Elsevier

Scientia Horticulturae

Volume 161, 24 September 2013, Pages 328-332
Scientia Horticulturae

Changes in leaf anatomy and photosynthesis of micropropagated banana plantlets under different silicon sources

https://doi.org/10.1016/j.scienta.2013.07.021Get rights and content

Highlights

  • CaSiO3 provides greater thickness of epidermis, mesophyll and palisade parenchyma.

  • The addition of CaSiO3 favors the photosynthetic rate of seedlings of banana plant.

  • CaSiO3 is more efficient source of Si to favor the morphophysiological leaf traits.

  • The production of chlorophyll in banana plants in vitro is favored by addition CaSiO3.

Abstract

The objective of this study was to verify the possible changes in leaf anatomy and photosynthetic characteristics of ‘Maçã’ (Silk) banana plantlets cultivated in vitro in the presence of different silicon sources. ‘Maçã’ (Silk) banana plantlets pre-established in vitro were transferred to MS medium containing 30 g L−1 sucrose, 1 mg L−1 NAA and 1.8 g L−1 Phytagel™ and 1.0 g L−1 of three different sources of silicon: Na2SiO3, K2SiO3 and CaSiO3. The control group was conduced without silicon addition. After 45 days, gas exchanges were measured in infrared gas analyser and the leaf anatomy and chlorophyll content were evaluated as well as the silicon content in plants. The presence of calcium and sodium silicates enabled higher levels of silicon in the leaves than in the roots, however, potassium silicate promoted higher levels of silicon in the roots. Plantlets grown in the presence of calcium silicate had a higher photosynthetic rate and chlorophylls content compared to other treatments. There was a thickening of the epidermis, increased stomatal density, thicker mesophyll, thicker palisade parenchyma and a higher proportion of palisade parenchyma in relation to spongy parenchyma in seedlings grown in the presence of calcium silicate than in the control and other treatments. Silicon promoted more functional features and greater adaptability of ‘Maçã’ (Silk) banana plantlets, and the calcium silicate is a more efficient source for the promotion of favorable features in the in vitro culture of this species

Introduction

Banana is one of the most consumed tropical fruits in the world and has great economic and social importance in producing countries (Donato et al., 2006). Among the production systems, cultivation in vitro of meristems and shoot tips became the basis for mass propagation of banana plants (Gübbük and Pekmezci, 2004). Thus, the micropropagation of banana plant is essential for producers of this species of great economic importance.

Cultivation in vitro promotes many benefits to the production of seedlings, however, in heterotrophic conditions, causes the development of poorly functional morpho-physiological features, such as reduced epicuticular wax deposition, reduced differentiation of the mesophyll, rudimental vascular bundles and low control of stomatal opening and closure (Romano and Martins-Loução, 2003, Yokota et al., 2007). All these changes result from the complex conditions formed in the microclimate of the culture bottles, including low irradiance, the presence of exogenous carbohydrates, low availability of CO2, high relative humidity and low gas exchanges with the ex vitro environment (Argita et al., 2002).

Cultivation in vitro promotes low development of photosynthetic tissues (Lamhanedi et al., 2003) due to the characteristics of the medium. However, plants need photosynthesis during acclimatization and transference to the ex vitro environment. Leaves of ‘Maçã’ (Silk) banana plant can produce changes in tissues associated with photosynthesis such as poorly functional stomata, high stomatal density and poorly developed palisade parenchyma (Costa et al., 2009a). However, changes in the microenvironment, as the replacement of artificial by natural light may promote a more appropriate development of the palisade parenchyma in ‘Maçã’ (Silk) banana plants (Costa et al., 2009b).

Silicon (Si) is one of the most abundant elements in Earth's crust, and although not considered essential for some plants, promotes positive effects for many species and may reduce many effects of environmental stresses (Currie and Perry, 2007). The use of silicon in cultivation in vitro can increase the content of hemicellulose and lignin, increasing cell wall stiffness and the survival of plants in the acclimatization (Camargo. et al., 2007). Silicon can also increase tolerance to UV-B stress and the production of chlorophyll a and b (Yao et al., 2010). In plants grown in vitro, silicon can promote beneficial changes in plants, such as greater development of photosynthetic tissues and chlorophyll production (Braga et al., 2009).

Thus, the objective of this study was to evaluate possible changes in the internal structure of leaves, as well as changes in the characteristics of gas exchange and chlorophyll production in ‘Maçã’ (Silk) banana plants cultivated in vitro with different sources of silicon.

Section snippets

Material and methods

The study was conducted in the Laboratories of Plant Tissue Culture, Department of Agriculture and Plant Anatomy, Department of Biology, Federal University of Lavras in the city of Lavras (MG), Brazil, 21°14′S, 45°17′W and 918 m in altitude.

Results

The concentration of silicon in leaf was 70.12% higher in seedlings grown in culture medium containing calcium silicate (CaSiO3) and sodium silicate (Na2SiO3) than in the control, and 45.90% higher than in potassium silicate (K2SiO3). For potassium silicate (K2SiO3) silicon was concentrated in the roots, with values 15 times higher than in plants grown in the absence of silicate and five times higher than in plants grown in calcium silicate (Table 1).

Seedlings grown with different sources of

Discussion

The differentiated accumulation of silica in roots and leaves of ‘Maçã’ (Silk) banana plant is consistent with Currie and Perry (2007) who report the possibility of differences in silica content in different parts of the same plant. These authors also report that silicon can be absorbed by specific transporters in the roots and translocated to the shoot by xylem. However, the large accumulation of silicon in roots of seedlings grown in potassium silicate can be partially explained by the

Conclusions

  • 1.

    Higher number of stomata and polar/equatorial diameters ratio are obtained using a source of silicon in the medium.

  • 2.

    Calcium silicate provides greater thickness of epidermis, of mesophyll and palisade parenchyma.

  • 3.

    The addition of calcium silicate to the medium favors the photosynthetic rate of seedlings of ‘Maçã’ (Silk) banana plant.

  • 4.

    The production of chlorophyll in ‘Maçã’ (Silk) banana plants grown in vitro is favored by the addition of silicate to the culture medium.

  • 5.

    Calcium silicate is a more

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