No abstract

Investigations on phosphorous uptake, photosynthetic 14CO2 fixation, assimilate translocation and endogenous cytokinin concentrations were carried out with carrot plants at low and high level phosphorus supply. Source/sink relations were changed in favour of the source (shoot) and at the expence of the sink (root) by GA3 sprays. Following GA3 treatments the 2‐isopentenyl adenine (2iP) concentration in the tap root was strongly decreased. However, though sink development was drastically reduced due to this treatment, the concentration of translocated labelled assimilates (mainly sucrose) was almost doubled in the tap root as compared to the untreated controls. In plants optimally supplied with phosphorus growth, 2iP concentration in the tap root, photosynthetic CO2 fixation and assimilate translocation were considerably increased in comparison with the low phosphorus treatment.

The decrease in yield productivity of carrots on nitrogen and phosphate depleted soil could be compensated by 6‐BA sprays. In nitrogen or phosphorus deficient plants the concentration of 2‐iP and 2‐iPA are lower than in the control and an increase could be observed following 6‐BA applications. Nitrogen or phosphorus uptake of deficient plants was virtually not affected by 6‐BA application. Consequently dry matter production per unit nutrient taken up by the plants (nutrient efficiency ratio) was increased as compared to the optimally with nitrogen and phosphate supplied control or the deficient plants.