Impact of elevated atmospheric CO₂ on aleurone cells and starch granule morphology in domesticated and wild rices

Wild rice species represent valuable germplasm for breeding of elite genotypes with enhanced resistance to biotic and abiotic stresses. However, differences in endosperm morphology between wild and cultivated rice, and how these are affected by enhanced levels of atmospheric CO₂ (eCO₂) predicted for later this century, are largely unknown. Accessions of native rice species from northern Australia, Oryza australiensis and O. meridionalis, and a local cultivar, O. sativa cv. Doongara, were grown to maturity in glasshouses at ambient (aCO₂, 400 ppm) and eCO₂ (700 ppm). Endosperm morphology was studied from transverse sections of mature grains using scanning electron microscopy. Aleurone cell length and width were higher in eCO₂ than in aCO₂ in the O. meridionalis accession Howard Springs, but lower in Doongara. The average starch granule size in Doongara was greater than in the wild genotypes in both CO₂ treatments. The area and length of the starch granule images were larger in eCO₂ than in aCO₂ in the O. meridionalis accession Cape York but smaller in Doongara. Responses of rice endosperm morphology to eCO₂ were dependent on genotype. We conclude that endosperm morphology responds differentially to eCO₂, both between and within rice species. Contrasts in these responses can be exploited by breeders.