Nanomaterial-aided seed regeneration in the global warming scenario: multiwalled carbon nanotubes, gold nanoparticles and heat-aged maize seeds

Abstract

Seeds in soil seed-banks count amongst organisms that are the most vulnerable to the extreme temperatures predicted in certain models of global warming. This work aims to examine the possibility of a nanomaterial-aided resuscitation of heat-damaged hybrid maize (Zea mays L. “Albatross”) seeds through a study of their germinability and growth after high heat exposures. Heat energy at constant ‘dose’ was delivered at the three temperatures of 40, 50 and 60 °C (40–60) and at a much higher dose at 60 °C (+). Seed germinability and seedling growth indices were studied in the presence/absence of multiwalled carbon nanotubes (MWCNT) and our laboratory synthesised and characterised (SEM, DLS, FTIR, UV–Vis) gold nanoparticles (AuNP). Overall, the MWCNT outperformed the AuNP. The seemingly erratic germination outcomes were rationalised from the standpoint of the biomechanics of water entry into seeds with heat-damaged seedcoats. Ficksian diffusion calculations applied to the interstitial channels of the seedcoat and cellwall showed that the former but not the latter, was an effective barrier to MWCNT entry and that both easily allowed water entry. The MWCNT treatments appear to catalyse the recovery of the (+) seeds and seedlings, promote biomass and the root-to-shoot water transport, whilst the parabolic biomass trend for 40–60 suggests opposing temperature-regulated factors possibly involving reactive oxygen species. Summarising, growth indices of heat-damaged seeds show a strong non-monotonic dose dependence where the MWCNT significantly altered the response, catalysing the recovery of the high heat ‘dose’ set. These results hold promise for the application of nano-biotechnology to agriculture in the global warming scenario.