Influence of vesicular trichomes of Atriplex nummularia on photosynthesis, osmotic adjustment, cell wall elasticity and enzymatic activity.

Vesicular trichomes play a key role in excluding toxic ions from some halophyte species, preventing the essential processes and functions of plants from being altered. Thus, the present study aimed to evaluate the influence of these structures on Atriplex nummularia irrigated using waters with three levels of osmotic potential (-0.1, -1.4 and -2.7 MPa), formulated with NaCl in plants with vesicular trichomes and plants with partial removal of trichomes. The experiment was conducted in a protected environment and plants were evaluated for physiological parameters (water, osmotic and pressure potentials, relative water content, osmotic adjustment, pressure-volume curve, gas exchange), electrolyte leakage, lipid peroxidation and enzymatic activity (superoxide dismutase, ascorbate peroxidase, catalase). The results obtained made it possible to identify the strong contribution of vesicular trichomes to physiological and biochemical parameters, with indication of cell wall stiffening and maintenance of turgor. Furthermore, the evaluation of the osmotic potentials obtained in the study suggests that the contribution of vesicular trichomes to the salinity tolerance of the species is greater than that of osmotic adjustment. Furthermore, gas exchange results suggest that the presence of trichomes was able to regulate stomatal processes so that the plant maintains its photosynthetic performance. Evaluation of electrolyte leakage, together with the increase in malondialdehyde content, showed that the maintenance of trichomes reduces the probability of oxidative stress. The activity of antioxidant enzymes was efficient in eliminating reactive oxygen species, especially the activity of ascorbate peroxidase, which stood out in terms of hydrogen peroxide detoxification.

Osmotic adjustment in cowpea plants: Interference of methods for estimating osmotic potential at full turgor.

Osmotic adjustment is a persisting controversy in studies on the effect of salt and water stress in cowpea crops. Our hypothesis is that the osmotic potential determination method interferes with the osmotic adjustment calculation. The objective of this study was to consider the osmotic adjustment comparing results obtained by pressure-volume (P-V) curves and osmometry. The experiment was conducted in a randomized block design, with six salt water concentrations 0, 20, 40, 60, 80, and 100 mmol L-1 of NaCl in a Fluvisol. The osmotic adjustment found through osmometry were lower than those found through P-V curves. The apoplastic water fraction of the cowpea had a dilution effect, denoting overestimation of the osmotic potential by the methodology based on osmometry. This may be the source of the different interpretations of osmotic adjustment in cowpea plants. Thus, osmotic adjustment should be calculated preferably using the osmotic potential determined by method of pressure-volume curves.