Planta

A cytokinin bioassay based on bud formation in 10-cell-long caulonema filaments of Funaria hygrometrica is described. The test has high specificity and sensitivity; is completed in 2 days; exhibits linearity between cytokinin concentration in the medium and bud number; and no buds are formed in the absence of a cytokinin.

Lipoxygenases (LOXs) are members of a large enzyme family that catalyze oxygenation of free polyunsaturated fatty acids into diverse hydroperoxide compounds, collectively called oxylipins. Although LOXs have been well studied in dicot species, reports of the genes encoding these enzymes are scarce for monocots, especially maize. Herein, we reported the cloning, characterization and molecular functional analysis of a novel maize LOX gene, ZmLOX6. The ZmLOX6 nucleotide sequence encodes a deduced translation product of 892 amino acids. Phylogenetic analysis showed that ZmLOX6 is distantly related to previously reported 9- or 13-LOXs from maize and other plant species, including rice and Arabidopsis. Although sequence prediction suggested cytoplasmic localization of this protein, ZmLOX6 protein has been reportedly isolated from mesophyll cell chloroplasts, emphasizing the unique features of this protein. Plastidial localization was confirmed by chloroplast uptake experiments with the in vitro translated protein. Analysis of recombinant protein revealed that ZmLOX6 has lost fatty acid hydroperoxide forming activity but 13-LOX-derived fatty acid hydroperoxides were cleaved into odd-chain ω-oxo fatty acids and as yet not identified C5-compound. In line with its reported abundance in mesophyll cells, ZmLOX6 was predominantly expressed in leaf tissue. Northern blot analysis demonstrated that ZmLOX6 was induced by jasmonic acid, but repressed by abscisic acid, salicylic acid and ethylene and was not responsive to wounding or insects. Further, this gene was strongly induced by the fungal pathogen Cochliobolus carbonum during compatible interactions, suggesting that ZmLOX6 may contribute to susceptibility to this pathogen. The potential involvement of ZmLOX6 in maize interactions with pathogens is discussed.

Kopyor and macapuno are two coconut mutants from Southeast Asia that are often described erroneously or interchangeably mismatched due to a lack of research, so future studies are encouraged. Coconut (Cocos nucifera L.; Arecaceae), a widely distributed plant with popular culinary applications, especially of the endosperm, has several nutritional and medicinal benefits. Two coconut mutants are widely recognized in Southeast Asia, namely kopyor and macapuno, specifically in Indonesia and Philippines, respectively. Kopyor coconut is known for its brittle solid endosperm while macapuno coconut is known for its gelatinous solid endosperm. Both mutant types have many other synonyms in other countries. Over many decades, the biology of macapuno coconut, including endosperm anatomy, histology, cytology, physiology, and genetics have been described, while kopyor coconut is still understudied. However, some literature and websites erroneously describe kopyor as macapuno coconut, or consider them interchangeably, which is an unintentional consequence of insufficient scientific research on these coconut mutants. Additionally, in Indonesia, there is another local mutant in Banten called wax coconut (“kelapa lilin”) that some researchers claim as the actual Indonesian macapuno coconut due to its strong resemblance to kopyor coconut. Unfortunately, wax coconut is not only understudied, it is rarely documented. Additional evidence of their differences, in terms of morphological, biochemical and genetic characteristics, is needed. Moreover, clear documentation will also be needed for a better comparison. Understanding the differences between kopyor and macapuno coconuts will not only help to further clarify their scientific description in the literature, but will also guide locals, researchers, and industries to characterize similar mutants, if found in specific regions, for future study and bioprospecting.

Osmotin is a pathogenesis-related protein exhibiting cryoprotective functions. Our aim was to understand whether it is involved in the cold acclimation of the olive tree (Olea europaea L.), a frost-sensitive species lacking dormancy. We exposed olive trees expressing tobacco osmotin gene under the 35S promoter (35S:osm) [in the same manner as wild type (wt) plants] to cold shocks in the presence/absence of cold acclimation, and monitored changes in programmed cell death (PCD), cytoskeleton, and calcium ([Ca2+]c) signalling. In the wt, osmotin was immunolocalized only in cold-acclimated plants, and in the tissues showing PCD. In the 35S:osm clones, the protein was detected also in the non-acclimated plants, and always in the tissues exhibiting PCD. In the non-acclimated wt protoplasts exposed to cold shock, a transient decrease in phallotoxin signal suggests a temporary disassembly of F-actin, a transient increase occurred instead in 35S:osm protoplasts exposed to the same shock. Transient increases in [Ca2+]c were observed only in the wt protoplasts. However, when F-actin was depolymerized by cytochalasin or latrunculin, and microtubules by colchicine, increase in [Ca2+]c also occurred in the 35S:osm protoplasts. Successive cold shocks caused transient rises in [Ca2+]c and transient decreases in the phallotoxin signal in wt protoplasts. No change occurred in [Ca2+]c occurred in the 35S:osm protoplasts. The phallotoxin signal transiently increased at the first shock, but did not change after the subsequent shocks, and an overall signal reduction occurred with shock repetition. Following acclimation, no cold shock-induced change in [Ca2+]c levels and F-actin signal occurred either in wt or 35S:osm protoplasts. The results show that osmotin is positively involved in the acclimation-related PCD, in blocking the cold-induced calcium signalling, and in affecting cytoskeleton in response to cold stimuli.

