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Chrysanthemum ‘Bai Tian Xing’, ‘Huang Ching Chin’, ‘Pink Pearl’, and ‘NCHU-001’ plants were preheated at 35 °C for 24 hours to induce heat tolerance. The recently fully expanded leaves were detached, kept in a moist Ziploc bag, and then subjected to 35, 40, 45, 47.5, 50, 52.5, 55, 60, or 65 °C for 20 minutes. After dark-acclimatized at room temperature for 30 minutes, leaves were measured for Fv/Fm value with a chlorophyll fluorescence parameter. Results showed that ‘Bai Tian Xing’ had the highest critical (Tcrit) and midpoint temperature (Tmid). Mean Tcrit and Tmid were shown to be 47 and 50 °C, respectively, and Tmid gave greater distinguishment of Fv/Fm value among cultivars. Plants of four cultivars were acclimatized at 15 to 40 °C for 3 days and 35 °C being the most effective temperature to induce a heat-tolerant response in chrysanthemum. Required inducing time to reach a stable leaf Fv/Fm value ranged from 4.6 to 11.1 hours among cultivars. All cultivars had similar required time to reach visible bud between summer and autumn crops (except NCHU-001), but all had delayed flowering in the summer crop. There is a negative linear relationship between flowering heat delay and leaf Fv/Fm value (R2 = 0.93). Progenies from reciprocal crossing of ‘Bai Tian Xing’ × ‘NCHU-001’ and ‘Huang Ching Chin’ × ‘Pink Pearl’ were also subjected to treatments for Fv/Fm measurements and observed for time to flowering in the summer crop. All combinations showed negative linear relationship between time to flowering and leaf Fv/Fm value (R2 = 0.70–0.87). Two plants, 109-W001Y and 109-W003Pi, showed early flowering habit and good flower performance under heat conditions were selected. All four cultivars and the two selected lines were measured for photosynthetic parameters under day/night temperatures of 35/30 or 25/20 °C in growth chambers. All cultivars and lines showed decreased net photosynthetic rate and dark respiration rate under 35/30 °C when compared with 25/20 °C. Relatively higher net photosynthetic rate and lower dark respiration rate in ‘Bai Tian Xing’, ‘109-W001Y’, and ‘109-W003Pi’ under 35/30 °C, when compared with the other three cultivars, might have contributed to better flowering performance in the summer.
In China, greenhouse soils often receive large rates of different manures and have a high content of soil organic matter (SOM). Understanding changes in nitrogen (N) mineralization in soils of newly built greenhouses after their construction is important for managing N. Soil samples were obtained from solar greenhouses of different ages (0, 1, 2, and 3 years) located in the south edge of the Loess Plateau, China, at 0- to 20- and 20- to 40-cm depth. N mineralization in the soils was measured with the Stanford and Smith long-term aerobic incubation method over 30 weeks. SOM, total N, and the mineralized N in the 0- to 20-cm and 20- to 40-cm soil layers were significantly increased in the older greenhouses. The cumulative mineralized N in the 0- to 20-cm soil layer in different cultivation years was increased in each year since the greenhouses were established. For the greenhouses with the same age, the cumulative mineralized N in the 0- to 20-cm soil layer was greater than that in the 20- to 40-cm layer. The potentially mineralizable N (N0) both in the 0- to 20-cm and the 20- to 40-cm soil layers increased with the greenhouses’ age. Regression analysis indicated that when SOM increased 1 g·kg−1, N0 in the 0- to 20-cm and 20- to 40-cm depth increased 22.6 and 8.4 mg·kg−1, respectively. Therefore, as the N supply in soil increases with the age of the solar greenhouse, we suggest that the application rates of manure and synthetic fertilizer be reduced.
Ethidium bromide (EB), at 10-5 to 10-4 M, progressively inhibits NAA-induced rooting of mung bean cuttings. Cycloheximide (CH), 6-methylpurine (6-MP) and kinetin (KIN) also inhibited rooting at the same concentrations, although CH and 6-MP were more effective.
At 70 and up to 130 hours of incubation, after cuttings received a 1-ml pulse of NAA (10-4 M), they exhibited a progressive increase in the number of observed adventitious roots. The addition of one of the inhibitors, 6-MP, EB or KIN to cuttings, pulsed 48 hours earlier with NAA, showed an initial slight inhibition with increased inhibition over time. CH, however, inhibited rooting immediately after addition. From these and other similar kinetic studies, it appears that 6-MP, EB and KIN operate at the transcriptional level and that CH inhibits translation.
Lineweaver-Burk plot analysis of NAA-induced rooting inhibition showed that EB may act as a competitive inhibitor of NAA. Since EB is a known intercalating agent and competitively inhibits NAA-induced rooting, NAA may influence gene expression by ultimately binding to DNA. Studies with space-filling and computer-generated models show that both NAA and EB can bind to certain dinucleotides by an intercalation mechanism.
