Curvature of carrot (Daucus carota L.) sticks is related to number and distribution of xylem vessels

Carrot sticks, marketed as vegetable snacks, often develop significant curv ature which is considered to be undesirable. Factors affecting curvature of sticks were investigated following incubation under defined conditions. Cu rvature was quantified by determining the angle between two tangents fitted to projections of a carrot stick. Curvature of commercially produced stick s following a 3 day-incubation period (5 degreesC, 75% RH) was highly varia ble and weakly related to segment angle (r = 0.23*) or the volume ratio of xylem to phloem tissue (r = -0.24*), but not affected by fresh mass of stic ks (r = -0.08), loss of fresh mass during incubation (r = 0.11) or volume o f xylem (r = -0.02) or phloem (r = 0.22). Since geometry and mass of commer cially produced sticks were variable, standardized sticks (80 mm length, 45 degrees segment angle, 5.5 +/- 0.5 g fresh mass and with a volume ratio of phloem to xylem of 1:0.33) were used in subsequent experiments. Curvature increased with increasing water vapor pressure deficit (range 20-566 Pa) at constant temperature (6 degreesC), but temperature (range 6-20 degreesC) a t constant water vapor pressure deficit (560 Pa) had no effect on curvature . Variation in curvature was larger For sticks prepared from different root s than for sticks from the same root. Proximal xylem vessels were arranged at high density in radial rays adjacent to the cambium (0-0.6 mm inwards fr om cambium), but distal vessels (0.6-5 mm inwards from cambium) were more r andomly distributed at markedly lower density. Curvature was related to the number of distal xylem vessels (r(2) = 0.43**) or to the ratio of number o f distal to proximal xylem vessels (r(2) = 0.66***), but only weakly to mas s loss (r(2) = 0.22*). Our data suggest that number and distribution of xyl em vessels were key factors determining curvature of carrot sticks. (C) 200 1 Elsevier Science B.V. All rights reserved.