Efficiency of the Polyethylene-Glycol (PEG) Embedding Medium for Plant Histochemistry.

Histochemical analyses in plants are commonly performed on hand-made sections of fresh materials. The disadvantages of embedding in historesin, paraffin or paraplast® are the alterations to cellular contents, the high costs and few evident results, depending on the test. Polyethylene-glycol (PEG), as a low cost, hydrophilic medium that maintains most of the cellular features similar to fresh conditions, may be useful for obtaining good histochemical results in thinner and homogeneous sections. The current study aimed to compare the efficiency of PEG as an embedding medium for histochemical analyses of primary and secondary metabolites accumulation. Using hand-made sections of fresh samples (T1) as a comparison, we tested the influence of the use of Karnovsky's solution as a fixative (T2) versus embedding in PEG (T3). The samples herein analyzed comprise leaves, stems, seeds and insect galls of different plant species. Neither the Karnovsky's fixative nor the embedding in PEG altered the histochemical results for starch, lipids, terpenoids, proteins and reducing sugars in T1, T2, and T3. However, PEG binds to phenols, such as tannins, flavonoids and lignins, thereby presenting false negatives in T3.