Laurício Endres

microRNAs Associated with Drought Response in the Bioenergy Crop Sugarcane (Saccharum spp.)

Sugarcane (Saccharum spp.) is one of the most important crops in the world. Drought stress is a major abiotic stress factor that significantly reduces sugarcane yields. However the gene network that mediates plant responses to water stress remains largely unknown in several crop species. Although several microRNAs that mediate post-transcriptional regulation during water stress have been described in other species, the role of the sugarcane microRNAs during drought stress has not been studied. The objective of this work was to identify sugarcane miRNAs that are differentially expressed under drought stress and to correlate this expression with the behavior of two sugarcane cultivars with different drought tolerances. The sugarcane cultivars RB867515 (higher drought tolerance) and RB855536 (lower drought tolerance) were cultivated in a greenhouse for three months and then subjected to drought for 2, 4, 6 or 8 days. By deep sequencing of small RNAs, we were able to identify 18 miRNA families. Among all of the miRNAs thus identified, seven were differentially expressed during drought. Six of these miRNAs were differentially expressed at two days of stress, and five miRNAs were differentially expressed at four days. The expression levels of five miRNAs (ssp-miR164, ssp-miR394, ssp-miR397, ssp-miR399-seq 1 and miR528) were validated by RT-qPCR (quantitative reverse transcriptase PCR). Six precursors and the targets of the differentially expressed miRNA were predicted using an in silico approach and validated by RT-qPCR; many of these targets may play important roles in drought tolerance. These findings constitute a significant increase in the number of identified miRNAs in sugarcane and contribute to the elucidation of the complex regulatory network that is activated by drought stress.

Trocas gasosas e fluorescência da clorofila a em variedades de cana-de-açúcar submetidas à deficiência hídrica

Water stress affects a great part of the worlds agriculture. Thus, this work was conducted to evaluate photosynthetic traits in four varieties of sugarcane (SP79-1011, RB72454, RB98710 and RB92579) submitted to water stress during the early stage of the vegetative period. The plants were cultivated in plastic pots (15 kg of soil). The study was a factorial (4 varieties x 3 levels of soil water content based on available water capacity (AWC)), in a completely randomized design with 5 replications. The levels of water content in the soil were as follows: control (80 to 100% of AWC), moderate water stress (40 to 60% of AWC) and severe water stress (0 to 20% of AWC). Water stress provoked a significant reduction in stomatic condutance (gs), foliar transpiration (E), net photosynthesis (A) and in the water use efficiency of production (WUEy), irrespective of varieties. The varieties SP79-1011 and RB98710 showed greater stomatal sensitivity, reducing gs and E by the 71 days after the beginning of the water stress treatments, even in the control. However, under such conditions A was little affected, indicating that the plants are capable to fixing CO2 with stomata partially closed. Water stress caused a small reduction in the potential photochemical efficiency (Fv/Fm ratio) in the studied varieties.

Ammonium and urea as nitrogen sources for bromeliads

Summary Epiphytic bromeliads have no contact with the pedosphere, so they need to draw their nutrients from the atmosphere as well as from the host tree and animal debris. Terrestrial bromeliads, like Ananas comosus, generally depend on the soil as their main nutrient source. The aim of this study was to investigate and compare some aspects of the nitrogen metabolism of two bromeliads with different growth habits: Ananas comosus, a terrestrial bromeliad, and Vriesea gigantea, an epiphytic tank bromeliad. Nitrogen-starved plants were grown in vitro for 3, 7, 15, 30, and 60 days, either with 5 mmol L −1 ammonium [(NH 4 ) 2 SO 4 ] or urea as the sole nitrogen source. When NH 4 + was supplied to the plants, it stimulated a faster increase of chlorophyll content in A. comosus than in V. gigantea . In the presence of urea, after 15 days of the plants in culture, there was a significant increase in tissue free-NH 4 + and total amino acids for V. gigantea only. V. gigantea presented a higher level of total free amino acids than A. comosus when nitrogen was supplied to the plants. Asparagine was the main amino acid accumulated in both bromeliads when plants were transferred to the medium with nitrogen. When the ratio of the main individual free amino acids between the bromeliads grown in NH 4 + and urea was compared, values such as 7.2 for asparagine, 5.3 for glutamate, and 1.8 for aspartate in A. comosus, and values such as 2.3 for asparagine, 1.1 for glutamate and 0.7 for aspartate in V. gigantea were observed, demonstrating that the last is more efficient in assimilating urea. The results prompted us to support the idea that V. gigantea, an epiphytic tank bromeliad, is better adapted to absorb and assimilate organic nitrogen, such as urea, while A. comosus, a terrestrial plant, is better adapted to inorganic nitrogen forms, such as ammonium. The natural exposure of tank bromeliads to urea is discussed in the paper.

