Lignin is a heterogeneous aromatic polymer responsible for cell wall stiffness and protection from pathogen attack. However, lignin represents a bottleneck to biomass degradation due to its ...recalcitrance related to the natural cell wall resistance to release sugars for fermentation or further processing. A biological approach involving genetics and molecular biology was used to disrupt lignin pathway synthesis and decrease lignin deposition. Here, we imaged three-dimensional fragments of the petioles of wild type and C4H lignin mutant Arabidopsis thaliana plants by synchrotron cryo-ptychography. The three-dimensional images revealed the heterogeneity of vessels, parenchyma, and fibre cell wall morphologies, highlighting the relation between disturbed lignin deposition and vessel implosion (cell collapsing and obstruction of water flow). We introduce a new parameter to accurately define cell implosion conditions in plants, and we demonstrate how cryo-ptychographic X-ray computed tomography (cryo-PXCT) provides new insights for plant imaging in three dimensions to understand physiological processes.
The role of bundle sheath conductance (
g
bs
) in sustaining sugarcane photosynthesis under nitrogen deficiency was investigated. Sugarcane was grown under different levels of nitrogen supply and
g
...bs
was estimated using simultaneous measurements of leaf gas exchange and chlorophyll fluorescence at 21% or 2% O
2
and varying air CO
2
and light intensity. Maximum rates of PEPC carboxylation, Rubisco carboxylation, and ATP production increased with an increase in leaf nitrogen concentration (LNC) from 1 to 3 g m
−2
. Low nitrogen supply reduced Rubisco and PEPC abundancies, the quantum efficiency of CO
2
assimilation and
g
bs
. Because of reduced
g
bs
, low photosynthetic rates were not associated with increased leakiness under nitrogen deficiency. In fact, low nitrogen supply increased bundle sheath cell wall thickness, probably accounting for low
g
bs
and increased estimates of CO
2
at Rubisco sites. Effects of nitrogen on expression of
Sh
PIP2;1
and
Sh
PIP1;2
aquaporins did not explain changes in
g
bs
. Our data revealed that reduced Rubisco carboxylation was the main factor causing low sugarcane photosynthesis at low nitrogen supply, in contrast to the previous report on the importance of an impaired CO
2
concentration mechanism under N deficiency. Our findings suggest higher investment of nitrogen into Rubisco protein would favour photosynthesis and plant performance under low nitrogen availability.
In the xylem of angiosperm plants, microscopic pits through the secondary cell walls connect the water-conducting vessels. Cellulosic meshes originated from primary walls, and middle lamella between ...adjacent vessels, called the pit membrane, separates one conduit from another. The intricate structure of the nano-sized pores in pit membranes enables the passage of water under negative pressure without hydraulic failure due to obstruction by gas bubbles (i.e. embolism) under normal conditions or mild drought stress. Since the chemical composition of pit membranes affects embolism formation and bubble behavior, we directly measured pit membrane composition in Populus nigra wood. Here, we characterized the chemical composition of cell wall structures by synchrotron infrared nanospectroscopy and atomic force microscopy-infrared nanospectroscopy with high spatial resolution. Characteristic peaks of cellulose, phenolic compounds, and proteins were found in the intervessel pit membranes of P. nigra wood. In addition, the vessel to parenchyma pit membranes and developing cell walls of the vascular cambium showed clear signals of cellulose, proteins, and pectin. We did not find a distinct peak of lignin and other compounds in these structures. Our investigation of the complex chemical composition of intervessel pit membranes furthers our understanding of the flow of water and bubbles between neighboring conduits. The advances presented here pave the way for further label-free studies related to the nanochemistry of plant cell components.
