Metabolic control of seed germination in legumes

Seed development, dormancy, and germination are connected with changes in metabolite levels. Not surprisingly, a complex regulatory network modulates biosynthesis and accumulation of storage products. Seed development has been studied profusely in Arabidopsis thaliana and has provided valuable insights into the genetic control of embryo development. However, not every inference applies to crop legumes, as these have been domesticated and selected for high seed yield and specific metabolic profiles and fluxes. Given its enormous economic relevance, considerable work has contributed to shed light on the mechanisms that control legume seed growth and germination. Here, we summarize recent progress in the understanding of regulatory networks that coordinate seed metabolism and development in legumes.

Implications of cell wall immunocytochemical profiles on the structural and functional traits of root and stem galls induced by Eriosoma lanigerum on Malus domestica

Alterations in cell wall composition imply in new structural and functional traits in gall developmental sites, even when the inducer is a sucking exophytophagous insect with strict feeding sites as the aphid associated to Malus domestica Borkh. This host plant is an economically important, fruit-bearing species, susceptible to gall induction by the sucking aphid Eriosoma lanigerum Hausmann, 1802. Herein, the immunocytochemical detection of arabinogalactan-proteins (AGPs), pectins, and hemicelluloses using monoclonal antibodies was performed in samples of non-galled roots and stems, and of root and stem galls on M. domestica. The dynamics of these cell wall components was discussed under the structural and functional traits of the galls proximal, median, and distal regions, according to the proximity of E. lanigerum colony feeding site. In the proximal region, the epitopes of AGPs and homogalacturonans (HGs) are related to cell growth and divisions, which result in the overproduction of parenchyma cells both in root and stem galls. In the proximal and median regions, the co-occurrence of HGs and arabinans in the cell walls of parenchyma and secondary tissues favors the nutrient flow and water-holding capacity, while the xylogalacturonans and hemicelluloses may function as additional carbohydrate resources to E. lanigerum. The immunocytochemical profile of the cell walls support the feeding activity of E. lanigerum mainly in the gall proximal region. The similarity of the cell wall components of the gall distal region and the non-galled portions, both in roots and stems, relates to the decrease of the cecidogenetic field the more distant the E. lanigerum colony is.

Dynamic shifts in primary metabolism across fruit development stages in Capsicum chinense (cv. Habanero)

The development of fleshy fruits involves changes in size and mass, followed by cell differentiation, which is associated with anatomical and histological changes. Parallel to these changes, metabolic alterations lead to the production of osmolytes and energy that modify cell turgor pressure, thereby promoting cell expansion and fruit growth. Detailed information is known about these processes in climacteric fruits (e.g. tomato); however, the regulation of metabolism and its association with anatomical changes in non-climacteric fruit development are poorly understood. In this study, we used detailed anatomical and histological analyses to define three developmental phases of chili pepper (Capsicum chinense cv. Habanero): cell division, cell expansion, and ripening. We showed that each was marked by distinct metabolic profiles, underpinning the switches in energy metabolism to support cellular processes. Interestingly, mitochondrial activity was high in the early stages of development and declined over time, with a modest increase in O2 consumption by pericarp tissues at the beginning of the ripening stage. This respiratory-like burst was associated with the degradation of starch and malate, which are the sources of energy and carbon required for other processes associated with fruit maturation.

Tree Species and Morphology of Holes Caused by Black-Tufted Marmosets to Obtain Exudates: Some Implications for the Exudativory

Knowledge of the pattern of exploitation of trees can help us understand the relationship between marmosets and plants, especially in declining forests, such as those in the Brazilian Cerrado. Black-tufted marmosets (Callithrix penicillata) regularly exploit exudates by gouging the bark of trees with their specialized teeth. Determining preferred tree species to exploit exudates is important for forest management aimed at maintaining an essential food source for urban marmosets. We characterized the tree species, dendrometry, and the characteristics of the holes made by marmosets to obtain exudates. Based on these data, we proposed a gouging effort index (Chiseling Suitability Index for Marmosets, ChiSI). We identified 16 species belonging to 10 families of trees with gouging marks made by marmosets. Eleven new tree species used by black-tufted marmosets for exudates were identified in urban forests in the Cerrado. Exudate exploration was predominantly of medium intensity, with round holes concentrated in the canopy. The species Tapirira guianensis and Croton urucarana were preferred. The ChiSI was characterized by a narrow range for both T. guianensis and C. urucarana. Despite the flexibility of obtaining exudates, the black-tufted marmosets concentrate their exploitation to only a few tree species. The T. guianensis and C. urucarana tree species should be considered the most important species for management plans and the preservation of black-tufted marmosets that live in urban forests in the Cerrado.

