Enhancement of leaf tipburn by restricting root growth in Chinese cabbage plants

SummaryIf Chinese cabbage (Brassica pekinensis) plants were grown in 10-1 pots, root growth was not restricted and leaf tipburn did not occur. However, in plants grown in 0.5-and 3.0-1 pots, root and shoot growth were restricted and tipburn developed, more so in the smaller pots. Restriction of root volume reduced soluble Ca++ content in young unaffected susceptible leaves; Ca++ was further lowered in leaves affected with tipburn. The levels of soluble Ca in the outer non-susceptible leaves were similar in the restricted and non-restricted plants. Irrigation with 10 mM of either Ca(NO3)2 or CaCl2 did not prevent tipburn in plants grown in the 0.5- and 3.0-1 pots. This treatment was also ineffective in increasing soluble Ca++ concentration in the susceptible young leaves. Abscisic acid levels were similar in the young leaves of the restricted and the non-restricted plants, suggesting that they did not experience drought stress. However, tipburn damage in the restricted plants was accompanied by an increase in ABA. It is therefore proposed that the increased ABA level is the result rather than the cause of the damage. The results suggest that the restriction of Chinese cabbage root growth by limiting root volume impairs Ca++ uptake and translocation into the young leaves, thereby causing tipburn.