Fleshy fruits using ethylene to regulate ripening have developed multiple times in the history of angiosperms, presenting a clear case of convergent evolution whose molecular basis remains largely unknown. Analysis of the fruitENCODE data consistint of 361 transcriptome, 71 accessible chromatin, 147 histone and DNA methylation profiles reveals three types of transcriptional feedback circuits controlling ethylene-dependent fruit ripening. These circuits are evolved from senescence orfloral organ pathways in the ancestral angiosperms either by neofunctionalisation or repurposing pre-existing genes. The epigenome, H3K27me3 in particular, has played a conserved role in restricting ripening genes and their orthologues in dry and ethylene-independent fleshy fruits. Our findings suggest that evolution of ripening is constrained by limited hormone molecules and genetic and epigenetic materials, and whole-genome duplications have provided opportunities for plants to successfully circumvent these limitations.
Previous studies suggest that abscisic acid (ABA) stimulates the activities of antioxidant enzymes under normal and chilling temperature and enhanced chilling resistance in Stylosanthes guianensis. The objective of this study was to test whether nitric oxide (NO) is involved in the ABA-induced activities of the antioxidant enzymes in Stylosanthes guianensis due to its nature as a second messenger in stress responses. Plants were treated with NO donors, ABA, ABA in combination with NO scavengers or the nitric oxide synthase (NOS) inhibitor and their effects on the activity of antioxidant enzymes and NO production were compared. The results showed that ABA increased the activities of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX). The effect of ABA on antioxidant enzyme activities was suppressed by the NOS inhibitor, N(omega)-nitro-L-arginine (L-NNA), and the NO scavenger, 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl3-oxide (PTIO). NO content increased after 5 h of ABA treatment. The NO-scavenger, PTIO, and the NOS-inhibitor, L-NNA, inhibited the accumulation of NO in ABA-treated Stylosanthes guianensis. NO donor treatment enhanced the activities of SOD, CAT, and APX. The results suggested that NO was involved in the ABA-induced activities of SOD, CAT, and APX in Stylosanthes guianensis. ABA triggered NO production that may lead to the stimulation of antioxidant enzyme activities.
Stylosanthes guianensis (Aublet) Sw. is an important pasture legume in tropical and subtropical countries. Chilling injury of S. guianensis is a serious problem in subtropical cultivated areas. An experiment was conducted under controlled conditions to study the effect of abscisic acid (ABA) on S. guianensis and its relation to antioxidant systems under chilling stress. Stylosanthes guianensis seedlings were sprayed with 10 mg L−1 ABA or water. One day later, the plants were transferred to a 10°C growth chamber and grown for 7 d with a 12‐h photoperiod at 160 μmol m−2 s−1 photosynthetic photon flux density. The chilling treated plants were then rewarmed to 28°C for 2 d. During the 9‐d treatment, a series of enzyme activities, relative water content (RWC), and electrolyte leakage were measured on sampled leaflets. The results showed that chilling increased electrolyte leakage of both water‐ and ABA‐treated plants, while RWC decreased under chilling conditions. ABA‐treated plants had lower electrolyte leakage and higher RWC than those of water‐treated plants. Activities of ascorbate peroxidase (APX) and catalase (CAT) and contents of reduced glutathione (GSH) and ascorbic acid (AsA) were transiently enhanced by ABA treatment before the plants were subject to chilling. ABA‐treated S. guianensis retained higher levels of superoxide dismutase (SOD), APX, GSH, and AsA than water‐treated ones under chilling conditions. The results suggested that ABA‐increased chilling resistance in S. guianensis is partially associated with enhanced scavenging systems.
A simple colorimetric method for determination of hydrogen peroxide in plant materials is described. The method is based on hydrogen peroxide producing a stable red product in reaction with 4-aminoantipyrine and phenol in the presence of peroxidase. Plant tissues was ground with trichloroacetic acid (5% w/v) and extracts were adjusted to pH 8.4 with ammonia solution. Activated charcoal was added to the homogenate to remove pigments, antioxidants and other interfering substances. The colorimetric reagent (pH 5.6) consisted of 4-aminoantipyrine, phenol, and peroxidase. With this method, we have determined the hydrogen peroxide concentration in leaves of eight species which ranged from 0.2 to 0.8 lmol g -1 FW. Changes in hydrogen peroxide concentration of Stylosanthes guianensis in response to heat stress are also analyzed using this method.
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