Physiological and gene expression changes during imbibition in maize seeds under low temperature conditions

Abstract

Maize is one of the most important crop species worldwide, but also extremely susceptible to the effects of increasingly higher temperatures and drought during the summer and its flowering and grain filling stage. Different strategies are being utilized to ensure a satisfying yield potential and quality even in the extremely unfavourable environmental conditions, which are the result of climate change. Some of them are cropping pattern changes and sowing alterations, including earlier sowing. Since this implies the exposure to suboptimal temperatures during early developmental stages, it leads to a demand for developing maize lines tolerant to low temperatures during these stages. This research focuses on the first phase of germination, imbibition. Maize tolerance to low temperatures is a complex trait that includes different mechanisms and strategies that all work together to ensure adaptation and survival, such as cell membrane changes, antioxidative system activation, etc. Additionally, the low temperature response of different maize inbreds varies substantially, so recognizing the different ways in which they respond to low temperatures during imbibition and other earlier stages of development is crucial. To accomplish this, seeds of two maize inbred lines of contrasting susceptibility to low temperatures were selected and exposed to control (20° C) and low temperature (8°C) conditions during the first 24h of imbition andthen further analyzed to assess their response. This included germination and tetrazolium assays; ascertaining membrane integrity by evaluating cell leakage and lipid peroxidation; determining the antioxidative capacity by assessing superoxide dismutase (SOD) and catalase (CAT) activity; and expression analysis of four genes included in the low temperature response (gibberellin insensitive dwarf 1 gibberellin receptor, gid1; fatty acid desaturases 2 and 6, fad2 and fad6; plastid-lipid-associated 2 protein, pap2). The results showed that, while there is not a significant difference in their germination rate, they differ in their survival rate, with more seeds of the tolerant genotype surviving the low temperature period. Significant differences between them were found in cell leakage (p<0,01), as well as gid1(p<0,05) and fad6 (p<0,05) gene expression assays. The present research brings light to our understanding of the effect of low temperatures on the first germination stage, - imbibition. It highlights the importance of choosing the right inbreds for earlier sowing and points to certain routes that could be taken for improving and accelerating the breeding process for low temperature tolerance.

Kukuruz je usev od izuzetne važnosti za poljoprivredu, koji se takođe odlikuje značajnom osetljivošću na visoke temperature i sušu tokom letnjih meseci, odnosno tokom faze cvetanja i nalivanja zrna. Jedna od strategija obezbeđivanja zadovoljavajuće produktivnosti i prinosa kukuruza, uprkos nepovoljnim uslovima životne sredine, jeste ranija setva. Ipak u tom slučaju su biljke kukuruza izložene suboptimalnim temperaturama u ranim fazama razvića, što stvara potrebu za razvojem linija tolerantnih na niske temperature u tim fazama, što je i fokus ovog istraživanja. Odgovor kukuruza na niske temperature je kompleksan i uključuje niz različitih mehanizama i strategija koje obezbeđuju opstanak, a takođe zavisi i od samog genotipa, faze razvića, itd. Iz tog razloga, odgovor kukuruza na niske temperature (8°C) je posmatran tokom faze imbibicije, kod dva genotipa, i to na nivou promena genske ekspresije (gid1; fad2; fad6; pap2), aktivnosti antioksidativnih enzima (SOD, CAT), integriteta ćelijskih membrana, stopa germinacije, kao i samog preživljavanja. Rezultati ukazuju da postoje statistički značajne razlike između genotipova kada je reč o stopi preživljavanja, integritetu ćelijskih membrana i ekspresiji gena gid1i fad6 (p<0,05). Ovo istraživanje ukazuje na moguće mehanizme aklimatizacije na niske temperature tokom faze imbibicije i ističe značaj odabira odgovarajućih linija za raniju setvu.