This study investigated the effect of AgNPs and AgNO3, at concentrations equivalent, on the production of primary and secondary metabolites on transgenic soybean plants through an NMR-based ...metabolomics. The plants were cultivated in a germination chamber following three different treatments: T0 (addition of water), T1 (addition of AgNPs), and T2 (addition of AgNO3). Physiological characteristics, anatomical analyses through microscopic structures, and metabolic profile studies were carried out to establish the effect of abiotic stress on these parameters in soybean plants. Analysis of the 1H NMR spectra revealed the presence of amino acids, organic acids, sugars, and polyphenols. The metabolic profiles of plants with AgNP and AgNO3 were qualitatively similar to the metabolic profile of the control group, suggesting that the application of silver does not affect secondary metabolites. From the PCA, it was possible to differentiate the three treatments applied, mainly based on the content of fatty acids, pinitol, choline, and betaine.
Embolism resistance of xylem tissue varies among species and is an important trait related to drought resistance, with anatomical attributes like pit membrane thickness playing an important role in ...avoiding embolism spread. Grafted Citrus trees are commonly grown in orchards, with the rootstock being able to affect the drought resistance of the whole plant. Here, we evaluated how rootstocks affect the vulnerability to embolism resistance of the scion using several rootstock/scion combinations. Scions of ‘Tahiti’ acid lime, ‘Hamlin’, ‘Pera’ and ‘Valencia’ oranges grafted on a ‘Rangpur’ lime rootstock exhibit similar vulnerability to embolism. In field‐grown trees, measurements of leaf water potential did not suggest significant embolism formation during the dry season, while stomata of Citrus trees presented an isohydric response to declining water availability. When ‘Valencia’ orange scions were grafted on ‘Rangpur’ lime, ‘IAC 1710’ citrandarin, ‘Sunki Tropical’ mandarin or ‘Swingle’ citrumelo rootstocks, variation in intervessel pit membrane thickness of the scion was found. The ‘Rangpur’ lime rootstock, which is known for its drought resistance, induced thicker pit membranes in the scion, resulting in higher embolism resistance than the other rootstocks. Similarly, the rootstock ‘IAC 1710’ citrandarin generated increased embolism resistance of the scion, which is highly relevant for citriculture.
Summary statement
Different Citrus rootstocks influence scion vulnerability to embolism, with ‘Rangpur’ lime inducing less vulnerability and thicker pit membranes. Besides, in field‐grown trees, measurements of leaf water potential did not suggest significant embolism formation even during the dry season.
Campos rupestres is an extremely phosphorus (P)‐impoverished rocky ecosystem in Brazil. Velloziaceae is an important plant family in this environment, and some species colonize exposed quartzite ...rock. However, we know virtually nothing about their root development and nutrient acquisition within the rock outcrops and their possible role in rock weathering and landscape formation.
We tested the hypothesis that Velloziaceae dissolve P from the rock, enhancing rock weathering. The study was carried out with two Barbacenia species (Velloziaceae) that colonize quartzite rocks. We assessed the root specializations and exudates, and determined the mineralogical composition of the rocks.
The quartzite rocks contained a low concentration of total P in a matrix composed predominantly of silica. Using transmission electron microscopy, we show root growth perpendicular to the rock‐bedding planes. A micro‐XRF set‐up at the XRF beamline of a synchrotron evidenced root‐associated rock dissolution.
The investigated roots show novel morphological and physiological specializations, coined vellozioid roots, which are highly effective at P acquisition. These carboxylate‐releasing roots function like other specialized roots in nutrient‐depleted soils. The rocks represent a barrier for most species, but due to their chemical and physical actions inside the rocks, vellozioid roots play a pivotal role in rock weathering, contributing to shaping the campos rupestres landscapes.
A plain language summary is available for this article.
