Effect of three anthocyaninless genes on seed aging in tomato (Lycopersicon esculentum
Mill.)
Balacheva, E. and Atanassova, B.
Institute of Genetics, Bulgarian Academy of Sciences, Sofia 1113, Bulgaria
In our previous studies it was found that three anthocyaninless mutants of tomato,
anthocyaninless of Hoffmann (ah), anthocyanin without (aw) and baby lea syndrome (bls),
germinated more rapidly than the wild type lines under both, optimal and a relatively large scale of
stress conditions (Atanassova et al., 1997 a, b). In order to establish whether the effect of the three
genes concern other seed characteristics, (other than velocity of germination) we designed
experiments aimed at studying the longevity of the mutant and wild type seeds.
The investigation was performed on isogenic/near isogenic lines (IL/NIL) (NIL) described by
Maxon-Smith and Ritchie (1982) and Philouze (1991), on seed dry-stored under laboratory
temperature and humidity.
As it can be seen from the results presented in Table 1, the initial quality of the seed,
examined a few months after seed production was high. Mutant seeds germinated more rapidly
than the wild type ones and the differences in the time to 50% germination between them varied
depending on the genotype. The same applied to seed stored for one, two or three years (data for
the first and second year of storage not presented as no significant differences in germination
responses between the seed produced throughout these three years had occurred).
Germination responses after four and five years of seed storage clearly demonstrated
difference in tolerance to storage between the wild type and mutant seeds. After four years of seed
storage the time to 50% germination in the anthocyaninless IL/NILs was equal or longer than that in
the wild type ones, and after five years of storage all wild type genotypes germinated more rapidly
than the mutant ones. Aging in the mutant seeds resulted also in significant decrease in seed
viability expressed as percentage of germination, while in Porphyre and Ailsa Craig after four years
of storage and in Apedice and Ailsa Craig after five years of storage differences in the percentage of
germination between aged and non-aged seeds were not significant.
Study of seed coat morphology and histochemistry provided evidence that the three mutant
alleles ah, aw and bls not only completely inhibited anthocyanin biosynthesis, but were also
associated with alterations in seed morphology and testa histochemistry (Atanassova et al., 2004).
It was found that wild type seeds possessed longer hairs than ah and bls mutant seeds. The aw
seeds were a dark yellowish-beige color, while wild type ones were light beige. The inner epidermal
testa layer of the three wild type genotypes contained condensed tannins while in the
anthocyaninless genotypes this compound was absent. Condensed tannins contribute to the
rigidification of cell structure (Haslam, 1993). Therefore their absence in seed coats could contribute
to its increased permeability that subsequently could lead to the more rapid water uptake and
germination observed in the mutant seeds (Atanassova et al., 1997 a, 2004). On the other hand,
according to Hedin and Waage (1986), Oigiangbe and Onigbinde (1996) condensed tannins are
important in plant tissue because they probably inhibit microbial invasion and growth of pathogens
and contribute to the resistance to infestation by insects. As the results presented in Table 1
showed that the mutant seeds possessed lower tolerance to storage than the wild type ones, it
might be assumed that the absence of condensed tannins in the mutant seed coat is the main seed
characteristic contributing to the reduced vigor and viability of aged mutant seeds.
Table 1.Germination responses of aged seeds of tomato IL/NILs differing in genes ah, aw and bls
Genotype
Time to 50% Germination(%) Time to 50%
Germination
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