Seasonal differences in the capacity of perennial ryegrass to respond to gibberellin explained

Abstract

Perennial ryegrass plants (Lolium perenne) were taken from an established field at two different stages in the season (mid-winter and again at mid-summer). They were then grown in a controlled environment to both "lock in" their contrasting developmental states and to look at the role of nitrogen supply, temperature, and developmental state separately to evaluate the potential of plants to respond to exogenous application of gibberellin. Responses to exogenous gibberellin (gibberellic acid, GA) were significant but were far smaller in summer-derived than winter-derived plants. The major difference in response to GA (compared with controls) between winter-derived and summerderived plants suggests that seasonal changes in plant developmental state have a major effect in the field on the capacity for the plants to respond to exogenous GA application. This effect is greater than that of temperature and N availability. This raises new prospects for making sustained increases in plant growth, but only if the fundamental mechanisms by which plants control their responses to environmental signals (e.g., temperature and soil N status) can be understood. The role of gibberellins (endogenous as well as externally applied) in changes in plant growth strategy presents a new challenge for forage plant science.