The influence of phosphorus nutrition and pH on the phosphatase activity of sugar beet roots

For the determination of acid phosphatase activity (P-ase) of sugar beet ro ots (cultivar Reka), plants were cultivated in nutrient solution with 1 or 100 mu M P in a growth chamber for 12, 18, 24, 30, 36 and 42 days. The phos phatase activity of intact roots was measured in buffer solutions with pH 4 to 7.2 and 14 mM p-Nitrophenylphosphate (NPP) after 10 min of incubation a t 20 degrees C. The influence of P nutrition on P-ase activity was signific ant at all intervals. At P deficiency the activity was increased by a facto r of 4 to 20. During the experimental period the pH optimum was 6. At pH 5 and 7.2 the P-ase activity reached only 63 and 64% respectively of the opti mum value. At P deficiency (1 mu mol P L-1) the absolute rate of NPP-hydrol ysis at pH 6 was 144 nmol min(-1) m(-1) root length (day 12 to 36). Thr pla nts which received optimum P supply showed only 10% of this value. Sugar beet roots with P deficiency have a high potential of P-ase activity from the acid to the neutral pH-range. Therefore, under this condition they may effectively use dissolved organic phosphorus compounds.