The effect of daylength on photosynthate partitioning into leaf starch and soluble sugars in a gibberellin-deficient dwarf mutant of Zea mays

The possibility that gibberellins (GAs) mediate the photoperiodic regulation of photosynthate partitioning into stored leaf carbohydrates (starch and soluble sugars) was investigated with the dwarf-5 mutant of Zea mays L., a single-gene recessive mutant with greatly reduced endogenous GA content relative to tall maize. The mutant responded to daylength as did tall maize, with higher rates of carbohydrate accumulation observed under short daylength (8.5 h of light) than under long day-length (14 h of light). Neither inhibitors of GA biosynthesis (CCC, (2-chloroethyl) trimethylammonium chloride], ancymidolα-cyclopropyl-α-( p -methoxy-phenyl)-5-pyrimidine methyl alcohol], and tetcyclacis 5-(4-chlorophenyl)- 3,4,5,9, 10-penta-azatetracyclo-5,4,1,0^2.6,0^8.11-dodeca-3.9-diene]) nor treatment with GAs further modified the response of partitioning to daylength even though biologically active GAs stimulated plant growth. The results indicate that photoperiodic modulation of endogenous GA titre is unlikely to be responsible for the photoperiodic response of photosynthate partitioning in Z. mays .