Studies On The Morphology And Physiological And Biochemical Characteristics Of A Dwarf Mutant Of Cymbidium Hybrids

Cymbidium is one of the most important genera of orchidaceae and has high ornamental and economic value for their unique flower pattern, gorgeous color, beautiful leaves, longer flowering period. With the improvement of living standard, traditional orchid species can not satisfy people’s needs in recent years. Cymbidium hybrid orchid can generate small type plant and varieties of fragrance, rightly making up the demand gap. Dwarf crops and garden plants, as the key germplasm resources to cultivating small type plant, have been obtained and applied in breeding. Also, of which the dwarfing mechanisms have been deeply studied. At present, some dwarf mutants of ornamental plant have been found, but they were given priority to direct application, and the dwarfing mechanism was rarely investigated. In this study, the stable dwarf mutant of Cymbidium plants which were isolated from the multiplicative stage of normal Cymbidium were prepared as experiment materials, and normal Cymbidium plants were used as control. We studied the relationship between the dwarf character and the morphological indexes, physiological and biochemical characteristics, photosynthetic characteristics and vegetation anatomical structure based on comparing the morphology, physiological-biochemical, photosynthetic characteristic and histologic features. Our goal is to preliminarily probe the dwarf mechanism and provide certain theoretical basis for future studies on screening genes which is responsible for dwarf phenotype. The major results were as followed.1. There were significant differences in morphological characteristics and physiological-biochemical characteristic between the dwarf mutant and normal Cymbidium hybrid. The specific differences as follows:dwarf mutant showed decreased height and the plant type changed from the loose vertical type to half upright and compact type. Dwarf mutant had more number of blades. Leaves on dwarf mutant were shorter, thicker, wider, shallower color. There were also existing great differences in proliferation, differentiation and rooting of rhizome between the two materials. The rhizome of dwarf mutant had much poor productive characters. At the same time, the dwarf mutant had lower levels of soluble sugar, soluble protein, starch and other energy supply material. However, they possessed higher levels of protective enzyme (SOD, POD, CAT) activity.2. In this study, dwarf mutant showed shorter, wider leaf epidermis cells, and increased cell number in leaves than that of normal one. The cell elongation of dwarf mutant pseudobulb was inhibited, while the cell division was normal. The numbers and areas of vascular bundles in dwarf mutant pseudobulb were much less than that in normal one. So did the root vascular bundles of dwarf mutant. The anatomical structure of rhizome had no significant difference between the dwarf mutant and the normal one, but dwarf mutant showed lower level of nutrition content. In general, the main reasons contributed to dwarf phenotype were the cell elongation and division inhibition in dwarf mutant leaves and cell elongation inhibition in the dwarf mutant pseudobulbs.3. The results of the comparative analysis of photosynthetic physiological characteristics between the two materials were as following. There were no significant differences in stomata length and width, guard cell length and width except stomatal density between the dwarf mutant and the control. Contents of chlorophyll a(chla), chlorophyll b(chlb), carotenoid(car) were significantly reduced in dwarf mutant, resulting in an increased chlorophyll a/b value. The net photosynthetic rate (Pn) and transpiration rate (Tr) in dwarf mutant were significantly lower than that in normal plant. The intercellular CO2 concentration (Ci) of dwarf mutant was much higher than that of normal one. There was no significant difference in stomatal conductance (Gs) between two materials. The maximum quantum yield of PS Ⅱ photochemistry(Fv/Fm), effective quantum yield of PS Ⅱ photochemistry (Fv’ /Fm’), effective quantum yield of photochemical energy conversion in PS Ⅱ(φ PSⅡ) and photochemical quenching(qP) in dwarf mutant and normal plant were at the similar level. However, dwarf mutant presented a much higher level of Non-photochemical quenching (NPQ).