Responses of plant seedlings to hypergravity: cellular and molecular aspects
Abstract
Hypergravity produced by centrifugation has been used to analyze the responses of plant seedlings to gravity stimulus. Elongation growth of stem organs is suppressed by hypergravity, which can be recognized as a way for plants to resist gravitational force. The mechanisms inducing growth suppression under hypergravity conditions were analyzed at cellular and molecular levels. When growth was suppressed by hypergravity, a decrease in the cell wall extensibility was brought about in various plants. Hypergravity also induced a cell wall thickening and an increase in the molecular mass of the certain hemicellulosic polysaccharides. Both a decrease in the activities hydrolyzing such polysaccharides and an increase in the apoplast pH were involved in such changes in the cell wall constituents. Thus, the cell wall metabolism is greatly modified under hypergravity conditions, which causes a decrease in the cell wall extensibility, thereby inhibiting elongation growth in stem organs. On the other hand, to identify genes involved in hypergravity-induced growth suppression, changes in gene expression by hypergravity treatment were analyzed in Arabidopsis hypocotyls by differential display method. Sixty-two genes were expressed differentially: expression levels of 39 genes increased, whereas those of 23 genes decreased under hypergravity conditions. The expression of these genes was further analyzed using RT-PCR. One of genes upregulated by hypergravity encoded hydroxymethylglutaryl-CoA reductase (HMGR), which catalyzes a reaction producing mevalonic acid, a key precursor of hormones such as gibberellic acid and abscisic acid. The expression of HMGR gene increased within several hours after hypergravity treatment. Also, compactin, an inhibitor of HMGR activity, prevented hypergravity-induced growth suppression, suggesting that HMGR is involved in suppression of Arabidopsis hypocotyl growth by hypergravity. In addition, hypergravity increased the expression levels of CCR1 and ERD15, which were shown to take part in the signaling pathway of environmental stimuli such as temperature and water. These cellular and molecular changes appear to be involved in a series of events leading to growth suppression of stem organs under hypergravity conditions.
- Publication:
-
34th COSPAR Scientific Assembly
- Pub Date:
- 2002
- Bibcode:
- 2002cosp...34E.913H