Growth-limiting phosphate nutrition suppresses nitrate accumulation in greenhouse lettuce

Asymmetric Synthesis of Oxygen Heterocycles via Pd‐Catalyzed Dynamic Kinetic Asymmetric Transformations: Application to Nucleosides

“…5 would mean that assimilated‐C accounted for approximately 76% of any osmotic effects resulting from differences in nitrate concentration across the range of accessions. The assumptions used in this calculation are only approximate, but the result is broadly consistent with measurements on individual lettuce cultivars, where the proportion of organic acids plus soluble carbohydrates used to balance nitrate ranged from 60 or 68%12 to figures approaching 100% 44. Any deficit in this balance may be made good by changes to the concentrations of other inorganic ions within the shoot and by adjustments to the shoot water content 13…”

“…The accumulation of alternative organic osmotica (including soluble carbohydrates, organic anions, etc.) in plants with lower nitrate concentrations also tends to increase their DM content10–13 and contributes to the reduction in the proportion of water present in their shoots. The parallel relationships within each experiment (Fig.…”

“…Plant nitrate concentrations tend to rise when its rate of uptake exceeds that of its chemical reduction,4, 5 particularly when environmental stresses such as low light intensity or short day length restrict the energy for photosynthesis and nitrate assimilation 6, 7. Any nitrate that accumulates in plant tissues is not only used as a temporary store of N8, 9 but also acts as a replacement osmoticum for other plant solutes,10–13 helping maintain turgor and drive leaf expansion 14–16…”

Rate of change of composition of lettuce in response to nitrogen depletion or re‐supply

“…However, conditions that increased sugars also decreased tissue nitrate. For lettuce grown under limiting phosphorus addition rates, nitrate was inversely related to the sum of sugars and organic acids 30. Nitrate varied from 75 to 25 mmol kg −1 fw, as sugars as hexoses increased from 50 to 75 mmol kg −1 fw, due to the growth restriction.…”

Screening for genotype and environment effects on nitrate accumulation in 24 species of young lettuce

“…Although all non‐leguminous crops accumulate nitrate to a greater or lesser extent, leafy vegetables such as lettuce and spinach frequently exhibit high nitrate concentrations 5–7. Nitrate accumulation in these crops is also greater when light intensity is low5, 8 because there is less energy to convert it into reduced forms of N. There are also fewer organic solutes available to maintain turgor, with the result that the plants use more nitrate instead 9–13. Thus, while nitrate concentrations in lettuce can vary widely with changing light levels, variations in total osmolality are always much smaller9, 10, 13, 14 because of the combined effects of concentration and volume regulation within the shoot 13…”