomical analyses revealed the presence of a more developed water-storage tissue in dehydrated leaves. During desiccation, leaves curl upwards and the adaxial V deep water-storage tissue is supported by two larger lateral vascular bundles. Cell wall folding and an increased proportion of arabinose-containing polymers was observed in leaves under dehydration, suggesting increasing of cell wall flexibility during desiccation. Such biochemical and morphological changes are consistent with the ability of P. burchellii to tolerate intense desiccation and behave as a resurrection species. Inst Bot, Nucleo Pesquisa Fisiol & Bioquim Plantas, Sao Paulo, SP, Brazil Univ Estadual Paulista, Inst Biociencias, Dept Bot, Rio Claro, SP, Brazil Univ Estadual Campinas, Programa Posgrad Biol Celular & Estrutural, Campinas, SP, Brazil Univ Estadual Paulista, Inst Biociencias, Dept Bot, Rio Claro, SP, Brazil FAPESP: 2012/16332-0 FAPESP: 2012/14339-7

Pitcairnia burchellii is a bromeliad found in Brazilian rocky outcrops. Given its capacity to cope with soil scarcity and extreme water deficit, this species is thought to behave as a resurrection plant. Herein, we evaluated water relations, gas exchange, the content of pigments, sugar and abscisic acid (ABA), and the metabolic profile of P. burchellii plants during desiccation and recovery after rehydration. During water withholding, the net photosynthesis rate, transpiration, and chlorophyll content decreased rapidly whereas leaf and root soluble carbohydrates increased presumably due to the starch breakdown. These drought-induced physiological changes were associated with a significant increase in leaf ABA content. Marked changes in amino acids, sugar alcohols such as galactinol and erythritol and dehydroascorbic acid levels were observed after desiccation. Our findings indicate that P. burchellii tolerates leaf protoplasmic dehydration and recovers its normal cellular metabolism within a short period after rehydration, as described for other resurrection species. However, plants of P. burchellii subjected to long-term desiccation presented a long delay in foliar tissue dehydration when compared with soil moisture loss, suggesting a cooperative role of the rhizome to cope with extreme water deficit.