Luis Mauro Gonçalves Rosa

Growth and carbon assimilation limitations in Ricinus communis (Euphorbiaceae) under soil water stress conditions

Water availability may influence plant carbon gain and growth, with large impacts on plant yield. Ricinus communis (L.), a drought resistant species, is a crop with increasing economic importance in Brazil, due to its use in chemical industry and for the production of biofuels. Some of the mechanisms involved in this drought resistance were analyzed in this study by imposing progressive water stress to pot-grown plants under glasshouse conditions. Water withholding for 53 days decreased soil water gravimetric content and the leaf water potential. Plant growth was negatively and significantly reduced by increasing soil water deficits. With irrigation suspension, carbon assimilation and transpiration were reduced and remained mostly constant throughout the day. Analysis of A/Ci curves showed increased stomatal limitation, indicating that limitation imposed by stomatal closure is the main factor responsible for photosynthesis reduction. Carboxylation efficiency and electron transport rate were not affected by water stress up to 15 days after withholding water. Drought resistance of castor bean seems to be related to a pronounced, early growth response, an efficient stomatal control and the capacity to keep high net CO2 fixation rates under water stress conditions.

Phenolic compounds profiles during ex vitro acclimatization of micropropagated Hypericum polyanthemum.

Accumulation of benzopyrans and total phenolic compounds were assessed in acclimatized field grown plants of Hypericum polyanthemum, an endemic species of southern Brazil, harvested at different developmental stages. The HPLC analysis of bioactive compounds 6-isobutyryl-5,7-dimethoxy-2,2-dimethylbenzopyran (HP1), 7-hydroxy-6-isobutyryl-5-methoxy-2,2-dimethyl-benzopyran (HP2) and 5-hydroxy-6-isobutyryl-7-methoxy-2,2-dimethyl-benzopyran (HP3) revealed that the three benzopyrans are accumulated both in the vegetative and reproductive parts with maximum contents observed after 18 weeks (in the former) and 20 weeks (in the later) of plant growth (1.92+/-0.085 g % DW and 2.62+/-0.13 g % DW in the vegetative and reproductive parts, respectively). Highest contents of HP1 (1.56+/-0.12 g % DW) and HP2 (0.19+/-0.01 g % DW) were quantified in the green floral buds of the plants, whereas HP3 reached the highest level (1.02+/-0.08 g % DW) in the overblown flowers. The evaluation of total phenolic compounds showed that the vegetative parts accumulated the highest levels of the metabolites (51.93+/-0.67 mg QE (g DW)(-1)) after 16 weeks of plant growth. Considering the reproductive parts, the open flowers accumulated the greatest levels of the bioactive compounds (75.99+/-0.95 mg QE (g DW)(-1)). The results show that H. polyanthemum can be efficiently propagated and acclimatized to produce benzopyrans and other phenolic compounds.

Hypocotyl of seedlings of the large-seeded species Araucaria angustifolia: an important underground sink of the seed reserves

Araucaria angustifolia exhibits cryptogeal germination, where the root–hypocotyl axis emerges first and penetrates into the soil. In Araucaria bidwillii, the whole process of transferring reserves from the seed to the seedling takes place before shoot emergence, and there is a major storage of these reserves in the underground hypocotyl, which assumes a tuberous form. In A. angustifolia, the shoot emerges before seed reserves are depleted. Though it does not grow like a tuber, the hypocotyl of A. angustifolia grows thicker than the adjacent taproot during initial growth, and we hypothesize that it may act as a major sink for seed reserves during this stage. The study tests this hypothesis by evaluating changes in the mass of different plant parts during initial growth. Four harvests were conducted during a ~6-month period to compare the dry mass of different fractions (attached seed, seedling, its shoot and root and the hypocotyl) of seedlings growing under darkness and high light. While seed reserves were still being depleted, the hypocotyl mass showed an initial increase and then a reduction. This was more abrupt when light was available. After seed mass had stabilized, the mass of the hypocotyl continued to decrease in the dark-grown seedlings, but showed a second increase in the light-grown ones. Results confirm the hypothesis that the hypocotyl represents a major sink for the seed reserves of A. angustifolia, acting as an underground storage structure for the growing seedling. Its reserves seem to be important for sustaining initial shoot growth and might also act as a storage sink for photosynthates.

