Premium
Alleviation of Copper Rhizotoxicity by Calcium and Magnesium at Defined Free Metal‐Ion Activities
Author(s) -
Parker David R.,
Pedler Judith F.,
Thomason David N.,
Li Huiying
Publication year - 1998
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1998.03615995006200040017x
Subject(s) - apoplast , elongation , chemistry , magnesium , calcium , copper , metal , chelation , metal ions in aqueous solution , nuclear chemistry , ionic strength , bioassay , inorganic chemistry , aqueous solution , metallurgy , biochemistry , ultimate tensile strength , materials science , biology , genetics , cell wall , organic chemistry
The common “hardness cations”, Ca and Mg, are at least partially capable of alleviating the toxicities of metal ions, but quantitative data for their effect on Cu rhizotoxicity are lacking. We used 2‐d root elongation of wheat ( Triticum aestivum L., cv. Yecora Rojo) in a simple medium (≥0.2 m M CaCl 2 ) as a sensitive bioassay for examining how Ca, Mg, and pH affect Cu rhizotoxicity. A fourfold increase in solution Ca T from 1 to 4 m M showed a slight alleviation of toxicity, but the effect could be completely ascribed to changes in ionic strength and thus in Cu 2+ activity. Subsequently, a 25‐fold range in Ca T (17‐fold range in Ca 2+ activity) was found to improve Cu‐inhibited root elongation by some 30 to 35%. Increases in solution Mg 2+ activity were equally or slightly more effective than comparable increases in free‐ion activity [denoted by parentheses, i.e., (Ca 2+ )] of Ca in alleviating Cu stress, an unexpected result because of reports of selective binding of Ca by apoplastic sites. Neither cation alleviated Cu rhizotoxicity as profoundly as they do with other metals such as Al. Lowering pH from 6.5 to 5.5 alleviated Cu stress slightly; a further decrease to pH 4.5 was more effective. Finally, seedlings were reared en masse in nine treatments selected from the previous root elongation studies, and root tips were analyzed for operationally defined apoplastic and symplastic Cu. Growth inhibition was only weakly correlated with symplastic Cu (or with apoplastic or total Cu), and the results suggested that Ca and Mg (but not H) afford some physiological protection against Cu that is not explained by simple competitive inhibition of Cu accumulation in the apical tissues.