Evaluation of hydration indexes in kale leaves

Abstract

Hydration indexes are practical variables for quantifying plant water stress and can be useful for agronomic purposes. Three adapted hydration indexes based on relative water content, volumetric hydration, and leaf turgor pressure were evaluated in kale (Brassica oleracea var. acephala) leaf segments. Relative water content and volumetric hydration were measured in leaf segments after a water infiltration procedure with the aim of filling its large intercellular volumes (@18%v/v). The infiltration was done using a hydrostatic weighing procedure and with the aid of vacuum to fully hydrate the leaf segments. These two relative indexes were proportional to the transpiration-induced leaf water loss. The third index, turgor pressure, was measured with a Wiltmeter® instrument. Similarly, the turgor pressure was proportional to the leaf water loss, and it decreased from @310kPa in recently harvested leaves to zero in dehydrated leaves, after a total water loss of @23%. Turgor pressure was correlated with the other two hydration indexes using approximations of leaf volumetric elastic modules. Similar estimates were obtained because the decline between turgor pressure and the natural logarithm of these relative leaf hydration indexes was numerically similar (@900kPa). However, the volumetric hydration index seemed to be more suitable as a model, not only for being more concise but also because it showed a clearer biomechanical representation of the leaf water deficit effects.