Heat treatment is widely used to break dormancy for seed germination and phytohormones could be deeply involved. However, effect of heat treatment on phytohormone related genes/proteins/metabolites and possible relationship with dormancy release remains unclear in oil palm. In this study, oil palm seeds were heat-treated at 39 °C for 60 days according to the method for commercial production. The embryos of seeds during heat treatment (0 d, 15 d, 30 d, 45 d and 60 d) and of germinated seeds (70 d and 75 d) were selected to discover the mechanisms involved in oil palm seed germination. RNA-seq and iTRAQ were applied to investigate DEGs and DEPs related to seed germination; qPCR and western blot were used as validation accordingly; endogenous phytohormones were determined by LC-MS/MS and exogenous phytohormones were also applied to validate their effects on seed germination. RNA-seq results showed that plant hormone signal transduction was one of the most important pathways and eight phytohormones involved, while six of them (ABA, GA, ET, CTK, IAA and JA) were also identified by iTRAQ. Both RNA-seq and iTRAQ results showed that the expression of ABA decreased after heat treatment, which was further validated by qPCR and western blot. Furthermore, changes in endogenous phytohormones showed that ABA decreased rapidly to about 9% of the control at 30 d and then stayed at very low levels until germination; GA and CTK increased while IAA was not affected by heat treatment. Besides, exogenous ABA treatments (10, 100, 1000 mg/L) showed that the germination rate decreased to 63, 42 and 16% of the control, respectively, suggesting that ABA suppress seed germination and the inhibition effect increase with higher concentration; while the germination rates of exogenous GA and IAA treatments barely changed among different concentrations. Phytohormones are deeply involved in oil palm seed germination and ABA acts as an inhibitor. Heat treatment can eliminate endogenous ABA and break dormancy, while GA and CTK may also involve in dormancy release. At least 30 days of heat treatment might be necessary. This study provided informative perspectives on oil palm seed germination, which could be also applicable in other palm species.

Oil palm (Elaeis guineensis) is the highest oil-yielding commercially grown perennial tree. Oil palm germplasm conservation and in vitro clonal propagation strengthened the world’s efforts to ensure future food security. Cryopreservation provides long-term storage for germplasm. The storage of plant material at cryogenic temperatures (−196 °C) following dehydration causes cryoinjury. The cryotolerance mechanism has rarely been studied in oil palm zygotic embryos (ZE) and embryogenic calli (EC). A simple and effective cryopreservation method was established for ZE. ZE surrounded by endosperm was air-dried for 3 days without any complicated chemical pre-treatments before cryopreservation, while the viability rate and following germination rate could reach up to 96.67% and 90.88%, respectively. As for EC, the preferred method could be pre-culture in liquid MS medium with 0.3 M sucrose for 12 h and PVS2 treatment for 5 min prior to cryopreservation, and the viability rate reached 68.33%. SSR markers were used to verify the genetic stability after cryopreservation. In addition, changes in enzyme activities (CAT, POD, and SOD) showed a consistent trend with H₂O₂ production among ZE samples, indicating that these antioxidants were involved in ROS scavenging. Furthermore, differently expressed genes (DEGs) related to ROS, osmotic, and cold stress responses were selected for correlation network analysis. Most genes involved in ROS production (RBOH, PAO, and PRX) and ROS scavenging (APX, PER, SOD, CAT, GPX, and AOX) showed higher expression levels in EC, suggesting that EC was more sensitive to oxidative stress than ZE. The cryotolerance mechanism was further summarized accordingly. These results contributed to cryopreservation methods and provided a better understanding of cryotolerance in oil palm.

The coconut palm (Cocos nucifera L.) is a perennial, cross-pollinated, oil-bearing tropical forest tree. Recently, the demand for coconut goods has surged to 5 to 10 times its former value; however, coconut production is in jeopardy. Coconut senility is one of the most apparent factors that influence productivity. Adequate replanting is urgently required to maintain the growing demand for coconut products. However, coconut palm mass replanting might not be possible with traditional approaches. To overcome this snag, micropropagation via somatic embryogenesis (SE) has enormous potential for proficient clonal propagation in the coconut palm. During SE, the stimulation of cell proliferation, acquisition of embryogenic cell competence, and induction of somatic embryos undergo a series of developmental events. This phenomenon requires regulation in gene expression patterns and the activation of specific signaling pathways. This review summarizes gene regulatory mechanisms involved in the cell cycle, dedifferentiation, totipotency, embryo initiation, and meristem development during somatic embryo formation. Plant hormonal signal transduction is also highlighted during the formation of SE in coconut.