Label-free quantitative proteomics analysis of Humulus scandens (Lour.) Merr. leaves treated by an odor compound of Periploca sepium Bunge

Allelopathic effects on vegetative propagation, physiological-biochemical characteristic of Alternanthera philoxeroides (Mart.) Griseb from Cinnamomum camphora (L.) Presl

Alternanthera philoxeroides (Mart.) Griseb is a well-known invasive plant species worldwide. Cinnamomum camphora (L.) Presl. is a plant species that is rich in allelopathic substances which can impede the growth of many other plants. In this study, the allelopathic effects of C. camphora on the growth and development, and physiological-biochemical characteristics of A. philoxeroides were investigated. The findings revealed that the leaves of C. camphora exhibited the capability to suppress the asexual reproduction of A. philoxeroides. The addition of C. camphora leaves resulted in inhibition of the fresh weight, stem length, and stem node number of A. philoxeroides new stems, with the strength of inhibition increasing in proportion to the quantity of C. camphora leaves added. Furthermore, the inhibitory effect of C. camphora leaves on A. philoxeroides was significantly amplified under high temperatures (≥ 30°C). Two allelochemicals had strong inhibitory effects on the vegetative reproduction of A. philoxeroides. The inhibition intensities were all up to 100 % on stem vegetative propagation, were 90.40 % and 100 % on root vegetative propagation from camphor and linalool, respectively. Physiological-biochemical analyses of roots indicated that the two allelochemicals promoted the accumulation of hydrogen peroxide and MDA, disrupting the balance of antioxidant enzyme systems. The two allelochemicals had a strong inhibitory effect on CAT activity and a strong promoting effect on POD activity. The effect on SOD activity was greatly affected by the type and concentration of allelochemicals. Moreover, the two allelochemicals significantly inhibited the accumulation of osmotic regulating substance. The contents of soluble sugar, soluble protein, and proline were significantly down-regulated. In summary, the allelochemicals from C. camphora induced damage to biological membranes, disrupting antioxidant enzyme systems and inhibiting osmoregulation. This resulted in the retardation of growth, development, and potential mortality of A. philoxeroides. These findings would contribute to the knowledge base for A. philoxeroides prevention and control, and enrich the understanding of C. camphora allelopathic substances.

Effect of the odour compound from Periploca sepium Bunge on the physiological and biochemical indices, photosynthesis and ultrastructure of the leaves of Humulus scandens (Lour.) Merr

Natural odour compounds could be a potential alternative to synthetic herbicides. The odour compound of Periploca sepium Bunge, named 2-hydroxy-4-methoxy-benzaldehyde (HMB), is a herbicidal compound. However, its herbicidal mechanism is unclear. In this experiment, the physiological and biochemical indices, ultrastructure, and photosynthetic function of the leaves of Humulus scandens (Lour.) Merr. treated by HMB were assessed to elucidate the herbicidal mechanism. The results of physiological and biochemical indices are as follows: First, after 4 h of treatment with 2.5 and 5.0 mg/mL, the damage rates in the membrane permeation assay were 74.7% and 89.1%, respectively. Second, compared to the negative control group, multiple physiological and biochemical indices of the two treated groups were changed, including catalase content (-18.5 and -26.5 ng/mL), superoxide dismutase content (-27.4 and -56.6 ng/mL), peroxidase content (382.0 and 880.0 ng/mL), reactive oxygen species content (16.7 and 27.2 ng/mL), malondialdehyde content (8.9 and 25.2 nmol/g), and water potential values (0.2 and 0.3 MPa), except for the photosynthetic pigment contents (chlorophyll a, b, and carotene). Furthermore, the results of transmission electron microscopy showed that the organelles in the mesophyll tissue cells disappeared and severe plasmolysis led to cell atrophy after 4 h of treatment. There were fewer starch granules after 24 h of treatment, but there was no obvious abnormality in the upper and lower epidermal cells. The results of photosynthetic function showed that in the light response, the net photosynthetic rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), and stomatal limitation value of the tested leaves were lower than those of the negative control group by 26.6 μmol·m^-2·s^-1, 7.7 mmol·m^-2·s^-1, 0.9 mol·m^-2·s^-1, and 0.2, respectively. However, the intercellular CO₂ concentration (Ci) increased and was higher than the air CO₂ concentration. In the CO₂ response, the Pn, Tr and Gs of the tested leaves first increased and then decreased, but the Ci value continuously increased and finally reached 1727.5 μmol·mol^-1. It is obvious that HMB may have inhibited the effect on the photosynthetic system of the tested leaves. Overall, HMB killed the weeds by destroying the structure and multiple physiological functions of the tested leaves.

Physiological response and proteomics analysis of Reaumuria soongorica under salt stress

Soil salinity can severely restrict plant growth. Yet Reaumuria soongorica can tolerate salinity well. However, large-scale proteomic studies of this plant’s response to salinity have yet to reported. Here, R. soongorica seedlings (4 months old) were used in an experiment where NaCl solutions simulated levels of soil salinity stress. The fresh weight, root/shoot ratio, leaf relative conductivity, proline content, and total leaf area of R. soongorica under CK (0 mM NaCl), low (200 mM NaCl), and high (500 mM NaCl) salt stress were determined. The results showed that the proline content of leaves was positively correlated with salt concentration. With greater salinity, the plant fresh weight, root/shoot ratio, and total leaf area increased initially but then decreased, and vice-versa for the relative electrical conductivity of leaves. Using iTRAQ proteomic sequencing, 47 177 136 differentially expressed proteins (DEPs) were identified in low-salt versus CK, high-salt versus control, and high-salt versus low-salt comparisons, respectively. A total of 72 DEPs were further screened from the comparison groupings, of which 34 DEPs increased and 38 DEPs decreased in abundance. These DEPs are mainly involved in translation, ribosomal structure, and biogenesis. Finally, 21 key DEPs (SCORE value ≥ 60 points) were identified as potential targets for salt tolerance of R. soongolica. By comparing the protein structure of treated versus CK leaves under salt stress, we revealed the key candidate genes underpinning R. soongolica’s salt tolerance ability. This works provides fresh insight into its physiological adaptation strategy and molecular regulatory network, and a molecular basis for enhancing its breeding, under salt stress conditions.