Effects of Low Irradiance Stress on Gibberellin Levels in Pea Seedlings

Using gas chromatography-selected ion monitoring with internal standards we analyzed endogenous levels of GA1, GA8, GA19, GA20, GA29, GA44 and GA53 in shoots of pea cv. Alaska grown under different levels of irradiance: high irradiance, 386±70μmol m-2s-1, control (100%); medium (50%); low (10%); darkness (0%). The average plant heights for medium and low irradiance and dark grown plants were 157%, 275%, and 460% of the control plants, respectively. Plants grown in medium and low irradiance developed the same numbers of internodes as control plants but plants in darkness developed fewer internodes and exhibited suppressed leaf expansion. The endogenous levels of GA1 GA8 and GA29 were higher in medium and low irradiance grown plants than those of the high irradiance control. In particular, the GA20 level of low irradiance plants was markedly higher (7.6-fold) than that of control plants. In dark-grown plants GA1, and GA8 levels also slightly increased but GA20 and GA29 levels decreased and the levels of GA19, GA44 and GA53 did not change. Feeding of GA1, and a GA biosynthesis inhibitor (uniconazole) to plants grown at reduced irradiance and in darkness suggests that the responsiveness of plants to GA1, also increased at low irradiance and in darkness. In conclusion, plants increase both GA1, and GA20 biosynthesis or altered catabolism and GA1, responsiveness under low irradiance stress