Summary Dispersal is a key step in land plant life cycles, usually via formation of spores or seeds. Regulation of spore‐ or seed‐germination allows control over the timing of transition from one generation to the next, enabling plant dispersal. A combination of environmental and genetic factors determines when seed germination occurs. Endogenous hormones mediate this decision in response to the environment. Less is known about how spore germination is controlled in earlier‐evolving nonseed plants.Here, we present an in‐depth analysis of the environmental and hormonal regulation of spore germination in the model bryophyte Physcomitrella patens (Aphanoregma patens).Our data suggest that the environmental signals regulating germination are conserved, but also that downstream hormone integration pathways mediating these responses in seeds were acquired after the evolution of the bryophyte lineage. Moreover, the role of abscisic acid and diterpenes (gibberellins) in germination assumed much greater importance as land plant evolution progressed.We conclude that the endogenous hormone signalling networks mediating germination in response to the environment may have evolved independently in spores and seeds. This paves the way for future research about how the mechanisms of plant dispersal on land evolved.
Plant root system plasticity is critical for survival in changing environmental conditions. One important aspect of root architecture is lateral root development, a complex process regulated by hormone, environmental and protein signalling pathways.Here we show, using molecular genetic approaches, that the MYB transcription factor AtMYB93 is a novel negative regulator of lateral root development in Arabidopsis.We identify AtMYB93 as an interaction partner of the lateral-root-promoting ARABIDILLO proteins. Atmyb93 mutants have faster lateral root developmental progression and enhanced lateral root densities, while AtMYB93-overexpressing lines display the opposite phenotype. AtMYB93 is expressed strongly, specifically and transiently in the endodermal cells overlying early lateral root primordia and is additionally induced by auxin in the basal meristem of the primary root. Furthermore, Atmyb93 mutant lateral root development is insensitive to auxin, indicating that AtMYB93 is required for normal auxin responses during lateral root development.We propose that AtMYB93 is part of a novel auxin-induced negative feedback loop stimulated in a select few endodermal cells early during lateral root development, ensuring that lateral roots only develop when absolutely required. Putative AtMYB93 homologues are detected throughout flowering plants and represent promising targets for manipulating root systems in diverse crop species.
Cotton fiber is a specialized unicellular structure useful for the study of cellular differentiation and development. Heat shock proteins (HSPs) have been shown to be involved in various developmental processes. Microarray data analysis of five Gossypium hirsutum genotypes revealed high transcript levels of GhHSP90 and GhHSP70 genes at different stages of fiber development, indicating their importance in the process. Further, we identified 26 and 55 members of HSP90 and HSP70 gene families in G. hirsutum. The treatment of specific inhibitors novobiocin (Nov; HSP90) and pifithrin/2-phenylethynesulfonamide (Pif; HSP70) in in-vitro cultured ovules resulted in a fewer number of fiber initials and retardation in fiber elongation. The molecular chaperone assay using bacterially expressed recombinant GhHSP90-7 and GhHSP70-8 proteins further confirmed the specificity of inhibitors. HSP inhibition disturbs the H2O2 balance that leads to the generation of oxidative stress, which consequently results in autophagy in the epidermal layer of the cotton ovule. Transmission electron microscopy (TEM) of inhibitor-treated ovule also corroborates autophagosome formation along with disrupted mitochondrial cristae. The perturbations in transcript profile of HSP inhibited ovules show differential regulation of different stress and fiber development-related genes and pathways. Altogether, our results indicate that HSP90 and HSP70 families play a crucial role in cotton fiber differentiation and development by maintaining cellular homeostasis.
Summary Armadillo‐related proteins regulate development throughout eukaryotic kingdoms. In the flowering plant Arabidopsis thaliana, Armadillo‐related ARABIDILLO proteins promote multicellular root branching. ARABIDILLO homologues exist throughout land plants, including early‐diverging species lacking true roots, suggesting that early‐evolving ARABIDILLOs had additional biological roles.Here we investigated, using molecular genetics, the conservation and diversification of ARABIDILLO protein function in plants separated by c. 450 million years of evolution.We demonstrate that ARABIDILLO homologues in the moss Physcomitrella patens regulate a previously undiscovered inhibitory effect of abscisic acid (ABA) on spore germination. Furthermore, we show that A. thaliana ARABIDILLOs function similarly during seed germination. Early‐diverging ARABIDILLO homologues from both P. patens and the lycophyte Selaginella moellendorffii can substitute for ARABIDILLO function during A. thaliana root development and seed germination.We conclude that (1) ABA was co‐opted early in plant evolution to regulate functionally analogous processes in spore‐ and seed‐producing plants and (2) plant ARABIDILLO germination functions were co‐opted early into both gametophyte and sporophyte, with a specific rooting function evolving later in the land plant lineage.
