Wild Hordeum species, from the four genome groups of X, H, I and Y, were assessed for physiological traits associated with tolerance to salinity and waterlogging. When grown in saline conditions, a number of wild Hordeum species had exceptional ‘exclusion’ of Na+ and Cl- from the young leaves, and also maintained tissue K+ concentrations, compared with Hordum vulgare ssp. vulgare (cv. ‘Golf’). For example, at 150 mol m-3 NaCl, the K+:Na+ in youngest, fully expanded leaf blades of wild Hordeum species averaged 5.2, compared with 0.8 in H. vulgare. H. marinum was more salt tolerant than H. vulgare, with a relative growth rate 30% higher than H. vulgare at 150 mol m-3 NaCl. At 300 mol m-3 NaCl, glycinebetaine plus proline contributed to 15% of πsap in expanding leaf blades of H. marinum, compared with 8% in H. vulgare. When grown in stagnant conditions, 16 accessions (approximately half of those evaluated) formed a barrier to radial O2 loss (ROL) in basal zones of adventitious roots. In the Triticeae, this trait had previously only been described in one species, H. marinum. The barrier to ROL occurred only in accessions from wetland or intermediate habitats, and was also related to genome type, being present in accessions with the X or the H genome (Hordeum vulgare has the I genome). In stagnant conditions, aerenchyma formed was, on average; 22% in accessions with the X genome; 19% in those with the H genome; and 15 and 16% in those with the I or the Y genomes, respectively. The combination of a barrier to ROL and aerenchyma enhances longitudinal O2 movement in adventitious roots, permitting roots to penetrate deeper into anaerobic substrates. In H. marinum, induction of the barrier to ROL was associated with a 97% reduction in apparent O2 diffusivity across the external layers of the basal zones of roots, compared with near the root tip. The barrier results from physical resistance to radial O2 movement, although when roots were cooled to suppress respiration some additional leakage of O2 was detected, indicating respiration also contributes to the low rates of ROL from the basal regions of roots. Low radial O2 permeability in the roots of stagnantly-treated H. marinum was associated with secondary thickening, putatively lignin or suberin deposits, in the hypodermis. These changes in root structure, however, did not influence root hydraulic conductivity, assessed for individual adventitious roots and whole root systems. Thus, diversity amongst Hordeum species in expression of traits for tolerance to waterlogging (an inducible barrier to ROL and aerenchyma) and salinity (Na+ and Cl- ‘exclusion’) were documented in this study. Traits for root aeration did not compromise the capacity of roots to take up water, presumably being of importance for growth in soils with fluctuating water levels (i.e. wet/dry cycles). The high degree of salinity tolerance in several Hordeum species, and especially in H. marinum, is consistent with field observations that these species occur in salt affected areas
| Identifer | oai:union.ndltd.org:ADTP/221166 |
| Date | January 2005 |
| Creators | Garthwaite, Alaina Jane |
| Publisher | University of Western Australia |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Alaina Jane Garthwaite, http://www.itpo.uwa.edu.au/UWA-Computer-And-Software-Use-Regulations.html |
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