Plain Language Summary
Abstract The effect of environmental gradients on the remarkable diversity of mountain‐associated plants and on the species' abilities to cope with climate change transcends species‐specific ...strategies. For instance, our understanding of the impact of thermal gradients on ecological divergences in populations of widely distributed species is limited, although it could provide important insights regarding species' response to climate change. Here, we investigated whether populations of an endemic species broadly distributed across an elevation gradient employ unique or multiple divergent ecological strategies according to specific environmental conditions. We hypothesised that populations employ distinct strategies, producing a tolerance‐avoidance trade‐off related to the thermal conditions they experience across elevations. We conducted our research with 125 individuals of Pitcairnia flammea (Bromeliaceae) sampled from various elevations spanning from sea level to ~2200 m and cultivated under the same conditions. To assess specific ecological strategies of P. flammea populations across elevations, we examined leaf temperature, heat and cold tolerances, as well as other structural/morphological, optical, physiological and biochemical leaf traits. We majorly observed that water‐saving traits diminish as elevation increases while membrane fluidity, majorly associated with unsaturated and very‐long‐chain lipids, enhances. Low‐elevation individuals of P. flammea invest in water storage tissues, which likely prevent excessive water loss through the intense transpiration rates under warming periods. Conversely, high‐elevation plants exhibit increased membrane fluidity, a possible response to the stiffening induced by low temperature. Our results revealed a tolerance‐avoidance trade‐off related to thermal strategies of populations distributed across an elevation gradient. Low‐elevation plants avoid excessive leaf temperature by investing in water‐saving traits to maintain transpiration rates. High‐elevation individuals, in turn, tend to invest in membrane properties to tolerate thermal variations, particularly cold events. Our findings challenge the conventional notion that plants' vulnerability to warming depends on species‐specific thermal tolerance by showing diverse thermal strategies on populations across an elevation gradient. Read the free Plain Language Summary for this article on the Journal blog.
Resumo O efeito dos gradientes ambientais na grande diversidade de plantas associadas a montanhas transcende as estratégias específicas de cada espécie. Nosso entendimento sobre o impacto dos gradientes térmicos nas divergências ecológicas em populações de espécies amplamente distribuídas, por exemplo, é limitado, embora possa fornecer informações importantes sobre a resposta das espécies às mudanças climáticas. Aqui, investigamos se populações de uma espécie endêmica e amplamente distribuída em um gradiente altitudinal, empregam estratégias ecológicas únicas ou múltiplas de acordo com condições ambientais específicas. Nossa hipótese é que as populações empregam estratégias que resultam em um equilíbrio entre tolerância e evitação relacionado às condições térmicas que experimentam em diferentes altitudes. Analisamos 125 indivíduos de Pitcairnia flammea (Bromeliaceae) amostrados em diversas altitudes, desde o nível do mar até cerca de 2.200 metros, e cultivados nas mesmas condições. Para avaliar as estratégias ecológicas específicas das populações de P. flammea , examinamos temperatura foliar, tolerâncias ao calor e ao frio, além de outros traços foliares estruturais/morfológicos, óticos, fisiológicos e bioquímicos. Vimos que características de economia de água diminuem à medida que a altitude aumenta, enquanto a fluidez da membrana, associada principalmente a lipídios insaturados e de cadeia muito longa, aumenta. Indivíduos de baixa altitude investem em tecidos de armazenamento de água, provavelmente prevenindo a perda excessiva de água durante períodos de aquecimento e com taxas intensas de transpiração. Por outro lado, plantas de altas altitudes possuem maior fluidez de membrana, uma possível resposta ao enrijecimento induzido por baixas temperaturas. Nossos resultados revelaram um equilíbrio entre tolerância e evitação relacionado às estratégias térmicas de populações distribuídas ao longo de um gradiente de altitude. Plantas de baixa altitude evitam temperaturas foliares excessivas investindo em características de economia de água para manter as taxas de transpiração. Indivíduos de alta altitude, por sua vez, tendem a investir em membranas que toleram variações térmicas, especialmente eventos frios. Nossas descobertas desafiam a noção convencional de que a vulnerabilidade das plantas ao aquecimento depende da tolerância térmica específica da espécie, mostrando estratégias térmicas diversas em populações ao longo de um gradiente de altitude.
