Differential Influx of Natural Plant Growth Regulators during Embryogeny in the Recalcitrant Seeds of Syzygium cumini (L) Skeels

Background: The hormonal up-regulation and down-regulation in recalcitrant seeds, on the other hand, has received little research. We tested fou plant growth regulators from distinct families of phytohormones at the same time to better understand their differential input from maternal tissues to growing Syzygium cumini seeds. Methods: During April-June 2020, seeds were collected in their native habitats in the Western Ghats. Seeds were chosen at random from each treatment. The embryonic tissues of seeds were chopped up and frozen for LC-MS/MS hormonal profiling. Result: Except for ABA, the dynamics of key plant hormones in this recalcitrant seed were identical to that of desiccation-tolerant orthodox seeds. When compared to other conventional seeds, SA was shown to accumulate at an unusually high level in mature embryonic tissues, demonstrating the highly hydrated seed’s defense mechanism against fungal attack following seed shedding.

Germination potential and methods for overcoming seed dormancy for domesticated and wild annatto populations after two years of storage

ABSTRACT: Annatto (Bixa orellana L.) is an arboreal species domesticated in Amazonia from its wild ancestor (B. orellana var. urucurana). Bixin extracted from its orthodox seeds is a natural dye widely used in the food industry. This study evaluated methods to overcome seed dormancy and determine the germination potential, comparing domesticated and wild annatto populations. Seeds from two domesticated-type populations and two families of a wild-type population, stored for two years after field collection, were submitted to five treatments to overcome dormancy: T1 - control; T2 - mechanical scarification (with sandpaper); T3 - mechanical scarification (with sandpaper) + immersion in water at 36 ºC overnight (12 hours); T4 - immersion in water at room temperature (23 ºC, on average) for 24 h; T5 - immersion in concentrated sulfuric acid (95 - 98%) for 15 min + running water for 3 min. Highly significant differences (P < 0.001) were observed in the germination percentage of annatto seeds between wild and domesticated types, and among the treatments tested. Domesticated types showed higher germination percentage (10 - 58%) over all treatments when compared to the wild type (0 - 44%). The best treatments were those performed with mechanical scarification. Given the simplicity, we concluded that mechanical scarification with sandpaper is a good alternative to overcome dormancy of annatto seeds.

The Orthodox Dry Seeds Are Alive: A Clear Example of Desiccation Tolerance

To survive in the dry state, orthodox seeds acquire desiccation tolerance. As maturation progresses, the seeds gradually acquire longevity, which is the total timespan during which the dry seeds remain viable. The desiccation-tolerance mechanism(s) allow seeds to remain dry without losing their ability to germinate. This adaptive trait has played a key role in the evolution of land plants. Understanding the mechanisms for seed survival after desiccation is one of the central goals still unsolved. That is, the cellular protection during dry state and cell repair during rewatering involves a not entirely known molecular network(s). Although desiccation tolerance is retained in seeds of higher plants, resurrection plants belonging to different plant lineages keep the ability to survive desiccation in vegetative tissue. Abscisic acid (ABA) is involved in desiccation tolerance through tight control of the synthesis of unstructured late embryogenesis abundant (LEA) proteins, heat shock thermostable proteins (sHSPs), and non-reducing oligosaccharides. During seed maturation, the progressive loss of water induces the formation of a so-called cellular “glass state”. This glassy matrix consists of soluble sugars, which immobilize macromolecules offering protection to membranes and proteins. In this way, the secondary structure of proteins in dry viable seeds is very stable and remains preserved. ABA insensitive-3 (ABI3), highly conserved from bryophytes to Angiosperms, is essential for seed maturation and is the only transcription factor (TF) required for the acquisition of desiccation tolerance and its re-induction in germinated seeds. It is noteworthy that chlorophyll breakdown during the last step of seed maturation is controlled by ABI3. This update contains some current results directly related to the physiological, genetic, and molecular mechanisms involved in survival to desiccation in orthodox seeds. In other words, the mechanisms that facilitate that an orthodox dry seed is a living entity.

