Leaf Trimming to Simulate Mowing Differentially Regulates Phytohormones and Polyamines in Creeping Bentgrass Leaves.

Turfgrasses are frequently mown for aesthetic and functional purposes. The objective of this study was to understand how phytohormones and polyamine (PA) contents are affected by trimming of creeping bentgrass leaves. Two growth chamber studies were performed by trimming leaves to simulate mowing practices or wounding of plants under optimal and heat stressed conditions. Trimming treatments included 1) no trim, 2) trimmed every three d to (7.6 cm) and trimmed only for sampling at 3) 0 min, 4) 15 min and 5) 30 min. Treatments 3, 4, and 5 were intended to investigate immediate changes in phytohormones and PA after wounding. Plants were evaluated for turf quality (TQ), photochemical efficiency (Fv/Fm), photochemical yield (YII), PA contents of [putrescine (Put), spermine (Spm), and spermidine (Spd)] and phytohormone content [abscisic acid (ABA), indole-3-acetic acid (IAA), jasmonic acid (JA), salicylic acid (SA), zeatin riboside (ZR) and gibberellic acid (GA1, GA4, GA20)]. Under heat stress on some days, TQ, YII, and Fv/Fm were significantly higher for plants that received trimming compared to plants that were not trimmed. Trimming every 3 d moderated the increase in SA and JA observed due to heat stress compared to untrimmed plants. Immediately after wounding (0, 15, and 30 min treatments), JA content increased successively due to wounding. Plants trimmed at 3 d intervals had higher ZR content compared to other treatments. Higher GA1 levels were in trimmed plants compared to untrimmed ones. Put levels exhibited a transient increase immediately after wounding as Put levels were higher for trim 15 min treatment compared to other treatments under optimal and heat stressed conditions in both experiments. Spd levels were reduced by trimming every 3 d compared to untrimmed plants. These results may help to reveal how mowing practices may affect creeping bentgrass responses to abiotic and biotic stresses.