Honey, being a natural product manufactured by honey bees is considered to be free from any extraneous material. The over-reliance on pesticides caused several environmental problems including pesticide residues in food. This constitutes a potential risk for human health, because of their sub acute and chronic toxicity. Therefore this study was carried out to know the extent of pesticide residue in honey produced in the various parts of Himachal Pradesh. Among different pesticides analysed in honey; HCH and its isomers were the most frequently detected followed by DDT and its isomers. Of the studied synthetic pyrethroids, only cypermethrin was found in honey samples. Residues of organophosphates viz. acephate, chlorpyriphos, ethion and monocrotophos were not detected, however malathion's residue was found exceeding the MRL (5 ppb) proposed by the Ministry of Commerce, Government of India. More over honey from natural vegetation contained lesser residues. It can be concluded that honey from Himachal Pradesh had low pesticide residues.
Naturally occurring autopolyploid species, such as the autotetraploid potato Solanum tuberosum, face a variety of challenges during meiosis. These include proper pairing, recombination and correct segregation of multiple homologous chromosomes, which can form complex multivalent configurations at metaphase I, and in turn alter allelic segregation ratios through double reduction. Here, we present a reference map of meiotic stages in diploid and tetraploid S. tuberosum using fluorescence in situ hybridisation (FISH) to differentiate individual meiotic chromosomes 1 and 2. A diploid-like behaviour at metaphase I involving bivalent configurations was predominant in all three tetraploid varieties. The crossover frequency per bivalent was significantly reduced in the tetraploids compared with a diploid variety, which likely indicates meiotic adaptation to the autotetraploid state. Nevertheless, bivalents were accompanied by a substantial frequency of multivalents, which varied by variety and by chromosome (7–48%). We identified possible sites of synaptic partner switching, leading to multivalent formation, and found potential defects in the polymerisation and/or maintenance of the synaptonemal complex in tetraploids. These findings demonstrate the rise of S. tuberosum as a model for autotetraploid meiotic recombination research and highlight constraints on meiotic chromosome configurations and chiasma frequencies as an important feature of an evolved autotetraploid meiosis.
Residues dynamics of Endosulfan (525.00 g a.i. ha(-1)), Imidacloprid seed treatment (21 g a.i. kg(-1)), Lambdacyhalothrin (75.00 g a.i. ha(-1)) and Spiromesifen (225.00 g a.i. ha(-1)) in nectar and pollen of mustard, Brassica juncea (L.) Czern. grown in Himachal Pradesh (India) were determined through bioassay (using Drosophila melanogaster Meig. as test organism) and GC (Gas chromatographic) and HPLC (High performance liquid chromatographic) methods. In general chromatographic methods were more sensitive for the determination of above given pesticides compared to bioassay method. Average recoveries in nectar samples varied between 82.85 and 88.90% by bioassay and 91.20 and 93.55% by chromatographic techniques. In pollen samples, recoveries varied between 81.44 and 86.44% by bioassay and 88.50 and 91.30% by chromatographic methods. Imidacloprid residues were neither found in nectar nor in pollen samples at the time of sampling i.e. 50% of flowering. The order of average half life of residues was: Lambdacyhalothrin (12.45 h) < Spiromesifen (19.99 h) < Endosulfan (27.49 h) for nectar and Spiromesifen (9.69 h) < Lambdacyhalothrin (12.44 h) < Endosulfan (17.84 h) for pollen samples. It was found that Imidcloprid seed treatment was practically harmless to honey bees, whereas a waiting period of 5 days must be observed on crops sprayed with these chemicals during blooms to avoid any accidental hazards to honey bees.
A granulosis virus strain infecting Pieris brassicae (PbGV) was isolated from the dry temperate region of northwestern Himalayas as a potential microbial agent for its management. The effect of different botanicals (having insecticidal action against P. brassicae) on the bioefficacy of PbGV was evaluated under laboratory conditions using leaf disc bioassays on cabbage for improving the insecticidal performance of the PbGV. The synergistic action of different botanical extracts was evident in terms of reduction in LC 50 values against different botanical extracts. Among different extracts, petroleum-ether extract of neem seed kernel (NSK) when combined with PbGV resulted in maximum reduction of LC 50 value (4.39×10 2 occlusion bodies [OBs] ml −1 ) followed by methanolic extract (7.38×10 2 OBs ml −1 ) and aqueous extract (9.36×10 3 OBs ml −1 ) as compared with PbGV alone (1.85×10 4 OBs ml −1 ) for 2nd instar larvae of the test insect. These trends were found analogous in cases of 3rd and 4th instars of P. brassicae with different solvent extracts of NSK. The other botanicals evaluated, viz., Eupatorium and Artemesia, also resulted in reduction of LC 50 values for 2nd, 3rd and 4th instars as compared with PbGV alone when different extracts were combined with virus for bioassays. The studies suggest that the PbGV in combination with botanical pesticides could be more useful as a bio-pesticide against cabbage butterfly (P. brassicae) in IPM programs.
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