Abstract
The capacity for ion compartmentalization among different tissues and cells is the key mechanism regulating salt tolerance in plants. In this study, we investigated the ion compartmentalization capacity of two upland cotton genotypes with different salt tolerances under salt shock at the tissue, cell and molecular levels. We found that the leaf glandular trichome could secrete more salt ions in the salt-tolerant genotype than in the sensitive genotype, demonstrating the excretion of ions from tissue may be a new mechanism to respond to short-term salt shock. Furthermore, an investigation of the ion distribution demonstrated that the ion content was significantly lower in critical tissues and cells of the salt-tolerant genotype, indicating the salt-tolerant genotype had a greater capacity for ion compartmentalization in the shoot. By comparing the membrane H+-ATPase activity and the expression of ion transportation-related genes, we found that the H+-ATPase activity and Na+/H+ antiporter are the key factors determining the capacity for ion compartmentalization in leaves, which might further determine the salt tolerance of cotton. The novel function of the glandular trichome and the comparison of Na+ compartmentalization between two cotton genotypes with contrasting salt tolerances provide a new understanding of the salt tolerance mechanism in cotton.
Highlights
The accumulation of excess salts in soil is a serious environmental problem that could adversely affect plant growth, geographical distribution, and crop productivity[1,2]
Most of the true leaves of the salt-sensitive genotype Nandanbadidahua (NH) seedlings had visibly dried after 72 h of salt treatment, but they dried to a lesser degree than did those of the salt-tolerant genotype Earlistaple 7 (E7) seedlings (Fig. 2B)
These results suggest that the higher Na+ absorption capacity of the roots and the lower level of Na+ in leaves of salt-tolerant genotypeE7 might prevent excessive Na+ from affecting shoot growth
Summary
The accumulation of excess salts in soil is a serious environmental problem that could adversely affect plant growth, geographical distribution, and crop productivity[1,2]. Halophytes have evolved unique mechanisms, such as salt glands, bladders, and succulence, to excrete Na+ from their organizational structures[12,13,14,15] These plants impart salt tolerance mechanisms that are coordinated between tissues and cells and mediated by membrane-related cation channels and transporters (tonoplasts and the plasmalemma Na+/H+ antiporter)[16,17,18,19]. Leidi & Saiz[24] and Sun & Liu[25] reported that the roots and leaves of some salt-tolerant cotton varieties could retain Na+ In many halophytes, another important salt resistance mechanism is salt secretion, which regulates salt tolerance by secreting salt (especially NaCl) through salt glands in the leaves and by modulating the internal ion concentrations to a lower level. It is unknown whether the GTs on the surface of cotton leaves can secrete NaCl
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