Dynamic secretion changes in the salt glands of the mangrove tree speciesAvicennia officinalisin response to a changing saline environment

Abstract

The specialized salt glands on the epidermis of halophytic plants secrete excess salts from tissues by a mechanism that is poorly understood. We examined the salt glands as putative salt and water bi-regulatory units that can respond swiftly to altering environmental cues. The tropical mangrove tree species (Avicennia officinalis) is able to grow under fluctuating salinities (0.7-50.0 dS m -1 ) at intertidal zones, and its salt glands offer an excellent platform to investigate their dynamic responses under rapidly changing salinities. Utilizing a novel epidermal peel system, secretion profiles of hundreds of individual salt glands examined revealed that these glands could secrete when exposed to varying salinities. Notably, rhythmic fluctuations observed in secretion rates were reversibly inhibited by water channel (aquaporin) blocker, and two aquaporin genes (PIP and TIP) preferentially expressed in the salt gland cells were rapidly induced in response to increasing salt concentration. We propose that aquaporins are involved and contribute to the re-absorption of water during salt removal in Avicennia officinalis salt glands. This constitutes an adaptive feature that contributes to salt balance of trees growing in saline environments where freshwater availability is limited.

Study on pathway and characteristics of ion secretion of salt glands of Limonium bicolor

“…More than 950 million hectares of land are salt affected (Munns 2002;Tan et al 2013) and the ability to grow crops on saline land is increasingly important (Rozema and Flowers 2008). A high concentration of salt in soil causes oxidative damage, water deficit and nutrient deficiency, which disrupts the intracellular ionic homeostasis and leads to retarded plant growth and development and sometimes death, causing great losses in agricultural production (Munns and Tester 2008;Chen et al 2010;Tarchoune et al 2012).…”

“…Salt glands in plants play an important role in regulating ion balance, maintaining the stability of osmotic pressure, and enhancing salinity tolerance (Ding et al 2009;Tan et al 2013). They are excretory organs scattered on leaf surfaces and stems that are adapted for dealing with salt accumulation in plants.…”

“…These excretory organs are highly evolved structures, which by their ability to secrete salt, enable plants to grow on saline-alkali soil without adversely suffering from salt damage (Flowers and Colmer 2008;Munns and Tester 2008). Salt glands represent a typical strategy for ion extrusion in several orders of plants, such as the Poales, Solanales, Lamiales, Caryophyllales, Ericales, and Myrtales (Flowers et al 2010;Tan et al 2013).…”

Functional characterization of the Arabidopsis heat shock factor A4A, identified by a novel genetic screen

“…Stress avoidance mechanisms reduce the potential damage by preventing the exposure to stressors, as for example the accumulation of salt inspecialized salt glands on the epidermis of halophytic species such the mangrove tree Avicennia officinalis (Tan, 2013); these organs contribute to salt resistance by excreting excess salts. Avoidance mechanisms are result of stable and inheritable genetic modifications in a population (Krasensky, 2012), therefore, the evolutionary changes are constitutive and resistance features are expressed even in the absence of environmental stress.…”

“…Major hormones involved in abiotic stress responses are abscisic acid (ABA), ethylene and salicylic acid. Besides, other growth regulators like gibberellins, cytokinins, auxins, jasmonates and brassinosteroids greatly contribute to the crosstalk that is important in the stress-related molecular processes (Kumar, 2013). ABA is accumulated in response to drought, salt and cold (Hirt, 2004); it mediates the activation of ABA-dependent signalling pathways that control genes involved in dehydration Some examples for stress responses mediated by ABA are the regulation of stomatal closure during water deficit stress and the inhibition of seed germination (Nakashima, 2013).…”