The effect of ultraviolet-depleted light on the flavonol contents of the cactus species Opuntia wilcoxii and Opuntia violacea

An early investigation at the Biosphere-2 Laboratory, an artificial ecosystem in the Arizona desert, had shown that the flavonoid content of cacti grown in glass-filtered solar light was lower than of cacti grown in normal solar light. This was attributed to the absence of ultraviolet (UV) radiation, which is required for flavonoid biosynthesis. In this study, two species of Opuntia cacti were grown in solar and UV-depleted light, and their flavonol contents of different tissues were determined by HPLC. O. wilcoxii, previously raised in the absence of UV light, was exposed to normal solar light. The flavonol content of young O. wilcoxii pads was 28-fold higher when grown in solar light as compared to UV-depleted light. The flavonol contents of mature outer tissues were only slightly higher. O. violacea, previously raised in solar light, was also maintained in the same UV-depleted artificial ecosystem. The flavonol content after hydrolysis of outer tissues was similar, whether grown in solar light or UV-depleted light. We attribute these responses to different biosynthetic and metabolic rates of young vs. mature plant tissues; slow-growing mature tissues neither produce nor metabolize compounds as quickly as immature tissues. These findings indicate that artificial ecosystems can influence the production of natural products in cultivated plants.     

Aetiology of Opuntia ficus-indica malformations and stunting disease

The phytoplasma aetiology of epidemic stunting of cladodes and stunted growth observed in a cactus pear plantation in Carlentini (Sicily, Italy) was investigated with graft inoculation trials and PCR/restriction fragment length polymorphism analyses of 16S ribosomal RNA (rRNA) gene and S3 ribosomal protein gene. After sequencing of the 1525‐bp from 16S rRNA gene of both naturally infected and graft‐inoculated symptomatic cactus pear samples, phytoplasma TS belonging to ribosomal subgroup 16SrII‐C were identified as aetiological agents of this worldwide spread disease.     

Agrobacterium tumefaciens-mediated transformation of Rhipsalidopsis gaertneri

A protocol for Agrobacterium tumefaciens-mediated genetic transformation of Rhipsalidopsis cv. CB5 was developed. Calluses derived from phylloclade explants and sub-cultured onto fresh callus induction medium over a period of 9–12 months were co-cultivated with A. tumefaciens LBA4404. Plasmid constructs carrying the nptII gene, as a selectable marker, and the reporter uidA gene were used. Transformed Rhipsalidopsis calluses with a vigorous growth phenotype were obtained by extended culture on media containing 600 mg l⁻¹ kanamycin. After 9 months of a stringent selection pressure, the removal of kanamycin from the final medium together with the culture of the transformed calluses under nutritional stress led to the formation of several transgenic adventitious shoots. Transformation was confirmed by GUS staining (for uidA gene), ELISA analysis and Southern blot hybridization (for the nptII gene). With this approach, a transformation efficiency of 22.7% was achieved. Overall results described in this study demonstrate that Agrobacterium-mediated transformation is a promising approach for this cactus species.     

Neuroprotective Effects of Cactus Polysaccharide on Oxygen and Glucose Deprivation Induced Damage in Rat Brain Slices

1. The neuroprotective effect of cactus polysaccharide (CP) on oxygen and glucose deprivation (OGD) and reoxygenation (REO)-induced damage in the cortical and hippocampal slices of rat brain was investigated. 2. Cell viability was evaluated by using the 2, 3, 5-triphenyl tetrazolium chloride (TTC) method. The fluorescence of propidium iodide (PI) staining was used for quantification of cellular survival, and lactate dehydrogenase (LDH) activity in incubation medium was assessed by LDH assay to evaluate the degree of injury. 3. The OGD ischemic condition significantly decreased cellular viability and increased LDH release in the incubation medium. CP (0.2 mg/l∼2 mg/l) protected brain slices from OGD injury in a dosage dependent manner as demonstrated by increased A 490 value of TTC, decreased PI intensity and LDH release. At the above concentration, CP also prevented the increase of nitric oxide (NO) content and inducible nitric oxide synthase (iNOS) activity induced by OGD. 4. CP can protect the brain slices (cortical and hippocampus) against injury induced by OGD. Its neuroprotective effect may be partly mediated by the NO/iNOS system induced by OGD insult. Xianju Huang and Qin Li have contributed equally to this article.     

