Effect of simulated microgravity conditions on a 3-dimensional clinostat on axillary bud growth induced by a removal of shoot apex in Alaska pea seedlings

Abstract

Effect of simulated microgravity (µG) conditions on a 3-dimensional (3-D) clinostat on outgrowth of the axillary (lateral) bud induced by a removal of shoot apex (decapitation) in pea (Pisum sativum L. cv. Alaska) seedlings was studied. After decapitation, decapitated seedlings were grown under 1 G or simulated µG conditions on a 3-D clinostat. When decapitation was made at 5 mm below the 1^st node in 5-day-old etiolated pea seedlings, an axillary bud started to outgrow at respective cotyledonary node. The application of auxin (indole-3-acetic acid) to the cut surface at the place of removed shoot apex substantially suppressed axillary bud outgrowth, indicating the outgrowth of axillary buds from the cotyledonary nodes is under the control of transported auxin. The outgrowth of the axillary buds was much larger on a 3-D clinostat than that under 1 G conditions. Similar tendency of the stimulation of axillary bud outgrowth in de-etiolated (light-grown) seedlings on a 3-D clinostat was observed. Together with our previous findings that in etiolated pea seedlings polar auxin transport is substantially reduced under true µG conditions in space as well as simulated ones on a 3-D clinostat, these results suggest that gravity-controlled polar auxin transport is involved in the regulation of decapitation-induced axillary bud outgrowth.