A system for genetic transformation of an elite prickly pear cactus (Opuntia ficusindica L., cultivar Villa Nueva) by Agrobacterium tumefaciens was developed. Beginning with direct bacterial infection by using a hypodermic syringe to the meristematic tissue termed areoles, transgenic plants were obtained by selection with 100 mg l -1 kanamycin. Transient and stable GUS activities were monitored on kanamycin-resistant shoots and regenerated plants, respectively. Genetic transformation of regenerated plants growing under selection was demonstrated by PCR and Southern blot analysis; transgene copy number in the genome of transgenic plants ranged from two to six, while the transformation frequency obtained by the system reported here was of 3.2%. This method may be useful for routine transformation and introduction of several important genes in prickly pear cactus.

The effects of pulsed light based-LEDs at eleven frequencies (0.1, 1, 10, 50, 100, 500 Hz, 1, 5, 10, 50 and 100 kHz) programmed at 50 % duty cycle were analyzed, obtaining important parameters of the fluorescence emission of chlorophyll such as: maximum fluorescence (Fm 0 ), minimum fluorescence, the fluorescence emission in steady state, maximum efficiency of PSII (Fv 0 /Fm 0 ), the fraction of PSII centers that are open, photochemical quenching, nonphotochemical quenching (NPQ), quantum efficiency of photosystem II (UPSII), electron transport rate (ETR) and quantum yield of CO 2 assimilation (/CO 2 ). For the study and validation of the results obtained in the experiments, the analysis of variance (ANOVA) was applied 0for each parameter with confidence intervals of 95 %. The results show that the frequencies of pulsed light had positive and negative effects on the fluorescence parameters with respect to the control treatment (continuous light). The frequencies that generated the best performance of Fv 0 /Fm 0 , NPQ, UPSII, ETR, /CO 2 in tomato plants were 0.1, 1, 100 Hz, and 1 kHz. The increase obtained in these parameters can represent an optimal growth and productivity conditions for optimal energy consumption.

Chemical and biochemical changes were studied in ripening prickly pears from three Opuntia morphospecies with different ripening behaviour: Naranjona (O. ficus-indica), Blanca Cristalina (Opuntia sp.), and Charola (O. streptacantha), of early, intermediate, and late ripening, respectively. At fullyripe stage (commercial maturity), Blanca Cristalina showed the biggest fruits, the hardest texture, and its pulp had the highest protein content. There were no significant differences among morphospecies in pH or total soluble solids in fully ripe fruits. The three species exhibited considerable levels of vitamin C, dietary fibre, and minerals such as calcium, iron, and zinc. Protein expression was analysed in pulp and skin from every species at physiological and commercial maturity. Some proteins appeared at both stages, while many others expressed differentially. This study evaluated prickly pear components important for human nutrition and health, and provided basic information on pricky pear ripening, with a view to its control and to improving shelf life.

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