Existence of Vivipary in Mango (Mangifera indica cv. ‘Amrapali’) – A Report

Aim: The Amrapalii cultivar of mango is known for its dwarf stature, high productivity and ability to capture the market late when mango from other regions of the country gets over. Vivipary is of unusual occurrence in mango. The aim of the study is to report the occurrence of vivipary in mango especially in cultivar Amrapali under the sub-Himalayan subtropics of India. Materials and Methods: Incidental occurrence of vivipary in mango has been reported from the Hamirpur district of Himachal Pradesh during the growing season of the year 2021. Upon observance of abnormal protuberances from the fruit surface, the harvesting was commenced at the weekly intervals and the per cent proportion of viviparous fruits was ascertained by cutting the fruits longitudinally and confirming the viviparous germination of the seeds. Weather data of the fruit development state were analysed for the accumulation of heat units and rainfall distribution. Efforts have been made for ascertaining the reason behind the viviparous seed development. Results and Discussion: The proportion of viviparous seeds increased with the progression of time and by the mid of September, more than 12% of seeds were found viviparous. The weather data show that there was an early accumulation of heat units. Also, the rainfall during the period of fruit development was high particularly at the time when fruits were advancing toward maturity. It has been observed that the seed maturity has preceded the fruit pulp maturity and ripening may be due to the early accumulation of heat units and high rainfall. This coincidence might have resulted in precocious germination of seed inside the fruit, leading to vivipary. Conclusion: The development of vivipary in Amrapali mango has been found to be associated with the early accumulation of heat units and high rainfall. Under the current changing climatic scenario, a need has been projected for strategic research for curtailing vivipary incidences and saving economic losses to the growers of late mango varieties in the sub-Himalayan subtropics.

Changes in abscisic acid metabolism in relation to the maturation of grapevine (Vitis vinifera L., cv. Mencía) somatic embryos

Background Somatic embryogenesis in grapevines is a complex process that depends on many physiological and genetic factors. One of its main limitations is the process of precocious germination of the somatic embryos in differentiation medium. This process lowers plant conversion rates from the somatic embryos, and it is probably caused by a low endogenous abscisic acid (ABA) content. Results Precocious germination of the somatic embryos was successfully avoided by culturing grapevine cv. Mencía embryogenic aggregates over a semipermeable membrane extended on top of the differentiation medium. The weekly analysis of the endogenous ABA and ABA-glucosyl ester (ABA-GE) contents in the aggregates showed their rapid accumulation. The expression profiles of 9-cis-epoxycarotenoid dioxygenase (VvNCED1), 8′-hydroxylase (VvHyd2), UDP-glucosyltransferase (VvUGT) and β-glucosidase (VvBG2) genes in grapevine revealed that the occurrence of a first accumulation peak of endogenous ABA in the second week of culture over the semipermeable membrane was mainly dependent on the expression of the VvNCED1 gene. A second increase in the endogenous ABA content was observed in the fourth week of culture. At this point in the culture, our results suggest that of those genes involved in ABA accumulation, one (VvNCED1) was repressed, while another (VvBG2) was activated. Similarly, of those genes related to a reduction in ABA levels, one (VvUGT) was repressed while another (VvHyd2) was activated. The relative expression level of the VvNCED1 gene in embryogenic aggregates cultured under the same conditions and treated with exogenous ABA revealed the significant downregulation of this gene. Conclusions Our results demonstrated the involvement of ABA metabolism in the control of the maturation of grapevine somatic embryos cultured over a semipermeable membrane and two important control points for their endogenous ABA levels. Thus, subtle differences in the expression of the antagonistic genes that control ABA synthesis and degradation could be responsible for the final level of ABA during the maturation of grapevine somatic embryos in vitro. In addition, the treatment of somatic embryos with exogenous ABA suggested the feedback-based control of the expression of the VvNCED1 gene by ABA during the maturation of grapevine somatic embryos.