Rock-degrading endophytic bacteria in cacti

A plant–bacterium association of the cardon cactus (Pachycereus pringlei) and endophytic bacteria promotes establishment of seedlings and growth on igneous rocks without soil. These bacteria weather several rock types and minerals, unbind significant amounts of useful minerals for plants from the rocks, fix in vitro N₂, produce volatile and non-volatile organic acids, and reduce rock particle size to form mineral soil. This study revealed the presence of large populations of culturable endophytic bacteria inside the seeds extracted from wild plants, from seeds extracted from the guano of bats feeding on cactus fruit, in seedlings growing from these seeds, in the pulp of fruit, and in small, mature wild plants, and are comparable in size to populations of endophytic populations in some agricultural crops. The dominant culturable endophytes were isolates of the genera Bacillus spp., Klebsiella spp., Staphylococcus spp., and Pseudomonas spp. Based on partial sequencing of the 16s rRNA gene, the isolated strains had low similarity to known strains in these genera. However, these strains have higher molecular similarity among endophytes obtained from seeds, endophytes from roots, and some bacterial strains from the rhizoplane. Seedlings developed from seeds with endophytes contain the similar species of endophytes in their shoots, possibly derived from the seeds. This study shows the involvement of endophytic bacteria in rock weathering by cacti in a hot, subtropical desert and their possible contribution to primary colonization of barren rock. This study proposes that cacti capable of acquiring diverse populations of endophytes may give them an evolutionary advantage to gain a foothold on highly uncompromising terrain.     

Arabinan-cellulose composite in Opuntia ficus-indica prickly pear spines

The ultrastructure of the spines decorating the cladodes of the cactus Opuntia ficus-indica was investigated by optical microscopy, scanning and transmission electron microscopy, wide angle X-ray, and solid state 13C NMR analyses. Each spine consisted of a compact parallel arrangement of slender cellulosic fibers (0.4 mm in length and 6-10 microm in diameter) with small lumens. The fibers were disencrusted by alkali and sodium chlorite bleaching, yielding a remarkable arabinan-cellulose (1:1) product. X-ray fiber diagrams of the spines before and after purification confirmed the presence of crystalline cellulose domains with molecular axis parallel to the spine axis. CP-MAS 13C T1 NMR data showed a strong interaction at a nanometric level of a fraction of the arabinan and the cellulose crystalline domains. By sequential hydrothermal extractions, followed by a trifluoroacetic acid treatment, a relatively pure cellulose was isolated while the extracted fibers became fibrillated into slender microfibrils having no more than 4-6 nm diameter. The hydrothermal extract yielded the alpha-L-arabinofuranan consisting of a chain of (1-->5)-linked L-arabinosyl residues with branching either at C-2 or C-3 or at both C-2 and C-3. Taken together, these observations suggest that the bulk of the spine fibers consists of an intimate composite of cellulose microfibrils embedded in an arabinan matrix.     

Functional Characterization of a Cactus Homolog from the Silkworm Bombyx mori

A cDNA encoding an IκB family protein was identified and the full nucleotide sequence was determined in the silkworm Bombyx mori. The IκB gene, designated BmCactus, was constitutively expressed mainly in the fat body and hemocytes. Transfection experiments on a B. mori cell line, NIAS-Bm-aff3, with expression vectors containing BmCactus, BmRelA, BmRelB, or the active portion of BmRelish1 showed that activation of the CecB1 gene promoter by either BmRelA or BmRelB, but not the active portion of BmRelish1, was strongly inhibited by BmCactus. In addition, activation of CecB1 gene by autoclaved E. coli in the cultured cells was observed regardless of the presence or absence of BmCactus. A gultathione S-transferase pull-down assay and analysis using a yeast two-hybrid system demonstrated that BmCactus interacted with the BmRel Rel homology domain, but not with the BmRelish Rel homology domain. These results suggest that BmCactus is involved in the Toll signal transduction pathway in B. mori.     

