Submergence stress alters fructan and hormone metabolism and gene expression in perennial ryegrass with contrasting growth habits

The experiment was designed to characterize fructan and hormone metabolism in a slow-growing commercial cultivar Silver Dollar (SD) and a fast-growing wild accession PI317452 (PI3-2) of perennial ryegrass (Lolium perenne L.) exposed to 3and 7-d of submergence stress in a growth chamber, respectively. PI3-2 grew more in height and had relatively higher reductions of leaf dry weight and fructan content than SD with an increasing time period of the stress. Submergence did not alter leaf indole-3-acetic acid (IAA) content in SD but increased IAA in PI3-2 at 7 d of stress. Gibberellic acid (GA3) content in SD increased at 3 d and decreased at 7 d of stress but remained unchanged in PI3-2 during the stress period. Both accessions showed large reductions in abscisic acid (ABA) content under stress, especially for PI3-2; while jasmonic acid (JA) content also decreased except for a stable JA found in PI3-2 at 3 d of stress. Gene expressions of 6-SFT, 1-SST and 6G-FFT involved in fructan biosynthesis were either upregulated or stable, except for a downregulation of 6G-FFT shown in the submerged SD. Expression of GA20ox and GA3ox for GA biosynthesis increased or remained unchanged, while expression of GA2ox4 for GA catabolism was upregulated; but a downregulation of GA2ox4 was noted in SD at 3d of stress. Submergence generally induced expressions of ZEP and NCED1 for ABA biosynthesis and elevated ABA8Ox1 for ABA catabolism with a few exceptions of stable transcript levels in either accession. Expression of Hb1 encoding hemoglobin protein was upregulated in both accessions during the stress periods. The results suggested that reductions of GA, downregulation of 6G-FFT, upregulation of NCED1 and stable expression of ABA8Ox1 possibly contributed to growth response in the slow-growing accession, while increased IAA and stable GA3 contents, stable expression of NCED1, and upregulation of ABA8Ox1 might affect growth in the fast-growing accession under an extended period of submergence stress.