Abstract
Regeneration of protoplasts into de novo plants was reported for a large number of seaweed species. The regeneration of protoplasts into different morphotypes as a result of epigenetic variations was discussed for the first time in this study. The loci assessed for methylation modifications in normal filamentous thalli showed a frequency of 32.43% as unmethylated DNA, 24.32% as a hemimethylated, and 20.27% as a methylation of internal cytosine at both the strands. The corresponding methylation values for disk-type thalli were 27.02%, 32.43%, and 14.86%, respectively. The hypermethylation condition was apparent in the disk-type thalli with methylation ratio of 72.97% compared to that of normal filamentous thalli with 67.56%. The frequency of methylation polymorphic sites among the two morphotypes was 53%. The present study reveals the distinct expression of cytosine methylation and is thus correlated to differential morphogenesis of plants regenerated from cultured cells. The number of protoplasts regenerating into filamentous thalli declined with increasing temperature from 15°C, 20°C, 25°C, and 30°C. The disk-type variant had higher thermal stability at 30°C over normal filamentous thalli. Further, this variant could maintain itself for more than a year in the laboratory indicating its suitability for in vitro germplasm maintenance and propagation.Electronic supplementary materialThe online version of this article (doi:10.1007/s10126-012-9434-7) contains supplementary material, which is available to authorized users.
Highlights
Plant protoplasts have been employed for investigating the various aspects of developmental biology and in vitro genetic manipulation techniques aimed at development of genetically improved strains of agronomic crops
Differentiation of protoplasts of U. reticulata into different morphotypes under the same in vitro culture condition was correlated with the epigenetic variations arising from polymorphic DNA methylation pattern and distribution
This is the first attempt made to understand the developmental polymorphism of seaweed protoplasts from the genome perspective
Summary
Plant protoplasts have been employed for investigating the various aspects of developmental biology and in vitro genetic manipulation techniques aimed at development of genetically improved strains of agronomic crops. Unlike higher plants, seaweed protoplasts regenerate and differentiate into a full thallus without any amendments of phytohormones to culture medium. The protoplasts from green seaweeds followed different types of regeneration patterns and gave rise to several phenotypically variable morphotypes such as sporangia, microthalli, saccate (or spherical), tubular (or spindle), irregular, and frondose with various life spans (Reddy et al 1989; Huang et al 1996; Chen 1998; Krishnakumar et al 1999; Chen and Shih 2000; Rusig and Cosson 2001). The reasons offered for differentiation of cells into such variable morphotypes in vitro were mostly speculative and primarily attributed to either axenic culture conditions employed (Singh et al 2011), age of source material used, or physical culture conditions such as temperature and irradiance (Chen 1998)
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