Relationships between endogenous hormonal levels and axillary bud development of Ananas comosus nodal segments

The effects of some endogenous hormones on the control of axillary bud development of pineapple Ananas comosus (L.) Merr. nodal segments cultivated in vitro were verified. Nodal segments with the apex (control) and decapitated nodal segments were used as explants and were cultured on hormone-free medium. Histological modifications occurring during the developmental process were also observed. Endogenous levels of indole-3-acetic acid (IAA) and four cytokinins (Cks) (isopentenyladenine (iP), isopentenyladenine 9-riboside (iPR), zeatin (Z) and zeatin riboside (ZR)) were quantified by means of high performance liquid chromatography (HPLC) and enzyme-linked immunosorbent assay (ELISA). During the first 4 h of culture, a marked reduction in the level of IAA (309%) of the decapitated nodal segment was detected and this coincided with the beginning of cell division in the leaf axil. Cks levels decreased during the first 12 h of culture in both explants. However, this reduction was 150% higher in the control, and occurred mainly due to a decrease in the level of ZR. The reduction in the level of IAA probably favored Cks biosynthesis and/or inhibited its degradation in the nodal tissue of the decapitated segment. After 16 h of culture, there was an increase in the level of IAA probably as a consequence of the establishment of the new auxin-producing shoot apex. After 1 d, a progressive increase in ZR occurred, suggesting that Z-type Cks have an important role in the leaf development of the new plant. Comparatively, auxin/total Cks ratio was always lower in the decapitated nodal segment throughout the process of the axillary bud development.

Photosynthesis and Water Relations in Brazilian Sugarcane

The expansion of sugarcane (Saccharum spp.) in Brazil has been boosted by the growing demand for bio-fuels all over the world and requires the occupation of new agricultural areas, including regions with unfavorable agro-climatic conditions. This observational study makes an analysis of the relationship between stomatal conductance, gas exchange and photosynthesis in sugarcane fields subject to different ambient conditions and growth phases. It was noted that the stomatal conductance had a much higher control on photosynthesis than on transpiration. Even under high stomatal con- ductance, photosynthesis maintained a high correlation to it. Sugarcane had an instantaneous water use efficiency of ap- proximately 4.4 μmol of fixed CO2 for each mmol of H20 expended in transpiration. Lower leaf water potential, besides leading to an internal reduction of CO2, also reduced the instantaneous carboxylation efficiency, indicating that the photo- synthesis apparatus was also affected. The variety RB92579, seems to have good water absorption system, because even under low leaf water potential, it maintained a good stomatal conductance, with a higher transpiration and photosynthesis than the others varieties. These results suggest that this variety has a tolerance mechanism to endure rather than avoid drought.

Environmental influence on the physico-chemical and physiological properties of Jatropha curcas seeds

The present study investigated the influence of two Brazilian environments on the physico-chemical and physiological properties of Jatropha curcas L. (physic nut) – an oilseed plant of great potential in biodiesel production. Fruits and seeds of plants grown in the Brazilian Atlantic rainforest (AF) and in the semiarid climate of Caatinga (SA) were compared. Fruits from the SA were longer, wider and heavier than those from the AF. In contrast, the AF seeds were larger and heavier than the SA seeds. Soluble sugars, protein, relative water content and electrical conductivity of the SA seeds significantly exceeded that of the AF seeds by 28%, 23%, 32% and 94%, respectively. Seeds of the AF had a significantly greater percentage germination (17.5%) and needed less time to germinate (10%) than did the SA seeds. Shoot dry biomass of seedlings grown from the AF seeds significantly exceeded that of the SA by 18.5%. Results suggest this pattern may be due to the higher carbon storage (i.e. sugars, proteins and oil) in the AF than SA seeds. Further studies are warranted to verify whether the differences observed between the seed sources investigated in the present study could be due to varietal or biotype factors.