Morphological Characterization and Physical Dormancy of Bauhinia winitii Seed: Living Collection of Purwodadi Botanic Garden

Bauhinia winitii Craib (Fabaceae, Caesalpinioideae) is a woody climber which is currently included in endangered species list. B. winitii seeds are orthodox seeds in which it has hard coat morphologically. Therefore, B. winitii seeds often undergo physical dormancy which can be broken through immersion in certain liquid media. This study aimed to characterize the morphology of B. winitii seeds and determine the pre-sowing treatment method to accelerate the seeds germination of B. winitii. External morphological characterization was carried out by observing the seeds quantitative and qualitative parameters. Characterization of seeds internal morphology was conducted using a digital microscope. Physical dormancy breaking was carried out by immersion in warm and cold water for 24 hours. Morphological characterization data were analyzed descriptively, while seed germination data were analyzed quantitatively by using one-way ANOVA followed by LSD test (with confidence level of 95%). B. winitii has pod-shaped fruits with 2-6 seeds per pod, the seeds are 1.36 cm x 1 cm in size, 0.47 cm thick and weighed 0.5 g, oblong to conical in shape, smooth and shine surface, with light to dark brown in color. Seeds immersion treatment in warm water could break the physical dormancy of B. winitii seeds thus 63% of the seeds were able to germinate and it was significantly different compared to control and cold water immersion treatment. Technical to germinate B. winitii seed can be known from pre-sowing treatment. This study can be used as a reference for seed identification and germination technical of B. winitii seed.

Cathodic Water Enhances Seedling Emergence and Growth of Controlled Deteriorated Orthodox Seeds

All orthodox seeds eventually deteriorate during storage, a well-known problem in seed banking. Here we used a greenhouse study to test if priming deteriorated seeds with cathodic water can improve the emergence and subsequent seedling growth of three South African tree species, Bolusanthus speciosus, Combretum erythrophyllum and Erythrina caffra. Other priming solutions investigated were calcium magnesium (CaMg) solution and deionized water. In the present study, seeds were subjected to an artificial deterioration by increasing their water content to 14% and keeping them at 40 °C and 100% RH until they had lost 50% of their germination under laboratory conditions. Fresh and deteriorated seeds were primed with cathodic water, CaMg solution and deionized water, with non-primed fresh and deteriorated seeds as controls. Controlled deterioration significantly reduced total emergence and the biomass and photosynthetic parameters of the resulting seedlings. In one species (Bolusanthus speciosus), priming the deteriorated seeds with cathodic water significantly improved emergence parameters. However, in all species cathodic water significantly improved the total biomasses and other growth parameters of the seedlings derived from deteriorated seeds. Priming with CaMg solution and deionized water had little effect on emergence and while improving the growth of seedlings derived from deteriorated seeds, they were less effective than cathodic water. In fresh seeds, priming with all solutions resulted in small improvements in some parameters. Controlled deterioration of fresh seeds reduced the membrane stability index (MSI) in two of the three species and in all species increased the levels of the lipid oxidation products MDA and 4-HNE. Priming deteriorated seeds with cathodic water increased the MSI and reduced the MDA contents in all species and the 4-HNE content in one species. Other priming solutions were generally less effective in ameliorating oxidative stress. Results suggest that the strong antioxidative properties of cathodic water can explain its ability to ameliorate deterioration. In conclusion, the present study shows that priming with cathodic water is an effective way of invigorating deteriorated orthodox seeds and that it may have considerable potential in orthodox seed conservation.

GA/ABA Antagonism in the Physiology of Seed Germination in the Recalcitrant and Vulnerable Tree- Vateria indica L.

