Interactive effects of mechanical impacts, temperature and humidity on water relations and tissue elasticity of stored carrots.
Herppich, W. B.; Mempel, H.; Geyer, M.;
Journal of Applied Botany Year: 2000 Vol: 74 Issue: 5/6 Pages: 271-276 Ref: 44 ref.
2000
บทคัดย่อ
In roots of the biennial carrots (Daucus carota L.) an environmentally controlled (winter-) dormancy can be easily induced by dark, cold and humid conditions. This makes it a suitable crop for long-term storage. However, in practice carrots are not always kept in optimum conditions, but are often exposed to drought stress during post-harvest handling. This negatively affects root water status and texture. Mechanical impacts during mechanised harvest and postharvest handling enhance the stress effects. Plants respond to water deficits by several distinct metabolical adaptation mechanisms. By means of a Scholander-type pressure bomb and a material testing machine we studied the interactive effects of mechanical impacts, temperature and air humidity on water status and tissue elasticity in stored carrots. Pressure volume analysis was used to characterize the interrelationship between these two parameters. Even short-term storage (3 d) at room temperature (ca 18 deg C) in high (ca 90% RH) and very h
igh (ca 98% RH) humidity led to a pronounced reduction of both water potential and pressure potential in hand-harvested carrots (control). Controlled artificial mechanical stress (24 falls from a 30 cm height onto a belt) significantly enhances these responses although relative water losses were only slightly increased. Carrots adapt to drought stress by osmotic adjustment, i.e. a net increase in osmotically active organic solutes. Cold (5 deg C) high humidity (98% rH) storage (15 d) diminished the reduction of water potential, pressure potential and water content but did not influence osmotic adjustment. At room temperature a decline in both the apparent compressive (E, determined from force-deformation curves), and in the volumetric ( epsilon , obtained from pressure-volume analysis) modulus of elasticity always accompanied the reduction of water status. However, during cold storage, E significantly increased in both control and mechanically stressed roots, indicating that carrots are able to adjust elasti
cally. Elastic adjustment is an effective metabolically controlled mechanism, which, in addition to osmotic adjustment, helps to maintain a positive turgor despite slow water losses. Mechanical stress, however, enhances the decline in water status and reduces the ability to metabolically adapt to water deficits thus reducing the storability of carrots.