Sugar metabolism and developmental stages of rubber tree (Hevea brasiliensis L.) seeds

Changes in the concentration of sugars and sucrose metabolism enzymes can characterize the developmental stages of a seed. In recalcitrant species such as Hevea brasiliensis L., little is known about these changes. We aimed to evaluate the three main stages of development of rubber tree seeds - histodifferentiation, cell elongation and accumulation of reserves. The activities of acid and neutral invertases (E.C. 3.2.1.26) and sucrose synthase (EC 2.4.1.13), and the concentrations of reducing sugars (RS), total soluble sugars (TSS) and sucrose (Suc) were determined concomitantly with the histochemical and anatomical evaluation of seed structure. Histodifferentiation in rubber tree seeds occurs up to 75 days after anthesis (DAA). The concentration of RS is high and of Suc is low during seed histodifferentiation, which occurs along with a visible increase in the number of cell divisions. After that period, there is an increase in the concentration of Suc (mg g^-1 ) and in the number and size of starch granules, and a decrease in the concentration of RS (mg g^-1 ). At that point, cell elongation occurs. At 135 DAA, there is an inversion in the concentration of these two sugars and an increase in reserve accumulation. Thus, in seeds of the evaluated clone, the period up to 75 DAA is characterized as the histodifferentiation stage, while from that time up to 120 DAA the cell elongation stage takes place. The final stage of seed maturation and reserve accumulation begins at 135 DAA, and the seed, including the embryo, is completely formed at 175 DAA.

Feeding habits of marmosets: A case study of bark anatomy and chemical composition of Anadenanthera peregrina gum

Primates of the genus Callithrix often obtain exudates from plants of the family Fabaceae. This study characterizes the chemical composition of exudates, and the anatomy and hystochemistry of the secretory ducts in the bark of Anadenanthera peregrina (L.) Speg. var. peregrina (Fabaceae). Exudates from this tree species represent an important component of the diet of hybrid marmosets, Callithrix spp. (Primates: Cebidae). A. peregrina was selected as the focal study tree because it is the only gum tree species exploited by Callithrix groups present within five urban forest fragments in the municipality of Viçosa, Minas Gerais State, Brazil. Gum samples were obtained directly from gouges made by the marmosets, while bark samples were obtained from A. peregrina plants, whether or not they were damaged by the marmosets. Constitutive secretory ducts were present in the bark of ungouged A. peregrina, whereas, marmoset damage caused induced secretory duct formation and an increase in the size of these ducts. The gum produced in the gouges made by the marmosets and in ungouged plants reacted positively to tests for polysaccharides, pectin, mucilage, and proteins. The gum from the gouges exhibited high water (41.0%), carbohydrate (38.2%), protein (19.0%), and mineral (Ca 0.4% and K 0.3%) content. We argue that the relatively high calcium content of A. peregrina gum plays an important nutritional role in, balancing a diet that is otherwise rich in phosphorous and poor in calcium.

The Stress-Induced Soybean NAC Transcription Factor GmNAC81 Plays a Positive Role in Developmentally Programmed Leaf Senescence

The onset of leaf senescence is a highly regulated developmental change that is controlled by both genetics and the environment. Senescence is triggered by massive transcriptional reprogramming, but functional information about its underlying regulatory mechanisms is limited. In the current investigation, we performed a functional analysis of the soybean (Glycine max) osmotic stress- and endoplasmic reticulum (ER) stress-induced NAC transcription factor GmNAC81 during natural leaf senescence using overexpression studies and reverse genetics. GmNAC81-overexpressing lines displayed accelerated flowering and leaf senescence but otherwise developed normally. The precocious leaf senescence of GmNAC81-overexpressing lines was associated with greater Chl loss, faster photosynthetic decay and higher expression of hydrolytic enzyme-encoding GmNAC81 target genes, including the vacuolar processing enzyme (VPE), an executioner of vacuole-triggered programmed cell death (PCD). Conversely, virus-induced gene silencing-mediated silencing of GmNAC81 delayed leaf senescence and was associated with reductions in Chl loss, lipid peroxidation and the expression of GmNAC81 direct targets. Promoter-reporter studies revealed that the expression pattern of GmNAC81 was associated with senescence in soybean leaves. Our data indicate that GmNAC81 is a positive regulator of age-dependent senescence and may integrate osmotic stress- and ER stress-induced PCD responses with natural leaf senescence through the GmNAC81/VPE regulatory circuit.

A priori choice of hybrid parents in plants

Plant breeding deals with high-yielding genotypes. However, how best to choose parents of these genotypes remains an unsolved question. Here, we focus on a priori choice based on parental distances by means of agronomic and molecular data. Despite numerous theoretical and empirical studies, a priori choice continues to be a controversial procedure. Both success and failure are commonly reported. We looked at these ambiguous results in order to investigate their possible causes. A total of 139 articles on genetic divergence were sampled to examine aspects such as type and number of markers utilized. We suggest that the mean number of 160, 281 and 25 for RAPD and RFLP markers, and SSR loci, respectively, which we found in these papers, should be increased for accurate analysis. A second sample composed of 54 articles was used to evaluate the divergence-heterosis association. Most of them (28) detected positive divergence-heterosis association, whereas 26 revealed negative or inconclusive results. We examined several causes that influence a priori choice positively and negatively.