Phenolic compounds accumulation in Hypericum ternum propagated in vitro and during plant development acclimatization

The phenolic compound content of Hypericum ternum was investigated after micropropagation establishment and during acclimatization over the phenological development of the plant. Plantlets cultured in vitro on full Murashige and Skoog medium without growth regulators displayed higher phenolic compound yields, were acclimatized, and field grown. Production of total phenolic compounds as well as hyperoside, chlorogenic acid, quercitrin, guaijaverin, isoquercitrin, and uliginosin B were quantified at vegetative, flowering and fructification stages, and different plant organs (roots, stems, leaves and reproductive parts) showing that reproductive parts at flowering stage and the leaves at fructification stage were the main repository site of secondary metabolites, except for uliginosin B. The stems were the least accumulative organ, while the roots accumulated only hyperoside and uliginosin B. Moreover, the accumulation of most of the flavonoids and uliginosin B in acclimatized plants surpassed the levels found in the wild plant, warranting further research with the species.

Nitrogênio disponível ao milho: crescimento, absorção e rendimento de grãos

This work aimed to quantify the available nitrogen (N) to a maize crop and evaluate its effects on leaf area index (LAI), shoot dry matter (SDM) production, N absorption by the above ground biomass, and grain yield. The evaluations were performed in a soil management experiment run since 1985, with three cropping systems (oat - Avena strigosa/maize, oat + vetch - Vicia sativa/maize and oat + vetch/maize + cowpea - Vigna unguiculata) and two rates of nitrogen (0 and 180 kg ha-1) applied to maize. In the 2000/2001 cropping year, four nitrogen rates were applied (0, 60, 120 and 180 kg ha-1). The estimated available N to the maize calculated from the contribution from the soil, cover crops and N fertilizer varied from 27 to 192 kg ha-1. All evaluated variables presented high dependence on available N, and reached its maximum level near to the highest level of available N (192 kg ha-1). With this level of availability, at the stage of pollination, the largest values of LAI (4.41) and the highest leaf N concentration were observed, however, the highest N accumulation in the above ground biomass was observed at the milk grain stage and the shoot dry matter accumulation at the dent stage. The maximum grain yield obtained was 8,920 kg ha-1, corresponding to 112 kg ha-1 of exported N by the grain.

Identification and physiological characterization of two sister lines of indica rice (Oryza sativa L.) with contrasting levels of cold tolerance

Abstract Exposure to low temperature during germination and vegetative growth is a limiting factor to the establishment and development of rice seedlings. Higher cold tolerance of japonica than indica subspecies is well documented. However, reports of cold tolerance in indica genotypes are rare. We screened a large number of indica rice genotypes for cold tolerance during germination and initial vegetative growth. The indica genotypes IRGA 959-1-2-2F-4-1-4-A and IRGA 959-1-2-2F-4-1-4-D-1-CA-1, derived from the same cross, were characterized, respectively, as tolerant and sensitive to low temperature. Indexes of photosynthetic performance during light absorption were heavily affected by cold in both genotypes, but recovered after cold exposure only in the tolerant genotype. Activities of the antioxidant enzymes SOD and CAT (at the vegetative stage) and CAT and APX (at the germination stage) were higher in the tolerant than in the sensitive genotype. Expression of 20 genes previously related to cold response in rice was evaluated. Expression of OsLIP9 and OsWCOR413 were higher in the tolerant genotype upon or prior to cold exposure, respectively. The two sister lines show different molecular and physiological responses to low temperature stress. Further in-depth studies with these lines may help to identify new cold tolerance mechanisms in rice.

