Embryos of Butia catarinensis are rudimentary and tolerant of desiccation and liquid nitrogen temperatures, but require GA3 to germinate

Authors: GROETEN, DANIELA - University Of Santa Catarina; Walters, Christina; Hill, Lisa; STEINER, NEUSA - University Of Santa Catarina

Submitted to: Plant Cell Tissue and Organ Culture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/23/2024
Publication Date: 3/5/2024
Citation: Groeten, D., Walters, C.T., Hill, L.M., Steiner, N. 2024. Embryos of Butia catarinensis are rudimentary and tolerant of desiccation and liquid nitrogen temperatures, but require GA3 to germinate. Plant Cell Tissue and Organ Culture. 156. Article e95. https://doi.org/10.1007/s11240-024-02717-5.
DOI: https://doi.org/10.1007/s11240-024-02717-5

Interpretive Summary: This paper is a continuation of studies to understand the storage physiology of seeds from palms and to genebank them to slow further attrition of genetic diversity of these species that are iconic to tropical and semi-tropical regions. The family of palms is quite diverse, and many species have ecological and economic significance. Palms produce among the largest seeds among all flowering plants; however, dry matter accumulates in the endosperm and the embryo remains small and undifferentiated in many species. This apparent paradox may lead to complex seed behaviors in which full tolerance to desiccation is not acquired and germination speed can be quite slow. For the species studied here, Butia catarinensis, we show the embryo's tendency to accumulate lipid in oil bodies, stimulation of germination in the presence of giberellic acid (a plant growth hormone), survival following removal of about 95% of the cell water, and normal growth following exposure of dried embryos to liquid nitrogen. These results indicate high feasibility to genebank this endangered species using cryogenic storage methods. Palms (Arecaceae) are distributed worldwide and are of extreme economic importance globally. These plants are propagated by seed and generally germinate slowly and in low proportions. Seeds from palms vary greatly in their tolerance of desiccation, making it difficult to preserve them ex situ as genetic resources. This study explores germination and desiccation tolerance of Butia eriospatha embryos, one of several species of Butia growing in the Brazilian rain forest. The first challenge of the study was to develop a reliable in vitro germination assay so that response to stress challenges could be measured. We found that B. eriospatha exhibited significant tolerance of drying and expressed post-drying metabolites that indicate stress and possible enzymatic recovery from oxidative damage. Because these embryos survive substantial water stress, it is possible to optimize water contents and cooling rates to avoid water freezing that is lethal to most recalcitrant (desiccation sensitive) seeds. For this reason, we are optimistic that the genetic resources of this important genus can be preserved in ex situ genebanks.

Technical Abstract: Palms have high ecological and economical importance in tropical and subtropical regions around the world. Preserving genetic resources of palms is hampered by poor understanding of the complex physiology of the seeds, which varies in desiccation tolerance and germination requirements depending on species and ecoregion. We show that embryos from seeds of Butia catarinensis, a species endemic to Brazil, exhibits physiological and cytological traits similar to embryos from palms that exhibit both desiccation tolerant and sensitive seeds. Embryos excised from fully mature seeds lacked differentiated cells, especially above the cotyledonary node. High germination (90%) of excised embryos in vitro was possible when gibberellin (GA3) was added to culture medium, suggesting that B. catarinensis seeds exhibit morphophysiological dormancy. Embryos from mature fruits were quite moist (1.42 gH2O gDW-1). The ultrastructure of meristematic cells had characteristics similar to embryos from other palm species that appear tolerant of extreme drying (e.g., vacuoles are small and cytoplasm is packed with lipid and protein reserves). However, cells of B. catarinensis embryos also had many mitochondria and endoplasmic reticulum, reminiscent of embryos from palm seeds that are sensitive to desiccation. Extreme embryo dehydration to 0.13gH2O gDW-1 causes ultrastructural deformation, including invagination of the cell walls, retraction of the plasma membrane and compression of nuclei. These noticeable cellular changes did not reduce the capacity of the embryo to germinate upon rehydration (82.5%). As a step toward cryobanking, we tested embryo response to immersion in liquid nitrogen (LN), and achieved a maximum germination rate of 77% normal seedlings post-thawing. We conclude that B. catarinensis embryos are desiccation tolerant and can be stored at liquid nitrogen temperatures and revived using cryobiotechnology strategies. This work provides crybiotechnology toolbox that are effective at protecting genetic diversity of threatened species as B. catarinensis from anthroprogenic threats.