After pulse-labelling with [3H]nucleosides and [3H]orotic acid of freely suspended callus cells of Petroselinum sativum and tissue fragments of the liverwort Riella helicophylla, rapidly labelled low molecular weight components were detected among the total nucleic acids when these were extracted in the presence of Mg2+ and finally precipitated with alcohol. These highly labelled species could clearly be distinguished from the 5 S- and 4 S-RNA on the basis of their migration in agarose-polyacrylamide gels (2.4%) and their elution from Sephadex G-150 columns. No degradation was obtained with DNase and RNase. By using [14C]ATP as a marker it was found that the low molecular components consisted mainly of nucleoside triphosphates. Only small amounts of nucleoside diphosphates were detected, which were obviously formed by degradation of the former. Nucleic acid preparations free of nucleoside phosphates were obtained by using Mg-free extraction buffers containing EDTA.

Bei den beiden untersuchten Crassulaceen,Bryophyllum calycinum undBryophyllum daigremontianum, besteht zwischen Stärke- und Zymohexosenschwund einerseits und Zunahme an organischen Säuren und ausgeschiedenem Kohlendioxyd andererseits ein klarer bilanzmäßiger Zusammenhang. Die Muttersubstanzen der organischen Säuren (insbesondere Äpfel- und Zitronensäure) sind demnach gärfähige Zucker bzw. solche Polysaccharide, die fermentativ in Zymohexosen übergeführt werden können. Die strenge Übereinstimmung im Ablaufe der Vorgänge der Säureanhäufung und der Stärkehydrolyse führt uns zu der Hypothese, daß der Eintritt einer Stärkehydrolyse nicht nur in stofflicher, sondern auch in reaktionsmechanischer Hinsicht eine wesentliche Voraussetzung dafür darstellt, daß die Pflanze zur Deckung ihres Energiebedarfs den lukrative Säurestoffwechsel einzuschlagen vermag. Zu den vonBennet-Clark geäußerten Vorstellungen über den Säurestoffwechsel der Crassulaceen wird Stellung genommen.

Majority of differentially expressed miRNAs with functional attributes have been recruited independently and parallelly during allopolyploidy followed by the millennia of human selection of both domesticated G. hirsutum and G. barbadense. The genus Gossypium is a marvelous evolutionary model for studying allopolyploidy and morpho-evolution of long-spinnable fibers from the ancestral wild-fuzz. Many genes, transcription factors, and notably, the regulatory miRNAs essentially govern such remarkable modern fiber phenotypes. To comprehend the impact of allopolyploidy on the evolutionary selection of transcriptional dynamicity of key miRNAs, comparative transcriptome profiling of vegetative and fiber tissues of domesticated diploid G. arboreum (A2) and allopolyploid cotton species G. hirsutum (AD1), and G. barbadense (AD2) identified > 300 differentially expressed miRNAs (DEmiRs) within or between corresponding tissues of A2, AD1 and AD2 species. Up to 49% and 32% DEmiRs were up- and down-regulated at fiber initiation stage of AD1 and AD2 species, respectively, whereas 50% and 18% DEmiRs were up- and down-regulated at fiber elongation stage of both the allopolyploid species. Interestingly, A-subgenome-specific DEmiRs exhibit expression dominance in the allopolyploid genetic backgrounds. Comparative spatio-temporal expression analyses of AD1 and AD2 species discovered that a majority of DEmiRs were recruited independently under millennia of human selection during domestication. Functional annotations of these DEmiRs revealed selection of associated molecular functions such as hormone-signaling, calcium-signaling and reactive oxygen species (ROS) signaling during fiber initiation and elongation. To validate the functional attributes of annotated DEmiRs, we demonstrated for the first time that the target-mimicry-based constitutive diminution of auxin-signaling associated miR167 directly affected the differentiation of floral and fiber tissues of transgenic cotton. These results strongly suggested that the evolutionarily favored DEmiRs including miR167 were involved in the transcriptional regulation of numerous genes during cotton evolution for enhanced fiber-associated agronomic traits.

Arabidopsis thaliana plants grown from ethyl methane sulfonate-treated seeds were screened for so-called que mutants, which are affected in non-photochemical energy quenching. Based on video imaging of chlorophyll fluorescence an energy dissipation mutant, que1, was identified, isolated and characterized. Similar to the npq mutants, the que1 mutant showed a drastically reduced capacity for pH-dependent energy dissipation, qE, but without affecting the Δ pH-dependent conformational changes at 535 nm (ΔA 535), which have been supposed to be obligatorily correlated with qE and to reflect pH-regulated binding of zeaxanthin to the PsbS protein. Western blot and DNA sequence analysis revealed that neither a reduced expression of the PsbS protein nor a mutation in the PsbS gene was responsible for the missing qE in que1. Measurements of 9-aminoacridine fluorescence quenching showed that the acidification of the thylakoid lumen was also not affected in the mutant. Furthermore, que1 was able to convert violaxanthin to zeaxanthin. However, unusual characteristics of zeaxanthin formation in the mutant pointed at an altered availability of violaxanthin for de-epoxidation. This was further accompanied by a decrease of the photochemical quenching of chlorophyll fluorescence (qP), an increase of the portion of oxidized P700 and a reduction of the electron transport rate. These characteristics indicate changes in the organization of the thylakoid membrane that affect linear electron transport (but not lumen acidification) and the formation of energy dissipation in photosystem II. Preliminary genetic analysis revealed that the phenotype of que1 is related to two different mutations, mapped to the lower arms of chromosomes 1 and 4.

Levels of free tryptophan in the leaves, phloem and xylem saps of Ricinus communis L. were determined by colorimetric assay. Values of 0.38 μg ml-1 in root pressure sap and 96.0 μg ml-1 in phloem sap were recorded. Tryptophan levels were highest in mature and senescing leaves. Levels of indoleacetic acid (IAA) in the phloem sap and leaves were determined by gas chromatography—mass spectrometry using a deuterated internal standard. A mean value of 13.0 ng ml-1 was recorded in phloem sap. The distribution in the leaves showed an inverse relationship to that of tryptophan, being highest in young leaves.