Effects Of Rhizosphere Ph On Growth, Ca²⁺ Absorption And Distribution In Malus Hupenensis（Pamp.） Rehd. Seedling

In this study, the plant growth, Ca2+absorption, distribution and transportation wereinvestigated in Malus hupehensis (Pamp.) Rehd. seedling with three pH (pH4.0,6.0, and8.0)treatments.The results showed that compared to the pH6.0treatment, the pH4.0and8.0treatments,significantly reduced the fresh weight, dry weight, shoot length, main root length, leaf area,chlorophyll (a, b, and a+b), net photosynthetic rate, transpiration rate and stomatalconductance, increased the intercellular CO2concentration. In addition, the respiration rate ofpH4.0treatment in the leaves and roots was higher than that in other treatments.Cytological structure of leaves and roots were changed under the three pH treatments. Inthe leaves, the number of palisade and spongy tissue cells were significantly decreased, butthe cell size remained large and closely arranged. The number of cells in pH6.0treatmentwas increased, tightly arranged. In meristematic zone of root tip, epidermis cells in pH4.0and8.0treatments had been fallen off. The shape of cells in pH8.0treatment was small,while in pH4.0treatment was blurring. Both the number and layers of meristematic zonecells in pH6.0treatment were more than the other treatments, with intact cell morphologyand rich inclusion. In vascular tissue of maturation zone in root tip, the root diameter in pH4.0treatment was decreased, and the epidermal cells were falled off. The cells in pH6.0treatment were intact and arranged closely, which appeared to be circular and oval. The rootdiameter in pH8.0treatment was smaller earlier and then become larger later, with thecortical cells irregular.The Ca2+concentrations in leaves and roots were affected by the three pH treatments.Compared with the pH6.0treatment, Ca2+concentration in leaves and roots was decreasedwhen they were treated with pH4.0and8.0. Observed the ultrastructure of the leaf, we foundthat a large number of Ca2+particles distributed in vacuole, cell wall and intercellular space.However, it was significantly reduced when the plants were treated with pH4.0and pH8.0，and part of Ca2+particles were appeared in the cytoplasm. In meristematic zone of root tip,there was a plenty of Ca2+particles in the nucleus and vacuoles, and it was decrease and alignalong the vacuole membrane, with the cells reformatted, when they came into pH4.0and8.0 treatment.In the outer epidermis cells of maturation zone of pH6.0treatment, a lot of Ca2+gatheredin the vacuole, nucleus and intercellular space. But it was apparently decreased when theplans were cultured in pH4.0and pH8.0treatment, which lied along the vacuole membrane.In the vascular bundle of the root, Ca2+particles were mainly distributed in the vacuole andthe cell wall. While treated with pH4.0and8.0, the number of Ca2+particles in vacuoleobviously reduced, at the same time the cells were out of shape with less inclusion. However,plenty of Ca2+particles appeared in cytoplasm.CAX1gene would be up-regulated with three pH treatments during the Ca2+transportation. However, the trends were different. After12days of treatment, the expressionof CAX1gene was raised, and was2and1.5times in the pH4.0and pH8.0treatments,respectively.