|Huynh, Le Nguyen|
Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/5/2004
Publication Date: 3/29/2005
Citation: Huynh, L., Vantoai, T.T., Streeter, J., Banowetz, G.M. 2005. Regulation of flooding tolerance of sag12:ipt arabidopsis plants by cytokinin. Journal of Experimental Botany. 56(415):1297-1407. Interpretive Summary: Flooding causes a severe constraint on crop growth and it affects about 16% of the agricultural production areas worldwide. Flooding can mean either waterlogging, where only the roots are flooded, or complete submergence where the entire plants are under water. A constructed gene which increases the production of the anti-aging plant hormone cytokinin, was introduced into Arabidopsis plants as a means to improve plant tolerance to flooding. Submergence and waterlogging were applied to two-week-old natural and altered plants for 1, 3, or 5 days. Following flooding, plants were allowed to recover for 5 days. Tolerance to flooding stress and post-flooding recovery were quantified by dry weight accumulation and soluble sugar and chlorophyll contents. Cytokinin accumulation was also determined at these same time points. Under waterlogging, altered plants accumulated greater quantities of cytokinin more rapidly, retained more chlorophyll, and increased both dry weight and sugar content. This study established the relationship between flooding tolerance and cytokinin accumulation and suggested that genetic transformation with the anti-aging gene is a potential approach to improve flooding tolerance of crops.
Technical Abstract: A SAG12: ipt gene construct which increases cytokinin biosynthesis in response to senescence was introduced into Arabidopsis plants in a strategy designed to delay the senescence induced by flooding stress. Submergence and waterlogging stresses were applied to two-week-old SAG12:ipt and wild-type plants for 1, 3, and 5 days. Plants of the post-flooding experiment were allowed to recover for 5 days. The phenotypic responses to flooding stress and post-flooding recovery were quantified as biomass accumulation, and carbohydrate and chlorophyll contents. Cytokinin and abscisic acid (ABA) accumulation were quantified at these same time points. Real-time RT-PCR studies were performed to quantify ipt and SAG12 gene expression. Under waterlogging stress, SAG12:ipt plants accumulated greater quantities of cytokinins more rapidly which accompanied the phenotypic adaptations including chlorophyll retention and increased biomass and carbohydrate content relative to wild-type plants. Similarly, SAG12:ipt plants showed improved recovery after waterlogging stress was removed. Expression of the ipt gene in submerged plants did not result in cytokinin accumulation; but after the submergence stress was removed, SAG12:ipt plants accumulated greater quantities of cytokinin and recovered to a greater extent than wild-type plants. This study established the relationship between flooding tolerance and cytokinin accumulation in SAG12:ipt plants and suggested that translation of ipt transcripts and subsequent cytokinin accumulation were diminished or delayed under submergence stress where oxygen is limited.