Characterization of Sprouting of Cyperus Rotundus L. Tubers under Fluctuating Temperatures

Abstract

Effects of fluctuating temperature on budbreak and shoot elongation, and the role of Ca2+ in bud break via heat pulse were determined in purple nutsedge {Cyperus rotundus L.) tubers Dormant tubers were transferred to 35C for 30 minutes from 20C and 80% to 92% budbreak occurred. Tubers at 20C without the heat treatment had 20% to 25% budbreak. Even a 3-minute 35C pulse caused 62% budbreak. Budbreak following 35C for 12 hours was 92%, similar to that obtained with seven cycles of 20/35C (12/12 hours). A change in temperature from 25 to 15C or from 20 to 25C did not promote budbreak compared with constant 25 or 20C respectively. Varying the rate of temperature increase from 0.02 to 0.5C per minute in a single temperature shift from 2 0 to 35C had no effect on budbreak. Tuber sprouts exposed to alternating temperatures with 12-hour 30C and 12-hour 40C elongated to 37 mm, 1.3 times higher than at constant 35C, an optimal mean temperature. Temperature differences of 2 and 4C in alternating cycle around the mean 24C had little effect on growth; an 8 C differential had 21 mm greater shoot length than at constant 24C. A single warm pulse of 35C for 1 h caused 60% to 70% budbreak of excised buds, and was substituted by ionomycin, and reduced by EGTA and verapamil. Excised buds without the single 35C pulse or with 1 mM verapamil had 36% to 42% budbreak. Suspension-cultured cells from purple nutsedge shoot tip loaded with fluo-3 AM resulted in cell expansion within 10 minutes. Intracellular [Ca2+J decreased or increased initially, then steadily increased with a 35C treatment, accompanied by the appearance of cytoplasmic strands. Withdrawal of heat stimulus did not cause a reduction of intracellular [Ca2+] in 30 minutes. In conclusion, a single warm pulse stimulated budbreak of purple nutsedge, but not shoot elongation; the shoot elongation response was thermoperiodic. Ca2+ may mediate the heat pulse-stimulated budbreak. The heat pulse also elevated the intracellular [Ca2+] of cultured cells.