Mortality over 16 years of cacti in a burnt desert grassland

Mortality of cacti after grassland fires is usually <25% within 2 years. Little, however, is known about long-term mortality. This study followed the fate of 50 marked plants of each of four species of small cacti (Coryphantha vivipara, Echinocereus pectinatus, Echinomastus intertextus and Mammillaria heyderi) on burnt and unburnt desert-grassland in Arizona. All marked plants were dead within 16 years. The first three species suffered increased mortality after being burnt while M. gummifera survived better after fire. The average rate of mortality of burnt plants over unburnt plants was 10.2 times higher in E. pectinatus, 3.7 times in C. vivipara and 1.5 times in E. intertextus. In M. heyderi, however, the mortality of burnt plants was 0.25 that of control plants. Fire more rapidly removed the breeding populations of the first three species, reducing seed availability in the occasional years favourable for establishment, increasing the risk of local extinction. Cacti did establish on the study areas and by the end were of a similar size to the dead cohort giving the superficial impression that the site was unchanged except for a reduction on unburnt sites in total cactus density (burnt: 445/ha in 1987, 401/ha in 2003; control: 2235/ha and 675/ha, respectively). Evidence of fire and dead plants rapidly disappeared, so without plants being marked the death of one population and establishment of another would have been easily missed. Estimates of growth rates support the assertion that the final plants established during the study.     

Past climate changes and ecophysiological responses recorded in the isotope ratios of saguaro cactus spines

The stable isotope composition of spines produced serially from the apex of columnar cacti has the potential to be used as a record of changes in climate and physiology. To investigate this potential, we measured the δ¹⁸O, δ¹³C and F¹⁴C values of spines from a long-lived columnar cactus, saguaro (Carnegiea gigantea). To determine plant age, we collected spines at 11 different heights along one rib from the stem apex (3.77 m height) to the base of a naturally occurring saguaro. Fractions of modern carbon (F¹⁴C) ranged from 0.9679 to 1.5537, which is consistent with ages between 1950 and 2004. We observed a very strong positive correlation (r = 0.997) between the F¹⁴C age of spines and the age of spines determined from direct and repeated height measurements taken on this individual over the past 37 years. A series of 96 spines collected from this individual had δ¹⁸O values ranging from 38‰ to 50‰ [Vienna standard mean ocean water (VSMOW)] and δ¹³C values from ?11.5‰ to ?8.5‰ [Vienna Peedee belemnite (VPDB)]. The δ¹⁸O and δ¹³C values of spines were positively correlated (r = 0.45, P < 0.0001) and showed near-annual oscillations over the ～15-year record. This pattern suggests that seasonal periods of reduced evaporative demand or greater precipitation input may correspond to increased daytime CO₂ uptake. The lowest δ¹⁸O and δ¹³C values of spines observed occurred during the 1983 and 1993 El Niño years, suggesting that the stable isotope composition recorded in spine tissue may serve as a proxy for these climate events. We compared empirical models and data from potted experimental cacti to validate these observations and test our hypotheses. The isotopic records presented here are the first ever reported from a chronosequence of cactus spines and demonstrate that tissues of columnar cacti, and potentially other long-lived succulents, may contain a record of past physiological and climatic variation.     

米邦塔仙人掌的研究进展与开发应用

米邦塔仙人掌是一种具有较高营养价值的新型保健蔬菜,有很高的应用价值和开发潜力。主要介绍了近年来米邦塔仙人掌引种我国后的栽种技术、营养成分、保健价值及其应用和开发进展等,在此基础上对其产业发展中存在的问题与对策进行了探讨。