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

Abstract

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, Pp, 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 Pp 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, Pa, 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, Pp, 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, Pp, when applied on species in which the aerenchyma constitutes most of the mesophyll volume is presented.

Water exchange between the Chlorenchyma and the Hydrenchyma and its physiological role in leaves with Crassulacean acid metabolism

“…Although confirming previous works that showed the reverse relationship between the two parameters on different plant species (e.g., Ehrenberger et al, 2012; Martínez‐Gimeno et al, 2017; Riboldi et al, 2016; Rüger et al, 2010a, b; Zimmerman et al, 2010, 2013), the novelty brought by the work here presented was that it allowed to assess changes in the hydrenchyma turgor pressure specifically and relate its diel pattern with CAM photosynthesis. Confirming the findings of Cabrita (2022), this is one more example of how the interpretation of the LPCP output pressure, P p , depends on the leaf structure on which the probes are applied. Gas exchange and LPCP measurements were done on Aloe vera (L) Burm f. plants, a typical CAM species, and compared against those made on banana ( Musa acuminata Colla), a C 3 plant.…”

“…In Aloe vera , α has been observed to be as low as 0.16 and hardly changing under different soil water availability (Silva et al, 2014). Therefore, from Equation (), the LPCP transfer function T f (Cabrita, 2022; Westhoff et al, 2009; Zimmerman et al, 2008) that defines the value of the output pressure, P p , in Aloe vera leaves (Figure 8) is given by: $$$$ {T}_f=\frac{K}{\propto^2{V}_h^3} $$$$ and is mostly determined by the leaf patch hydrenchyma volume, V h (Figure 8). From Equation (), one has that the change of the LPCP output pressure, P p , with time in Aloe vera leaves is given by: $$$$ \frac{{\partial P}_p}{\partial t}=-{P}_p\left(\frac{3}{V_h}\frac{{\partial V}_h}{\partial t}+\frac{2}{\alpha}\frac{\partial \alpha }{\partial t}\right) $$$$ …”

“…The changes in the values of the output pressure, P p , in Aloe vera leaves are essentially dictated by changes in the hydrenchyma volume, V h ; i.e., changes in its turgor pressure, P c , ultimately. Thus, combining Equations (), (), and () and following the rationale to determine the dependence of the transfer function, T f , Equation (), on the hydrenchyma turgor pressure, P c , (Cabrita, 2022; Westhoff et al, 2009; Zimmerman et al, 2008), one obtains that the LPCP output pressure, P p , in Aloe vera leaves (Equation ()) can be written as: $$$$ {P}_p={\left(\frac{b}{aP_c+b}\right)}^{\frac{3}{a}}{P}_{in} $$$$ where a and b are constants depending on the viscoelastic properties of the cell wall and the value and duration of the applied input pressure, P in , (Westhoff et al, 2009; Zimmerman et al, 2008). From Equation (), one has that the change in the LPCP output pressure, P p , with time in Aloe vera leaves is given by: $$$$ \frac{{\partial P}_p}{\partial t}=-\frac{3{P}_p}{aP_c+b}\frac{{\partial P}_c}{\partial t} $$$$ …”

“…Unless otherwise specified, the magnetic pad containing the pressure sensor was applied on the abaxial leaf surface, and data was recorded with a 1-minute sampling interval. The relaxation time constants of the changes in the output pressure, P p , values during the transition between the light periods, τ on (when lights were turned on) and τ off (when lights were turned off), were determined following Cabrita (2022) taking into consideration the first 60 min after lights were turned on and off, respectively.…”

“…Namely, how the water exchange between the chlorenchyma and the hydrenchyma depends on and follows the CAM photosynthetic diel pattern of the former. Considering the presence of a voluminous hydrenchyma on most terrestrial CAM plant leaves and the principle behind the leaf patch clamp pressure probe (LPCP) (Cabrita, 2022; Zimmermann et al, 2008, 2013), it was hypothesized that the changes in its output pressure, P p , reflected changes in the hydrenchyma turgor pressure, P c . Although confirming previous works that showed the reverse relationship between the two parameters on different plant species (e.g., Ehrenberger et al, 2012; Martínez‐Gimeno et al, 2017; Riboldi et al, 2016; Rüger et al, 2010a, b; Zimmerman et al, 2010, 2013), the novelty brought by the work here presented was that it allowed to assess changes in the hydrenchyma turgor pressure specifically and relate its diel pattern with CAM photosynthesis.…”