Researches On Physiology And Tissue Morphology Of Lotus Under Deepwater Stress

Nelumbo nucifera Gaertn is one of the ten traditional flowers in our country, plays an important role in flower production with high ornamental and economic value. It’s rainy in summer in our country, floods often occur in the period which is lotus’ full bloom, and the growth of water level make irreversible damage to growth of lotus. Submerging will not only affects the growth of the lotus, but also affects the development of flowering, pollination and fruit, and has a significantly impact on economic output in result. Most varieties of lotus are only planted in shallow water, deepwater area severely restricted the extensive of cultivation and industrialization production of lotus. So it’s with great significant importance to carry out deepwater tolerant lotus varieties screening. Research the growth and development, physiological metabolism and changes in cellular level of lotus in deepwater stress to investigate the rules and adaptation mechanisms response to deepwater stress in lotus, which will help to promote the lotus deepwater resistant germplasm and breeding of new varieties. The contents and main conclusions of this study are as followed:1) 20 cultivars of N. nucifera Gaertn as experimental materials, Pot plants submerged in 1.0m water initially with raised water were exposed to mimicked deepwater treatment. In terms of the morphological changes under the deepwater treatment, the level of deepwater damage was classified into 7 grades. Five morphological criteria, i. e. leaf color, leaf morphology, petiole height, petiole thickness and survival rate, were quantified via grading and scoring. The deepwater tolerance was identified by the comprehensive scores of the five criteria, thus the evaluation system was established. Meanwhile the deepwater tolerance was identified in 20 cultivars of N. nucifera Gaertn as well. The results showed that the 1.2m water was critical deepwater to identify deepwater tolerance cultivar in N. nucifera Gaertn. The most cultivars of N. nucifera Gaertn are more susceptible to deepwater(1.2m), which belongs to less sensitive class. Two materials showing highly deepwater tolerance were screened out.2)’guifeizuijiu’and’taichengfucui’ as experimental materials, in this experiment, we determined the morphological and physiological indexes of two lotus species,’guifeizuijiu’ and’taichengfucui’, in different deepwater treatment. The results showed that under normal growth conditions, there were no significant differences on morphological and physiological changes in the leaves between these two lotus varieties. However, the petiole height of ’taichengfucui’ was significantly higher than ’guifeizuijiu’ in different deepwater treatment. And the content of chlorophyll a, b and a+b increased at first and decreased subsequently, ’taichengfucui’changed much more than ’guifeizuijiu’. The content of MDA and relative conductivity in leaves increased gradually in different treatment time, the increased rate of ’taichengfucui’ was significantly less than ’guifeizuijiu’; the soluble sugar content of ’taichengfucui’ decreased was also significantly less than ’guifeizuijiu’ with treatment time increasing. Overall there was no significant differences in soluble protein content of leaves, and the increased rate of leaf SOD and POD activity in ’taichengfucui’ was significantly higher than ’guifeizuijiu’ in different treatment time. It indicated that ’taichengfucui’ has a more completed physiological and biochemical mechanism to tolerant deepwater and stronger ability to adapt the deepwater stress than ’guifeizuijiu’.3) ’guifeizuijiu’ and ’taichengfucui’ as experimental materials, in this study, we determined the morphological criteria of two Nelumbo nucifera Gaertn varieties,’guifeizuijiu’ and ’taichengfucui’, in different deepwater treatments, and observed the paraffin section of petiole apical tissue structure. The results showed that under normal growth conditions there were no obvious differences between the two varieties of Nelumbo nucifera Gaertn in morphological criteria and tissue structure. However, the petiole height, petiole apical cell length, growth rate of ’guifeizuijiu’ were significantly lower than ’taichengfucui’ in different deepwater treatments. Furthermore, under the deep water stress the two varieties of Nelumbo nucifera Gaertn exhibited cell elongation, which belonged to’escape strategy’ growing.4) ’taichengfucui’ as experimental materials, In this study, we determined physiological indexes in the leaves of a deepwater tolerance Nelumbo nucifera Gaertn variety, ’taichengfucui’, in different deepwater treatments, and observed the paraffin section and transmission electron microscope of petiole apical tissue structure. The results showed that ethylene level of petiole apical tissue increased at first and decreased subsequently from the plant submerged to the leaf grew out of the water. The length of petiole apical parenchyma cells increased first when the plant submerged, then the cytoderm thickness increased significantly after the leaf grew out of the water. The growth elongated from petiole apical tissue and many miniature ventilated cavities formed around the vascular bundle of petiole apical tissue in ’taichengfucui’ under deepwater treatment. By contrast, under normal growth conditions(CK) there were no obvious changes in these indexes. These results showed that ’taichengfucui’ adapt to deepwater stress through ethylene accumulation to promote cell elongation in petiole apical tissue, forming and inreasing of ventilated cavities.