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Dendrobium cruentum Rchb. f. is a native Thai orchid species that has faced extinction because of its attractive characteristics. Consequently, conservation of this species is urgently needed. In this study, cryopreservation technique was applied to D. cruentum Rchb. f. seeds for long-term conservation. A successful protocol for D. cruentum Rchb. f. seed cryopreservation was developed by using D cryo-plate and V cryo-plate techniques. Seed viability was tested by TCC solution and 93.8 % of dyed seeds were shown. For cryo-plate technique, seeds were encapsulated over the cryo-plate by using 2 % (w/v) sodium alginate and polymerized with 100 mM CaCl2. Encapsulated seeds were desiccated by using a laminar airflow and PVS2 solution treatment with the same exposure time (0, 30, 60, 90, and 120 min). After cryopreservation, encapsulated seeds were cultured on modified VW agar medium. From the results, the maximum germination and regrowth percentage were observed; D cryo-plate technique with 60 min of dehydration time gave the highest germination (68.9 %) and regrowth (57.8 %). Thus, the excess of dehydration may cause the reduction of germination and plant regeneration. In conclusion, D cryo-plate technique proved to be appropriate for D. cruentum Rchb. f. seed cryopreservation. [ABSTRACT FROM AUTHOR]

Natural rubber (cis-1,4-polyisoprene) is a product of the isoprenoid biosynthesis pathway which requires an allylic pyrophosphate and isopentenyl pyrophosphate (IPP) to initiate and elongate the rubber molecule. The biosynthesis of IPP occurs via two distinct routes: the mevalonate (MVA) and methylerythritol phosphate (MEP) pathways. In this study, the expression of 34 genes related to rubber biosynthesis were compared between high and low latex yielding trees of two rubber tree clones, PB 217 and PB 260. Almost all tested genes revealed no significantly differential expression related to latex yield. Only mitochondrial pyruvate dehydrogenase (PDCE1) showed specific up-regulation in the high latex yielding trees of both tested clones. Interestingly, the expression of PDCE1 involving in the production of acetyl-CoA in mitochondria was also significantly induced by latex loss upon tapping. The increasing of acetyl-CoA and energy production may favor rubber tree to produce more latex. The in silico analysis showed that HbPDCE1 promoter contained ethylene and copper-responsive elements. Ethylene is worldwide used rubber stimulant while copper sulfate was also reported to be able to stimulate the latex yield. This suggested that HbPDCE1 may be transcriptionally regulated by these two compounds however the in vivo regulation of this gene should be further investigated. [ABSTRACT FROM AUTHOR]

Natural rubber is synthesized in specialized articulated cells (laticifers) located in the inner liber of Hevea brasiliensis. Upon bark tapping, the laticifer cytoplasm (latex) is expelled due to liber tissue turgor pressure. In mature virgin (untapped) trees, short-term kinetic studies confirmed that ethylene, the rubber yield stimulant used worldwide, increased latex yield, with a concomitant decrease in latex total solid content, probably through water influx in the laticifers. As the mature laticifers are devoid of plasmodesmata, the rapid water exchanges with surrounding liber cells probably occur via the aquaporin pathway. Two full-length aquaporin cDNAs (HbPIP2;1 and HbTIP1;1, for plasma membrane intrinsic protein and tonoplast intrinsic protein, respectively) were cloned and characterized. The higher efficiency of HbPIP2;1 than HbTIP1;1 in increasing plasmalemma water conductance was verified in Xenopus laevis oocytes. HbPIP2;1 was insensitive to HgCl2. In situ hybridization demonstrated that HbPIP2;1 was expressed in all liber tissues in the young stem, including the laticifers. HbPIP2;1 was upregulated in both liber tissues and laticifers, whereas HbTIP1;1 was down-regulated in liber tissues but up-regulated in laticifers in response to bark Ethrel treatment. Ethylene-induced HbPIP2;1 up-regulation was confirmed by western-blot analysis. The promoter sequences of both genes were cloned and found to harbor, among many others, ethylene-responsive and other chemical-responsive (auxin, copper, and sulfur) elements known to increase latex yield. increase in latex yield in response to ethylene was emphasized to be linked with water circulation between the laticifers and their surrounding tissues as well as with the probable maintenance of liber tissue turgor, which together favor prolongation of latex flow. [ABSTRACT FROM AUTHOR]