Abstract
The effects of auxin and the endogenous levels of reserve compounds of Phalaenopsis amabilis (L.) Blume (Orchidaceae) were analyzed in vitro. Rootless plants were inoculated in modified MS media supplemented with IBA or NAA (0.0, 0.2, 1.0 and 5.0 mg L-1) and with 2,4-D (0.000, 0.032, 0.160 and 0.800 mg L-1). The biochemical parameters of endogenous levels of soluble carbohydrates and starch and of total soluble protein in roots, leaves and shoots were analyzed after 30 and 120 days. Carbohydrate levels in leaves showed similar patterns for all treatments. At 30 days, there was an increase in the endogenous carbohydrate level along with an increase in the concentration of auxins. At 120 days, the endogenous carbohydrate level in leaves had decreased, while the auxin concentration had continued to increase, demonstrating the mobilization of the carbohydrates. The leaf carbohydrate levels decreased from day 30 to 120; for both IBA and 2,4-D treatments, there was starch accumulation in roots as a function of the collection date. The 2,4-D concentration of 0.0032 mg L-1 decreased the level of total soluble protein in roots. The in vitro plants exhibit different growth patterns depending on the classes and concentrations of growth regulators. Biochemical analyses exhibited that metabolic activity and the degradation and accumulation of substances occurs in leaves, roots and shoots, demonstrating that roots contribute to the maintenance of plant metabolism and also act as reserve organs, even in epiphytic plants. Key words: Storage compounds, soluble carbohydrates, starch, soluble proteins.
Highlights
The genus Phalaenopsis has sixty described species and thousands of hybrids derived from crosses betweenPhalaenopsis amabilis (L.) Blume and Phalaenopsis stuartiana (Rchb. f) (Harper, 2004)
The present study aimed to correlate the effects of different concentrations of the auxins IBA, NAA (α-naphthalene-acetic acid) and 2,4-D (2,4dichlorophenoxyacetic acid) with the endogenous levels of soluble carbohydrates, starch and proteins from plants of P. amabilis hybrids cultivated in vitro, to obtain plants with greater levels of reserve compounds that would exhibit better growth
Both the leaves and roots of P. amabilis are rich in carbohydrates that may allow their re-mobilization under certain culture and propagation conditions
Summary
Phalaenopsis amabilis (L.) Blume and Phalaenopsis stuartiana (Rchb. f) (Harper, 2004). The main compounds of plant reserves, including those in roots, are carbohydrates (starch and water-soluble carbohydrates), acting as an energy source for growth and as carbon skeletons for young tissue, as well as maintaining the osmotic potential of the cell (Itai and Birnbaum, 1996). The increase in soluble carbohydrate flux upon correct auxin action correlates with the C:N ratios, osmotic potentials, and formation of new organs (buds and adventitious roots), and auxins function as signaling molecules (Gibson, 2005; Börner, 2011). The present study aimed to correlate the effects of different concentrations of the auxins IBA (indole-butyric acid), NAA (α-naphthalene-acetic acid) and 2,4-D (2,4dichlorophenoxyacetic acid) with the endogenous levels of soluble carbohydrates, starch and proteins from plants of P. amabilis hybrids cultivated in vitro, to obtain plants with greater levels of reserve compounds that would exhibit better growth
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