Effects Of Sub-low Temperature And Water On Morphology And Physiology In Tomato Seedlings

With potted in climatic chamber, we studied plant height, stem diameter, leaves area, fresh weight, dry weight, root/shoot, root morphology, the content of leaves water, osmotic substances, reactive oxygen, antioxidase activities, AsA-GSH recycle, photosynthetic pigment content, characteristics of photosynthetic and fluorescence, and distribution of excited energy and electron flow of tomato under sub-low temperature(15 ℃/8 ℃ day/night) and drought(65~55% of field capacity). The aim of the present work which studied the change of tomato growth, water content, reactive oxygen metabolism and characteristics of photosynthetic and fluorescence kinetics was to provide a theoretical basis for water management of greenhouse in winter. The results showed that:Sub-low temperature stress significantly inhibited plant growth, decreased plant height, leaves area, root length and root surface area, increased root average diameter and root volume. Under simultaneously of sub-low temperature and drought stress, plant height, leaves area, root length and root surface area, and root average diameter were the least. Drought stress decreased stem diameter and root volume under optimum or sub-low temperature. Stress mainly inhibited accumulation of shoot weight, increased root/shoot.Relative water content of leaves declined under sub-low temperature, and didn’t recover under simultaneously treatment. Pro was acted as the main osmotic substances under drought, soluble sugar under chilling, and both of them were the highest under sub-low temperature and drought. Both MDA and relative permeability of simultaneously stress were greater than separately of sub-low temperature and drought. The generation and elimination mechanism of reactive oxygen was different with various treatments. Under sub-low temperature, reactive oxygen was accumulated mainly by superoxide anion, and cleared by SOD and CAT. Under drought, reactive oxygen was accumulated mainly by H2O2, and cleared by SOD and POD. Under simultaneously of sub-low temperature and drought stress, ROS content, SOD and CAT were the highest. Meanwhile APX, GR, AsA and GSSG were also highest in AsA-GSH recycle.Photosynthetic pigment content declined under sub-low temperature stress, but increased under drought stress. Both sub-low temperature stress and drought stress made significantly decreased of intercellular CO2 concentration, stomatal conductance and photosynthetic rate, and increased of stomatal limitation. It was increased that the distribution of excited energy to PSⅡand excess excited energy. Meanwhile, it was declined that photochemical efficiency, total electron flow and alternating electrons flow. Thermal dissipation and the ratio of alternating electron flow were elevated to dissipate the excess energy. Compared with separately treatment of sub-low temperature and drought stress, the simultaneously treatment made photosynthetic rate further decreased and thermal dissipation higher, but did not make alternating electrons flow further increase.Temperature and water stress significantly inhibited plant growth, and decreased water content of leaves. Tomato plants maintain the water balance by increasing the content of osmotic adjustment substances. Stress also lead to oxidative damage of leaves, which start the mechanism of active oxygen scavenging and excess light energy dissipation. Tomato leaves was more sensitive to sub-low temperature. The greenhouse should be timely warming when sub-low temperature appeared in winter and spring. The damage caused by sub-low temperature can be mitigated by reasonable irrigation.