Albinism in Plants: A Major Bottleneck in Wide Hybridization, Androgenesis and Doubled Haploid Culture

Abstract

Albinism is a common problem encountered in interspecific crosses and tissue culture experiments including anther culture and generation of doubled haploids. It is characterized by partial or complete loss of chlorophyll pigments and incomplete differentiation of chloroplast membranes. This in turn impairs photosynthesis and the plants eventually die at a young stage without reaching maturity. Environmental conditions such as light, temperature, media composition and culture conditions play some role in determining the frequency of albino plant formation. Genetic factors are even more important, and are major determinants in albinism. Genetic studies in different crops show that it is a recessive trait governed by many loci. Both the nuclear and chloroplast genomes affect albinism and incompatibilities between the two are a probable cause of many pigment defects in hybrid progenies. Such incompatibility has been reported in a large number of angiosperms. The mechanisms behind these incompatibilities are poorly understood. Studies of plastid DNA inheritance together with observations using electron microscopy have established that the transmission of plastids can be maternal, paternal or biparental, even within the same genus, especially following wide crosses; contrary to the widespread belief that plastids are almost always transmitted from the maternal parent. Albinism has been overcome in some crop species through somatic hybridization and development of cybrids (cytoplasmic hybrids). However, the strict requirement of efficient protoplast regeneration is a major limitation of these techniques. This review focuses on albinism following interspecific crosses or development of doubled haploids facilitated by tissue culture experiments, underlying mechanisms, and the possibilities for dealing with this important biotechnological limitation.

Keywords:

• pigment
• plastid inheritance
• interspecific hybrids
• androgenesis
• doubled haploids
• plastome-nuclear genome incompatibility
• deletions

ACKNOWLEDGMENTS

We would like to thank Professor John Kuo and staff at The Centre for Microscopy, Characterization and Analysis at UWA for assistance with TEM of chickpea albinos. Professor Craig Atkins' review of the manuscript was most helpful, and comments by Adjunct Professor Tanveer Khan are also acknowledged. The Department of Education, Science and Training, Australia, supported the visit of Dr Maya Kumari from India to Australia through an Endeavour Research Fellowship for Postdoctoral research, while UWA and the Grains Research and Development Corporation provided operating funds.

Referee: Professor Craig Atkins, School of Plant Biology, Faculty of Natural and Agricultural Sciences, The University of Western Australia, Crawley WA 6009, Australia.]