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1.  Effect of external stress on density and size of glandular trichomes in full-grown Artemisia annua, the source of anti-malarial artemisinin 
AoB Plants  2012;2012:pls018.
The experiments demonstrate that stress treatments to large Artemisia annua plants have a minor promoting effect on the initiation of glandular trichomes in developing leaves, and a maturing effect on glandular trichomes later in the life time of the individual trichome.
Background and aims
Glandular trichomes (GT) of Artemisia annua produce valuable compounds for pharmaceutical and industrial uses, most notably the anti-malarial artemisinin. Our aim was to find out whether the density, number and size of GT can be manipulated to advantage by environmental stress. A range of external stress treatments, including stress response regulators, was therefore given to fully grown plants under field and greenhouse conditions.
In a field experiment (Ex1), seed-grown plants were subjected to chemical or physical stress and plants analysed after 5 weeks. In a greenhouse experiment (Ex2), three groups of clonally derived plants were stressed at weekly intervals for 5 weeks. Stress treatments included sandblasting, leaf cutting and spraying with jasmonic acid, salicylic acid, chitosan oligosaccharide (COS), H2O2 (HP) and NaCl (SC)at different concentrations. Leaves from an upper and a lower position on the plants were analysed by fluorescence microscopy to determine the density and size of GT.
Principal results
Densities of GT on upper leaves of full-grown A. annua plants generally showed no response to external stress and only plants from one clone of Ex2 supported the hypothesis that increased density of GT was inducible in upper leaves by stress (significant for SC, HP and COS). The density of GT on lower leaves was not affected by stress in any experiment. Glandular trichomes were significantly smaller on the lower leaves in response to stress in Ex2, and a similar non-significant trend was observed in Ex1.
The results indicate a dynamic system in which stress treatments of large A. annua plants had a minor promoting effect on the initiation of GT in developing leaves, and a maturing effect of GT later in the lifetime of the individual GT. The hypothesis that applying stress can induce larger GT or more numerous GT was rejected.
PMCID: PMC3404549  PMID: 22833781
2.  Investigation of Genetic and Morphological Variation in the Sago Palm (Metroxylon sagu; Arecaceae) in Papua New Guinea 
Annals of Botany  2004;94(1):109-117.
• Background and Aims The genetic and morphological variation in the sago palm (Metroxylon sagu, Arecaceae) in Papua New Guinea (PNG) was investigated.
• Methods Amplified fragment length polymorphism (AFLP) was used to investigate the genetic structure of 76 accessions of M. sagu, collected in seven wild and semi‐wild stands in PNG.
• Key Results An analysis of ten quantitative morphological variables revealed that most of these were mutually correlated. Principal component analyses of the same morphological variables showed that neither armature (presence or absence of spines) nor geographical separation was reflected clearly in the quantitative morphological variation. Similarity matrices of genetic, quantitative morphological, geographical and armature data were tested for pair‐wise correlations, using Mantel’s test. The results only showed a significant correlation between genetic and geographical distances. Visual inspection of principal component analyses plots and a neighbour‐joining dendrogram based on genetic distances supported this trend, whereas armature showed no relation with genetic distances.
• Conclusions Geographical distribution defines some weak patterns in the genetic variation, whereas the genetic variation does not reflect any patterns in the morphological variation, including armature. The present study supports the accepted taxonomy of M. sagu, recognizing only one species of M. sagu in PNG.
PMCID: PMC4242368  PMID: 15155379
Metroxylon sagu; sago palm; AFLP; genetic variation; morphological variation; Papua New Guinea

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