Evaluating Parameters for the Optimization of Jatropha curcas Cell Cultures for Microgravity Studies

Jatropha (Jatropha curcas) is a tropical perennial species in the Euphorbiaceae, which has been identified as a potential biofuel crop.  The oil characteristics are of excellent quality and biodiesel from jatropha has been successfully tested in diesel engines and in jet fuel mixes.  However, studies on breeding and genetic improvement of jatropha are incipient. We have initiated in vitro studies aiming the development of clonal propagation and regeneration protocols. Such studies involve evaluating the effects of microgravity in jatropha cell cultures for growth, multiplication and regeneration, and gene expression as an attempt to identify genetic changes that could help accelerate a breeding program for jatropha.  Microgravity studies are performed at the International Space Station National Laboratory.  However, before microgravity studies can be successfully performed, pre-flight experiments are necessary to evaluate flight hardware conditions and to optimize parameters for such studies. The objectives of this study were to compare the in vitro growth of three explant sources (cotyledon, leaf, and stem) from three jatropha accessions (Brazil, India, and Tanzania) outside and inside the Group Activation Pack (GAP) flight hardware (BioServe, University of Colorado).  In vitro cell cultures were established using a modified MS medium dispensed in petri dishes and maintained in a plant growth chamber at 25 ± 2 ºC in the dark. Ten plates were randomly per GAP with an average of 30 replications per parameter evaluated. Percent area (A), dry weight (DW) and fresh weight (FW) increases were evaluated at 7 and 12 weeks to simulate the period of microgravity studies. No differences were observed for A, FW and DW for cells cultures within the same accession and for the same explant type between inside and outside the GAP.  However, differences were observed for accession and explant type for both inside and outside the GAP.  Here we report only the results for inside the GAP as they have higher relevance to microgravity studies.  The accession from Tanzania had higher A and FW inside the GAP, followed by Brazil and India, respectively. Cotyledon tissues had higher A, FW and DW inside the GAP, followed by leaf and stem tissue, respectively. The present study demonstrated that jatropha cell cultures are capable of survival and growth inside GAPs for a period of 12 weeks and therefore justify a model for microgravity studies. Genotype and explant source play a major role in determining the success of such studies and must be optimized accordingly.