Bulb Dormancy In Vitro—Fritillaria meleagris: Initiation, Release and Physiological Parameters

In ornamental geophytes, conventional vegetative propagation is not economically feasible due to very slow development and ineffective methods. It can take several years until a new plant is formed and commercial profitability is achieved. Therefore, micropropagation techniques have been developed to increase the multiplication rate and thus shorten the multiplication and regeneration period. The majority of these techniques rely on the formation of new bulbs and their sprouting. Dormancy is one of the main limiting factors to speed up multiplication in vitro. Bulbous species have a period of bulb dormancy which enables them to survive unfavorable natural conditions. Bulbs grown in vitro also exhibit dormancy, which has to be overcome in order to allow sprouting of bulbs in the next vegetation period. During the period of dormancy, numerous physiological processes occur, many of which have not been elucidated yet. Understanding the process of dormancy will allow us to speed up and improve breeding of geophytes and thereby achieve economic profitability, which is very important for horticulture. This review focuses on recent findings in the area of bulb dormancy initiation and release in fritillaries, with particular emphasis on the effect of plant growth regulators and low-temperature pretreatment on dormancy release in relation to induction of antioxidative enzymes’ activity in vitro.

Transcriptome and targeted metabolome reveal the regulation network of Lilium davidii var. unicolor during dormancy release

Background：Regulation and control of bulb dormancy are critical for ensuring annual production and high-level cultivation of lily. Application of low temperatures is the most effective method for breaking lily bulb dormancy, but the molecular regulatory mechanism underlying this response is unclear. Results：Herein, targeted metabolome and transcriptome analyses were performed with buds of Lilium davidii var. unicolor bulbs stored for 0, 50 and 100 days at 4°C. Dormancy release mainly depended on the accumulation of GA4 and GA7, which are synthesized by the "non13-hydroxylation" pathway, rather than GA3, and ABA was degraded in the process. The contents of nonbioactive GA9, GA15 and GA24, the precursors of GA4 synthesis, increased with bulb dormancy release. Altogether, 113,252 unique transcripts were de novo assembled through high-throughput transcriptome sequences, and 639 genes were continuously differentially expressed. Enrichment analysis showed that the carbohydrate metabolism and hormone metabolism pathways play major roles in dormancy release. Energy sources during carbohydrate metabolism mainly depend on glycolysis and the PPP pathway rather than on the TCA cycle. Association analysis of the transcriptome and target metabolome showed that genes related to ABA, GA, starch and sucrose metabolism and some TF families, such as MYB, WRKY, NAC and TCP, involved in dormancy release were highly correlated with the target metabolome. Coexpression analysis further confirmed that ABI5, PYL8, PYL4 and PP2C, vital ABA signaling elements, regulated GA3ox and GA20ox in the GA4 biosynthesis pathway. The TFs WRKY32, WRKY71, MYB, DAM14, NAC8, ICE1, bHLH93 and TCP15 also participated in the ABA/GA4 regulatory network, and ICE1 may be the key factor linking temperature signals and hormone metabolism. Conclusions：These results will help to reveal the bulb dormancy molecular mechanism and to develop new strategies for high-quality bulb production.

Pematahan Dormansi Umbi Bawang Putih (Allium sativum L.) Varietas Lumbu Hijau dengan Perlakuan Lama Penyimpanan Umbi pada Suhu Rendah dan Aplikasi Giberelin

Low temperature and gibberellin treatments affected on breaking dormancy. The effects of low temperature in storage duration and gibberellin treatrments on breaking of dormancy of garlic were examined in this study. The aims of this study to determinate the best treatments for breaking garlic bulb dormancy. The sorted garlic bulbs were stored at 4 ± 0.4 ° C for 0 (control), 15, 30 and 45 days. The bulbs that have been treated by low temperature then treated by gibberellins at various concentrations including 0, 75, 150, and 225 mgL-1 by soaking for 24 hours. The bulbs were planted in the seedling house. The low temperature storage (4±0,4ᵒC) for 45 days is more effective than 0, 15 and 30 days, while the concentration of gibberellins were not have a significant effect on breaking dormancy. GA3 endogenous was increased during low temperature storage, on the other hand, it accelerated on breaking dormancy . The highest percentage of sprouting bulb produced by treatment at low temperature storage for 45 days. Growth parameters such as shoot length, shoot dry weight and leaves get the best at 45 days storage time. Low temperature storage (4±0,4ᵒC) is effective in breaking dormancy of garlic bulb.

Transcriptome Analysis of Low-Temperature-Induced Breaking of Garlic Aerial Bulb Dormancy

The long history of asexual reproduction of garlic using garlic cloves has resulted in virus accumulation and genetic depression. Propagation of garlic seedlings by tissue culture can both eliminate viruses and improve breeding efficiency. Aerial bulbs are the first-choice materials for breeding virus-free garlic seedlings under external conditions, but they show dormancy just like garlic bulbs. However, low temperatures can quickly break dormancy. In this research, we used a high-throughput sequencing method to sequence aerial bulbs during dormancy and after low-temperature-induced breaking of dormancy to screen out the key differentially expressed genes (DEGs) associated with low temperature and to provide a theoretical basis for exploring the molecular mechanism of low-temperature-induced breaking of aerial bulb dormancy. The high-throughput transcriptome sequencing results showed that 6,675 DEGs were upregulated and 36,596 DEGs were downregulated in the aerial bulbs given low-temperature treatment. Then, 19,507 DEGs were assigned KEGG annotations, among which most DEGs were annotated to the metabolism pathway (11,817 genes, accounting for 60.58%), followed by the genetic information processing pathway (4,521 genes, accounting for 23.18%). The DEGs were mostly concentrated in pathways such as protein processing in the endoplasmic reticulum, plant-pathogen interaction, plant hormone signal transduction, and ribosome biogenesis in eukaryotes, with significant enrichment. The key DEGs related to calcium signaling, hormonal signaling, and transcription factors were screened out, including CaM, CDPK, and CML in accessory pathways of calcium signaling; GA20ox, GAI1, and GA2ox in accessory pathways of hormonal signaling; and transcription factor genes such as MYB, AP2/ERF, bHLH, MADS, and bZIP. qRT-PCR verification results were consistent with the sequencing results, indicating that the transcriptome sequencing data were accurate and reliable. Our results provide a theoretical basis for breaking the dormancy of aerial bulbs with low-temperature treatment to produce virus-free seedlings and increase the output and quality of garlic.