Cl. Tonkinson et al., EFFECT OF THE RHT3 DWARFING GENE ON DYNAMICS OF CELL EXTENSION IN WHEAT LEAVES, AND ITS MODIFICATION BY GIBBERELLIC-ACID AND PACLOBUTRAZOL, Journal of Experimental Botany, 46(290), 1995, pp. 1085-1092
The second leaf of wheat was used as a model system to examine the eff
ects of the Rht3 dwarfing gene on leaf growth. Compared to the rht3 wi
ld type, the Rht3 allele decreased final leaf length, surface area and
dry mass by reducing the maximum growth rates, but without affecting
growth duration. Gibberellic acid (GA(3)) increased final leaf length
and maximum growth rate in the rht3 wild type, but was without effect
on the Rht3 mutant, which is generally regarded as being non-responsiv
e to gibberellin (GA), Paclobutrazol, an inhibitor of GA biosynthesis,
decreased final leaf length and maximum growth rate in the rht3 wild
type to values similar to those in the untreated Rht3 mutant. Neither
GA(3) nor paclobutrazol affected the duration of leaf growth. The decr
ease in leaf length was produced by reduction of cell length rather th
an cell number. The maximum relative elemental growth rate (REGR) for
cell extension was essentially the same in all treatments, as was the
time between the cells leaving the meristem and achieving maximum exte
nsion rate. The differences between the genotypes and treatments were
all almost entirely due to differences in the time taken from the atta
inment of maximum REGR of cell extension to the cessation of extension
. This was reflected in the length of the extension zone, which was ap
proximately 6-8 per cent of final leaf length. The effects of the Rht3
allele, GA(3) and paclobutrazol all appear to be on the processes whi
ch promote the cessation of cell elongation.