Changes Of The Endogenous Hormones In Submerged Macrophytes And Their Implications For Environmnental Responsiveness

Physiological ecologists have long recognized the importance of hormones in integrating environmental signals and controlling flexible physiological responses. Several environmental factors influence the growth and distribution of submerged macrophytes. Among them, light, CO₂, heavy metals and water velocity are recognized to play key roles in aquatic plant growth and survival. This dissertation mainly studied their effects on hormonal level in Vallisneria spinulosa, a common submerged macrophyte distributed in Yangtze River Basin. In addition, hormonal actions linked to life history transformation were also discussed in other submerged macrophytes, Potamogeton malaianus and Vallisneria natans. The results are as follows:Phytohormones played critical roles in maturation, growth and dormancy of three submerged macrophytes, Potamogeton malaianus, Vallisneria natans and Vallisneria spinulosa. Among the studied hormones, ABA and CTKs acted independently and often oppositely on the tissues of submerged macrophytes, exerting major influences plant development and growth.These hormones also played important roles in stress responses of submerged macrophytes. Low light intensity induced significant hormonal changes in V. spinulosa seedlings. IAA, GA₃ and ABA increased in leaves. However, ABA, ZR and iPA in roots decreased while IAA increased in roots.Low and high concentration of CO₂ did not affect ABA accumulation either. This result indicated that all of the tested CO₂ concentrations might not be stressful to V. spinulosa seedlings. More rapid growth at high CO2 might be due to the increase of IAA and ZR in both leaves and roots while the decrease of GA3 in leaves.V. spinulosa seedlings were more tolerant to Cd than to Cu. Although Cu is necessary for plant growth, it induced a sharper decrease in water content, chlorophyll and soluble protein in the plants, when compared with Cd. On the contray, less ABA was induced in Cu-treated seedling. When pre-treated with ABA, no significant difference appeared between Cu- and Cd-treatments.Survival and growth of seedlings of two Vallisneria species (V. natans and V. spinulosa) were measured experimentally for increasing current velocity. All seedlings survived in all treatments and showed positive growth. The most rapid...