Gilvano Ebling Brondani

Pre-procambial cells are niches for pluripotent and totipotent stem-like cells for organogenesis and somatic embryogenesis in the peach palm: a histological study

AbstractThe direct induction of adventitious buds and somatic embryos from explants is a morphogenetic process that is under the influence of exogenous plant growth regulators and its interactions with endogenous phytohormones. We performed an in vitro histological analysis in peach palm (Bactris gasipaes Kunth) shoot apexes and determined that the positioning of competent cells and their interaction with neighboring cells, under the influence of combinations of exogenously applied growth regulators (NAA/BAP and NAA/TDZ), allows the pre-procambial cells (PPCs) to act in different morphogenic pathways to establish niche competent cells. It is likely that there has been a habituation phenomenon during the regeneration and development of the microplants. This includes promoting the tillering of primary or secondary buds due to culturing in the absence of NAA/BAP or NAA/TDZ after a period in the presence of these growth regulators. Histological analyses determined that the adventitious roots were derived from the dedifferentiation of the parenchymal cells located in the basal region of the adventitious buds, with the establishment of rooting pole, due to an auxin gradient. Furthermore, histological and histochemical analyses allowed us to characterize how the PPCs provide niches for multipotent, pluripotent and totipotent stem-like cells for vascular differentiation, organogenesis and somatic embryogenesis in the peach palm. The histological and histochemical analyses also allowed us to detect the unicellular or multicellular origin of somatic embryogenesis. Therefore, our results indicate that the use of growth regulators in microplants can lead to habituation and to different morphogenic pathways leading to potential niche establishment, depending on the positioning of the competent cells and their interaction with neighboring cells.n Key message Our results indicate that the use of growth regulators in microplants can lead to habituation and to different morphogenic pathways leading to potential niche establishment, depending on the positioning of the competent cells and their interaction with neighboring cells.UNLABELLEDnThe direct induction of adventitious buds and somatic embryos from explants is a morphogenetic process that is under the influence of exogenous plant growth regulators and its interactions with endogenous phytohormones. We performed an in vitro histological analysis in peach palm (Bactris gasipaes Kunth) shoot apexes and determined that the positioning of competent cells and their interaction with neighboring cells, under the influence of combinations of exogenously applied growth regulators (NAA/BAP and NAA/TDZ), allows the pre-procambial cells (PPCs) to act in different morphogenic pathways to establish niche competent cells. It is likely that there has been a habituation phenomenon during the regeneration and development of the microplants. This includes promoting the tillering of primary or secondary buds due to culturing in the absence of NAA/BAP or NAA/TDZ after a period in the presence of these growth regulators. Histological analyses determined that the adventitious roots were derived from the dedifferentiation of the parenchymal cells located in the basal region of the adventitious buds, with the establishment of rooting pole, due to an auxin gradient. Furthermore, histological and histochemical analyses allowed us to characterize how the PPCs provide niches for multipotent, pluripotent and totipotent stem-like cells for vascular differentiation, organogenesis and somatic embryogenesis in the peach palm. The histological and histochemical analyses also allowed us to detect the unicellular or multicellular origin of somatic embryogenesis. Therefore, our results indicate that the use of growth regulators in microplants can lead to habituation and to different morphogenic pathways leading to potential niche establishment, depending on the positioning of the competent cells and their interaction with neighboring cells.nnnKEY MESSAGEnOur results indicate that the use of growth regulators in microplants can lead to habituation and to different morphogenic pathways leading to potential niche establishment, depending on the positioning of the competent cells and their interaction with neighboring cells.

Decreased morphogenetic potential in peach palm stem-like cells in long-term in vitro conditions

Peach palm ( Bactris gasipaes Kunth) has been micropropagated from pre-procambial cells that provide stem-like cell niches, (i.e., pre-procambial cells), multipotent, pluripotent and totipotent for direct vascularization, adventitious buds and somatic embryogenesis, respectively. The direct induction of adventitious buds and somatic embryogenesis reduces the frequency of mutations when compared to indirect morphogenesis. Long-term in vitro cultivation of perennial species such as peach palm cause the clones to age and deteriorate; however, the consequences for morphogenesis potential are not fully clear. The morphogenic potential of peach palm clones established and in vitro cultivated for 8xa0years (regeneration of adventitious buds without callus formation) was investigated in leaves, roots and stem bases using histological and histochemical analyses. Data from long-term cultures (8-years-old) was compared to data from short-term cultures (1-year-old). Morphogenic pathways monitoring for direct induction of somatic embryos and adventitious buds revealed a strong morphogenic reduction potential in the pre-procambial cells, parenchyma cells in the proximal region of stem bases, and external cells of leaf sheaths. Initial cells of shoot apical meristems and pre-procambial cells commit cell reprogramming to the undifferentiated state and subsequent acquisition of cellular competence. These results are applicable in the micropropagation of peach palm, with consideration to obtaining clones and their long-term in vitro culture.

Mini-incubators improve the adventitious rooting performance of Corymbia and Eucalyptus microcuttings according to the environment in which they are conditioned

We addressed a major challenge in the in vitro clonal propagation of Corymbia citriodora, Eucalyptus urophylla and E. benthamii by using an ex vitro adventitious rooting strategy in a mini-incubator. Mini-incubators were placed in four environments for rooting. A shade house with no fogging system and a greenhouse with no ventilation but with a fogging environment had the best performance in terms of rooting, root growth and survival of microcuttings. Daily recording of the temperature within each mini-incubator in each environment allowed the verification of negative correlations between the maximum average temperature and the survival, adventitious rooting and root growth. The ideal maximum air temperature for the efficient production of clonal plants was 28.4°C (± 5.5°C), and the minimum was 20.3°C (± 6.2°C). E. benthamii was more sensitive to higher temperatures than C. citriodora and E. urophylla. Nevertheless, placing mini-incubators in the shade house with no fogging system resulted in a stable and uniform performance among the three species, with 100.0% survival and 81.4% rooting. Histological sections of the adventitious roots revealed connection with the stem vascular cambium. Therefore, our experimental system demonstrated the potential of mini-incubators coupled with the proper environment to optimize the adventitious rooting performance of microcuttings.

Phosphorus nutrition in the growth of Bauhinia forficata L. seedlings - DOI: 10.4025/actasciagron.v30i5.787

One of the greatest problems in the elaboration of forestation programs using native species is the lack of knowledge about seedling production. This study aimed to evaluate the growth of Bauhinia forficata seedlings submitted to phosphorus levels. Elevenday-old seedlings were transplanted to small tubettes (110 cm3) with pinus bark and vermiculite substratum base. The experiment was conducted in an entirely randomized delineation, with six P treatments: TO-control (substratum without P addition), T1-50, T2100, T3-150, T4-200 and T5-250 mg dm-3, with five replications and 20 seedlings per replication. After 60 days, the seedlings presented a 98.2% survival rate and good root formation. The height varied in function of P levels, with maximum production up to the P dose of 250 mg dm-3; 60 days after the transplant, similar behavior for leaf area and dry matter production was observed. Furthermore, the P incorporation increased the phosphorus (P), potassium (K) and nitrogen (N) accumulation in vegetable tissues. Seedling growth was positively influenced by P levels, and the maximum growth occurred up to the P dose of 250 mg dm-3. In conclusion, this characteristic showed that the species requires high levels of P during initial growth, under the tubette system.