Requirement of Mineral Nutrient Elements and its Estimation for Crops

Ca binding to pectins and all other Ca-dependent processes. Additionally, A1 phosphates can be precipitated in the vascular system, and this inhibits vater and substance transports betv een plant organs the result is seen as plant vilting. 

In many higher plants mechanisms exist which facilitate adaptation to such unfavorable conditions. This can be achieved by avoidance of the stress factor, by tolerance, or by both strategies. The relative importance of the various mechanisms depends on plant species and ecotypes, as well as on the special element. The following seven possibilities are most important  

Release of organic acids for complexing ions outside the root apoplast plays a role in Ah -tolerant cultivars of maize and wheat. The excreted (or exuded) malic and/or citric acid incorporates Ah into negatively charged stable anion complexes which are harmless for roots and which are not taken up (Jones etal. 1996). 

Binding to cell walls is important for cations of Cd, Zn, Fe, and Cu. These are sorbed at negatively charged sites of poly-galacturonic acids, or precipitated for instance as Zn silicate (Neumann and Zur Nieden 2001). Copper can also be bound to glycoproteins or proteins (Van Cutsem and GUlet 1982). 

Restricted influx through the plasma membrane is the most important mechanism for excluding distinct ions from the protoplasm. The ion specificity of transporters is operating within the limits outlined above. 

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Requirement of Mineral Nutrient Elements and its Estimation for Crops I 297... 

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