Background: Seed recalcitrance is a major problem associated with many tropical plants, limiting their natural regeneration. Vateria indica L. is a vulnerable and endemic tree species in South-Western Ghats of India, which is also recalcitrant. ABA and gibberellins are the most important plant hormones required for seed germination. It is the balance between ABA and GA which is responsible for desiccation tolerance in orthodox seeds. Exogenous hormones pretreatment has been also reported to influence seed germination. But such studies had been sparsely done in the case of recalcitrant seeds. This study aims to find out whether GA/ABA antagonism in recalcitrant plants is operating in the same way, like that in the orthodox seeds.Methods: The effect of the exogenous pre-soaking application of phytohormones viz. GA3 and ABA individually as well as their combinations on seed germination and growth of Vateria indica L. were carried out in the present work. The seeds were collected from April to July 2018 and the experiment was designed at Post Graduate and Research Department of Botany, Government College for Women, Thiruvananthapuram. When different concentrations of each phytohormone were externally given to the seeds, ABA reduced the germination and growth in almost all the concentrations. But GA3 gave better results. When combinations of GA3 and ABA were used, germination was poor in the sample where ABA was more than GA3, But in samples with same concentrations of both the hormones and with more GA3 gave better results. Result: This study clearly showed that GA3 when given externally along with ABA, might have affected the endogenous ABA in this recalcitrant seed and suppressed its retarding effect. Thus ABA/GA antagonism is working out, here, in the same way as in orthodox seeds. Since the germination of recalcitrant seeds is a less investigated area, the present study will form a basis and a lot more for further such studies.

Epigenetic Integrity of Orthodox Seeds Stored under Conventional and Cryogenic Conditions

The level of 5-methylcytosine (m5C) in DNA has been observed to change in plants in response to biotic and abiotic stress factors. Little information has been reported on alterations in DNA methylation in orthodox tree seeds in response to storage conditions. In the current study, epigenetic integrity was analyzed in seeds of Pyrus communis L. in response to conventional and cryogenic storage. The results indicate that conventional storage under optimal conditions resulted in a significant increase in m5C. In contrast, a decrease in m5C level after cryostorage at high water content (WC) was observed, not only in seeds but also in 3-month-old seedlings which were smaller than seedlings obtained from seeds cryostored at optimal WC. This shows that non-optimal cryostorage conditions increase epigenetic instability in seeds and seedlings. Optimal procedures for germplasm conservation are very important for germplasm banking since they have serious implications for the quality of stored collections. Maintaining epigenetic integrity during WC adjustment and optimal storage is a characteristic feature of orthodox seeds. The current results underline the importance of proper protocols and techniques for conventional storage and particularly cryopreservation as a method for conservation of true-to-type germplasm for long periods.

Seed traits linked to differential survival of plants during the Cretaceous/Paleogene impact winter

In past investigations the pattern of differential survival of plants across the K/Pg boundary has been viewed as incompatible with severe asteroid impact winter scenarios (i.e., an impact winter lasting more than a few months), particularly the enigmatic survival of coryphoid palms and Pandanus (screw pine). Stateof- the-art climate models based on soot, sulfate and nano-sized dust aerosols predict a global impact winter that drastically reduced precipitation and resulted in a transient period of total darkness and permafrost conditions. This suggests that the plants most likely to have been affected by the global mass-extinction event were tropical phanerophytes that produce recalcitrant seeds, which by definition are desiccation-intolerant, survive less than a year, and cannot survive freezing. However, this hypothesis has never been tested. In this study I sampled over 100 plant species from the global fossil record that have a high probability of having produced either recalcitrant seeds/disseminules (n1 = 58) or orthodox seeds (n2 = 59), based on their phylogenetic relationships with extant taxa that either are monomorphic for these traits or specifically exhibit a genetic marker for abscisic acid inhibition associated with seed dormancy and recalcitrance. A one-tailed z-test for the difference between two proportions revealed that plant taxa with a high probability of having produced recalcitrant seeds had significantly lower survivorship than plant taxa with a high probability of having produced orthodox seeds (p < 0.0001). Based on these data, it can be concluded that plants which formed a frost-tolerant seed bank during the latest Maastrichtian were significantly more likely to survive the K/Pg impact winter than plants which did not (including palms). These data clearly indicate that the K/Pg impact winter probably lasted longer than a year and that it selected for seed-based traits that effectively sorted correlated functional traits of mature plants (i.e., leaf physiognomic features). This novel hypothesis stands as an alternative to J.A. Wolfe’s classic hypothesis that a mild K/Pg impact winter selected for fast-growing angiosperms with deciduous leaves and did not affect the plant communities of the Southern Hemisphere. Potential mechanisms for the rare survival of tropical, recalcitrant-seeded plants are discussed.