Centipedegrass [Eremochloa ophiuroides (Munro) Hack] is a native grass of China, and information on soil adaptation ranges, including acid soils, among centipedegrass cultivars is limited. Therefore, objectives of this study were 1) to conduct a preliminary evaluation of relative aluminum tolerance of 48 centipedegrass accessions plus a cultivar, TifBlair, and a common centipedegrass under aluminum (Al) stress (0 and 1500 μM Al) by using a solution culture method; and 2) to determine Al effects on nutrient uptake between resistant-group and sensitive-group accessions among the 50 accessions and cultivars. Differences were found among accessions and cultivars, and the CV of relative root weight, relative shoot weight, and relative total weight were 39.9%, 32.9%, and 33.6%, respectively. After growing 28 days in an acid subsoil, the resistant-group accessions showed much better growth than the sensitive-group accessions. The Al concentrations in roots and shoots of the two groups of accessions were increased under Al treatment, but most absorbed Al remained in roots with greater Al absorption among the sensitive group compared with the resistant group. The concentrations of phosphorus (P), magnesium (Mg), calcium (Ca), and potassium (K) in the two groups were reduced under Al stress with reductions of 59.3%, 54.8%, 47.9%, and 41.3% in shoots and reductions of 8.70%, 52.5%, 43.2%, and 34.4% in roots, respectively. Under Al stress, differences in P, Mg, and Ca concentrations were found between the two groups; however, differences were not found for K. The resistant-group accessions maintained higher concentrations of Mg and Ca than the sensitive group.
White rust (causative pathogen Puccinia horiana) is a destructive disease of commercial chrysanthemum crops. A panel of 19 accessions of commercial chrysanthemum near-relatives (four Ajania species, 11 Chrysanthemum species including five accessions of Chrysanthemum indicum) were screened for their reaction to white rust infection in separate greenhouse trials carried out at two independent sites in eastern China, one in 2010 and the other in 2012. The reaction of the accessions to artificial inoculation ranged from immune to highly susceptible. Accessions of Chrysanthemum indicum, C. yoshinaganthum, C. makinoi var. wakasaense, C. nankingense, C. vestitum, C. lavandulifolium, C. crassum, and Ajania tripinnatisecta were immune, and strong resistance was present in C. japonense, C. × shimotomaii, and A. przewalskii. Most of the accessions behaved similarly in the two trials, but two of the C. indicum accessions produced inconsistent results, each being highly resistant in one trial but susceptible in the other. Because wide crosses are relatively easy to achieve in the chrysanthemum complex, these immune and highly resistant accessions represent promising germplasm for white rust resistance breeding.
Nothodoritis zhejiangensis Z. H. Tsi is a rare and endangered epiphytic orchid restricted to a narrow distribution in China. The species is threatened with extinction as a result of loss of suitable habitats. An efficient propagation system is part of this species’ conservation plan. Seed germination reached 64.7% on Knudson's C (KC) medium containing 1.0 mg·L−1 α-naphthaleneacetic acid (NAA), 10% coconut water, and 0.1% activated charcoal. After 50 days culture, most callus (71.3%) from seed-derived protocorms formed on KC medium with 1.0 mg·L−1 2,4-dichlorophenoxyacetic acid and 10% coconut water. Callus could be subcultured 12 times during ≈2 years with more than a 3.0-fold increase from the third to the twelfth subculture. Furthermore, 84% of callus from the tenth sub-culture on KC media supplemented with 1.0 mg·L−1 NAA, 5% coconut water, and 0.1% activated charcoal formed protocorm-like bodies (PLBs). Many (57%) protocorms on KC medium containing 1.0 mg·L−1 6-benzylaminopurine and 10% coconut water formed PLBs. Both callus and PLBs formed simultaneously from different protocorms on KC medium containing 0.01 to 1.0 mg·L−1 thidiazuron and 10% coconut water. PLBs were incubated 12 times during ≈2 years with an approximate 2.4-fold increase per sub-culture. Both callus and PLBs maintained their competence to regenerate plantlets. Hyponex N026 medium supplemented with 1.0 mg·L−1 NAA, 50 g·L−1 banana homogenate, and 0.1% activated charcoal was suitable for plantlet formation and growth of 95.5% of plantlets that developed from PLBs. The roots of plantlets 2 cm in height or taller were wrapped in Chilean sphagnum moss and fixed to a fir bark block; 69.3% of plantlets survived after 180 days in a greenhouse. This protocol is an efficient means for the large-scale propagation of this endangered orchid.
