Exposure of maize seeds to liquid nitrogen modifies the morphology and hormonal response of young plants.

BACKGROUND: Cryopreservation currently represents the most suitable strategy for the long-term conservation of plant germplasm. While much effort has focused on the development of protocols to enable successful cryostorage, there are few, if any reports, that consider the effect of cryogenic temperatures on the phytohormone status of the seed and developing seedlings. OBJECTIVE: To investigate the effect of cryopreservation on external seed coat features as well as levels of indole-3-acetic acid (IAA), abscisic acid (ABA) and 1-aminocyclopropane-1-carboxylic acid (ACC) in maize. MATERIALS AND METHODS: Two groups of seeds at 6% moisture content were compared: one was maintained at 4 degree C (control) while the other was exposed to LN within cryo-vials. RESULTS: Seeds exposed to cryogenic temperatures were characterized by the presence of large cracks in the seed coat compared with control seeds. Cryogenic exposure also resulted in a reduction in biomass and plant height. Results from the phytohormone analysis showed an initial reduction in the levels of IAA, ABA and ACC after 7 days of growth followed by sharp increase in levels relative to the control by 14 days. Whilst the roles of ABA and ethylene (and by extension, its precursor ACC) are well studied as stress response molecules, much less is known about the potentially vital role of auxins in regulating plant growth under conditions of low temperature stress. CONCLUSION: It is postulated that the interaction of all three hormones modulate crosstalk between various stress responses and recovery pathways to ameliorate the damage caused by freezing stress and enable plant survival. Given the dearth of information on phytohormones in cryobiology, more studies are needed to fully elucidate these relationships in the context of freezing stress caused by liquid nitrogen. Doi.org/10.54680/fr23610110612.

Isolation and characterization of mutants of Arabidopsis thaliana with increased resistance to growth inhibition by indoleacetic acid-amino acid conjugates.

Two mutants of Arabidopsis thaliana that are resistant to growth inhibition by indole-3-acetic acid (IAA)-phenylalanine have been isolated. Both mutants were 2- to 3-fold more resistant than wild type to inhibition by IAA-phenylalanine, IAA-alanine, and IAA-glycine in root growth assays. The mutant icr1 (but not icr2) also shows some resistance to IAA-aspartate. Studies using 3H-labeled IAA-phenylalanine showed that the uptake of conjugate from the medium by icr1 was the same as wild type and was reduced by about 25% in icr2. No differences in hydrolysis of the exogenous conjugate were detected between the mutants and their wild-type parents. There was no significant metabolism of the IAA released from the [3H]IAA-phenylalanine, whereas exogenous [3H]IAA was rapidly metabolized to two unidentified products considerably more polar than IAA. Analysis of a cross between icr1 and icr2 indicated that these mutations were at distinct loci and that their effects were additive, and preliminary mapping data indicated that icr1 and icr2 were located at the top and bottom of chromosome V, respectively.