Photosynthesis and leaf anatomy of 'Anthurium' cv. Rubi plantlets cultured 'in vitro' under different silicon (Si) concentrations

Abstract

The silicon can induce beneficial changes in plants, such as the further development of tissues and increased photosynthetic rate. Thus, studies on the anatomical changes resulting from in vitro culture are key to better understanding the development of micropropagated plants. Therefore, this study was undertaken to evaluate the morphological and physiological differences in plants with the use of silicon added to the medium for the in vitro culture of Anthurium adreaenum cv. Rubi. Nodal segments of seedlings were established in vitro and inoculated in Pierik medium supplemented with 30 g L-1 sucrose and solidified with 1.8 g L- 1 PhytagelTM. Different concentrations of sodium silicate (Na2SiO3) (0.0, 0.5, 1.0 and 2.0 mg L-1) were added to the medium. The experimental design was completely randomized with 30 repetitions. The segments were maintained for 100 days in a growth chamber under controlled conditions and evaluated anatomically and scanning electron microscopy (ultrastructurally) and for their photosynthetic capacities. Medium containing 1.0 mg L-1 sodium silicate promoted the development of higher stomatal densities on the sheets. For the polar (31.38 m) and equatorial (31.33 m) diameter of the stomata of the abaxial leaf, the highest averages occurred in the treatment with 2.0 mg L-1. Greater relative polar and equatorial diameters were estimated with a peak concentration of 1.2 mg L-1. The increase in the sodium silicate concentration led to thinning of the abaxial and adaxial epidermis. The thickness of the central rib had a sharp decrease up to 1.3 mg L-1. For the mesophyll, the control displayed a higher thickness, whereas the addition of sodium silicate to the culture medium promoted a decrease. Seedlings grown in sodium silicate displayed significant differences, with increased photosynthetic and transpiration rates, stomatal conductance and internal CO2 concentrations. As for the ratio between the internal and external concentrations of CO2, no significant differences were observed. The addition of sodium silicate resulted in increased epicuticular wax deposition and the formation of structures reserved for depositing calcium. Therefore, under in vitro conditions, the addition of sodium silicate to the culture medium affected the photosynthesis and leaf anatomy of A. andraeanum cv. Rubi, developing anatomical and physiological characteristics that contributed to the survival ex vitro.