Paulo Eduardo Ribeiro Marchiori

Respostas biométricas e fisiológicas ao deficit hídrico em cana-de-açúcar em diferentes fases fenológicas

The aim of this work was to evaluate the biometric and physiological responses of sugarcane (Saccharum spp.) to water deficit (WD), during different phenological phases. Genotypes IACSP 94-2094 and IACSP 96-2042 were subjected to WD conditions during the initial, maximum and sucrose accumulation phases. The experiment was carried out in a completely randomized design. Susceptibility to WD was established by reduction in stalk dry matter and soluble solids. Water deficit reduced leaf gas exchange in all phenological phases of both genotypes. Lower plant height, less stalk dry matter and soluble solids, and reduction in number and length of internodes were only observed during the initial growth phase of the IACSP 96-2042 clone. In the initial growth phase, tolerance to WD was observed for IACSP 94-2094, with evidence of physiological acclimation, and for IACSP 96-2042 in reduction phytomass production and its soluble solid content, caused by lower stomatal conductance and lower apparent carboxylation efficiency which limit photosynthesis. Regardless of the phenological phase, genotype IACSP 94-2094 was tolerant to WD, since its phytomass production was maintained even with impairment of leaf gas exchange.

A non-invasive plant-based probe for continuous monitoring of water stress in real time: a new tool for irrigation scheduling and deeper insight into drought and salinity stress physiology

The non-invasive, magnetic leaf patch clamp pressure probe (also termed ZIM-probe) allows for the first time to measure continuously turgor pressure changes of plant leaves over long periods of time with high precision and in real time. The probe has become an important tool in plant physiology, molecular biology and ecology, but also in agriculture because the probe is very robust and user-friendly. Growers receive the information about the water status of their plants by wireless telemetry, mobile network and internet on an as-needed basis and can thus adjust very precisely both the timing of irrigation and the quantity of water to apply. Effects of air and leaf temperature, relative humidity, illumination and wind on turgor pressure can be monitored very sensitively both under indoor and outdoor conditions. Even the effects of blue and red light as well as of oscillations of stomata aperture on turgor pressure can be monitored by the probe with high sensitivity. Similarly, water deficit due to increase of the osmotic pressure in the nutrition solutions resulted in significant changes of the probe signals. Multiple probe readings open up new possibilities to resolve (together with other techniques) the mechanisms of short- and long-distance water transport, particularly how plants can cope with water shortage. The applications of the magnetic probe are numerous and one can expect highly interesting developments in plant water relations in the nearest future.

How can crop modeling and plant physiology help to understand the plant responses to climate change? A case study with sugarcane

Global climate changes are now well accepted to happen and can likely impact agriculture. Process-based dynamic crop models are able to estimate a range of crop responses to the environment and to assess the biophysical effects of future climate scenarios on crop growth and yield. They are hence scientifically accepted as a predictor of future agricultural scenarios, and the multi-model approach has shown the best performance in such prediction activities. The need of several models for such studies is mainly a consequence of the different physiological and physical approaches applied by model developers. Physiological processes are in fact essential elements for improving plant modeling, and most of the model weakness would be overcome by better understanding of the main physiological aspects related to plant growth and development. Sugarcane (Saccharum spp.) is an important crop for coping with climate change mitigation as a source of bioenergy and food. In this paper we aim to demonstrate how important is plant physiology for advancing the process-based crop models by briefly reviewing the history of the modeling along the last five decades and presenting the key physiological process considered in crop models. The paper was based in the DSSAT/CANEGRO sugarcane model and a set of field experiments for exemplifying some model responses to key climatic variables expected to vary in the following decades. Those responses were discussed under the light of plant physiology knowledge. We selected two sites in the State of Sao Paulo for an exercise of local sensitivity analysis. As air CO2 concentration is the most likely environmental variable expected to change, we stressed the CO2 effects on plant photosynthesis and water use to highlight the model strengths and opportunities for model improvements based on plant physiology findings.