Gas exchange alteration caused by water deficit during the bean reproductive stage

Neste trabalho, se analisaram as trocas gasosas das folhas e parâmetros de produtividade de feijao (Phaseolus vulgaris, L.) submetido a dois periodos de deficiencia hidrica e se empregaram tres regimes hidricos, a saber: W1 (1,0 ETo durante todo o ciclo da cultura); W2 (1,0 ETo ate a floracao e suspensao da irrigacao do 37 ao 51o dia apos a semeadura (DAS), correspondendo a fase de floracao) e W3 (alem da fase reprodutiva tambem se aplicou um deficit hidrico durante a fase vegetativa). A fotossintese foi um dos principais fatores fisiologicos afetados pelo deficit hidrico devido nao so ao fechamento estomatico, mas, tambem, a reducao da eficiencia de carboxilacao, resultante de um dano metabolico; este efeito, contudo, foi neutralizado 24 h apos reidratacao. Durante a floracao o deficit hidrico causou reducao sensivel da produtividade da cultura, com reducao tambem do numero de vagens e numero de sementes por vagem, independentemente do deficit durante a fase vegetativa, porem a massa de 100 sementes nao se alterou em nenhum dos regimes; esses resultados sugerem que o deficit hidrico leva a uma reducao dos fotoassimilados prejudicando a producao final; no entanto, uma vez formada, a semente se desenvolve plenamente, sendo esta uma estrategia da planta em produzir poucas sementes, mas viaveis para perpetuar a especie, mesmo sob condicoes de estresse.

Alteration of Hormonal Levels in a Rootless Epiphytic Bromeliad in Different Phenological Phases.

Abstract. Major changes in indole-3-acetic acid (IAA) and cytokinin (CK) levels occur at different phenological phases of Tillandsia recurvata shoots. This epiphytic rootless bromeliad was chosen as suitable material for hormonal analysis because CK synthesis is restricted to the shoots, thus avoiding problems in the interpretation of results caused by translocation and interconversion of CK forms between roots and leaves encountered in plants with both organs. Young plants of T. recurvata have weak apical dominance because side shoots appeared early in development, and branch growth was correlated with a strong increase in the level of zeatin. The flowering phase was characterized by a significant increase in free base CKs, zeatin, and isopentenyladenine compared with the levels found in adult vegetative shoots. In contrast, both free-base CKs declined in the fruiting phenological phase, and the IAA level increased dramatically. It was concluded that in phases characterized by intense organ formation, such as in the juvenile and flowering stages, there was an enhancement of CK content, mainly caused by zeatin, leading to a lower IAA/CK ratio. Higher ratios were correlated with phases that showed no organogenesis, such as adult and fruiting phenologies.

In vitro nitrogen nutrition and hormonal pattern in bromeliads

SummaryFour cytokinins (CKs), indole-3-acetic acid (IAA) and its ester and amino conjugates, and abscisic acid (ABA) levels of two bromeliads, Ananas comosus (L.) Merril and Vriesea gigantea Gaudich., grown in 5 mM (NH4)2SO4 or urea as the sole nitrogen (N) form, were investigated. In both bromeliads, zeatin (Z) and zeatin riboside ([9R]Z) were the most abundant CKs. In A. comosus, CKs levels decreased drastically (≊ 12 times) after 7 and 30 d in media with ammonium and urea, respectively. After 3 d in media with N, V. gigantea CK levels decreased 30 and 20 times in the presence of ammonium and urea, respectively. N-starved A. comosus and V. gigantea exhibited similar ABA levels, but ABA decreased faster in V. gigantea when plants were transferred to media with N. Free IAA levels decreased until the 15th and 30th day when A. comosus was transferred to a medium with ammonium and urea, respectively. N-starved A. comosus amide, ester, and free IAA amounted to 81%, 14%, and 4%, respectively. There was a transient increase in the proportion of amide IAA and a corresponding decrease of the ester and the free IAA proportion when N-starved plants were transferred to media with N. The relationship between the internal hormonal patterns and the different ecological adaptations of the two bromeliads are discussed.

Sugars levels of four sugarcane genotypes in different stem portions during the maturation phase

Maturation is a characteristic of sugarcane plant (Saccharum spp.) and even when grown under the same soil and climate conditions the varieties differ on the maturation curve. Thus, studies that allow establishing maturation curves of different sugarcane genotypes in the local soil and climate may indicate the proper harvesting period to ensure better quality of the raw material. This study aimed to analyze the levels of soluble sugars during the maturation phase and assess the technological and productivity indexes of four irrigated sugarcane genotypes in the region of Rio Largo, Alagoas. The experiment was conducted in randomized blocks in a 4 x 2 x 5 factorial: four genotypes (RB92579, RB98710, RB99395 and RB961003), two stem portions (internodes 1-4 and internodes 5-8) and five seasons (82, 49, 25, 13 and 3 days before harvesting), each treatment with three replications. Internodes 1-4 showed the highest levels of reducing sugars, while the largest accumulation of sucrose and total soluble solids occurred in internodes 5-8. RB99395 genotype showed more stability in the sugar levels during sugarcane maturation, which can indicate early maturation and high agricultural yield.