Somaclonal variation-induced mutation in an aluminum tolerant inbred line
--Sergio T. Sibov, Marilia Gaspar, David H. Moon, Marcio J. da Silva, Laura M. M. Ottoboni and Anete P. de Souza

Somaclonal variation-induced multiple mutations were observed in progenies of an R0 plant regenerated from type I calli of the aluminum tolerant inbred line Cat-100-6. After five generations of self pollination, 14 progenies were tested for aluminum (Al) sensitivity in a nutrient solution containing 6 mg/l of Al. All of the 14 somaclones tested were sensitive to Al as defined by root tip morphology and relative growth values. The most Al-sensitive progeny, S1587-17, was selected for further study.

To study the effect of aluminum on Cat-100-6 and S1587-17 roots, seeds were germinated at 30 C between layers of moist filter paper. After 3 days, the primary root lengths were measured and the seedlings were transferred to polystyrene holders, which were then floated on an appropriate volume of an aerated nutrient solution. Aluminum, in the form of AlK3(SO4)3, was added to the nutrient solution at a concentration of 6 mg/l of Al and seedlings were removed at various exposure times (0, 1, 2, 4, and 6 days). Fig. 1 shows the progressive destruction of normal root tip morphology in the sensitive plant with time of exposure to Al (Fig. 1F-J) and the lack of effect on the tolerant plant root tip (Fig. 1A-E). After 1 day of exposure to Al, the sensitive root tip (Fig. 1G) showed signs of swelling and by 2 days the root tip was clearly swollen (Fig. 1H). The root tip structure was drastically changed after 4 days of exposure (Fig. 1I); after 6 days (Fig. 1J)
the root tip was completely lost leaving a blunt swollen end and lateral root growth had commenced very close to the root apex. In contrast, the tolerant root tip showed no symptoms of Al toxicity over the same time period (Fig. 1A-E).

The genetics of Al tolerance was investigated in a F2 population obtained from Cat-100-6 x S1587-17 and a BC2 population obtained by crossing the F1 with S1587-17. The analysis indicated that the Al tolerance of Cat-100-6 is determined by a single dominant gene, as tolerant and sensitive plants segregate in typical Mendelian ratios (Table 1). [ed. note: The symbol alm1 is applied to this locus in place of al, as posed by the author, inasmuch as al refers to albescent; als and alt are also previously assigned.]

Figure 1. Effects of Al, after 0, 1, 2, 4, 6 d exposure, on the roots of tolerant Cat-100-6 (A to E) and sensitive S1587-17 (F to J) plants. Plants were grown in nutrient solution in the presence of 6 mg/l Al. The arrow in pictures G to J indicates the progressive destruction of the root tip, and in J the appearance of lateral root meristems.

Table 1. Segregation of aluminum tolerant (Alm-) and aluminum sensitive (alm alm) plants among F2 and BC progenies and their recurrent parents.
 

	Genotype
Progenies	Alm-	alm alm	Total	X2a
Parents
Cat-100-6	44	0	44
S1587-17	0	48	48
F1
Cat-100-6	56	0	56
F2	174	56	230	0.051 NS
BC1
C-100-6 x (Cat-100-6xS1587-17)	60	0	60
BC2
(Cat-100-6xS1587-17) x S1587-17	47	45	92	0.43 NS
S1587-17 x (Cat-100-6xS1587-17)	72	64	136	0.47 NS

^aX² analysis based on (#) 3:1 or 1:1 segregation frequency.

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