Modification by gibberellin of the growth-temperature relationship in mutant and normal genotypes of several cereals.

High-resolution growth measurements were conducted using a linear variable displacement transformer in conjunction with a temperature-programmed meristem-cooling collar. Chilling and rewarming profiles were determined for a range of Gramineae, in the presence and absence of varying concentrations of gibberellic acid (GA3). In wheat (Triticum aestivum L.) seedlings, the growth-constraining temperature (Pe) was progressively lowered by increasing GA3 concentration, with a difference of-4.8°C between controls and material treated with 10(-4) M GA3. Dwarf-5 maize (Zea mays L.) seedlings had a higher Pe than tall segregates and the difference was markedly reduced by exposure to a saturating concentration of GA3. A similar effect was observed with Tanginbozu dwarf rice (Oryza sativa L.). The growth ratetemperature responses of Rht3 gibberellin-insensitive dwarf wheat seedlings were unaffected by GA3 and the Pe values for these segregates were around 5° C higher than for normals. Slender (s1) barley (Hordeum vulgare L.) genotypes had Pe values of-7° C, compared with +4° C for wild-type material, and did not show positive hysteresis for growth rate during the rewarming phase. These studies indicate that GA3 modifies the thermal sensitivity of meristem function in Gramineae in a manner which enhances low-temperature growth.