Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 1, 2000
Publication Date: June 1, 2001
Citation: BRAUER, D.K. 2001. RAPID INHIBITION OF ROOT GROWTH IN WHEAT ASSOCIATED WITH ALUMINUM UPTAKE AS FOLLOWED BY CHANGES IN MORIN FLUORESCENCE. JOURNAL OF PLANT NUTRITION. 24(8):1243-1253. Interpretive Summary: Soil acidity limits crop yields and increases the cost of production in many parts of the United States and the world. Acidic soils need continual additions of lime or alkaline materials for optimum crop production. The addition of lime every few years increases the cost of production by $20 to $40 per acre per year. Soil amendments remain the greatest discretionary spending by farmers in many parts of the United States. Thus, the cost of producing agricultural commodities and the land available for agricultural production would be increased if breeds of crops with enhanced tolerance to acidic soil conditions could be developed and widely used. Knowledge of how Al inhibits plant growth is needed by plant breeders and bioengineers to develop molecular markers for resistance to acidic soils. To date, there is no definite answer to the important question of whether or not the site at which Al, a toxic metal common in acidic soils, inhibits growth outside of or inside of the root cells. This study utilized fluorescence microscopy and the Al sensing dye, morin, to determine that inhibition of root growth was associated with the entry of Al into root cells. These results strengthen the case that Al must get into root cells to inhibit growth. These results are of interest to plant physiologists and plant breeders who are trying to develop breeds of plants with improved tolerance to acidic soils.
Technical Abstract: Acidic soils limit the land available for crop production and increase the cost of production in many regions of the United States and the world. The use of Al-resistant germplasm is one means of reducing the impact of acidic soils and development of such germplasm is limited by our understanding of the processes that confer resistance. This study sought to associate changes in root growth rate with Al entry into the tissue of two cultivars of wheat (Triticum vulgare L.) differing in sensitivity to Al. Changes in the spectral characteristics of morin were characterized to determine if a dual excitation or emission assay for Al could be developed. It was not possible to develop such a protocol. However, an assay based on changes in fluorescence intensity of morin was adopted from the work of Vitorello and Haug (Physiologia Plantarum 97:36-544, 1996). Addition of Al to a total concentration of 5 uM resulted in a 50% decrease in root elongation rate with the Al-sensitive cultivar, Atlas, but little change in root elongation with the Al-resistant cultivar, Scout. Inhibition of root growth occurred without a noticeable lag. The addition of Al to the external solution of bathing Atlas roots caused an increase in the fluorescence of intracellular morin, indicative of Al entry into the root cells. No increase in morin fluorescence was observed with Scout roots exposed to 5 uM Al. Therefore, there was an association between morin fluorescence, thus presumably Al entry, and inhibition of root growth.