EFFECTS OF FOLIAR POTASSIUM CONCENTRATION ON MORPHOLOGY, ULTRASTRUCTURE AND POLYAMINE CONCENTRATIONS OF SCOTS PINE NEEDLES

We examined the effects of three foliar potassium concentrations (high , intermediate and low) on the morphology, ultrastructure and polyamin e concentrations of current-year and 1- and 2-year-old needles of 30-y ear-old Scots pine (Pinus sylvestris L.) trees. Foliar K concentration had only a slight effect on needle morphology. The sclerenchyma cell walls were thinner, the xylem area was larger, and the resin ducts wer e smaller in needles with a low K concentration than in needles with a high or intermediate K concentration. In addition, the bundle sheath cells were collapsed in needles having a low K concentration. The seco ndary growth of phloem tissue and the mesophyll area were greater in n eedles with a high or intermediate K concentration than in needles wit h a low K concentration, possibly indicating greater production of pho toassimilates in these trees. At the ultrastructural level, mesophyll cells with enlarged central vacuoles and small vacuoles containing ele ctron-dense material were common in needles having a low K concentrati on. Enlargement of the central vacuole coincided with an exponential i ncrease in putrescine concentration in needles with a low K concentrat ion, suggesting that the central vacuole may function as a storage sit e for putrescine.