This experiment was undertaken to characterize the physiological changes taking place during the petal senescence of Hibiscus syriacus. Five distinctive developmental stages were chronologically suggested. Flower bud dry weight increased almost linearly from Stage I to Stage IV at a rate of ≈15 mg/day. Fresh weight and fresh/dry weight ratio increased much more rapidly between Stage III and Stage IV than during the early stage of development. It showed that petal expansion was partially due to an increased water uptake. The highest osmolality (411 mmol) was found in the fully open flowers. During the subsequent senescence and collapse of the flower, from Stage IV to Stage V, there were a rapid loss of fresh and dry weight and the fall of fresh/dry weight ratio, corresponding to the wilting that characterizes early senescence. A rise in cell sap osmolality coincided with the increase in soluble sugar content and fresh/dry weight ratio, and with the expansion of Hibiscus syriacus petal. Therefore, buds at Stage III, where they are under physiological maturity, might be appropriate to harvest. Hibiscus syriacus flowers showed a small but respiratory peak at Stage IV. The maximum rate of respiration was obtained with fully open flowers (Stage IV), whereas ethylene production remained extremely low until the petals started to open. Ethylene production, ACC synthase, and ACC content increased as the fresh weight of the flowers started to decline. At Stage V, there were a loss of petal fresh weight and a considerable increase in ethylene production (9 nL/g per h). The results of the present study have shown that petal tissue at Stage IV, presenescent stage, was characterized by the increase of soluble sugar and fresh weight, which might be expected to lead to petal expansion and limit turgidity. ABA and the stomata on petal might promote the disorganization.
Hye Jin Kwon, Song Kwon, and Ki Sun Kim
Hye Jin Kwon, Song Kwon, and Ki Sun Kim
Five distinctive developmental stages were chronologically suggested. Cells at Stage I and II were essentially free of cytoplasmic or vacuolar abnormalities and the cytoplasm contained numerous electron-dense mitochondria with well-developed cristae. At Stage III, there were a localized dilation of mitochondria matrix and a partial-diluted cytoplasm in mesophyll cells. At Stage IV, characterized by high levels of fresh weight and osmolality, most mesophyll cells were seen to be ruptured, resulting in a general mixing of cell contents and diluting cytoplasm. It can be explained as an irreversible senescence phenomena that tonoplast in mesophyll cell was ruptured partly, corresponding to rapid increase in petal cell size and turgidity. Petal turgidity was due to an increase of content in soluble sugar. At Stage V, there was a loss of petal fresh weight. With a loss of turgidity, most mesophyll cells have collapsed completely. There were a notable plasmolysis in vasculature. The activity of protease in petals was found to increase between Stage II and III, and then decreased rapidly at Stage IV, resulting in the decrease of total protein content before senescence. Unexpectedly, there were stomata in hibiscus petals. Ultrastructural disorganization, like as a broken tonoplast, was observed in mesophyll cells at Stage IV. ABA and the stomata on petal might promote the disorganization. The final stages of senescence involved breakdown of cellular organization leading to hydrolysis of previously separated compartments. The cellular disorganization triggered during the flowers are still in the process of opening may be one of the earliest physiological signal that senescence is under way.
Xiaoling Jin, Xijun Hu, Youping Sun, Donglin Zhang, and Ping He
Zelkova sinica Schneid. is a popular landscape plant in China because of its wide adaptation, strong disease resistance, large crown, and beautiful fall color. Immature embryos from Z. sinica seeds were cultured on woody plant medium (WPM) supplemented with 4.5 μM 6-Benzylaminopurine (BA) and 5.4 μM α-naphthaleneacetic acid (NAA) to induce callus, and 60% of immature embryos formed callus. The cream-white, friable, nodular callus with proembryogenic structures was then cultured on WPM containing 5.4 μM NAA in combination with 9.0 or 11.2 μM BA to regenerate shoots; approximately five shoots per explant were induced on 70% callus. Shoots were rooted on WPM containing 0.5 μM indole-3-butyric acid (IBA), on which 62.3% shoots developed roots with an average of 4.2 roots per shoot at 4 weeks. The regenerated plantlets were acclimatized and transplanted into the field. This protocol could be used for mass production for field plantation, genetic improvement, and germplasm exchange of Z. sinica.
