Longevity of dry Myrothamnus flabellifolius in simulated field conditions.

Farrant, J; Kruger, L

Longevity of dry Myrothamnus flabellifolius in simulated field conditions.

Journal Article

2001

Journal Title

Plant Growth Regulation

Link to Journal

http://link.springer.com/journal/10725

Publisher

Springer

Publisher

University of Cape Town

Abstract

This study tested the length of time the desiccation-tolerantMyrothamnus flabellifolius could remain in the dry stateunder simulated field conditions, without losing viability. Dry plants werekeptat 50% relative humidity, with a 25/16 °Cday/night temperature regime and a daylight intensity of 1200μmol·m−2 s−1. At threemonthly intervals plants were rehydrated and the ability to resume respiration,photosynthesis, protein synthesis and transcription was assessed and changes insubcellular organisation and plant growth regulator content (zeatin, zeatinriboside and abscisic acid) monitored. Plants survived in the dry state foronly one year. The ability toresurrect metabolism in existing leaves was lost after nine months, after whichsurvival occurred due to regrowth of new leaves from meristems. There waslittleevidence of subcellular damage in leaf tissues of plants kept dry for up to sixmonths. These plants recovered respiration before the onset of translation (andthus repair) suggesting considerable subcellular protection of this metabolismagainst desiccation damage. Furthermore, full recovery of metabolism, includingphotosynthesis, occurred before the onset of transcription in these plants.Somesubcellular damage occurred in plants maintained dry for nine months. There wasincreased electrolyte leakage indicative of membrane damage which was repairedwith the onset of protein synthesis. Since this repair occurred before theonsetof transcription, it is likely that stored mRNA, present in the dry leaves, wasused. Recovery of photosynthesis in plants dried for 9 months was delayed untilthe onset of transcription. We propose that mRNA for recovery of thismetabolismis not stored during drying and thus damage to the photosynthetic apparatus canbe repaired only upon de novo transcription of the genome.In leaves that were able to resurrect, cytokinin content increasedtransiently just prior to onset of chlorophyll biosynthesis and translation,andabscisic acid content increased just prior to the onset of transcription. Theseplant growth regulator changes did not occur in leaves which did not resurrect,but we cannot distinguish whether it was the lack of signal, or the extent oftissue damage (or both) which prevented the repair and recovery of metabolisminthese tissues.