Somatic embryogenesis in Citrus SPP.: Carbohydrate stimulation and histodifferentiation

Abstract

Somatic embryogenesis from nucellus-derived callus cultures of five cultivars, including three (Caipira, Seleta Vermelha, and Valencia) of sweet oranges (C. sinensis L. Osbeck), Rangpur lime (C. limonia L. Osbeck), and Cleopatra mandarin (C. reticulata Blanco) (lines I and II), were studied. Callus lines maintained on MT medium supplemented with 50 g l 21 sucrose were transferred to MT medium supplemented with different carbohydrate sources: galactose, glucose, lactose, maltose, or sucrose at 18, 37, 75, 110, or 150 mM, or glycerol at 6, 12, 24, 36, or 50 mM. Globular embryos were observed after approximately 4 wk, in several treatments. Cultures of Valencia and Caipira sweet oranges and Cleopatra mandarin (line I) showed high numbers of embryos on medium containing galactose, lactose, and maltose. Histological studies showed somatic embryos in all developmental stages with a normal histodifferentiation pattern. The other two cultivars (Rangpur lime and Cleopatra mandarin, line II) formed very few embryos, which did not develop further following the globular stage. Some of the abnormalities observed were lack or dedifferentiation of protoderm and absence of apical meristems and procambial strands. Embryos that followed the normal sequence of development were easily converted into plants. Non-embryogenic cultures continued as proliferating callus cultures, eventually forming a few embryos which did not convert into plants. Statistical analyses of the callus response to carbohydrate treatments was done using an overdispersion Poisson model.

Somatic embryogenesis in Citrus sinensis, C. reticulata AND C. nobilis x C. deliciosa

“…The number of plantlets produced by the different treatments is presented in Table 2. These results corroborated those of Tomaz et al (2001), who reported that for citrus variety 'Seleta Vermelha', the highest number of plantlets was obtained in medium with 44 mM of sucrose, which was 16% greater when compared to the medium supplemented with 37 mM of maltose. Where as, 73 mM of sucrose in the absence of activated charcoal followed by 29 mM of sucrose without charcoal favored the production of the highest number of plantlets for 'Cravo' mandarin.…”

“…The favorable effect of galactose on somatic embryogenesis was verified by Tomaz et al (2001), who reported that 110 mM of galactose caused a higher number of somatic embryos of callus derived from the Caipira sweet orange. On the other hand, Kunitake et al (1991) observed that the formation of embryos from callus of 'Satsuma' mandarin was induced only when lactose, at the concentration of 15 mM, was the carbon source, while no embryos were formed when 15 mM of glucose or sucrose was used.…”

“…Similar results were also documented by Kochba et al (1982), who showed that concentrations higher than 32 mM of sucrose inhibited the formation of embryos in callus from the tested varieties of Citrus. Tomaz et al (2001) found that in the presence of sucrose only a few somatic embryos were derived from the calli of the Caipira sweet orange and Cleópatra mandarin. Moreover, the inefficiency of sucrose was also observed by Mendesda-Glória et al (2000).…”

“…Moreover, these carbohydrates, at 64 mM concentrations promoted a substantial increase in the number of embryos derived from calli of 'King' mandarin (C. nobilis Loureiro), and 'Navel' sweet orange (C. sinensis). According to Tomaz et al (2001), galactose, lactose or maltose had a great effect on somatic embryogenesis for the lines of calli from 'Valencia' and Caipira sweet oranges (C. sinensis) and for the Cleopatra (C. reshni Hort. ex Tanaka) mandarin.…”

“…Studies done by Tomaz et al (2001) on the effect of activated charcoal on the germination of somatic embryos derived from the variety 'Seleta Vermelha' (C. sinensis) revealed that the number of non-germinated somatic embryos was much higher than the regenerated plantlets. This suggests that activated charcoal adsorbed compounds involved in the germination process.…”