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.

Exposure of Calophyllum antillanum seeds to liquid nitrogen delays seedling emergence and decreases leaf anthraquinones.

BACKGROUND: Trees within the Calophyllum genus are multi-use trees that produce valuable wood, phytochemicals with a range of biological activities, and seed oil as a source of biodiesel. As a consequence of climate change, there is a need to develop strategies to preserve valuable plant genetic resources. Cryopreservation represents the most suitable option for the long-term storage of germplasm with minimal space and maintenance requirements. OBJECTIVE: To determine appropriate methods to cryopreserve seeds of Calophyllum antillanum and maintain secondary compound production. MATERIALS AND METHODS: Seeds at a moisture content of 6% were used to evaluate two treatments: seeds immersed in liquid nitrogen and control seeds. Biosynthetic pathway efficiency was assessed post-cryo by determining anthraquinone contents in roots, stems and leaves following 30 and 75 d of seedling growth. RESULTS: The results indicated that exposure to liquid nitrogen delayed germination and seedling emergence for a period of up to 45 d after seed sowing. By 60 d of cultivation, no significant differences in plant growth were observed for cryostored and control seeds. The levels of anthraquinones, which were also measured in seeds and seedlings, were lower in plants regenerated from cryostored seeds following 30 d of growth, but there were no differences in roots and stems by 75 d of growth. Furthermore, the difference in leaf anthraquinone levels for cryopreserved and control seeds at 75 d was much smaller than at 30 d. CONCLUSION: The low initial anthraquinone levels in emerging seedlings correlated with the initial slow growth of cryopreserved seeds.

Cryopreservation of seeds of the highly valued tropical timber species Swietenia mahagoni.

BACKGROUND: Swietenia mahagoni wood is one of the most valuable in world trade and, as a result, natural populations have been decimated due to unsustainable harvesting. The decline in natural population levels is being exacerbated by climate change. In order to ensure the preservation of valuable genotypes, there is an urgent need to develop strategies to conserve the genetic diversity present within this species. At present, cryopreservation is the most viable option for the long-term storage of plant germplasm, particularly for long-lived species which are challenging to maintain in the field. OBJECTIVE: To cryopreserve intact seeds of S. mahagoni, with the dual goal of retaining the biosynthetic capacity of plants, which is critical since this species is highly valued for medicinal purposes. MATERIALS AND METHODS: Seeds at a moisture content of 6% were immersed in liquid nitrogen (LN) before warming and recovery. Plantlet establishment and growth were assessed over a period of 70 days and anthraquinone synthesis was determined in roots, stems and leaves. RESULTS: The results showed an initial lag in the germination rate of cryopreserved seeds compared with control seeds; however, this difference disappeared over time. The lag in seedling emergence observed in cryostored seeds was also evident in the plant characteristics measured following 30 days of culture when all plant parameters measured were significantly higher in plants produced from control than cryostored seeds. However, after 70 days of growth, these differences were no longer apparent. Anthraquinone levels were also initially lower (at 30 days) in plants regenerated from cryopreserved seeds than those from control seeds, however, this difference was substantially reduced by 70 days thereby indicating the ability of these plants to accumulate secondary metabolites, albeit at a reduced rate, during the early stages of development. CONCLUSION: In S. mahagoni, the delay in anthraquinone production in plants regenerated from cryostored seeds during the early stages of development may have occurred as a consequence of the preferential allocation of resources towards the initiation of recovery processes in response to the stresses imposed by cryopreservation. Once the stresses were overcome and plant growth resumed, resources could be directed to secondary processes such as anthraquinone synthesis. doi.org/10.54680/fr22610110412.