Determination of the threshold acceleration for the gravitropic stimulation of cress roots and hypocotyls

• Published in: Advances in space research 1998-01, Vol.21 (8), p.1203-1207
• Main Authors: Laurinavicius, R., Svegzdiene, D., Buchen, B., Sievers, A.
• Format: Article
• Language: English
• Subjects: Acceleration; Brassicaceae - growth & development; Centrifugation; Gravitation; Gravitropism - physiology; Hypocotyl - growth & development; Kinetics; Plant Roots - growth & development; Rotation; Space life sciences; Time Factors
• ISSN: 0273-1177; 1879-1948
• DOI: 10.1016/S0273-1177(97)00636-4

To determine the range of the threshold acceleration (a-threshold) for the gravitropic stimulation of Lepidium sativum L. roots and hypocotyls, experiments were performed on a centrifuge-clinostat with two-orthogonal axes. The rotation rate of the clinostat was 4 rpm (≤ 1.8 × 10 −4 g), while that of the centrifuge was from 3 to 17 rpm (3 × 10 −3 to 10 −1 g). The gravitropic response was determined: (i) after growth of roots and hypocotyls in their normal vertical position and subsequent gravitropic stimulation for 3 h by accelerations of 4 × 10 −3 to 10 −1 g, and (ii) after continuous stimulation in the lateral direction by centripetal accelerations of 4 × 10 −3 to 10 −1 g. The a-threshold was defined by an extrapolation of the regression line of R = p + rx, where x was either ln a or l/a for 3 h or a continuous stimulation respectively. The a-threshold estimated after 3 h stimulation was equal to 2.6 x 10 −3 g for roots and 3.1 × 10 −3 g for hypocotyls. The threshold accelerations that were unable to evoke a gravitropic response even with continuous stimulation of cress roots and hypocotyls were approximately 3.1 × 10 −3 g and 3.6 × 10 −3 g respectively. Increasing the stimulation acceleration up to 4.1 × 10 −3 g led to a statistically confirmed gravitropic response of a definite proportion of both the root and hypocotyl populations. In the experiments where acceleration and stimulation time were variable, the threshold dose (D-threshold) for roots was determined to be about 14 to 22 g × s, depending on the stimulation duration and the range of accelerations. The kinetics of gravitropic response at a nearthreshold acceleration (4 × 10 −3 to 1.9 × 10 −2 g) differed from that at 1 g (horizontal stimulation). At low forces, the maximal response dependent on the magnitude of acceleration could not be enhanced by increasing the stimulation time up to at least 210 min.