Microscopic Observation And Mechanism Research On Stem End Blockage Of Some Cut Flowers

Stem blockage is regarded as a common postharvest disorder often occurs in the basal stem-ends of various cut flowers, which may seriously impede water uptake and transport in vascular tissues, and then result in the water amount of uptake is lower than that of loss, finally cause water imbalance in cut flowers and damage their ornamental quality and commercial value. However, so far there are very limited researches on occurrence process and regulation mechanism of stem blockage in cut flowers. Thus, this thesis focused on microscopic observation and perspective of morphological changes of vascular tissues in the stem-ends of some mainstream cut flowers, including gladioli(Gladiolus hybridus), carnations(Dianthus caryphyllus), roses(Rosa hybrid) and lilies(Lilium longiflorum), to explore the occurrence process of stem blockage and its regulation mechanism. The main research results and conclusions were as follows:1. The effects of nano-silver(NS), a new-type antibacterial agent, on postharvest water metabolism and ornamental quality of cut gladioli ‘Eerde’ and carnations ‘Dianthus caryphyllus’ were investigated. The results showed that:(1) As compared with the deionized water(DIW)control, the pretreatments with NS at 10, 25 and 50 mg L-1 for 24 h could significantly prolong the longevity of cut gladiolus spikes, and especiaaly 25 mg L-1 NS pretreatment could significantly increase their water uptake and decrease water loss, enhance floret openingopening rate and daily ornamental value, and improve ornamental quality;(2) Similarly, the pretreatments with NS at 75 mg L-1 for 24 h could also significantly prolong the vase life of cut carnations and maintain their ornamental quality, improve water uptake and reduce water loss, and effectively delay the decline of hydraulic conductance in their stem-ends during vase period.2. The spatial-temporal features of microbial blockage at the basal stem-ends of cut gladioli ‘Eerde’ and carnations ‘Master’ during vase period were observed with paraffin section, confocal laser scanning microscopy and scanning electron microscopy(SEM). The results showed that:(1) Cut gladioli and carnations were prone to the bacterial blockage, mainly caused by the bacterial colonization and biofilm formation on the stem-end cut surface;(2) The pretreatments for cut gladioli and carnations with 25 and 75 mg L-1 NS for 24 h respectively, could significantly inhibit the bacterial clonization and biofilm architecture formation in their basal stem-ends, and thus delay and alleviate the bacterial blockage formation;(3) After 24 h in vitro culture of the bacterial microflora isolated from the stem-ends of cut gladioli and carnations, respectively, mature bacterial biofilms with an organized architecture of abundant bacteria cells interwoven with extracellular polysaccharide materials formed for the control, name with no NS in medium. In contrast, only limited bacterial cell numbers and scanty extracellular polysaccharide materials were observed, however the biofilm formation was not evident.3. The bacterial diversity in the basal stem-ends of cut gladioli and carnations was analyzed by means of high-throughput sequencing technology on the basis of 16 S rDNA, the results showed that:(1) NS treatment significantly reduced bacterial richness index and diversity index, and evidently changed the bacterial community structure at the stem-ends of cut gladiolus spikes and carnation during vase period;(2) As dominan bacteria, Acinetobacter, Enterobacteriaceae_unclassified, Aquitalea, Pantoea and Enterobacter and so on, probably were the main bacterial microflora that caused the bacteria-related blockage in stem-ends of cut gladioli during vase period;(3) As dominan bacteria, Acinetobacter, Enterobacteriaceae_unclassified, Aquitalea, Pantoea, Enterobacter, Clostridium, Pectobacterium, Aeromonas, Pseudomonas, Bacillus, and so on, probably were the main bacterial microflora that caused the bacteria-related blockage in stem-ends of cut carnations during vase period.4. The spatial-temporal features of physiological blockage at the basal stem-ends of cut gladioli ‘Eerde’, carnations ‘Master’, roses ‘Movie Star’, and lilies ‘White Heaven’ were preliminarily observed with Pb(CH3COO)2 staining, paraffin section and SEM, the results showed that:(1) Quinones, dyed into black substances by Pb(CH3 COO)2, were evidently observed in xylem vessels of the basal stem-ends of cut gladiolui treated with 25 mg L-1 NS for 24 h and carnations treated with 75 mg L-1 NS for 24 h at day 6 and 4 of their vase period. Additionally, at day 6 of their vase period, it was observed that the bacterial blockage and physiological blockage occurred simultaneously and both interweaved together;(2) Unknown amorphous substances were evidently observed on the surface of xylem vessels and even in their interior of the basal stem-ends of cut roses at day 8 of their vase period.(3) Browning occurred in the basal stem-ends of cut lilies at day 3 of their vase period. Meanwhile, a lot of blockage substances were seen on the vascular surface of the basal stem-ends with further SEM observations, which were cubic crystal particles, probably are involved in the physiological blockage.