Adaption Research Of The Cuticular Wax In Alpine Meadow Plants

The cuticle wax is ubiquitous for the survival of terrestrial plants and is composed of soluble lipids embedded in apolyester matrix. It mainly consists of very long-chain fatty acids, alkanes, primary alcohols, secondary alcohols, aldehydes, ketones and esters and so on. The cuticular layer forms different microstructures, and plays important roles as the medium between plant and environment. It can decrease non-stomatal transpiration and the lease of nutrient substances, control leaf temperature, and protect plants from external mechanical damage and harmful solar radiation. The constituents and amounts of cuticular wax are affected by many environmental factors. The knowledge of the contents and the crystal structure of leaf cuticular wax under natural environment will benefit the clarification of the responsive mechanism of cuticular waxes to environment changes, and thus provide important theoretical basis for studying the response and adaption of plants to global climate change.In this study, alpine meadow plants, which were grown at the eastern edge of Qing-Hai Tibet plateau, were selected to analyze the crystal structure, amount and composition of leaf cuticular waxes under natural conditions. We set nine sampling sites according to latitudes, including Leiwuqi, Xialaxiu, Qingshuihe, Bayankala Mountain, Huangheyuan, Hekasuidao, Hekazhen, Bakatai, and Menyuan, respectively. The vegetation in these nine sampling sites were surveyed, the amounts and composition of cutiuclar wax in alpine meadow plants were analyzed using GC and GC-MS technology, and the crystal morphology of cuticular wax was observed by SEM. The main results were as follows:1. Results from vegetation survey showed that only four plant species were distributed in all sampling sites, including Leontopodium nanum, Potentilla nivea, Anaphalis lacteal and Kobresia humilis. The vegetation coverage, numbers of species and dominant species were significantly different among sampling sites. The plant species mainly included Gramineae, Compositae, Leguminosae, Ranunculaceae, Cyperaceae, and Scrophulariaceae. Androsace and Saussurea were widely distributed in higher altitude(>4800m) but not in areas below 4200m. There had no significant correlation between the species richness and diversity index and the latitude and altitude. It indicated that the plant diversity was a response of plant community to integrated environment factors.2. The cuticular wax was composed of n-alkane, acid, primary alcohol, secondary alcohol, aldehyde, ester, ketone and so on. The contents of cuticular wax were different among species and sampling sites. The proportion of n-alkane was the highest in total cuticular wax. The contents of rc-alkane, acid, ketone and ester differed among L. nanum, P. nivea, A. lacteal and K. humilis, but there was not specific pattern under natural environments. L. nanum and P. nivea had more primary alcohols, secondary alcohols and ketones in Bayankala Mountain, while Hekazhen had less of them. The content of aldehyde was the lowest in all sampling sites.The total cuticular waxes from Leiwuqi and Xialaxiu which located in lower latitude sites were significantly higher than that of other sites, it was the result of higher annual average temperature and annual average rainfall of Leiwuqi and Xialaxiu. The contents of total cuticular wax in L, nanum and A. lacteal which covered with trichome were higher than P. nivea and K. humilis which had no trichome.3. The n-alkane distribution of cuticular wax was studied in seven plants of Compositae which were grown at Menyuan. The results showed that the amounts and relative contents of n-alkanes in the cuticular wax were different among plant species. It was the result of the evolution pressure of plants and environmental factors. The relative content of odd-number n-alkanes was significantly higher than that of even-number n-alkanes. The most abundant n-alkanes in many plants were C29, C31 and C33, while the relative contents of C25 and C27 were higher in some plants. The relative contents of n-alkanes<C27 and>C33 were relatively lower. The CPI of seven species ranged from 1.38 to 20.60, showing odd/even predominance. ACL ranged from 26.88 to 30.61. The proportions of longer chain n-alkane were higher in seven species. Seven plant species in Compositae could be clustered into two groups, one included Artemisia capillaris, Taraxacum mongolicum and Saussurea pulchra containing higher relative content of C29, another included Saussurea leontodontoides, Aster tataricus, A. lacteal and L. nanum containing higher relative content of C31. It indicated that the n-alkane distribution of cuticular wax could not be a determining factor, which can be used for the classification of plant morphology.4. Scanning electron microscope analysis showed that a dense diffused wax film covered on leaf surface with crystals spreaded over the film. The wax crystals differed among species. The predominant wax crystal types in K. humilis were plate, lump, and granular, while those in P. nivea were plate and lump. The morphology of cuticular wax differed among different sampling sites. The cuticular wax crystal in Bayankala Moutain and Huangheyuan was vertical plate, while that in Hekasuidao, Hekazhen, Xialaxiu and Leiwuqi was folded. The wax crystal in P. nivea melted somewhat in all sampling sites. No wax crystal morphology could be observed in L. nanum and A. lacteal due to high dense of trichome. The results indicated that alpine meadow plants might improve their adaptation by altering their leaf cuticular wax crystal morphology due to environmental changes in different sampling sties.