Salt glands play a pivotal role in the salt resistance of four recretohalophyte Limonium Mill. species

Abstract

Limonium Mill. plants are typical recretohalophytes, as they withstand salt stress by secreting excess salt onto the leaf surface through salt glands. However, little is known on the salinity thresholds of these plants and the function of salt glands in salt tolerance.• Here, we investigated the salinity thresholds of salt tolerance of the Limonium species L. aureum (Linn.) Hill, L. gmelinii (Willd.) Kuntze, L. otolepis (Schrenk) Kuntze and L. sinuatum (L.) Mill grown with various concentrations of NaCl.• The salinity thresholds of L. otolepis, L. aureum, L. sinuatum and L. gmelinii were 300, 350, 400 and 420 mM NaCl, respectively. Correlation analysis indicated that total dry weight, chlorophyll content and intercellular CO 2 concentration were highly positively correlated with the total fresh weights of all four Limonium species and could therefore be used as indicators of plant salt tolerance. Furthermore, as the salt gland density on the leaf surface increased, the rate of salt secretion per salt gland also increased, allowing more Na + to be secreted from the plant. Redundancy discriminant analysis indicated that salt gland density, Na + content and Na + secretion rate per salt gland were positively correlated with salt concentration.• These observations support the notion that salt glands play important roles in the adaptation of Limonium species to high salinity conditions.

Adaptive Mechanisms of Halophytes and Their Potential in Improving Salinity Tolerance in Plants

“…Halophytes, particularly recretohalophytes, directly secrete remarkably higher contents of salt ions onto the leaf surface, for dealing with maintenance of cellular ion homeostasis, through a unique epidermal structure called salt glands, making them superior compared with other classes of halophytes and non-halophytes [50] (Figure 3). Several species of the Limonium genus, including L. bicolor, L. aureum, L. gmelinii, L. otolepis, and L. sinuatum, are good examples of recretohalophytes, which boost salt tolerance by enhancing salt secretion via the salt glands [66][67][68] (Table 1). Species of another recretohalophyte genus, Tamarix, are salt-tolerant by increasing the density of salt glands and the rate of salt secretion per salt gland [69] (Table 1).…”

Mechanisms of Salt Tolerance and Molecular Breeding of Salt-Tolerant Ornamental Plants

“…If the ornamental plant could grow and survive at the salt level at or over 200 mM NaCl that could be considered as a halophyte, thus the ornamental plants can be divided in halophytic and non-halophytic ones according to their salt tolerant ability. For example, the salinity threshold was 400 mM NaCl of the halophytic Limonium sinuatum under laboratory conditions ( Mi et al, 2021 ). Many research findings have indicated that the development of salt-tolerant ornamental flowers is a viable approach.…”

“…Under saline conditions, the response mechanisms triggered are different in different ornamental species. In some ornamental species with salt secreting structures like salt glands or salt bladders, especially Limonium species ( Feng et al, 2014b ; Leng et al, 2018 ; Lu et al, 2020 ; Mi et al, 2021 ), excess salt ions transported to aboveground parts of the plant are also excreted outside of the plant body through salt glands ( García-Caparrós et al, 2016 ). Limonium species have remarkable salt tolerance thanks to their typical salt excreting salt glands in the leaves; they can grow and develop well in environments containing NaCl concentrations of more than 200 mM NaCl ( Souid et al, 2016 ; Mi et al, 2021 ).…”

“…In some ornamental species with salt secreting structures like salt glands or salt bladders, especially Limonium species ( Feng et al, 2014b ; Leng et al, 2018 ; Lu et al, 2020 ; Mi et al, 2021 ), excess salt ions transported to aboveground parts of the plant are also excreted outside of the plant body through salt glands ( García-Caparrós et al, 2016 ). Limonium species have remarkable salt tolerance thanks to their typical salt excreting salt glands in the leaves; they can grow and develop well in environments containing NaCl concentrations of more than 200 mM NaCl ( Souid et al, 2016 ; Mi et al, 2021 ). Besides excreting excess salt ions out of the leaves, some of the absorbed salt ions are regionalized; they accumulate in vacuoles and regulate the osmotic potential of leaf cells ( González-Orenga et al, 2021 ).…”

Effect of Recurrent Salt and Drought Stress Treatments on the Endangered Halophyte Limonium angustebracteatum Erben

“…As typical recretohalophytes, Limonium species possess peculiar morpho-anatomical structures responsible for salt excretion, i.e., salt bladders and salt glands, which are absent in glycophytes [ 18 , 19 ]. Furthermore, their salt tolerance is based on the presence of constitutive stress tolerance mechanisms, such as the active accumulation of mono and divalent ions in the leaves [ 20 , 21 , 22 ] and the high production of stress-induced osmolytes (especially proline and fructose) for osmotic adjustment, together with enhanced activity of antioxidant enzymes and the synthesis of antioxidant compounds [ 23 , 24 ].…”