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.

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.

Respiratory rates and freezing tolerance of embryos of Inga vera Willd. subsp. affinis (DC.) T.D. Penn. from different regions

ABSTRACT: Recalcitrant seeds are sensitive to desiccation and low storage temperatures, but there is a gradient of recalcitrance between different species and between populations of the same species. Therefore, tolerance to drying and low temperatures, as well as the respiratory rates of seeds, can be conditioned by the source of the material. The present study aimed to evaluate the relationship among desiccation and low temperature tolerance, and respiratory rates of Inga vera embryos from different regions. The embryos were submitted to three drying levels and incubated for up to fifteen days at -4, -2, 2 and 5 °C. Then, they were evaluated for respiration, germination and electrical conductivity. The embryos tolerated freezing at -4 °C since they were associated with certain levels of drying and a consequent change in the energy status of water. In conclusion, the conditions in which the embryos are formed define their degree of maturation at dispersal, hence their tolerance to desiccation and freezing.

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.

Changes in Proline Levels during Seed Development of Orthodox and Recalcitrant Seeds of Genus Acer in a Climate Change Scenario

In the present study, we examined the utility of proline usage as a biochemical indicator of metabolic changes caused by climate change (mean temperature and precipitation) during seed development of two Acer species differing in desiccation tolerance: Norway maple (Acer platanoides L.—desiccation tolerant—orthodox) and sycamore (Acer pseudoplatanus L.—desiccation sensitive—recalcitrant). In plants, proline is an element of the antioxidant system, which has a role in response to water loss and high temperatures. Our study considered whether proline could be treated as an indicator of tree seed viability, crucial for genetic resources conservation. Proline content was measured biweekly in developing seeds (between 11 and 23 weeks after flowering) collected in consecutive years (2017, 2018, and 2019). We showed that proline concentrations in recalcitrant seeds were positively correlated with mean two-week temperature. In contrast, in orthodox seeds no such relationship was found. Proline content proved to be sensitive to thermal-moisture conditions changes, which makes it a promising biochemical marker of seed desiccation tolerance in different climatic conditions.

Cryopreservation for Tree Species with Recalcitrant Seeds: the Avocado Case

Recent developments in the cryopreservation space has increased the trend in germplasm collections established through cryopreserved in vitro material. Cryopreservation of recalcitrant seeds through embryos and embryonic axes, is not uncommon. Tropical and sub-tropical plants are not acclimated to the cold season, therefore have no in-built natural resilience to the cold. Also, larger seeds from trees, such as avocado (Persea americana Mill.), mango (Mangifera indica) and durian (Durio zibethinus L.) are sensitive to desiccation, chilling and freezing stress, making them unsuitable for seed banking or cryopreservation. Alternatively, as seeds do not carry the same genetic make-up as the mother plant, especially in the context of woody rainforest species of which the cross-pollination is dominant; seed conservation does not serve the purpose of germplasm preservation. Other plant material and methods are needed for these plants to be successfully stored in liquid nitrogen (LN). One such method commonly used is shoot-tip cryopreservation which ensures the clonal fidelity of germplasm. There are many problems when using shoot tips of tropical recalcitrant-seeded species. These include: 1) the toxic effects of cryoprotective agents towards structural integrity; 2) optimum developmental stage for success and 3) oxidative stress associated with excision injury leading to necrosis triggering cell death and hindering regeneration for the shoot tips in culture. A pre-requisite for any cryopreservation system is the availability of an established tissue culture regeneration platform. This review will outline conservation strategies for avocado with special emphasis on attempts and improvements made in the cryopreservation space for storing this horticulturally important crop &lsquo;avocado&rsquo; at ultra-low temperatures.