Rapid Accumulation of Proline Enhances Salinity Tolerance in Australian Wild Rice Oryza australiensis Domin

Abstract

Proline has been reported to play an important role in helping plants cope with several stresses, including salinity. This study investigates the relationship between proline accumulation and salt tolerance in an accession of Australian wild rice Oryza australiensis Domin using morphological, physiological, and molecular assessments. Seedlings of O. australiensis wild rice accession JC 2304 and two other cultivated rice Oryza sativa L. cultivars, Nipponbare (salt-sensitive), and Pokkali (salt-tolerant), were screened at 150 mM NaCl for 14 days. The results showed that O. australiensis was able to rapidly accumulate free proline and lower osmotic potential at a very early stage of salt stress compared to cultivated rice. The qRT-PCR result revealed that O. australiensis wild rice JC 2304 activated proline synthesis genes OsP5CS1, OsP5CS2, and OsP5CR and depressed the expression of proline degradation gene OsProDH as early as 1 h after exposure to salinity stress. Wild rice O. australiensis and Pokkali maintained their relative water content and cell membrane integrity during exposure to salinity stress, while the salt-sensitive Nipponbare failed to do so. An analysis of the sodium and potassium contents suggested that O. australiensis wild rice JC 2304 adapted to ionic stress caused by salinity by maintaining a low Na+ content and low Na+/K+ ratio in the shoots and roots. This demonstrates that O. australiensis wild rice may use a rapid accumulation of free proline as a strategy to cope with salinity stress.

Physiological Response and Proteomics Analysis of Reaumuria soongorica Under Salt Stress

“…The inhibition of seedling growth under high salt conditions is likely due to the limited ability to isolate Na + and Cl − in vacuoles 28 . The proline content in R. soongorica leaves increased signi cantly with a greater salt concentration, a result consistent with ndings of previous studies, possibly because the proline synthesis gene was activated or the expression of proline degradation gene was inhibited under salt stress 25 .…”

“…In addition, the generation and transport of biomass is also an important factor in assessing the degree of salt stress in plants 23 . Studies have shown that salt stress reduces plant biomass synthesis, and that plant leaves are capable of responding to salt stress via the rapid accumulation of proline [24][25][26] . In our experiment, under the stress condition of low salt B (200 mM NaCl), the fresh weight and root/shoot ratio of R. soongorica seedlings increased, and low salt had a signi cant promotional effect on their growth.…”

Commercial Cultivation of Australian Wild Oryza spp.: A Review and Conceptual Framework for Future Research Needs

“…Wild Oryza species possess advantageous features, supporting their commercialization. They have a wide stress tolerance capability for a range of biotic and abiotic stresses, enabling better acclimation to arid climatic conditions than commercial genotypes [4,5]. Further, an initial assessment of their grain quality attributes supports their commercial potential due to their high nutritional value, including unique starch properties [6][7][8].…”

“…Australian wild Oryza populations can tolerate a greater range of biotic and abiotic stresses than cultigen rice (i.e., tolerance towards heat, drought, salinity, and disease stresses) due to their unique genetic material. Their isolation from domesticated rice varieties prevents the contamination potential by gene flow from the cultivated rice genotypes [1,5]. The stress tolerance capacity could enable them to grow under varying environmental conditions, underpinning its successful cultivation and subsequent commercialization.…”

“…Wild Oryza are underexploited native grass species in Australia. To date, most studies on Australian native Oryza species have focused on comparative genetics and genomics studies such as; (i) using novel alleles from Australian native rice for improving traits in cultigen rice [4]; (ii) assessing the phylogenetic relationship between Australian and Asian wild rices [18,25]; (iii) chloroplast and nuclear gene analysis [25,26]; (iv) heritability for grain yield under stress [27]; (v) ex-situ and in-situ conservation of the genetic resources [4]; (vi) stress tolerance capability of Australian wild Oryza [5,28]; and (vii) genome sequencing of wild Australian and Asian rices [19]. Although these studies provide a useful genetic background of these valuable species, they have not enabled an understanding of the optimum agronomic protocols for their commercial production as a native food.…”