Sugarcane (Saccharum spp.) is currently one of the most efficient crops in the production of first-generation biofuels. However, the bagasse represents an additional abundant lignocellulosic resource ...that has the potential to increase the ethanol production per plant. To achieve a more efficient conversion of bagasse into ethanol, a better understanding of the main factors affecting biomass recalcitrance is needed. Because several studies have shown a negative effect of lignin on saccharification yield, the characterization of lignin biosynthesis, structure, and deposition in sugarcane is an important goal. Here, we present, to our knowledge, the first systematic study of lignin deposition during sugarcane stem development, using histological, biochemical, and transcriptional data derived from two sugarcane genotypes with contrasting lignin contents. Lignin amount and composition were determined in rind (outer) and pith (inner) tissues throughout stem development. In addition, the phenolic metabolome was analyzed by ultra-high-performance liquid chromatography-mass spectrometry, which allowed the identification of 35 compounds related to the phenylpropanoid pathway and monolignol biosynthesis. Furthermore, the Sugarcane EST Database was extensively surveyed to identify lignin biosynthetic gene homologs, and the expression of all identified genes during stem development was determined by quantitative reverse transcription-polymerase chain reaction. Our data provide, to our knowledge, the first in-depth characterization of lignin biosynthesis in sugarcane and form the baseline for the rational metabolic engineering of sugarcane feedstock for bioenergy purposes.
In 2015, Brazil faced the worst environmental disaster in its history, when the collapse of an iron ore dam dumped millions of tons of tailings into the Doce River. In this paper, we describe two
...Hippeastrum
species native to localities directly involved in the tragedy. The dam was located in the foothills of Serra do Caraça, a mountain range in the state of Minas Gerais, from where we describe the endemic
H.
carassense
;
H.
velloziflorum
was first found on an inselberg located on the banks of the Doce River, in the neighboring state of Espírito Santo. Comments on their distribution, ecology, and phenology are provided, as well as comparisons with the most similar taxa. The conservation status of the two new species is preliminarily assessed, and both are considered threatened with extinction. We also compared their leaf anatomy and micromorphology with related species of Amaryllidaceae. Based on nrDNA ITS, we infer the phylogenetic position of
H.
velloziflorum
, a taxon with several unique morphological characters for
Hippeastrum
, as the first branch in subgenus
Hippeastrum
. The placement of
H.
velloziflorum
in
Hippeastrum
is also supported by anatomical and cytological data. The somatic chromosome number was 2
n
= 22, and the karyotype formula was 2
n
= 8m + 12sm + 2st chromosome pairs. An identification key to the species of
Hippeastrum
occurring in the Doce and Jequitinhonha River basins is presented.
Dirigent (DIR) proteins, encoded by
DIR
genes, are referred to as “dirigent” because they direct the outcome of the coupling of the monolignol coniferyl alcohol into (+) or (−) pinoresinol, the first ...intermediates in the enantiocomplementary pathways for lignan biosynthesis. DIR domain-containing or DIR-like proteins are, thus, termed for not having a clear characterization. A transcriptome- and genome-wide survey of DIR domain-containing proteins in sugarcane was carried out, in addition to phylogenetic, physicochemical and transcriptional analyses. A total of 120 non-redundant sequences containing the DIR domain were identified and classified into 64 groups according to phylogenetic and sequence alignment analyses. In silico analysis of transcript abundance showed that these sequences are expressed at low levels in leaves and genes in the same phylogenetic clade have similar expression patterns. Expression analysis of
ShDIR1
-
like
transcripts in the culm internodes of sugarcane demonstrates their abundance in mature internodes, their induction by nitrogen fertilization and their predominant expression in cells that have a lignified secondary cell wall, such as vascular bundles of young internodes and parenchymal cells of the pith of mature internodes. Due to the lack of information about the functional role of DIR in plants, a possible relationship is discussed between the
ShDIR1
-
like
transcriptional profile and cell wall development in parenchyma cells of sugarcane culm, which typically accumulates large amounts of sucrose. The number of genes encoding the DIR domain-containing proteins in sugarcane is intriguing and is an indication per se that these proteins may have an important metabolic role and thus deserve to be better studied.
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