Aluminium-induced gene expression in sugarcane roots.
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Date
2002
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Abstract
Due to the increasing prevalence and severity of Al phytoxicity in certain regions of the South
African sugar industry, a research programme has been initiated at SASEX to elucidate the
molecular mechanisms by which sugarcane detects and responds to the metal. As part of this
larger investigation, the current study aimed to assess the response of a reportedly Al tolerant
cultivar, Saccharum spp. hybrid cv. N12, to phytotoxic levels of Al. Hydroponically-grown
plants of this commercial genotype were used in Al inhibition studies, the results of which
indicated that exposure of plants to 250µM Al for 24 hours resulted in maximum reduction of
root elongation. Under these conditions, root growth was inhibited by approximately 36%,
compared with only 4% for the 50µM Al treatment. Subsequently, this exposure regime was
used to gather the terminal 5 to 10mm of root tips, the site of the primary Al lesion, of
challenged and control, unchallenged plants for molecular analysis.
Total RNA was extracted from the Al challenged and control root tips, from which mRNA was
subsequently isolated, reverse transcribed and converted to double-stranded cDNA. The two
populations of cDNA were reciprocally subtracted from each other and used to construct
subtractive cDNA libraries in Lambda ZAP®II phages. Randomly selected clones, 576
representatives from each of the libraries, were screened using membrane-based array
technology. Results indicated that only 33% (190) of the Al-treatment specific library cDNAs
were found to be more highly expressed under conditions of Al stress than under control
conditions. Of these potentially Al response-related cDNAs, 25 were sequenced and submitted
to sequence databases for the assignment of putative identities. No genic sequences known to be
directly associated with the Al stress response were identified, however, several were found to
be related to pathogenesis or general stress pathways. Although further Northern hybridisation
work is required to validate these results, they suggest that the induction of general stress
response pathways may be involved in the aluminium stress response of this sugarcane cultivar.
Such Al stress-related sequences could have applications in marker-assisted breeding
programmes and as candidate genes for the genetic engineering of tolerant genotypes.
Description
Thesis (M.Sc.)-University of Natal, Durban, 2002.
Keywords
Sugarcane--Genetics., Sugarcane--Roots., Plants--Effect of aluminium on., Theses--Botany.