Mature seeds of most of the higher plants harbor dormant embryos and go through the complex process of germination under favorable environmental conditions. The germination process involves dynamic physiological, cellular and metabolic events that are controlled by the interplay of several gene products and different phytohormones. The small non-coding RNAs comprise key regulatory modules in the process of seed dormancy and germination. Recent studies have implicated the small RNAs in plant growth in correlation with various plant physiological processes including hormone signaling and stress response. In this review we provide a brief overview of the regulation of seed germination or dormancy while emphasizing on the current understanding of the role of small RNAs in this regard. We have also highlighted specific examples of stress responsive small RNAs in seed germination and discussed their future potential.
Seed germination paves the way for the dormant embryo to establish itself as a new plant marking the first critical step in postembryonic plant growth and development. Germination starts with the uptake of water (imbibition), followed by induction of transcription, translation, energy metabolism, and cell division processes. Although small RNAs have been implicated in many developmental processes, their role during seed germination stages and conditions remained elusive. Here we show that seed germination conditions, like imbibition and temperature, dynamically regulate the expression of many developmentally important miRNAs and their targets. We have identified 58 miRNAs belonging to 30 different families at different seed germination conditions. Amongst these, 15 miRNAs and their targets were significantly differentially expressed in Arabidopsis seeds in dry and 12 h, 24 h and 48 h of imbibition. Interestingly, differential expression of miR390, which targets trans-acting siRNA locus (TAS3) derived transcripts, resulted in alteration of tasiR-ARF mediated regulation of expression of target AUXIN RESPONSE FACTORs (ARF2/3/4). Our results suggest that the dynamic expression of several miRNAs, their targets, and a crosstalk between miRNA and ta-siRNA pathways contribute to the regulation of seed germination in Arabidopsis thaliana.
Summary Cytomixis associated with chromosomal anomalies was recorded in the meiotic division of pollen mother cells of the wild genotypes of Chlorophytum tuberosum (Roxb.) Baker for the first time. The migration of chromosomal substances was more prevalent in Meiosis-I than Meiosis-II. Cytomixis has been found both in juxtaposed cells by direct contact as well as between remote cells through cytoplasmic strands. During cytomixis, various chromosomal abnormalities, such as chromosomal stickiness, laggards, chromosomal bridges, unequal separation of chromosome, micronuclei formation and loss of chromosome, were recorded. A significant number of empty pollen formations leading to pollen sterility was recorded which is assumed to be a direct result of cytomixis.
Suaeda maritima (L.) Dumort of the family Chenopodiaceae is an annual succulent mangrove herb. This annual salt marsh is quite regularly used by the local people for food and pharmaceutical. This species has been cursorily noted to have variation in some morphological characters. Earlier reports indicated the presence of triterpenoid e.g. alpha amyrin in some species of Suaeda. However, no report on the variation in the quantity of it in this species was presented. The present study has furnished an account of subtle variation in morphology of this herb growing on different sites in the area under study. It also shows a difference in the amount of alpha amyrin in the plant individuals of different places, revealed through the HPTLC study. Morphological variations have been noted mostly in respect of the characteristics of the stem and leaf of the species.
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