Non-invasive assessment of the physiological role of leaf aerenchyma in Hippeastrum Herb. and its relation to plant water status

MAIN CONCLUSION: The leaf patch clamp pressure probe combined with gas exchange measurements provides a non-invasive approach for measuring leaf aerenchyma pressure and study its physiological role in plants. ABSTRACT: The non-invasive leaf patch clamp pressure probe (LPCP) measures the output pressure, P(p), in response to the pressure applied by two magnets clamped to a leaf. In many plant species, it has been observed that the diel pattern of P(p) follows the changes in the leaf turgor pressure reversely. The genus Hippeastrum comprises 143 species and many hybrids and cultivars of high economic value within Amaryllidaceae. Their leaves are characterized by the presence of aerenchyma composed of lacunae, running throughout the leaf and composing most of the mesophyll volume. In Hippeastrum, the diel changes of the LPCP output pressure are the reverse of that observed on the air pressure in the leaf aerenchyma, P(a), which depends on the changes in the leaf vapor pressure occurring during photosynthesis. A theoretical model is proposed and confirmed experimentally by LPCP and gas exchange measurements. The output pressure, P(p), in Hippeastrum can be related to the plant water status through the gas exchange processes that occur during photosynthesis. Considering the natural habitats of Hippeastrum species, these results agree with the physiological role of leaf aerenchyma in facilitating gas transport and light scattering in leaves, thus contributing to the photosynthetic efficiency of these plants under adverse environments. A second, but supplemental, interpretation of the LPCP output pressure, P(p), when applied on species in which the aerenchyma constitutes most of the mesophyll volume is presented.