The influence of relative humidity on vitrification, growth and morphology of Gypsophila paniculata L.

A vitrification scoring system was devised that comprised a visual assessment of vitrification in vitro followed by transplanting of plantlets ex vitro and recording of plantlet survival rates. This proved to be a simple method of predicting survival of plantlets ex vitro and demonstrated that vitrification severity is more important than acclimitization procedures in promoting survival ex vitro. Growth of normal plantlets in liquid medium in an environment where plantlets are able to transpire made it clear that lack of transpiration as opposed to high water availability is the primary cause for induction of vitrified growth. Finally, small decreases in relative humidity in vitro were found to be sufficient to increase plantlet transpiration to the extent that vitrification is greatly reduced and survival ex vitro increased. Small differences in relative humidity also influenced plantlet morphology with plantlets grown at a higher relative humidity being larger and consisting of more shoots than plantlets grown at a lower relative humidity. It is suggested that in vitro relative humidity may be manipulated to produce plantlets of a particular morphology and should be measured in tissue culture experiments and included in the materials and methods sections of papers to ensure correct interpretation of results.