Developmental dynamics of crassulacean acid metabolism (CAM) in Opuntia ficus-indica

BACKGROUND AND AIMS

The relative contributions of C3 photosynthesis and crassulacean acid metabolism (CAM) during the earliest stages of development were investigated to assess how much each might contribute to cactus pear (Opuntia ficus-indica) productivity.

METHODS

The developmental progression of C3 photosynthesis and CAM was assessed in seedlings and daughter cladodes of mature plants by titratable acidity, δ13C isotopic values and diel gas exchange measurements.

KEY RESULTS

Nocturnal acidification was observed in seedling cladodes and cotyledons at the earliest stages of development and became highly significant by 75 days of development. Seedling cotyledons showed mean δ13C values of -21.4 and -17.1 ‰ at 30 and 100 days of age, respectively. Seedling cladodes showed mean δ13C values of -19.4 and -14.5 ‰ at 30 and 100 days of age, respectively. These values are typical of CAM plants. Net CO2 assimilation was negative, then occurred in both the day and the night, with nighttime fixation becoming predominant once the primary cladode reached 5 cm in size. Emergent daughter cladodes growing on mature plants showed nocturnal titratable acidity at the earliest stages of development, which became significant when daughter cladodes were >2.5-5 cm in height. Emergent daughter cladodes showed mean δ13C values of -14.5 to -15.6 ‰, typical of CAM plants. CO2 assimilation studies revealed that net CO2 uptake was negative in daughter cladodes <12 cm in length, but then exhibited net positive CO2 assimilation in both the day and the night, with net nocturnal CO2 assimilation predominating once the daughter cladode grew larger.

CONCLUSIONS

Developing O. ficus-indica primary and daughter cladodes begin as respiring sink tissues that transition directly to performing CAM once net positive CO2 fixation is observed. Overall, these results demonstrate that CAM is the primary form of photosynthetic carbon assimilation for O. ficus-indica even at the earliest stages of seedling or daughter cladode development.

Assessment of cactus pear leather (pestil) as a new snack food

In this study, selected nutritional and functional properties of cactus pear and cactus pear leather (pestil) processed with different dryers (oven type and pilot scale tray dryers) were evaluated. For this aim, the fruits collected from three different districts of Turkey were processed and the most suitable region and processing method were investigated. Processing with different dryers had significant (p < 0.05) impact on total acidity, total phenolic content, antioxidant capacity, color and hydroxymethylfurfural values of pestil samples and the best results including antioxidant capacity (66.91-70.25%) and total phenolics (1.79-2.01 g gallic acid equivalent per kg) were obtained with the tray dryer. On the other hand, mineral contents (Na, K, Ca, Mg and Fe) of the products were not significantly (p > 0.05) affected from different dryers. Pestil obtained by tray drying gave the highest rate for the taste. According to the results, the fruits collected from the Aegean region of Turkey were more convenient for processing. Because there is a limited number of studies on this fruit, data provided in the present study may also contribute to further studies.

Genetic diversity and relationships among Nopalea sp. and Opuntia spp. accessions revealed by RAPD, ISSR and ITS molecular markers

BACKGROUND

Dactylopius opuntiae (Cockerell) (carmine cochineal) is an insect pest highly noxious that has spread through cactus pear crops in the Brazilian semiarid region. Knowledge of diversity and genetic relationships of the cactus pear accessions is fundamental to create new varieties resistance to carmine cochineal. Therefore, this investigation was undertaken to assess the genetic diversity and genetic relationships that existed among cactus pear accessions of Nopalea sp. and Opuntia spp. with contrasting resistance to D. opuntiae.

METHODS AND RESULTS

We conducted a molecular analysis in seven cactus pear accessions from the "reference collection" of the Agronomic Institute of Pernambuco, Brazil using RAPD, ISSR and ITS molecular markers. A total of 242 bands were detected from 26 polymorphic primers. The high percentage of polymorphism by RAPD (89.8%), ISSR (81.2%) and ITS (75%) markers suggests that the cactus pear accessions have high genetic diversity. The combined analysis of markers systems enabled the accessions discrimination of about the genus and ploidy, but were incongruous in relation to resistance level to D. opuntiae.

CONCLUSIONS

Genetic diversity, discrimination of about the genus and ploidy was confirmed by merging information from ISSR, RAPD and ITS markers systems. The IPA-200016, IPA-200149, IPA-100004, IPA-200205 accessions are genetically divergent, therefore could be potentially incorporated into any further breeding programs directed to create new varieties of cactus pear resistant to D. opuntiae.

