Growth and metabolism of cucumber in phosphate-deficient conditions

The influence of phosphate deficiency on the growth, phosphatase activity, CO2 exchange, and sugar accumulation in the leaves and roots of cucumber (Cucumis sativus L.) was studied during 4 weeks of plant culture, The growth on nutrient medium without phosphate decreased Pi (inorganic orthophosphate) content in leaves and roots of plants to about 10% of control. Phosphate starvation significantly decreased growth of shoots and mass of roots, whereas root elongation growth was enhanced (diameter of root decreased). Intensity of root elongation was most pronounced at the beginning of culture on P-deficient medium and remained similar even after transfer to full nutrient medium. Phosphate-deficient cucumber plants had higher acid phosphatase activity both in extracts from roots and leaves and in root exudates when compared to samples from phosphate-sufficient plants. Photosynthesis rate was not affected at the beginning of culture but decreased significantly in leaves of 36-day-old -P (phosphate-deficient) plants. Reducing sugars and sucrose content increased in all tissues of phosphate-deficient plants as compared to control plants but only at a moderate stage of phosphate deficiency (24-day-old plants). Carbohydrate content declined during the subsequent week of growth, possibly because of inhibitory effects of advanced phosphate deficiency on photosynthesis and sugar production.