Physiology and Molecular Biology of Stress ... - KHAM PHA MOI

210
K. Janardhan Reddy
18. MOLECULAR BIOLOGY OF MINERAL NUTRITION
Earlier work on the genetic basis of mineral uptake and efficiency was initiated by plant
scientists to check better varieties for cultivation of soybean by U.S.D.A. In soybean
(Glycine max) Bernard and Howell (1964) found that a pair of alleles at a single locus
named Np and nP control the response to high level of phosphate in the soils. Genotype
NpNp showed little sensitivity to high phosphate (P-tolerant) as compared to
other genotype having npnp being very sensitive (intolerant) to phosphate. Application
of heavy doses of phosphorus fertilizers is accompanied by P-induced zinc deficiency.
In such cases the need to look for genotypes from vast germplasm available
should be made. The criteria for selection of genotypes should be those which give
good yields with reference to
1. Adaptability to low P
2. Ability to gather P from low P soils
3. Responses to P
4. Tolerance to reasonably to high P without inducing Zn deficiency
Brown (1987) emphasized molecular approach to the problem of physiology of genotypic
differences in Zn, Mn, Cu uptake in rice and tomato. The greater Zn and Cu uptake
rates in rice was due to greater affinity of carrier sites in the root apices. In tomato, rapid
uptake of Zn and Cu was due to greater capacity to absorb these ions due to higher
concentrations of carrier molecules in roots. Ni et al., (1996) discusssed the genotypic
differences in phosphorus stress induced changes in rice seedlings.
Novel approaches for genetic improvement of plant cultivars through recombinant
DNA technology will throw up new avenues to tailor plants for better yields and
efficient mineral nutrition. Isolation and characterization of genes involved in the uptake
of minerals and their interaction within the various plant tissues will undoubtedly
throw light on the mechanism operating in the optimum utilization of minerals for developing
healthy and productive plants. Lee et al., (2003) found that transgenic Arabidopsis
thaliana plants shown resistance to heavy metal stress with reduced uptake of lead
and cadmium in heavy metal contaminated soils. For iron transport LeNramp1 protein
was identified by Bereczky et al., (2003) in roots of tomato. Hussain et al., (2004) demonstrated
that HMA 4
(transporter protein) was responsible for the transport of zinc in
leaves of Arabidopsis thaliana. ShMTP1 located in the intracellular membrane of roots
and leaves of Stylosanthes hamata was involved in the transport of manganese (Delhaize
et al., 2003). Wintz and Vulpe (2002) found three copper chaperones in Arabidopsis
thaliana. They suggested that these chaperones (metal receptors proteins) are involved
in the uptake of copper as well as transport from cells.
Infact, efforts are underway to characterize structural and regulatory genes,
signal transduction pathway, operating during ion mobilization by roots, their transport