Histomorphological and biochemical characterization of callus induction in <i>Cenostigma pyramidale</i> [Tul.] Gagnon & G.P. Lewis

Abstract

Cenostigma pyramidale [Tul.] has timber, forage and medicinal uses, and due to the exploitation of its natural resources, it may become endangered. This work aimed to induce callus in Cenostigma pyramidale and to identify the embryogenic potential by histomorphological and biochemical analysis. Leaf segments were inoculated in MS culture medium containing different concentrations (0.0; 2.5; 5.0 and 10.0 μM) of 2,4-dichlorophenoxyacetic acid (2,4-D), combined with 6-benzylaminopurine (BAP; 0.0; 2.5 and 5.0 μM) and glutamine (0.0; 0.342 and 0.684 mM). The growth curve was performed at 7-day intervals until day 77, and samples were collected for histomorphological analysis and determination of reducing sugars (RA), sucrose, and total soluble sugars (TSS) content. Callus induction is possible using leaf segments in treatment with 5.0 μM of BAP, 7.0 µM of 2.4-D and 0.684 mM of glutamine. The growth curve shows sigmoidal behavior with five distinct phases: lag, exponential, linear, deceleration and decline. It was verified the presence of cells with meristematic characteristics from the 7th day of induction, suggesting that the calli have embryogenic potential. However, differentiation of somatic embryos was not observed. There was a reduction in RA content and increase in AST and sucrose during the lag phase and beginning of the exponential phase, followed by degradation in the exponential phase until the decline phase, showing the involvement of these carbohydrates with callus growth. These results are unprecedented for the species and suggest future studies related to callus maturation aiming the differentiation of somatic embryos.