Water loss and photosynthesis of plum plantlets is influenced by relative humidity during rootingin vitro

Abstract

SummaryShoots of Mr. S. 2/5, a plum rootstock selected from Prunus cerasifera seedlings, were rooted in vitro at 100%, 90%, 80% and 70% relative humidity (r.h.). Decreases in r.h. led to increased resistance to water loss when the plantlets were subsequently exposed to a low environmental relative humidity. Statistically significant differences were observed after only 20 min of exposure. Differences increased progressively over time up to the end of the 90 min exposure period. In 80% and 70% r.h. treatments, the leaf waxy mesh was denser and presented thicker filaments. In addition, the reduction in r.h. induced a decrease in stomatal density; stomata were also more ellipsoidal and had a smaller opening. Net photosynthetic activity at the end of the in vitro rooting stage showed a slower rate in plantlets obtained from the 80% r.h. treatment compared with 100% r.h. plantlets; however, the total CO2 uptake over an 8 h period of illumination tended to be similar in plantlets from both r.h. treatments.