Wounding and methyl jasmonate increase cyanogenic glucoside concentrations in Sorghum bicolor via upregulation of biosynthesis.

The cyanogenic glucoside, dhurrin, present in Sorghum bicolor is thought to have multiple functions, including in defence against herbivory. The hormone methyl jasmonate (MeJA) is also induced by herbivory and is key to instigating defence processes in plants. To investigate whether dhurrin is induced in response to herbivore attack and also to the associated presence of MeJA, sorghum plants were either wounded or exogenous MeJA was applied. We show that specific wounding (pin board and perforation) and the application of MeJA increases dhurrin concentration in leaves and sheath tissue 12 h after treatment. Quantitative PCR shows that the expression of two genes, SbCYP79A1 and SbUGT85B1, involved in the synthesis of dhurrin are significantly induced by exogenous MeJA and by wounding. Analysis of 2 kb of sequence upstream of the start codon of SbCYP79A1 identifies several cis-acting elements that have been linked to MeJA induction. A promoter deletion series, coupled to GFP, and transiently expressed in Nicotiana benthamiana suggests that there are potentially three sequence motifs (~-925 to -976) involved in the binding of transcription factors that result in increased expression of SbCYP79A1 and the synthesis of dhurrin in response to MeJA.

Dhurrin increases but does not mitigate oxidative stress in droughted Sorghum bicolor.

MAIN CONCLUSION: Droughted sorghum had higher concentrations of ROS in both wildtype and dhurrin-lacking mutants. Dhurrin increased in wildtype genotypes with drought. Dhurrin does not appear to mitigate oxidative stress in sorghum. Sorghum bicolor is tolerant of high temperatures and prolonged droughts. During droughts, concentrations of dhurrin, a cyanogenic glucoside, increase posing a risk to livestock of hydrogen cyanide poisoning. Dhurrin can also be recycled without the release of hydrogen cyanide presenting the possibility that it may have functions other than defence. It has been hypothesised that dhurrin may be able to mitigate oxidative stress by scavenging reactive oxygen species (ROS) during biosynthesis and recycling. To test this, we compared the growth and chemical composition of S. bicolor in total cyanide deficient sorghum mutants (tcd1) with wild-type plants that were either well-watered or left unwatered for 2 weeks. Plants from the adult cyanide deficient class of mutant (acdc1) were also included. Foliar dhurrin increased in response to drought in all lines except tcd1 and acdc1, but not in the roots or leaf sheaths. Foliar ROS concentration increased in drought-stressed plants in all genotypes. Phenolic concentrations were also measured but no differences were detected. The total amounts of dhurrin, ROS and phenolics on a whole plant basis were lower in droughted plants due to their smaller biomass, but there were no significant genotypic differences. Up until treatments began at the 3-leaf stage, tcd1 mutants grew more slowly than the other genotypes but after that they had higher relative growth rates, even when droughted. The findings presented here do not support the hypothesis that the increase in dhurrin commonly seen in drought-stressed sorghum plays a role in reducing oxidative stress by scavenging ROS.

Utilization of a high-throughput shoot imaging system to examine the dynamic phenotypic responses of a C4 cereal crop plant to nitrogen and water deficiency over time.

The use of high-throughput phenotyping systems and non-destructive imaging is widely regarded as a key technology allowing scientists and breeders to develop crops with the ability to perform well under diverse environmental conditions. However, many of these phenotyping studies have been optimized using the model plant Arabidopsis thaliana. In this study, The Plant Accelerator(®) at The University of Adelaide, Australia, was used to investigate the growth and phenotypic response of the important cereal crop, Sorghum bicolor L. Moench and related hybrids to water-limited conditions and different levels of fertilizer. Imaging in different spectral ranges was used to monitor plant composition, chlorophyll, and moisture content. Phenotypic image analysis accurately measured plant biomass. The data set obtained enabled the responses of the different sorghum varieties to the experimental treatments to be differentiated and modelled. Plant architectural instead of architecture elements were determined using imaging and found to correlate with an improved tolerance to stress, for example diurnal leaf curling and leaf area index. Analysis of colour images revealed that leaf 'greenness' correlated with foliar nitrogen and chlorophyll, while near infrared reflectance (NIR) analysis was a good predictor of water content and leaf thickness, and correlated with plant moisture content. It is shown that imaging sorghum using a high-throughput system can accurately identify and differentiate between growth and specific phenotypic traits. R scripts for robust, parsimonious models are provided to allow other users of phenomic imaging systems to extract useful data readily, and thus relieve a bottleneck in phenotypic screening of multiple genotypes of key crop plants.

Generative cells of Lilium longiflorum possess translatable mRNA and functional protein synthesis machinery.

Metabolic labelling with [35S]-methionine demonstrated that generative cells of Lilium longiflorum possess their own set of mRNA and are capable of synthesising proteins independently from the vegetative cell. The isolated generative cells synthesised ten proteins, of which six were unique to these specialised cells. Isolation of generative cells from pollen grains after [35S]-methionine labelling resulted in an identical protein profile, therefore the synthesis of these proteins was not due to isolation shock. Addition of cycloheximide, abolished TCA-precipitable counts, whilst actinomycin D had no qualitative effect on the observed protein profile, indicating active translation of pre-existing mRNAs by the generative cells.

Male gametes and fertilization in angiosperms.

Double fertilization appears to have evolved as a product of change directly related to an accelerated rate and timing of reproduction. In this review, the focus is on the angiosperm male gametophyte, where changes include a reduction in the number of mitoses, establishment of the male germ unit and involvement of both members of the pair of sperm cells in reproduction. The organization of the generative cell during mitosis indicates that there may be basic similarities between this process in plant and animal cells. The microtubular organization of generative cells alters after isoiation. However, mitosis in Allamanda, proceeds as usual during in vitro culture. The presence of actin microfilaments within generative cells has previously been shown in Rhododendron and here we provide further evidence that actin microfilaments are indeed present in generative cells. Two different kinds of intermediate-filament-like systems (IFS) are present in the generative cells of Allamanda: one in the cytoplasm and the other closely associated with the surface domain of chromosomes, both identified by the use of monoclonal antibodies. This is the first report of an IFS existing in the vegetative nucleus of pollen. Two alternate views have been proposed for the involvement of sperm cells in double fertilization of angiosperms. First, the chance hypothesis assumes that sperm fusions with the egg and central cell are random interactions. Second, the specific receptor hypothesis proposes that one of the pair of sperm (the true male gamete) is destined to fuse specifically with the egg. Support for this latter view has come from demonstrations of sperm cell dimorphism, both in size and content of mitochondria and plastids. The production of monoclonal antibodies which bind to surface domains on the reproductive cells of higher and lower plants, and specifically to the cytoplasm of generative and sperm cells also suggest that directed fertilization occurs. Recently, the existence of translatable mRNA pools within the generative and sperm cells indicates that, with the use of recent technological advances such as the polymerase chain reaction, the potential exists to identify male gamete-specific genes. Contents Summary 679 I. Introduction 680 III. A cell biological perspective 681 IV. Two hypotheses for double fertilization 687 V. Isolation of living sperm from flowering plants 687 VI. Sperm surface antigens of plants 688 VII. Molecular characterization 690 VIII. Conclusions 691 Acknowledgements 691 References 692.