Oil tea (Camellia oleifera) is an important edible oil tree. However, its growth and yield are strongly limited by drought. This study investigated the physiological and metabolic responses of two common oil tea cultivars, Huajin and Changlin53, to moderate and severe drought stress. Based on the photosynthetic and physiological indices, ‘Changlin53’ may be more tolerant to drought than ‘Huajin’. A total of 41 key metabolites induced by drought stress, including 12 amino acids, 12 organic acids, 10 carbohydrates, 3 fatty acids, and 4 phenols, have been identified by liquid chromatography-mass spectrometry. Under moderate drought stress, the contents of carbohydrates, amino acids, and some organic acids in ‘Changlin53’ were significantly increased; however, under severe drought stress, the contents of soluble sugars were decreased and the synthesis ability of amino acids and organic acids were enhanced. The glutamic acid–mediated proline biosynthesis pathway and salicylic acid synthesis were continuously upregulated in ‘Changlin53’ under moderate and severe drought stress, which could regulate osmotic pressure and maintain intracellular environmental stability. Under moderate drought stress, the contents of monosaccharides, amino acids, and organic acids increased in ‘Huajin’ leaves. Furthermore, the shikimic acid–mediated secondary metabolite synthesis pathway was weakened. More secondary metabolites were used to increase glycolysis and tricarboxylic acid cycle to accelerate energy production and to enhance the glutamic acid–mediated proline biosynthesis pathway, which are necessary to increase osmotic regulation. Under severe drought stress, the contents of carbohydrates, organic acids, and some amino acids were significantly decreased in ‘Huajin’ leaves, indicating serious damage. These results deepened our understanding of the mechanisms involved in oil tea drought tolerance, which will help improve water management of oil tea seedlings.
Adventitious root formation (rooting) in `Berken' mungbean [Vigna radiata (L.) Rwiclz.] cuttings is stimulated by indole-3-acetic acid (IAA). To understand the molecular events that occur during IAA-induced adventitious root initiation, a λgt11 cDNA library was made from mungbean hypocotyls treated with 500 μm IAA for 3 hours and differentially screened. Two cDNAs MII-3 and MII-4 were isolated. Southern analysis revealed that both cDNAs are encoded by different genes. Expression studies showed different patterns for both genes. Both MII-3 and MII-4 were highly expressed in IAA treated hypocotyls, whereas MII-4 was also induced in IAA treated epicotyls. There was no expression of either MII-3 or MII-4 in control or IAA treated leaves. With increasing concentrations of IAA from 100 to 1000 μm there was an increase in the average root number per cutting as well as a stimulation in MII-3 and MII-4. Both MII-3 and MII-4 showed a stimulation in expression 4 hours following treatment with 500 μm IAA reaching a maximum from 4 to 8 hours followed by a decline thereafter. Basal expression of MII-3 was evident between 2 and 8 hours, whereas, a high degree of basal expression was found with MII-4 from 1 to 8 hours followed by a sharp decline. Cycloheximide (50 μm) dramatically reduced rooting and MII-3 expression, whereas MII-4 was only slightly affected.
Although tolerance to high temperature is crucial to the summer survival of Iris germanica cultivars in subtropical areas, few physiological studies have been conducted on this topic previously. To remedy this, this study explored the physiological response and expression of heat shock factor in four I. germanica cultivars with varying levels of thermotolerance. The plants’ respective degrees of high-temperature tolerance were evaluated by measuring the ratio and area of withered leaves under stress. Several physiological responses to high temperatures were investigated, including effects on chlorophyll, antioxidant enzymes, proline, and soluble protein content in the leaves of four cultivars. CaCl2 was sprayed on ‘Gold Boy’ and ‘Royal Crusades’ considered being sensitive to high temperatures to study if Ca2+ could improve the tolerance, and LaCl3 was sprayed on ‘Music Box’ and ‘Galamadrid’ with better high-temperature tolerance to test if calcium ion blocker could decrease their tolerance. Heat shock factor genes were partially cloned according to the conserved region sequence, and expression changes to high-temperature stress with CaCl2 or LaCl3 treatments were thoroughly analyzed. Results showed that high temperature is the primary reason for large areas of leaf withering. The ratio and area of withered leaves on ‘Music Box’ and ‘Galamadrid’ were smaller than ‘Gold Boy’ and ‘Royal Crusades’. CaCl2 slowed the degradation of chlorophyll content and increased proline and soluble protein in ‘Gold Boy’ and ‘Royal Crusades’ but had no significant effect on activating peroxidase or superoxide to improve high-temperature tolerance. Genetic expression of heat shock factor in ‘Gold Boy’ and ‘Royal Crusades’ was upregulated by Ca2+ at later stages of leaf damage under high-temperature stress. LaCl3 down-regulated the physiological parameters and expression level of heat shock factor in ‘Music Box’ and ‘Galamadrid’. These results suggest that different I. germanica cultivars have varying high-temperature tolerance and furthermore that Ca2+ regulates their physiological indicators and expression level of heat shock factor under stress.