Fotossíntese, relações hídricas e crescimento de cafeeiros jovens em relação à disponibilidade de fósforo

The objective of this work was to evaluate how high soil phosphorus (P) availability affects the photosynthesis and growth of young coffee arabica plants (Coffea arabica). Four months old coffee seedlings of the Ouro Verde cultivar, cultivated in good hydric conditions, were exposed to three P availability treatments: P dosage recommended in the literature (RP); two times the recommended dosage (P+); and without P (P-). Seventy days after treatment application, evaluations of leaf gas exchange, photochemical activity, leaf water potential, plant hydraulic conductance (KL), dry matter partitioning, leaf contents of pigments and carbohydrates, and leaf chemical composition were done. The treatment without P caused reduction in photosynthesis, leading to lower plant growth. The plants of the P+ treatment showed the highest leaf P concentrations (~1.9 g kg-1), with increasing leaf CO2 assimilation and instantaneous carboxylation efficiency, and higher photochemical activity - higher effective quantum efficiency of photosystem II and apparent electron transport rate - when compared to plants exposed to RP treatment. Plants exposed to the double P recommended dosage exhibited higher KL, higher leaf carbohydrate content and higher chlorophyll content, resulting in higher dry matter production as compared to RP and P-.

Plant growth, canopy photosynthesis and light availability in three sugarcane varieties

Phytomass production is a result of physiological processes occurring at plant canopy level, with canopy architecture affecting the availability of solar radiation to photosynthesizing tissues. The aim of this study was to identify a possible association between light availability, canopy photosynthesis and plant growth in three sugarcane varieties under field conditions. As a hypothesis, higher canopy photosynthesis and plant growth are probably found in sugarcane varieties with higher light availability at bottom canopy positions. Measurements of diurnal course of leaf gas exchange were taken in two canopy positions of the sugarcane varieties IACSP93-2060, IACSP95-3028 and IACSP95-5000, maintaining the natural leaf inclination. All sugarcane varieties exhibited similar values of diurnal CO2 uptake at the upper canopy position. On the other hand, the bottom canopy position had an important role on photosynthesis of IACSP95-3028 sugarcane, with slight changes in leaf inclination causing significant variation of photosynthetic active radiation at the bottom canopy positions. High light availability at the bottom canopy position of IACSP95-3028 caused increased photosynthesis and improved plant vegetative growth, given by increases in tillering, leaf area and leaf and stalk phytomass accumulation.

Photosynthetic and antioxidant responses to drought during sugarcane ripening

Water deficit is an important exogenous factor that enhances the influx of sucrose into sugarcane (Saccharum spp.) stem internodes during ripening, when photosynthetic ability in supplying sinks is essential. The aim of this study was to test the hypothesis that drought tolerance in sugarcane is associated with an effective antioxidant protection during the ripening phase that might maintain a favorable redox balance in chloroplasts and protect photosynthesis under drought conditions. Two commercial sugarcane varieties, IACSP94-2094 (tolerant) and IACSP96-2042 (sensitive), with contrasting behavior under water deficit, were subjected to water withholding during the ripening stage. Our results revealed that the tolerant variety was less affected by water deficit, maintaining photosynthesis for a longer period and showing a faster recovery after rehydration as compared to the sensitive one. As consequence, the tolerant variety faced lesser excess of light energy at PSII. The maintenance of photosynthesis under water deficit and its fast recovery after rehydration resulted in the lower leaf H2O2 concentration and favorable redox status in the drought-tolerant genotype, which was associated with stimulation of superoxide dismutase during ripening. Our results also revealed that ferric superoxide dismutase isoforms were strongly enhanced under drought conditions, playing an important role in chloroplast redox homeostasis.

Physiological and transcriptional analyses of developmental stages along sugarcane leaf

BackgroundSugarcane is one of the major crops worldwide. It is cultivated in over 100 countries on 22 million ha. The complex genetic architecture and the lack of a complete genomic sequence in sugarcane hamper the adoption of molecular approaches to study its physiology and to develop new varieties. Investments on the development of new sugarcane varieties have been made to maximize sucrose yield, a trait dependent on photosynthetic capacity. However, detailed studies on sugarcane leaves are scarce. In this work, we report the first molecular and physiological characterization of events taking place along a leaf developmental gradient in sugarcane.ResultsPhotosynthetic response to CO2 indicated divergence in photosynthetic capacity based on PEPcase activity, corroborated by activity quantification (both in vivo and in vitro) and distinct levels of carbon discrimination on different segments along leaf length. Additionally, leaf segments had contrasting amount of chlorophyll, nitrogen and sugars. RNA-Seq data indicated a plethora of biochemical pathways differentially expressed along the leaf. Some transcription factors families were enriched on each segment and their putative functions corroborate with the distinct developmental stages. Several genes with higher expression in the middle segment, the one with the highest photosynthetic rates, were identified and their role in sugarcane productivity is discussed. Interestingly, sugarcane leaf segments had a different transcriptional behavior compared to previously published data from maize.ConclusionThis is the first report of leaf developmental analysis in sugarcane. Our data on sugarcane is another source of information for further studies aiming to understand and/or improve C4 photosynthesis. The segments used in this work were distinct in their physiological status allowing deeper molecular analysis. Although limited in some aspects, the comparison to maize indicates that all data acquired on one C4 species cannot always be easily extrapolated to other species. However, our data indicates that some transcriptional factors were segment-specific and the sugarcane leaf undergoes through the process of suberizarion, photosynthesis establishment and senescence.