Xi Shan, Heng Zhou, Ting Sang, Sheng Shu, Jin Sun, and Shirong Guo
We investigated the effects of exogenous spermidine (Spd) on the carbohydrate, nitrogen (N), and endogenous polyamine status of tomato (Solanum lycopersicum) seedlings exposed to high-temperature stress [38/28 °C (day/night)]. High-temperature stress reduced the contents of pyruvate and succinate and inhibited plant growth. The application of exogenous Spd alleviated the inhibition of plant growth induced by high temperature, and also led to an increase in pyruvate, citrate, and succinate levels. High temperature markedly increased the NH4 +-N content and reduced the activities of nitrate reductase (NR), glutamine synthetase (GS), and glutamate dehydrogenase (GDH). Spd significantly alleviated the negative effects on NH4 +-N assimilation induced by high-temperature stress. Moreover, Spd significantly increased the activities of NR and GDH in the high-temperature-stressed tomato leaves. In contrast, Spd application to high-temperature-stressed plant leaves counteracted high-temperature-induced mRNA expression changes in N metabolism. Spd significantly upregulated the transcriptional levels of NR, nitrite reductase, GS, GDH, and glutamate synthase (GOGAT). In addition, exogenous Spd significantly increased endogenous polyamines. These results suggest that Spd could improve carbohydrate and N status through regulating the gene expression and activity of key enzymes for N metabolism, thus confers the tolerance to high temperature on tomato seedlings.
Lantian Du, Baojian Huang, Nanshan Du, Shirong Guo, Sheng Shu, and Jin Sun
Soil sickness from the continuous cropping of cucumbers has become a major limiting factor for protected cucumber cultivation. The use of reasonable cropping systems and the employment of allelopathy between different crops are considered to be the major safe and effective measures for alleviating soil sickness. The objective of this study assessed the effects of garlic (Allium sativum L. cv. Yusuan No. 1)/cucumber (Cucumis sativus L. cv. Jinchun No. 4) relay intercropping on soil enzyme activities and the microbial environment in a continuous cropping regime. Cucumbers and garlic were selected and planted in plastic barrels. The following four treatments were included in the experiment: continuous cropping without crops (Cont), monoculture cucumbers (C), monoculture garlic (G), and the relay intercropping of garlic with cucumbers (CG). The results showed that relay intercropping with garlic promoted cucumber plant growth and attenuated damage caused by soil sickness. In comparison with the Cont treatment, the C treatment decreased soil urease, catalase, invertase, and phosphatase activities; by contrast, the CG treatment enhanced all soil enzyme activities. The C treatment resulted in lower numbers of soil bacteria and actinomycetes and a lower bacteria/fungi ratio, but there were a higher number of soil fungi than there were in the Cont treatment. However, the CG treatment increased the numbers of soil bacteria and actinomycetes as well as the bacteria/fungi ratio, and it decreased the number of soil fungi. In comparison with the Cont treatment, the C treatment reduced the microbial biomass carbon (MBC) and soil basal respiration (BSR) without affecting the metabolic quotient (qCO2), whereas the CG treatment increased all three variables. A polymerase chain reaction denaturing gradient gel electrophoresis (PCR-DGGE) analysis revealed decreased bacterial community diversity and increased fungal community diversity in soil with the C treatment; the opposite trend was observed in the CG treatment. The results indicated that the relay intercropping of garlic with cucumbers improved soil enzyme activities and promoted the conversion of continuous cropping soil from a “fungal” type to a “bacterial” type. Additionally, relay intercropping altered the soil bacterial community structure, increased the bacterial diversity indices, and enriched the dominant bacterial populations in the soil. These mechanisms improved the soil microbial environment and effectively alleviated damage caused by soil sickness, thus promoting cucumber plant growth.
Shutian Tao, Danyang Wang, Cong Jin, Wei Sun, Xing Liu, Shaoling Zhang, Fuyong Gao, and Shahrokh Khanizadeh
Lignin is the main component of stone cells, and stone cell content is one of the crucial factors for fruit quality in chinese white pear (Pyrus ×bretschneideri). The lignin biosynthesis pathway is complex and involves many enzymatic reactions. Cinnamate-4-hydroxylase [C4H (EC.22.214.171.124)] is an essential enzyme in lignin metabolism. This study was conducted to investigate the effect of bagging on lignin metabolism during fruit development in chinese white pear. The study showed that bagging had little effect on stone cell content, lignin content, C4H activity, and C4H gene expression and that there was a positive correlation between C4H gene expression and lignin content as well as stone cell content. Moreover, a full-length complementary DNA (cDNA) encoding C4H (PbrC4H, GenBank accession number KJ577541.1) was isolated from chinese white pear fruit. The cDNA is 1515 bp long and encodes a protein of 504 amino acids. Sequence alignment suggested that the deduced protein belongs to the P450 gene family and that C4H might be located subcellularly in the cell membrane. The results indicate that bagging cannot change the lignin and stone cell content significantly and that C4H catalyzes a step in lignin biosynthesis. These findings provide certain theoretical references and practical criteria for improving the quality of chinese white pear.
