Heading cabbage plants, Brassica oleracea L. (Capitata group) grown under humidity conditions which allowed root pressure flow to occur during the dark period, as indicated by the occurrence of guttation from the leaf margins, remained free of tipburn. Plants grown under conditions which prevented root pressure flow from occurring developed tipburn on both wrapper and inner head leaves. The effect of root pressure flow on 45Ca transport was studied in cabbage plants in the rosette stage of growth. Heads were simulated by covering the inner leaves of the plants. 45Ca was readily transported to inner “head” leaves under high humidity which allowed root pressure flow to occur, while very little 45Ca was moved to these leaves under low humidity which prevented root pressure flow. The data indicate that root pressure flow is required to move adequate amounts of Ca to prevent tipburn in head leaves of cabbage.
Seedlings of carrot (Daucus carota L.) develop leaf necrosis when subjected to conditions which encourage rapid growth in controlled-environmental chambers. Necrosis occurred on the 4th and 9th developing leaves and was apparent as they unfolded. Injury was determined to be calcium-related, since foliar CaCl2 applications reduced injury and covering the plants during the dark period to promote translocation of Ca by root pressure flow stopped injury completely. Young unfolding leaves in covered plants had 50% greater Ca concentrations than those plants maintained in the chamber without covering. Carrot cultivars had different degrees of sensitivity to the leaf necrosis with ‘Red Core Chantenay’ > ‘Danvers’ > ‘Carousel’ > ‘Scarlet Nantes’.