| Strigolactones have recently been found to play roles in regulating plant morphology.However,it remains unclear how strigolactones mediate growth of perennial grass species,especially the effect of strigolactones under high temperature stress.Cool season grass could be used as turfgrass and forage,which were widely used in China.In this study,cool season grass species,tall fescue and perennial ryegrass were used as the plant material.The plants were treated with GR24(a synthetic strigolactones)under non stress condition,heat stress condition and dark environment.The morphological indexes,physiological indicators and relative gene expression were measured.This study was aimed to lay the foundation of the effect of strigolactones on perennial grass species.The main results showed as following:1.Strigolactones of low concentration(0.01 μM)promotes root and leaf elongation in cool season grass tall fescue under normal temperature condition and heat stress condition.The morphological features showed that the number of lateral root and tiller were inhibited under GR24(a synthetic strigolactones)treatment,while the length of crown root and leaf were improved under both normal temperature condition and heat stress condition.Cell number and length in root tips was measured under confocal microscope.Cell number in leaves was measured under microscope.Expression level of genes related to cell growth was determined.Strigolactones improved root and leaf elongation through promoting cell division in meristematic zone.2.The strigolactones-mediated increase in root and leaf elongation of tall fescue may involve the effect of auxin transport.In this work,in order to investigate the crosstalk between strigolactones and auxin in the growth process of cool season grass,tall fescue were treated with GR24,NAA(α-naphthylacetic acid)and NPA(an auxin transport inhibitor)or their combination.The results of the morphology indexes and expression levels of genes related to auxin transport showed that the positive effects of strigolactones for promoting crown root and leaf elongation in tall fescue under both non-stress and heat stress could be mainly due to involve the interference of auxin transport.3.Strigolactones of high concentration accelerate leaf senescence in cool season grass perennial ryegrass.The results of chlorophyll content,photochemical efficiency and electrolyte leakage showed that GR24 of low concentration(0.01 μM)had no effect of leaf senescence of perennial ryegrass while GR24 of high concentration(1 μM or above)accelerated leaf senescence significantly.Strigolactones also promoted the production of abscisic acid and salicylic acid.4.Strigolactones may involved in ethylene production in the leaf senescence progress.In order to further study the crosstalk between strigolactones and ethylene in the leaf senescence progress,cool season grass perennial ryegrass were treated with GR24,AVG(an ethylene biosynthesis inhibitor)or their combination.The results of chlorophyll content,photochemical efficiency,electrolyte leakage and the expression levels of genes related to leaf senescence were affected by AVG application.Strigolactones improved ethylene production and the expression levels of genes related to ethylene-biosynthesis and signaling during leaf senescence progress,suggesting that strigolactones effect ethylene production during the leaf senescence progress.5.Strigolactones-accelerated leaf senescence was associated with the down-regulation of four chlorophyll biosynthesis-associated genes and up-regulation of four chlorophyll degradation-associated genes.AVG had counteractive functions to strigolactones,suppressing leaf senescence by down-regulating chlorophyll-degradation genes and strigolactonesynthesis genes.The results suggested that strigolactones and ethylene interactively regulated leaf senescence,mainly by controlling chlorophyll degradation induced by darkness in perennial ryegrass. |
