| Description: | Soluble aluminum (Al3+) is toxic to plants. Aluminum stress (Al-stress) is a major limiting factor for crop production on greater than 30% of the world's arable land. How plants respond to Al-stress is not well understood at the molecular level, while our understanding is better at the physiological and genetic levels. This is a proposal to screen for Al-inducible and repressible genes, using microarray technology, to better characterize the molecular aspects of Al-stress response in the light of physiological and genetic information. Al-stress has the ultimate effect of inhibiting root growth and function. Al-stressed plants have poorly developed roots that acquire nutrients and water inefficiently. The root apex is the most sensitive part of the root to this stress. Cell elongation and division are inhibited within minutes of the root being exposed to Al. Cellular metabolism is disturbed in several ways, as Al can displace essential cationic cofactors (e.g. Mg2+), thus inactivating proteins, and also lead to the generation of free radicals. The root apex is also the site of stress perception and response. In maize and wheat, root apices release organic acid ligands (e.g. citrate) to exclude Al within minutes of root exposure. Arabidopsis performs similarly to these plants. Citrate release is induced by Al-stress. Al-tolerance genes have been identified by QTL mapping, using the Col x Ler population. Functions for two of the four QTL have been proposed; candidate genes are being evaluated for further assessment. A confounding factor of these experiments is that Al is only soluble in acidic conditions. Thus, all experiments are carried out at pH 4.2. Arabidopsis tolerates growth at pH 4.2, but does not thrive as the acid stress also has physiological consequences. To identify changes in gene expression that are directly related to the Al-stress, we will grow both the Al-treated and control populations of Columbia seedlings (7 days old) at pH 4.2. Comparisons between existing data sets from Col roots grown under standard hydroponic conditions and both experimental treatments should clarify which genes respond to the acid stress and which respond to Al. RNA will be isolated from the roots of liquid culture grown plants eight hours after transfer to fresh acidic media with and without added Al. According to other studies, an eight-hour treatment should be sufficient to elicit most changes in gene expression |
NASCArrays Information at The BAR
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