Investigation On The Influence Of Plant Growth Retardants On Plant Growth And Bulb Carbohydrate Accumulation In Lilium Oriental Hybrids 'Sorbonne'

Lilium Oriental Hybrids'Sorbonne'is one of the most popular lily cultivars in Chinese market. Most qualified lily bulbs are imported and the purchase of bulbs approximately accounts for 80% of total production cost. In order to solve problems for domestic breeding of bulbs, we applied three plant growth retardants to test their influences on carbohydrate accumulation in bulbs. Morphological parameter, endogenous hormone contents and starch-synthesizing enzyme activities have been detected to explain the internal mechanism of carbohydrate accumulation in bulbs. The following are the main results:(1) The association between plant growth developments and carbohydrate distributionThe distribution of carbohydrates is closely associated with plant growth developments. The lily plant development was divided into four periods according to the conversion of carbohydrates in bulbs:At 0-6 WAP, the starch content decreased while the sucrose content increased in bulbs, demonstrating that reserve material in bulbs was hydrolyzed and utilized for vegetative growth. At 6-9 WAP, starch and sucrose contents in bulbs increased simultaneously, which indicated that bulbs did not provide carbohydrates for vegetative growth any longer. At 10-12 WAP, starch content decreased but sucrose content increased, suggesting the starch was hydrolyzed again for bud growth. At 13-18 WAP, starch content regained a persistent and remarkable increase, which indicated the assimilates began to be accumulated in bulbs.The source organs and sink organs exhibit a partner relationship in lily plants. The bulbs provide reserves for stem and leave growth at vegetative growth period, and the leaves synthesize assimilates and transit to bulbs after blossoming as feedback. The flower bud formation and development is a key turning point of carbohydrate conversion in bulbs.(2) The promotion of carbohydrate accumulation in bulbs in response to plant growth retardantsThe results demonstrated that CCC and UCZ are more effective in promoting carbohydrate accumulation in lily bulbs when compared to PBZ. After blossoming, the UCZ treatments could improve starch content up to 47.65% to 69.81%, while the CCC treatments could elevate starch content up to 28.11% to 51.24%; however, the PBZ treatments could only increase starch content by 19.65% to 30.38%. (3) The influence of plant growth retardants on starch-synthesizing enzyme activities in bulbsThe starch-synthesizing enzyme activities (AGPase, SSS and GBSS) were first reveals in storage organs of bulb flowers. It was found that the activities of three enzymes were quite low or even undetectable during vegetative growth period, but increased markedly at blossoming period. The peak values of enzyme activities were achieved after blossoming, suggesting massive starch synthesis. The plant growth retardants significantly increased enzyme activities thereby resulting in superior starch accumulation. Taking uniconazole treatment (80mg/L) for example, the AGPase, SSS and GBSS activities were 131.65%,80.47% and 31.47% higher than those of control, respectively, leading to a 69.81% increase in starch accumulation when compared to that of control.(4) The influence of plant growth retardants on endogenous hormone contents in bulbsAll plant growth retardant treatments decrease GA content to improve the formation of interior scales and accumulation of carbohydrates, which proved that decreased GA content was an essential condition for interior scale renewal. The increase of ZR and IAA contents were detected in both treated and un-treated bulbs since blossoming, which might mainly be due to the formation of new interior scales. Plant growth retardants could improve scale formation and carbohydrate accumulation by elevating ZR and IAA contents. The increase of ZR and IAA content also coincided with the high starch-synthesizing enzyme activities. ABA contents in bulbs of all treated and un-treated plants increased since full blossoming period, suggesting ABA could facilitate carbohydrate accumulation. However, the increases of ABA content in treated bulbs were lower than that of control, suggesting ABA was not the definitive factor in carbohydrate accumulation. However, the low ratio of GA/ABA was still considered to facilitate assimilates transfer from leaves to bulbs.(5) The influence of plant growth retardants on vegetative growth of lily plantsTreatments of paclobutraol (100mg/L,200mg/L,400mg/L) and uniconazole (40mg/L, 80mg/L,160mg/L) significantly decreased plant height and appreciably diminished leaf area, however increase leaf thickness with a small coefficient. These two treatments also depress the flower diameter and flower fresh weight which is not considered to be favorable commercial value. In contrary, chlorocholine chloride significantly improved vegetative growth in lily plants. The leaf number, leaf area, leaf thickness and chlorophyll contents of treated plants were significantly higher than those of control. The flower diameter and flower fresh weight reached 21.86cm and 17.4g, respectively, at full blossoming period. Thus, low dose of chlorocholine chloride was a promising way to improve ornamental value by promoting vegetative growth and flower development.Moreover, uniconazole and chlorocholine chloride could increase chlorophyll contents and carbohydrate contents in leaves thereby providing abundant assimilates for bulb growth during and after blossoming period. Paclobutraol did not exert significant influence on leaf growth.