Abstract
Low temperature is one of the important limiting factors for growing season and geographical distribution of plants. Zoysiagrass (Zoysia Willd) is one of the widely used warm-season turfgrass that is distribute in many parts of the world. Zoysaigrass native to high latitude may have evolved higher cold tolerance than the ones native to low latitude. The objective of this study was to investigate the cold stress response in zoysiagrass native to diverse latitude at phenotypic, physiological and metabolic levels. Two zoysiagrass (Z. japonica) genotypes, Latitude-40 (higher latitude) and Latitude-22 (lower latitude) were subjected to four temperature treatments (optimum, 30/25°C, day/night; suboptimum, 18/12°C; chilling, 8/2°C; freezing, 2/-4°C) progressively in growth chambers. Low temperature (chilling and freezing) increased leaf electrolyte leakage (EL) and reduced plant growth, turf quality, chlorophyll (Chl) content, photochemical efficiency (Fv/Fm) and photosynthesis (Pn, net photosynthetic rate; gs, stomatal conductance; intercellular CO2; Tr, transpiration rate) in two genotypes, with more rapid changes in Latitude-22. Leaf carbohydrates content (glucose, fructose, sucrose, trehalose, fructan, starch) increased with the decreasing of temperature, to a great extend in Latitude-40. Leaf abscisic acid (ABA), salicylic acid (SA) and jasmonic acid (JA) content increased, while indole-3-acetic acid (IAA), gibberellic acid (GA3) and trans-zeatin ribside (t-ZR) content decreased with the reduction of temperature, with higher content in Latitude-40 than in Latitude-22. Chilling and freezing induced the up-regulation of C-repeat binding factor (ZjCBF), late embryogenesis abundant (ZjLEA3) and dehydration-responsive element binding (ZjDREB1) transcription factors in two genotypes, whereas those genes exhibited higher expression levels in Latitude-40, particularly under freezing temperature. These results suggested that zoysiagrass native to higher latitude exhibited higher freezing tolerance may attribute to the higher carbohydrates serving as energy reserves and stress protectants that stabilize cellular membranes. The phytohormones may serve signals in regulating plant growth, development and adaptation to low temperature as well as inducing the up-regulated ZjCBF, ZjLEA3 and ZjDREB1 expressions thus result in a higher cold tolerance.
Highlights
Low temperature is the primary determining factor limiting geographical distribution and growing season of plants [1]
After exposure to cold acclimating conditions, the leaves freezing tolerance (LT50) of the two zoysiagrass genotypes decreased from -2.4 to -4.5 ̊C and -6.8 ̊C for Latitude-22, and decreased from -3.9 to 5.8 ̊C and -8.6 ̊C for Latitude-40 under suboptimum and chilling temperature, respectively
The results of this study showed that low temperature lead to an increase in abscisic acid (ABA) and decline in trans-zeatin ribside (t-ZR) content in leaves of zoysiagrass
Summary
Low temperature is the primary determining factor limiting geographical distribution and growing season of plants [1]. Chilling stress is often leading to growth and photosynthesis reduction, leaf wilting and chlorosis or even necrosis, cellular membrane damages as well as oxidative stress in plants [4]. Temperatures declined below 0 ̊C caused freezing stress, which result in the formation of ice crystals within the cell, mechanical damages as well as metabolic dysfunction in plants [5]. Plants have evolved complex mechanisms to tolerate chilling and freezing stresses, such as accumulation of carbohydrates and proteins, resulting in large quantities of soluble sugars, amino acids and cold induced stress-related proteins [6], as well as hormone homeostasis inducing the gene expression that function to stabilize membranes against freezing-induced injury [7,8]
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