Species, resistant plant

Aluminium toxicity is a major stress factor in many acidic soils. At soil pH levels below 5.0, intense solubilization of mononuclear A1 species strongly limits root growth by multiple cytotoxic effects mainly on root meristems (240,241). There is increasing evidence that A1 complexation with carboxylates released in apical root zones in response to elevated external Al concentration is a widespread mechanism for Al exclusion in many plant species (Fig. 10). Formation of stable Al complexes occurs with citrate, oxalate, tartarate, and—to a lesser extent— also with malate (86,242,243). The Al carboxylate complexes are less toxic than free ionic Al species (244) and are not taken up by plant roots (240). This explains the well-documented alleviatory effects on root growth in many plant species by carboxylate applications (citric, oxalic, and tartaric acids) to the culture media in presence of toxic Al concentrations (8,244,245) Citrate, malate and oxalate are the carboxylate anions reported so far to be released from Al-stressed plant roots (Fig. 10), and Al resistance of species and cultivars seems to be related to the amount of exuded carboxylates (246,247) but also to the ability to maintain the release of carboxylates over extended periods (248). In contrast to P deficiency-induced carboxylate exudation, which usually increases after several days or weeks of the stress treatment (72,113), exudation of carboxylates in response to Al toxicity is a fast reaction occurring within minutes to several hours... 

Paraquat (l,r-dimethyl-4,4 -bipyridinium) and its dichloride salt (1,1 -dimethyl-4,4 -bipy-ridinium dichloride) are broad-spectrum contact plant killers and herbage desiccants that were introduced commercially during the past 35 years. Today, they rank among the most widely used herbicides globally and are frequently used in combination with other herbicides. The recommended field application rates for terrestrial weed control usually range between 0.28 and 1.12 kg paraquat/ha (0.25 and 1.0 pounds/acre) for aquatic weed control, it is 0.1 to 2.0 mg/L. Target plant species are unable to metabolize paraquat and tend to contain elevated residues paraquat-resistant... 

Meharg AA, Hartley-Whitaker I. 2002. Arsenic uptake and metabolism in arsenic resistant and nonresistant plant species. New Phytologist 154 29-43. 

It seems reasonable that susceptibility and resistance of different plant species and different varieties within a species should depend on concentrations of endi enous antioxidants. The results of such studies do not give a clear picture Hanson et al. concluded that the range of susceptibility in petunia varieties depended on the ascorbic acid concentration, but Menser found that the ascorbic acid content of tobacco varieties was not related to ozone susceptibility. Ozone resistance of plants can be conferred by application of antioxidants. In the... 

Umemura K, Tanino S, Nagatsuka T, Koga J, Iwata M, Nagashima K, Amemiya Y (2004) Cerebroside eheitor confers resistance to fusarium disease in various plant species. Phytopathology 94 813-818... 

Other cyclic tetrapeptides have also been isolated by Japanese workers and AM toxins I, II, and III, isolated from Alternaria mail., are extremely toxic to certain plant species (9.10). These are constructed of L- i-hydroxyisovaleric acid, L-alanine, c-amino-acrylic acid and, in AM toxin I, L-6(-amino- -( .-methoxyphenyl)-valeric acid. The phenyl residue in AM toxin II is L-t(-amino-S-phenylvaleric acid, while in AM toxin III, it is L-ol-amino-( .-hydroxyphenyl)valeric acid (Figure 2), All the AM toxins produce leaf spot, or necrosis, in apple but as might he expected slight change in substitution (R-group) on the phenyl ring radically alters the specific activity of the molecule. Both AM toxin I and III induce interveinal necrosis in the "Indo" apple cultivar, which is also highly susceptible to A. mail. at concentrations as low as 0.1 pph within 18 h after treatment. In contrast, the resistant apple cultivar "Jonathan" is only affected by 1 ppm of AM toxin I and 10 ppm of AM toxin III. 

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