Baixa temperatura noturna e deficiência hídrica na fotossíntese de cana‑de‑açúcar

The objective of this work was to evaluate the photosynthetic responses of sugarcane to the simultaneous and isolated effects of low night temperature (TN) and water deficit (DH). After 128 days of planting, plants of the cultivar IACSP94-2094 were subjected to the following treatments: control, without DH and with TN of 20°C (TN20); with DH and TN of 20°C (DH/TN20); without DH and with TN of 12°C (TN12); and with DH and TN of 12°C (DH/TN12). After the period of treatment, plants were irrigated and subjected to TN of 20°C for four more days, for recovery. There were decreases in CO2 assimilation in all treatments. Total recovery of CO2 assimilation was observed only in plants from the treatment TN12. The simultaneous occurrence of low night temperature and water deficit caused a accentuated and persistent effect on stomatal conductance, on the maximum capacity of ribulose‑1,5‑bisphosphate carboxylase, on the electron transport rate, on the efficiency factor, and on the operational efficiency of photosystem II, which resulted in diffusive, biochemical, and photochemical limitations of photosynthesis of sugarcane plants.

Reference genes for normalization of qPCR assays in sugarcane plants under water deficit

AbstractBackgroundSugarcane (Saccharum spp.) is the main raw material for sugar and ethanol production. Among the abiotic stress, drought is the main one that negatively impact sugarcane yield. Although gene expression analysis through quantitative PCR (qPCR) has increased our knowledge about biological processes related to drought, gene network that mediates sugarcane responses to water deficit remains elusive. In such scenario, validation of reference gene is a major requirement for successful analyzes involving qPCR. ResultsIn this study, candidate genes were tested for their suitable as reference genes for qPCR analyses in two sugarcane cultivars with varying drought tolerance. Eight candidate reference genes were evaluated in leaves sampled in plants subjected to water deficit in both field and greenhouse conditions. In addition, five genes were evaluated in shoot roots of plants subjected to water deficit by adding PEG8000 to the nutrient solution. NormFinder and RefFinder algorithms were used to identify the most stable gene(s) among genotypes and under different experimental conditions. Both algorithms revealed that in leaf samples, UBQ1 and GAPDH genes were more suitable as reference genes, whereas GAPDH was the best reference one in shoot roots.ConclusionReference genes suitable for sugarcane under water deficit were identified, which would lead to a more accurate and reliable analysis of qPCR. Thus, results obtained in this study may guide future research on gene expression in sugarcane under varying water conditions.

Short-term physiological changes in roots and leaves of sugarcane varieties exposed to H2O2 in root medium.

The aim of this study was to evaluate the differential sensitivity of sugarcane genotypes to H2O2 in root medium. As a hypothesis, the drought tolerant genotype would be able to minimize the oxidative damage and maintain the water transport from roots to shoots, reducing the negative effects on photosynthesis. The sugarcane genotypes IACSP94-2094 (drought tolerant) and IACSP94-2101 (drought sensitive) were grown in a growth chamber and exposed to three levels of H2O2 in nutrient solution: control; 3 mmol L(-1) and 80 mmol L(-1). Leaf gas exchange, photochemical activity, root hydraulic conductance (Lr) and antioxidant metabolism in both roots and leaves were evaluated after 15 min of treatment with H2O2. Although, root hydraulic conductance, stomatal aperture, apparent electron transport rate and instantaneous carboxylation efficiency have been reduced by H2O2 in both genotypes, IACSP94-2094 presented higher values of those variables as compared to IACSP94-2101. There was a significant genotypic variation in relation to the physiological responses of sugarcane to increasing H2O2 in root tissues, being root changes associated with modifications in plant shoots. IACSP94-2094 presented a root antioxidant system more effective against H2O2 in root medium, regardless H2O2 concentration. Under low H2O2 concentration, water transport and leaf gas exchange of IACSP94-2094 were less affected as compared to IACSP94-2101. Under high H2O2 concentration, the lower sensitivity of IACSP94-2094 was associated with increases in superoxide dismutase activity in roots and leaves and increases in catalase activity in roots. In conclusion, we propose a general model of sugarcane reaction to H2O2, linking root and shoot physiological responses.