Growth Response and Gene Expression to Deficit Irrigation and Recovery of Two Perennial Ryegrass Accessions Contrasting in Drought Tolerance

Abstract

Perennial ryegrass (Lolium perenne) is an important cool-season forage and turfgrass species. Growth and physiological responses of perennial ryegrasses to chronic deficit irrigation (DI) and recovery following a water deficit event are not well understood. The objective of this study was to characterize plant growth, water status, and gene expression in response to DI and recovery of perennial ryegrass. Two accessions, PI598453 (drought tolerant) and PI403847 (drought susceptible), were subjected to irrigation treatments with 100% evapotranspiration (ET) replacement every other day as the control (100% ET) and 70% ET replacement as DI treatment for 21 days in a greenhouse. After the treatment period, the DI-treated plants were shifted back to 100% ET for 7 days for recovery. The grasses were cut every 7 days, for a total of three times. Leaf relative water content (LRWC) significantly decreased at 21 days of 70% ET for both accessions, compared with the control; but to a greater extent in the more susceptible PI403847. Water-use efficiency (WUE) significantly increased 1.6-fold for PI598453 and 1.3-fold for PI403847 under 70% ET, whereas 33% reduction of leaf dry weight (LDW) was found only in PI403847. Plant height (HT) and leaf length (LL) were unaffected by 70% ET after the first two cuttings, but decreased after the third cut and did not recover to the control level for both accessions. Reductions in leaf width (LW) under 70% ET were found at 8 and 6 days after cutting for PI598453 and for PI403847, respectively. The transcript levels of heat shock protein (HSC70), iron superoxide dismutase (FeSOD), and plasma membrane intrinsic protein type 1 (PIP1) in both leaves and stems were generally downregulated during 70% ET treatment with a few exceptions but fully recovered to 100% ET after rewatering. The expression levels of cytosolic copper/zinc superoxide dismutase (cyto Cu/Zn SOD) and light-harvesting Chl a/b-binding proteins (LHCB) did not alter under 70% ET for both accessions. Differential growth and physiological responses of perennial ryegrass accessions to DI could be used for further studying of molecular mechanisms of drought tolerance in perennial ryegrass.