Chunlian Jin, Dan Sun, Chang Wei, Zhenhua Guo, Chunmei Yang, and Fan Li
Gypsophila paniculata is an ornamental crop with medicinal value. To date, limited information has been reported about the natural products in G. paniculata to explain its medicinal function. The current study reports the natural products found in G. paniculata stem for the first time. Thirty-three compounds were isolated from the extract of G. paniculata stem and identified by gas chromatography-mass spectrometry, 10 of which have contents >2%. These were 2-O-methyl-D-mannopyranose (37.4706%), glycerol (12.5669%), two tetratetracontane isomer (7.6523 + 3.5145%), tetrahygro-4-pyranol (5.3254%), 1,6-anhydro-beta-d-glucopyranos (4.7507%), palmitic acid (4.1848%), 4-hydroxy-3-methoxystyrene (3.7439%), methyl-octadeca-9,12-dienoate (2.7490%), and 2-deoxy-D-galactose (2.6193%). Another bioactive compound, condrillasterol, was identified with 1.3384% content. We also reported that G. paniculata possesses antioxidant activity possibly associated with the presence of a phenolic chemical 4-hydroxy-3-methoxystyrene. Our data collectively demonstrate that G. paniculata contains some bioactive compounds with high contents and antioxidants, consistent with its role as a medicinal herb.
Qing Xu, Shi-Rong Guo, He Li, Nan-Shan Du, Sheng Shu, and Jin Sun
The use of grafted seedlings in vegetable crops has increased in recent years to enhance the resistance to biological and abiotic stresses, and improve yields. However, incompatibility restricts the wide application of grafting. In this study, two pumpkin (Cucurbita) cultivars, with great differences in grafting affinity and symbiotic affinity, were used as rootstocks and cucumber (Cucumis sativus) seedlings were used as the scion. The effects of compatibility or incompatibility on histological aspects, antioxidant enzyme activities, phenylpropanoid contents, and chlorophyll fluorescence were studied. The results showed that compatible graft combinations present a stronger resistance to the oxidative damage resulting from grafting and had relatively weak phenylpropanoid metabolisms. The results also indicated that the chlorophyll fluorescence levels of incompatible combinations were lower, except compared with the original fluorescence. Finally, a necrotic layer existed earlier in compatible graft combinations. These differences at the morphological, physiological, and cellular levels may govern compatibility and incompatibility, and may provide valuable information for determining the symbiotic affinity of grafted seedlings at an early stage.
Jing Tian, Li-Ping Wang, Yan-Juan Yang, Jin Sun, and Shi-Rong Guo
Heat tolerance is considered to be an essential feature for cucumber (Cucumis sativus) production, and it has been suggested that higher antioxidant ability could prevent the oxidative damage in plants caused by high-temperature stress. We aimed to investigate whether the application of exogenous spermidine (Spd) increases antioxidant activities and, therefore, elevates the heat tolerance of cucumber. Cucumber seedlings (cv. Jinchun No. 4) showing moderate heat tolerance were grown in climate chambers to investigate the effects of exogenous Spd (1 mm) foliar spray treatment on the activities and isozyme levels of antioxidative enzymes under both high-temperature stress 42/32 °C (day/night) and normal temperature 28/18 °C (day/night). On high-temperature stress, the activities of superoxide dismutase and ascorbate peroxidase were significantly reduced; the catalase activity was initially lower and then increased, whereas the peroxidase activity was initially higher and then decreased. The levels of these isozymes also changed differently. On treatment with exogenous Spd, the activities of these antioxidant enzymes were noticeably enhanced, and the isozyme zymogram expression had some changes. It was concluded that foliar spray with Spd effectively improved the total antioxidant ability of cucumber seedlings and, therefore, enhanced the tolerance of the plants to high-temperature stress.
Bin Li, Ting Sang, Lizhong He, Jin Sun, Juan Li, and Shirong Guo
To examine whether 1 mm of spermidine (Spd) modifies plant ethylene production in response to short-term salt stress, cucumber (Cucumis sativus) seedlings were grown in nutrient solution with or without 75 mm NaCl stress for 3 days, and the leaves were sprayed with 1 mm Spd or water (control). We investigate the effects of the treatments on ethylene production, 1-aminocyclopropane-1-carboxylate (ACC) content, 1-(malonylamino) cycolpvopane-1-carboxylic acid (MACC) content, activities of 1-aminocyclopropane-1-carboxylate synthase (ACS), and 1-aminocyclopropane-1-carboxylate oxidase (ACO) and gene expression of acs2, aco1, and aco2 in the cucumber leaves. The results indicate that ethylene production was increased significantly under salt stress as did ACC and MACC content, the activities of ACS and ACO, and the transcriptional level of acs2, whereas the gene expression of aco1 and aco2 was somewhat decreased. However, exogenous Spd treatment depressed the content of ACC and MACC, ACS activity, and the level of acs2 transcripts in the leaves of salt-stressed cucumber. Although the activity of ACO and gene expressions of aco1 and aco2 increased by Spd, ethylene emission was inhibited. Our results suggest that application of exogenous Spd could reverse salinity-induced ethylene production by inhibiting the transcription and activity of ACS under salt stress. We conclude that exogenous Spd could modify the biosynthesis of ethylene to enhance the tolerance of cucumber seedlings to salt stress.