Several mutants of corn--Pt, Tu, sk and bk2--were treated with growth regulators in an attempt to normalize the plants. The long glumes in the female spikelets (tunicate) and the proliferation of pistillate tissue (polytypic) could be due to an excessive accumulation of endogenous gibberellins or auxin, while lack of silk formation in silkless might be due to an inadequate endogenous cytokinin or auxin. Since NAA is reported to stimulate stalk stiffness (Nickerson and Lindahl, 1962, MGN 36:97), brittle stalk (bk2) plants were treated with NAA.
The dose and application schedule for various families is summarized below:
With the help of a 0.5 or 1 ml pipette, the solutions were introduced below the ligule in the axil of the tenth leaf of 40-day-old Pt, Tu and sk plants. The solution was retained in the space formed due to the encirclement of culm by sheath. At the time of first application, the ear shoot at node 10 was less than 1 mm long and female florets had not been initiated. In the bk2 family, NAA solution was dropped in the apical cup starting with 14-day-old plants. Each treatment included 5 to 8 plants.
The expression of tunicate and polytypic was not suppressed in any of the treatments. In the tunicate stock, in the plants receiving 0.1 and 1 mM TIBA the ear shoot at node 10 remained short or failed to develop and functional ears developed one or two nodes higher than in untreated plants. In the polytypic plants receiving 1 mM AMO 1618, growth of 12-14 axillary shoots per plant (one per node) was observed. But only one or two of these at nodes 12-15 developed into functional ears.
In none of the treatments were silks restored and the ratio of silkless:normal was close to 1:1 in the treated family (the plants in this family were derived from a cross between sk/+ x sk/sk). Similarly NAA did not restore normal stalk strength in the brittle stalk family. NAA-treated and untreated plants were equally brittle.
These negative results indicate that in the mutants tested, endogenous hormonal imbalance may not be involved. The mutant phenotype may be due to specific cell limited gene products. At present it is not known if the expression of Pt, Tu and sk is cell autonomous in ear shoots. However, brittle stalk seems to be cell autonomous and a single sectored plant (half brittle, half normal) has been recorded earlier (Coe, 1960, MGN 34:62).
M. M. Johri
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