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|Title:||Physiological Studies on Nitrate Absorption and Accumulation in Lettuce (Lactuca Sativa L.) Genotypes|
|Author(s):||Freiji, Fadi George|
|Doctoral Committee Chair(s):||Swiader, John M.|
|Department / Program:||Horticulture|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Biology, Plant Physiology|
|Abstract:||Nitrate uptake by lettuce from nutrient solution over concentrations below 100 $\mu$M NO$\sb3\sp-$ showed a single-phase saturation pattern typical of Michaelis-Menten kinetics. The NO$\sb3\sp-$ uptake system was saturated at NO$\sb3\sp-$ concentrations between 40 and 90 $\mu$M, and exhibited relatively high net uptake capacity and high affinity for NO$\sb3\sp-$.
Initially, depletion of NO$\sb3\sp-$ was considerably slower in plants pretreated with minus-N solution ($-$N) for 45 hours before depletion than in plants continuously supplied with NO$\sb3\sp-$ (+N). Root NO$\sb3\sp-$ concentrations were significantly decreased by the $-$N pretreatment. Net NO$\sb3\sp-$ influx decreased while the root affinity for NO$\sb3\sp-$ increased with increasing plant age and lower root NO$\sb3\sp-$ concentrations. The data suggest that NO$\sb3\sp-$ uptake in lettuce is an efficient process inducible by internal NO$\sb3\sp-$. The results also support the hypothesis of allosteric regulation of NO$\sb3\sp-$ uptake by internal NO$\sb3\sp-$ concentration, and the contention that the NO$\sb3\sp-$ uptake carriers may exhibit gradual degradation during prolonged NO$\sb3\sp-$ deprivation.
Genetic variation in leaf NO$\sb3\sp-$ accumulation was evident among the four lettuce genotypes used. Leaf NO$\sb3\sp-$ accumulation in butterhead genotypes (but not in cos lettuce) decreased as organic N concentrations in the roots increased. Genotypic differences in leaf NO$\sb3\sp-$ accumulation, however, could not be explained on the basis of differences in root organic N concentration. Apparently, accumulation differences of NO$\sb3\sp-$ among genotypes were not solely the result of variation in their root reduction capacity. Nitrate levels in the leaves were not affected by the NO$\sb3\sp-$ partitioning pattern between the roots and leaves of the lettuce genotypes. A differential capacity for NO$\sb3\sp-$ uptake of whole plants was noted among cultivars which was consistent with their differential capacity to accumulate NO$\sb3\sp-$ in the leaves. All genotypes, however, had similar root uptake capacities.
It is proposed that root organic N concentration could be a good indicator of the leaf NO$\sb3\sp-$ accumulation potential in lettuce. However, breeding efforts should not focus only on increased production of organic N in the roots, but also on developing lettuce cultivars with relatively faster growth rates resulting in growth dilution of the NO$\sb3\sp-$ absorbed and translocated from the roots to the leaves.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1988.
|Date Available in IDEALS:||2014-12-16|