Maturation and conversion of somatic embryos are two crucial steps that hamper the development of efficient somatic embryogenesis systems in olive. Herein, a simple and efficient protocol for the maturation and conversion of olive somatic embryos is reported. Globular somatic embryos derived from seeds of cv. Dahbia were cultured on either half-strength olive (OM) or olive cyclic embryogenesis (ECO) media, with and without plant growth regulators (PGRs). The embryos reached the cotyledonary stage in 9 weeks, but those cultured on ECO medium containing 0.1 mg·L⁻¹ 6-(dimethylallylamino)purine (2iP), 0.1 mg·L⁻¹ 6-benzyladenine (BA) and 0.05 mg·L⁻¹ indole-3-butyric acid (IBA) exhibited the largest sizes, with an average of 4.7 mm. Somatic embryo conversion into plantlets was evaluated using different culture media (half-strength OM or one-third strength Murashige and Skoog (MS)), light conditions (light or dark) and desiccation pretreatments. The highest rate of somatic embryo conversion (45%) was observed under a 16 h photoperiod on half strength OM medium containing 0.1 mg·L⁻¹ gibberellic acid (GA₃) and 0.1 mg·L⁻¹ 1-naphthalene acetic acid (NAA). The embryos that failed to germinate showed either necrosis, cotyledon greening with no further conversion, adventitious bud formation or secondary embryogenesis. The findings of this study will be beneficial for biotechnological applications in olive.

Cadmium (Cd) is one of the most toxic elements in soil, affecting morphological, physiological, and biochemical processes in plants. Mineral plant nutrition was tested as an effective approach to mitigate Cd stress in several crop species. In this regard, the present study aimed to elucidate how different phosphorus (P) fertilization regimes can improve some bio-physiological processes in tomato plants exposed to Cd stress. In a hydroponic experiment, the impact of two phosphorus fertilizer forms (Polyphosphate (poly-P): condensed P-form with 100% polymerization rate and orthophosphate (ortho-P): from orthophosphoric acid) on the photosynthetic activity, plant growth, and nutrient uptake was assessed under three levels of Cd stress (0, 12, and 25 µM of CdCl₂). The obtained results confirmed the negative effects of Cd stress on the chlorophyll content and the efficiency of the photosynthesis machinery. The application of poly-P fertilizer significantly improved the chlorophyll stability index (82%) under medium Cd stress (Cd₁₂), as compared to the ortho-P form (55%). The analysis of the chlorophyll α fluorescence transient curve revealed that the amplitude of Cd effect on the different steps of electron transfer between PSII and PSI was significantly reduced under the poly-P fertilization regime compared to ortho-P, especially under Cd₁₂. The evaluation of the RE₀/RC parameter showed that the electron flux reducing end electron acceptors at the PSI acceptor side per reaction center was significantly improved in the poly-P treatment by 42% under Cd₁₂ compared to the ortho-P treatment. Moreover, the use of poly-P fertilizer enhanced iron uptake and its stoichiometric homeostasis in the shoot tissue which maintained an adequate absorption of iron under Cd stress conditions. Findings from this study revealed for the first time that inorganic polyphosphate fertilizers can reduce Cd toxicity in tomato plants by enhancing photosynthesis activity, nutrient uptake, plant growth, and biomass accumulation despite the high level of cadmium accumulation in shoot tissues.