Browsing by Subject "Desiccation-tolerance"

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    Longevity of dry Myrothamnus flabellifolius in simulated field conditions.
    (Springer, 2001) Farrant, J; Kruger, L
    This study tested the length of time the desiccation-tolerantMyrothamnus flabellifolius could remain in the dry stateunder simulated field conditions, without losing viability. Dry plants werekeptat 50% relative humidity, with a 25/16 °Cday/night temperature regime and a daylight intensity of 1200μmol·m−2 s−1. At threemonthly intervals plants were rehydrated and the ability to resume respiration,photosynthesis, protein synthesis and transcription was assessed and changes insubcellular organisation and plant growth regulator content (zeatin, zeatinriboside and abscisic acid) monitored. Plants survived in the dry state foronly one year. The ability toresurrect metabolism in existing leaves was lost after nine months, after whichsurvival occurred due to regrowth of new leaves from meristems. There waslittleevidence of subcellular damage in leaf tissues of plants kept dry for up to sixmonths. These plants recovered respiration before the onset of translation (andthus repair) suggesting considerable subcellular protection of this metabolismagainst desiccation damage. Furthermore, full recovery of metabolism, includingphotosynthesis, occurred before the onset of transcription in these plants.Somesubcellular damage occurred in plants maintained dry for nine months. There wasincreased electrolyte leakage indicative of membrane damage which was repairedwith the onset of protein synthesis. Since this repair occurred before theonsetof transcription, it is likely that stored mRNA, present in the dry leaves, wasused. Recovery of photosynthesis in plants dried for 9 months was delayed untilthe onset of transcription. We propose that mRNA for recovery of thismetabolismis not stored during drying and thus damage to the photosynthetic apparatus canbe repaired only upon de novo transcription of the genome.In leaves that were able to resurrect, cytokinin content increasedtransiently just prior to onset of chlorophyll biosynthesis and translation,andabscisic acid content increased just prior to the onset of transcription. Theseplant growth regulator changes did not occur in leaves which did not resurrect,but we cannot distinguish whether it was the lack of signal, or the extent oftissue damage (or both) which prevented the repair and recovery of metabolisminthese tissues.
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    A proteomic investigation of the rhizomes of the resurrection fern Mohria caffrorum L. (Desv.) in response to desiccation
    (2015) Shoko, Ryman; Farrant, Jill M; Rafudeen, Mohamed S
    As there is limited information on the mechanisms of vegetative desiccation-tolerance in resurrection plant rhizomes, this work was undertaken to study the mechanisms of desiccation-tolerance in Mohria caffrorum rhizomes. Fronds of this plant have been previously characterized as being desiccation-tolerant in summer and desiccation-sensitive in winter. Since fern rhizomes are perennial organs, it was of interest to establish whether these organs are also perennially desiccation-tolerant and, whether or not the rhizomes regulate desiccation-tolerance in the fronds. Ultra-structural evidence using transmission electron microscopy and viability studies using electrolyte leakage analysis showed that the rhizomes were desiccation-tolerant throughout the seasons. Quantitative proteomics analysis using isobaric tags for relative and absolute quantification was employed to investigate molecular mechanisms of desiccation-tolerance in the rhizomes of this plant. Using a custom fern rhizome specific peptide sequence database, 236 proteins were identified. Of these, 16 proteins increased in abundance while 14 declined, in the summer collected rhizomes. On the other hand, 16 proteins increased in abundance and 20 declined in the winter form. Western blot analysis confirmed the expression trends of heat shock protein 70-2 and superoxide dismutase-[Cu-Zn], which were among the differentially expressed proteins. Bioinformatics analysis of the differentially expressed proteins was carried out using network enrichment tools, to identify key molecular processes and pathways involved in the rhizome response to desiccation stress. Results indicate that the rhizomes use different molecular mechanisms to achieve desiccation-tolerance in winter and summer. Potential cross-talks and cross-tolerances were identified in which mechanisms protecting the rhizomes against desiccation-tolerance appeared to also protect them against heat stress, and in winter an apparent cross-talk against desiccation and pathogen stresses was also identified. This study is the first report of evidence that M.caffrorum rhizomes are the 'master-regulator organs' responsible for regulating desiccation-tolerance in the fronds. This role was inferred from the rhizome's predicted up-/down-regulation of biological processes and pathways that relate to leaf senescence, shoot system morphogenesis and gametophyte development, among others.