Characterization of a microbial consortium with potential for biological degradation of cactus pear biomass for biofuel production

Cactus pear (Opuntia ficus-indica) is a crassulacean acid metabolism (CAM) species that serves as a food, feed, and bioenergy crop. O. ficus-indica is an attractive alternative biofuel feedstock due to its low water demand and high biomass productivity. Current ethanol yields from O. ficus-indica are not commercially viable due to low concentrations of released fermentable carbohydrates. Axenic strains of bacteria and fungi were isolated and characterized from a soil microbial community consortium that effectively degrades cladodes into soluble components. The consortium consisted of species representing 14 genera of eubacteria and four genera of fungi. The digestion efficiency of each axenic isolate was evaluated by measuring the release of soluble material after aerobic digestion of cladodes and direct measurement of cellulase and pectinase activities in the culture supernatants. Pectobacterium cacticida was the most effective eubacterial species identified for degrading cladodes among all isolates evaluated. Thus, P. cacticida holds great promise for increasing the release of fermentable sugars and improving overall ethanol yields.

Changes on physicochemical and rheological properties of biscuits substituted with the peel and alcohol-insoluble solids (AIS) from cactus pear (Opuntia ficus-indica)

Cactus pear fruit consists of the peel, seeds and pulp. The peel is a major waste in cactus pear pulp based products accounting about 37.72% of the fruit weight. The aim of this study was to utilized and characterized the physicochemical and rheological properties of biscuits substituted with extracted cactus pear peel (CPP) and alcohol-insoluble solids (AIS) from cactus pear (Opuntia ficus-indica). To prepare AIS, peels were shredded and dropped in ethanol (70%) for 15 min. The mixture was boiled at 70 °C for 30 min, filtered and washed with ethanol 70% and the washing repeated until no sugars. The residue was washed and dried at room temperature. Changes in physiochemical and rheological properties of extracted CPP and AIS from cactus pear to qualify determine their use in the production of them to produce a fiber-rich food product. The water-holding capacity was 3.7 ml/g for the peel and 1.5 ml/g for the AIS, and the oil-holding capacity was approximately the same for both the CPP and AIS. The protein content was 3.5% for the CPP and 3.72% for the AIS. The CPP and AIS contained little fat (1.22% and 1.44%, respectively). Potassium and calcium in the AIS had the highest concentration, at 21.49 g/kg and 44.04 g/kg, respectively, and these minerals were found at 22.07 g/kg and 16.66 g/kg, respectively, in the CPP. The dominant phenolic compounds found in the CPP were pyrogallol, catechol, catechin, and alpha-coumaric acid. The results showed that the AIS contained pyrogallol (61.67 ppm), benzoic acid (10.68 ppm), vanillic acid (7.66 ppm), catechin (4.65 ppm) and salicylic acid (4.51 ppm). The CPP was rich in glucose (25.95%) and fructose (21.36%) compared to the AIS. The sensory evaluation indicated that 7.5% dried cactus pear peel or 7.5% AIS can be successfully used in substitution of wheat flour biscuits. It could be conducted cactus pear as major by-product can be important for the industrial utilization.

Rapid, simple and potentially universal method for DNA extraction from Opuntia spp. fresh cladode tissues suitable for PCR amplification

In Opuntia spp., the cladode tissues contain many polysaccharides and secondary metabolites that interfere with obtaining high-quality deoxyribonucleic acid (DNA), using currently available methods. To circumvent this problem, three commercial kits, three modified versions of the conventional cetyltrimethylammonium bromide method (CTAB) method and one combined method were tested in Opuntia ficus-indica, O. robusta, O. dillenii and O. elata species. We obtained a rapid and simple protocol that allows the extraction of DNA from all the tested species with good DNA yield and purity, namely, the combined method. With this method (DNeasy® Plant Mini Kit combined with the CTAB method), DNA yields from 13.2 ± 7.8 to 15.9 ± 11.3 µg g^-1 of fresh tissue were obtained in the four Opuntia species. The purity, evaluated by the ratio A₂₆₀/A₂₈₀ ratio, ranged from 1.67 ± 0.12 to 2.01 ± 0.25, revealing low levels of problematic metabolites. The extracted DNA quality was confirmed by amplifying a set of nuclear microsatellites obtained for the genus. Reliable reproducible bands and electropherogram profiles were obtained. The combined method has potential to be universal for good-quality DNA extraction in cacti, particularly in the Opuntia genus and other difficult-to-extract species.