Submitted to: Northeastern Naturalist
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/20/2009
Publication Date: 8/15/2009
Citation: Chaney, R.L., Fellet, G., Torres, R., Centofanti, T., Green, C.E., Marchiol, L. 2009. Using Chelator-Buffered Nutrient Solutions to Induce Ni-Deficiency in the Ni-Hyperaccumulator Alyssum murale. Northeastern Naturalist 16 (Special Issue 5):215-222. Interpretive Summary: Ni deficiency has recently been shown to have economic significance to pecan and other crops. Controlled study of Ni deficiency has been very difficult because of the low requirement of plants for Ni, and levels present as contaminants in soils and nutrients used in nutrient solution study. Further, this group has been studying species such as Alyssum murale which can accumulate over 20,000 mg Ni/kg without injury and can be used to phytomine soil Ni as an alternative to traditional mining technologies. Based on earlier studies, it seemed possible that the Alyssum species may require higher amounts of Ni than normal crop plants and it might be easier to induce Ni deficiency in a species with a higher Ni requirement. Thus, several Alyssum species and tomato were grown in chelator-buffered nutrient solutions to control the concentration of Ni free ions to very low levels (10E-16 mol/L). One experiment appeared to induce strong Ni deficiency, and additional Ni had to be added to obtain normal growth of the plants; this study suggested that the hyperaccumulator plants required 10E-11.9 mol Ni/L for growth. A second study was conducted using a different chelating agent to buffer Ni at higher levels. In this test, the plants did not show Ni deficiency, so the experiment was split with half the plants used in treatments equivalent to the first study. After 30 days, higher Ni activity gave increased shoot biomass and higher shoot Ni. No clear symptoms were seen, however. Analysis of the seeds showed they contained 7000-9000 mg Ni/kg, and that the seeds could supply enough Ni to prevent deficiency for at least several grams of shoots. The experiments indicate a range of Ni free ion activity required for growth, and indicate that seed lower in Ni should be used in such studies.
Technical Abstract: Ni is essential for all plants due to its role in urease. Many Alyssum species are known to hyperaccumulate Ni to over 20 g kg-1 dry weight (DW) while normal plants require only about 0.1 mg kg-1 DW. As part of our research on Ni hyperaccumulation by plants, we conducted experiments to measure the activity of free Ni2+ required for growth of Alyssum murale, Alyssum corsicum, Alyssum montanum and tomato grown in a modified Hoagland nutrient solution with 2 mM Mg and 1 mM Ca to simulate serpentine soil solutions. We used chelator-buffered nutrient solution to control the activity of free ions of the micronutrient cations. In the first experiments we used hydroxyethyl-ethylene-diaminetriacetate (HEDTA) to achieve Ni2+ levels as low as 10-16 M. With urea-N supply, the plants did not grow after transfer to the low Ni solutions, while nitrate-grown plants thrived. Symptoms agreed with urea toxicity/Ni deficiency. We had to add additional Ni to obtain growth with the HEDTA system and estimated the requirement at 10-11.9 M Ni2+ for normal growth with urea-N.; A. montanum behaved similarly as the hyperaccumulators. A second Ni deficiency test was conducted using cyclohexane-ethylenediamine-tetraacetate (CDTA) to supply higher activities of buffered Ni2+ and cover the range of the requirement estimated from the first experiment. By the end of the test period, yields were reduced at lower Ni activity but strong symptoms of deficiency did not occur apparently due to the supply of Ni from seeds (7000-9000 mg Ni kg-1). Chelator buffering supplied controlled levels of Ni2+ for all test species, and very low plant Ni levels were attained. Reaching frank Ni deficiency will require longer growing periods or using seeds with lower initial Ni levels, such as from plants grown on normal soils rather than serpentine soils.