Effect of 24-Epibrassinolide on Growth of in Vitro Shoot Tips of Different Yam (Dioscorea Spp.) Species

Cryopreservation is a process where organelles, cells, tissues, extracellular matrix, organs or any other biological constructs susceptible to damage caused by unregulated chemical kinetics are preserved by cooling to very low temperatures (liquid nitrogen, −196˚C). It is a safe and cost-effective option for long-term conservation of vegetatively propagated plants such as yam.

24-epibrassinolide (EBR) belongs to brassinosteroids (BRs), a class of plant steroid hormones which possess significant growth controlling activity and are involved in the promotion of cell elongation, cell division, differentiation, disease resistance, stress tolerance, and senescence throughout the plant life cycle.

In this work, the authors compared the effect of the growth regulator content of the culture medium on the growth of in vitro shoot tips of five yam accessions belonging to four yam species (one Dioscorea alata, one D. rotundata, one D. cayenensis and two D. trifida). Medium S contained 0.6 μM benzyl adenine, 1.07 μM naphthalene acetic acid and 0.23 μM gibberellic acid while medium EBR contained 0.23 μM gibberellic acid and 0.1 μM 24-epibrassinolide. The experiment was performed once, with three replicates of 10 shoot tips per experimental condition. After 1 and 2 months of culture on medium S or EBR, the size of shoot tips (mm) was measured and the oxidation level was evaluated using a scale from 0 (no oxidation) to 3 (very high oxidation). One-way ANOVA was performed to compare the growth of shoot tips and oxidation levels on medium S and EBR. Means were statistically differentiated using Duncan test at a significance level of Po < 0.05.

The results showed that after 2 months of culture, oxidation level was significantly reduced on medium EBR compared to medium S for four of the five accessions tested. By contrast, medium EBR did not have any positive effect on shoot length since length of shoots produced after 2 months of culture on medium S and EBR were similar, except with accession 3-45T, for which shoot length was shorter on medium S compared to medium EBR.

In conclusion, these results underline the potential of 24-epibrassinolide to reduce oxidation phenomena during in vitro culture and call for its utilization for regeneration of cryopreserved yam shoot tips, which is often impeded by oxidation phenomena.

Article by Isabelle Engelmann-Sylvestre and Florent Engelmann, from France.

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