Clay content drives carbon stocks in soils under a plantation of Eucalyptus saligna Labill. in southern Brazil

Soil carbon accumulation is largely dependent on net primary productivity. To our knowledge, there have been no studies investigating the dynamics of carbon accumulation in weathered subtropical soils, especially in managed eucalyptus plantations. We quantified the seasonal input of leaf litter, the leaf decomposition rate and soil carbon stocks in an commercial plantation of Eucalyptus saligna Labill. in southern Brazil. Our goal was to evaluate, through multiple linear regression, the influence that certain chemical characteristics of litter, as well as chemical and physical characteristics of soil, have on carbon accumulation in soil organic matter fractions. Variables related to the chemical composition of litter were not associated with the soil carbon stock in the particulate and mineral fractions. However, certain soil characteristics were significantly associated with the carbon stock in both fractions. The concentrations of nutrients associated with plant growth and productivity, such as phosphorus, sulfur, copper and zinc, were associated with variations in the labile carbon pool (particulate fraction). Clay content was strongly associated with the carbon stock in the mineral fraction. The carbon accumulation and stabilization in weathered subtropical Ultisol seems to be mainly associated with the intrinsic characteristics of the soil, particularly clay content, rather than with the quantity, chemical composition or decomposition rate of the litter.

Heliotropism and water availability effects on flowering dynamics and seed production in Macroptilium lathyroides

The experiment was carried out in pots in a glasshouse, with one plant per pot and nine repetitions per treatment. The treatments consisted of free or restricted leaves, submited to 90-100% or 60-70% soil field capacity (FC). Only independent effects of water availability or leaf movement were observed on yield components. Plants under well-watered conditions and with freely orienting leaves were taller, and had a larger number of ramifications. The greater development favored the setting of a higher number of inflorescences per plant in these treatments. This behavior resulted in a high number of flowers, green and mature legumes per plant, thus resulting in high seed production which was the most evident response to water availability. Although individual seed weight was higher in the water stress treatment, total seed production was higher for well- watered plants, with no statistically significant effect of leaf movements. RESUMO - O experimento foi conduzido em casa de vegetacao, em vasos, com uma planta por vaso e nove repeticoes por tratamento. Os tratamentos constituiram: plantas com folhas livremente orientadas ou restritas, submetidas as condicoes hidricas de 90-100% e 60-70% da capacidade de campo. Foram observados efeitos independentes da disponibilidade hidrica e da movimentacao foliar para os componentes do rendimento de sementes ao longo do periodo experimental. Plantas submetidas a alta disponibilidade hidrica e com folhas livremente orientadas apresentaram maior numero de ramificacoes por planta. Este melhor desenvolvimento favoreceu a emissao de maior numero de inflorescencias por planta, proporcionando maior numero de flores, legumes verdes e legumes maduros por planta que, por sua vez, gerou maior producao diaria de sementes. Esta resposta foi evidenciada ao se avaliar o efeito da disponibilidade hidrica. Apesar da massa individual da semente ter apresentado valores superiores para o tratamento com restricao hidrica, a producao total de sementes foi superior no tratamento com alta disponibilidade hidrica, nao se observando efeito significativo para a movimentacao foliar.

Calibrated heat-pulse method for the assessment of maize water uptake

Plant water requirements are important aspects of crop production to be determined in the field, in order to judiciously manage crop water usage. Water uptake by field grown maize (Zea mays L.), under well-watered conditions was verified with the heat-pulse system. The temperature difference between two radially inserted thermocouples, one 9 mm above and the other 4 mm below a heater piercing the maize stem, was measured every 0.3 seconds following emission of a heat-pulse. Comparisons of the heat-pulse system outputs, lysimetric measurement and transpiration model estimates were monitored on an hourly and daily basis. At normal and low atmospheric demand daily and hourly values of heat-pulse outputs and lysimetric measurement showed good agreement. Hourly agreement of a modified Penman-Monteith energy balance equation estimate and heat-pulse outputs showed accordance between measurement of sap flow and the plant water-loss theory. Study of the relationship between maize canopy water loss rate and heat velocity in the stem showed that these two parameters were proportional and a calibration factor of 1.51 for full soil foliage coverage was verified.