The genomic and transcriptomic foundations of viviparous seed development in mangroves

Vivipary in plants refers to a specific seed development and reproductive strategy where seeds minimize the dormancy stage and germinate while still attached to their maternal plants. It is one of the most unique adaptive genetic features used by many mangrove species where elongated hypocotyls aid in quick root emergence to anchor the seedling in coastal intertidal wetlands. The genetic mechanisms behind mangrove vivipary, however, remain elusive. Using comparative genomic and transcriptomic technologies to investigate viviparous mangroves and their close inland relatives, we found that a full array of gene expression profiles were altered, including key plant hormone metabolic pathways, high expression of embryonic signature genes, and reduced production of proanthocyanidins and storage proteins. Along with these changes, a major gene regulating seed dormancy, Delay of Germination-1 (DOG1), is entirely missing or defunct within the entire linage of the four genera with true viviparous characteristics. These results suggest a systemic level change is required to warrant the genetic program of mangrove vivipary. Understanding of the molecular processes of vivipary could benefit the design of pregerminated propagules for forestation in harsh environments or prevent precocious germination of grain crops pre- and post-harvest.

The effect of ABA and AMO-1618 on the preharvest sprouting of triticale caryopses

The experiments were conducted on developing triticale var. Grado caryopses. Treatment of freshly gathered, unripe triticale caryopses with abscisic acid (ABA) decreased their precocious germination throughout the entire period of development and ripening. The more mature the embryos that were germinated, the lower the inhibition by ABA. This indicates that the sensitivity of the embryo to ABA decreases during the course of caryopsis development and that the role that this hormone can play in the prevention of spouting in ears during the final stages of maturation, is limited. A known inhibitor of gibberellin synthesis, the retardant AMO-1618, was also tested in these experiments. This compound caused the reduction of germination capability only in the initial stages of development of triticale caryopses. Its most visible effect was noted during the germination of caryopses collected 30 days after flowering. The effect of this compound on the precocious germination of isolated embryos also decreased as the degree of maturity of these embryos increased. In the opinion of this author, this is connected with the fact that intense gibberellin synthesis and accumulation occurs only in the early stages of caryopsis development.

The role of the embryoless parts of triticale caryopses in inhibiting precocious germination and transcription in the embryo during development and maturation of caryopses

The experiments were conducted on developing and ripening triticale cv. Dagro caryopses. Increasing capability for precocious germination of the caryopses was seen as development and maturation progressed. A significant role of the embryoless parts of the caryopses (testa, pericarp and endosperm) in preventing germination processes was found. Isolated embryos (after 8 days of incubation) germinated by 100% from the 32nd day after flowering, while only 10% of whole caryopses from this sample germinated. Removal of the outer pericarp strongly stimulated germination of unripe caryopses. However, incising the caryopses near the embryo only slightly stimulated this process, which indicates that hypoxia of the embryo is not the cause of triticale embryo dormancy. Another very sensitive indicator of release of dormancy in the caryopses was the increased synthesis of embryo polyribosomal RNA induced by germination. The results of investigations on RNA synthesis in embryos - which undergoes extreme intensification when germination processes are initiated in the caryopses - were in agreement with those of biological studies based on observation of the elongation of the radicle. The lowest inhibition of transcription in the embryo was found when it was completely separated from the testa, pericarp and endosperm. A smaller effect was seen upon removal of the outer pericarp from developing and ripening caryopses, and decidedly the smallest effect still of incising the caryopses near the embryo.

Precocious germination and its regulation in embryos of triticale caryopses

Triticale var. Lasko embryos, isolated from grain gathered at milk ripeness, the beginning of wax ripeness and at full ripeness, were allowed to germinate for 48 h on agar with glucose. The highest incorporation of tritiated adenosine into polyribosomal RNA during germination was found in the ribosome fractions from embryos of grain gathered at full ripeness, lower incorporation was in preparations from embryos of milk ripe grain and the lowest in preparations from embryos of wax ripe grain. Different tendencies were observed in respect to the synthesis of ribosomal proteins. The highest incorporation of ¹⁴C-amino acids into ribosomal proteins was found in preparations of ribosome fractions from embryos of milk ripe grain, lower in preparations of embryos from fully ripe grain, the lowest in preparations of embryos from wax ripe grain. ABA (10^-4 M) completely inhibited the external symptoms of germination of immature embryos, while its inhibition of the synthesis of polyribosomal RNA and ribosomal proteins was greater the more mature the embryos that were germinated. The greatest stimulation of precocious germination by exogenous BA and GA₃ was demonstrated in the least mature embryos isolated from milk ripe grain. Under the influence of both stimulators, an increase of the proportion of polyribosomes in the total ribosome fraction occurred in this sample, as did a rise in the intensity of ribosomal protein synthesis. The incorporation of ³H-adenosine into polyribosomal RNA, however, was lower than in the control sample. The results obtained suggest that the regulation of precocious germination of triticale embryos by phyto-hormones is not directly related to transcription.