Physiological Studies on Nitrate Absorption and Accumulation in Lettuce (Lactuca Sativa L.) Genotypes
Freiji, Fadi George
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https://hdl.handle.net/2142/71789
Description
Title
Physiological Studies on Nitrate Absorption and Accumulation in Lettuce (Lactuca Sativa L.) Genotypes
Author(s)
Freiji, Fadi George
Issue Date
1988
Doctoral Committee Chair(s)
Swiader, John M.
Department of Study
Horticulture
Discipline
Horticulture
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(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.
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